i

ENVIRONMENTAL ASSESSMENT OF

GULDAGER MØLLEDAM & GULDAGER MØLLEBÆK

Masters of Environmental Technology and Management

Presented by: Aghogho Ekpruke

Elinor Slotte

Fabian Sander

Samuel Obiri-Yeboah

Supervisor: Prof. Jens Peter Thomsen

ii

ACKNOWLEDGEMENT

We would like to thank Prof. Jens Peter Thomsen for his guidance during the course of this

project (the ping-pong was fun). We are also grateful to the entire staff of the Chemical and

Biological laboratory of the University of Aalborg, Esbjerg campus for their kind assistance,

advice and support.

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DECLARATION

This project was submitted to Aalborg University, Esbjerg as a part of the Masters

programme in Environmental Technology and Management.

We hereby declare that the information in the project is either reference based or based on our

own thoughts and ideas. The references used are stated in the text as well as a list of

references is attached in the end.

With our signature we give the authorization to publish and use this project for scientific

purposes.

7th

of December 2009, Aalborg University, Esbjerg, Denmark

……………………………. ……………………………..

Aghogho Ekpruke Elinor Slotte

……………………………. ………………………………

Fabian Sander Samuel Obiri-yeboah

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ABSTRACT

The environmental state of Guldager Mølledam and Guldager Møllebæk has been evaluated

in this project and the results have been compared with its previous environmental state and

current legislation. The study also looks at the lake restoration project carried out in

1998/1999 to see if it has been successful.

The results indicate that Guldager Mølledam is shallow, well mixed (no stratification), has a

high buffering capacity and a high dissolved oxygen content. It functions as a sink and source

of filter for external load of nutrients that flows into it from its catchment. Phosphorus

content in the sediment is low and is mainly bound to iron. The cholorophyll α content in the

lake suggests that the trophic state of Guldager Mølledam is mesotrophic, and the results

from the Secchi depth as well as dissolved phosphorus indicates the same. There is a

relatively high abundance of diatoms and macrophytes. While Guldager Møllebæk showed a

Danish Stream Fauna Index value of 4.

The results show that the restoration project was successful as the lake quality is improved

since and the quality is within the range of current environmental standards

However, these results are only applicable to the condition of the lake as at the time and date

of sampling and analysis.

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TABLE OF CONTENTS

1 INTRODUCTION ............................................................................................................. 1

2 LAKES ............................................................................................................................... 3

2.1 Classification of Lakes ................................................................................................ 3

2.1.1 Based on origin .................................................................................................... 3

2.1.2 Based on Water source and type of outflow ........................................................ 4

2.1.3 Based on formation process ................................................................................. 4

2.1.4 Based on productivity .......................................................................................... 4

2.2 Lake restoration and factors affecting lake water pollution ........................................ 5

2.2.1 Lake restoration ................................................................................................... 5

2.2.2 Restoration related to problematical algal growth ............................................... 7

2.2.3 Problems related to Macrophyte growth .............................................................. 8

3 Guldager Mølledam and Guldager Møllebæk ................................................................... 9

3.1 Mølledam and Møllebæk before the restauration ....................................................... 9

3.2 Guldager Mølledam and Møllebæk today ................................................................. 12

3.3 Legislation ................................................................................................................. 14

3.3.1 European legislation........................................................................................... 14

3.3.2 Danish legislation............................................................................................... 15

4 FACTORS AFFECTING LAKES AND THEIR INTERACTIONS .............................. 17

4.1 Light, Primary production and Respiration ............................................................... 17

4.2 Dissolved Oxygen (DO) ............................................................................................ 18

4.3 Temperature, density and seasonal changes .............................................................. 19

4.4 Thermal stratification in lakes ................................................................................... 20

4.5 Nutrient loading and primary production .................................................................. 22

4.6 Limiting factor for lakes ............................................................................................ 23

5 PARAMETERS FOR LAKE QUALITY ASSESSMENT ............................................. 24

5.1 Physical properties .................................................................................................... 24

5.1.1 Temperature ....................................................................................................... 24

5.1.2 pH ....................................................................................................................... 25

5.1.3 Turbidity and transparency ................................................................................ 26

5.1.4 Secchi-depth ....................................................................................................... 26

5.1.5 Conductivity ....................................................................................................... 27

5.1.6 Total solids ......................................................................................................... 27

vi

5.1.7 Alkalinity ........................................................................................................... 28

5.2 Chemical properties................................................................................................... 30

5.2.1 Dissolved Oxygen .............................................................................................. 30

5.2.2 Organic matter ................................................................................................... 30

5.2.3 Nutrients ............................................................................................................. 30

5.2.4 Iron ..................................................................................................................... 32

5.2.5 Biochemical Oxygen Demand (BOD5) .............................................................. 33

5.3 Biological properties ................................................................................................. 34

5.3.1 Aquatic macrophytes ......................................................................................... 34

5.3.2 Phytoplankton .................................................................................................... 35

5.3.3 Zooplankton ....................................................................................................... 36

5.3.4 Chlorophyll α ..................................................................................................... 36

5.3.5 Macroinvertebrates ............................................................................................ 37

5.4 Danish Stream Fauna Index (DSFI) .......................................................................... 38

6 SAMPLING AND ANALYSIS OF SAMPLES ............................................................. 39

6.1 In-situ measurements................................................................................................. 39

6.2 Water sample measurements ..................................................................................... 41

6.2.1 Sampling.................................................................................................................... 41

6.2.2 Analysis of water samples ......................................................................................... 42

6.3 Sediment sample measurements................................................................................ 46

6.3.1 Sampling.................................................................................................................... 46

6.3.2 Analysis of sediment samples ................................................................................... 47

6.4 Biological measurements .......................................................................................... 49

7 RESULTS ........................................................................................................................ 53

7.1 Results of In-situ measurements ............................................................................... 53

7.2 Results of water sample measurements ..................................................................... 56

7.3 Results of sediment sample measurements ............................................................... 61

7.4 Results of biological measurements .......................................................................... 63

8 DISCUSSION OF RESULTS ......................................................................................... 68

8.1 In-situ measurements................................................................................................. 68

8.2 Water sample measurements ..................................................................................... 70

8.3 Sediment sample measurements................................................................................ 71

8.4 Biological measurements .......................................................................................... 72

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8.5 Comparison with legislation ..................................................................................... 72

8.6 Comparison with previously performed assessments ............................................... 74

9 CONCLUSION ................................................................................................................ 77

REFERENCES ........................................................................................................................ 77

APPENDICES ......................................................................................................................... 85

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LIST OF TABLES

Table 1 The morphological and hydrological data for Guldager Mølledam 1987 .................... 9

Table 2 Data from inlet and outlet streams at Guldager Mølledam ......................................... 11

Table 3 Results from water samples taken in Guldager Mølledam ......................................... 11

Table 4 Results from sediment samples, in g/kg dry stuff, taken in Guldager Mølledam ....... 12

Table 5 Concentration of metals analysed in the sediment samples ........................................ 12

Table 6 Classification of lakes and ponds based on alkalinity. ............................................... 29

Table 7 The average results from in-situ measurements ......................................................... 53

Table 8 The flow measurements for the inlet .......................................................................... 54

Table 9 Flow measurements for outlet..................................................................................... 54

Table 10 Results from alkalinity measurements ...................................................................... 56

Table 11 Total Solids results .................................................................................................... 57

Table 12 Total phosphorus in the Inlet, Lake and Outlet ........................................................ 59

Table 13 Ortho-phosphate in the Inlet, Lake and Outlet ......................................................... 60

Table 14 Iron content results .................................................................................................... 60

Table 15 Chlorophyll a results ................................................................................................. 60

Table 16 Sediment analysis results .......................................................................................... 61

Table 17 Macro-invertebrates in Guldager Møllebæk ............................................................. 65

Table 18 Limit values for total phosphorus concentrationin shallow and deep lakes ............. 73

Table 19 Comparison of limit values and our measurements .................................................. 73

Table 20 Comparison of results ............................................................................................... 74

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LIST OF FIGURES

Figure 1 Solubility of oxygen in water. ................................................................................... 19

Figure 2 Various strata’s in a stratified lake. ........................................................................... 20

Figure 3 Seasonal temperature cycles in stratified lakes ......................................................... 21

Figure 4 Distribution of temperature and dissolved oxygen during summer thermal

stratification of an eutrophic lake. ........................................................................................... 25

Figure 5 Secchi disk depth measurement................................................................................. 27

Figure 6 Forms of inorganic carbon at different pH levels. ..................................................... 29

Figure 7 Macrophytes in a lake ................................................................................................ 35

Figure 8 Phytoplankton ............................................................................................................ 35

Figure 9 Some species of Zooplankton .................................................................................... 36

Figure 10 Structure of Blue green algae (Left) and Algae bloom (Right) ............................... 37

Figure 11 Field analyzers used for the in-situ measurements: Secchi disk (Left); and pH and

Conductivity meter (Right) ...................................................................................................... 40

Figure 12 Current meter as used in the flow measurement ..................................................... 40

Figure 13 Lake water sampling ................................................................................................ 42

Figure 14 Radiometer Analytical ............................................................................................. 43

Figure 15 Oxitop BOD5 determination flasks. ........................................................................ 43

Figure 16 FIASTAR 5000 ....................................................................................................... 45

Figure 17 Location of sampling points for sediment samples and lake depths ....................... 47

Figure 18 Location of sampling points for sediment samples and lake depths ....................... 48

Figure 19 Atomic Absorption Spectrometer ............................................................................ 48

Figure 20 Net for collecting phytoplankton ............................................................................. 50

Figure 21 Olympus 249113 Microscope used for identification of plankton .......................... 50

Figure 22 Kick sampling and pick sampling ........................................................................... 51

Figure 23 Microscope for Macro-invertebrate analysis ........................................................... 52

Figure 24 BOD5 Results .......................................................................................................... 56

Figure 25 Total Nitrogen (mg/l) results ................................................................................... 58

Figure 26 Nitrogen Oxides (mg/l) results ................................................................................ 59

Figure 27 Organic Matter in Sediment samples ...................................................................... 62

Figure 28 Various species of Phytoplanktons .......................................................................... 65

Figure 29 Macrophytes at Guldager Mølledam ....................................................................... 67

x

Figure 30 Variations in temperature, pH, and DO between inlet, lake, and outlet water .Error!

Bookmark not defined.

1

1 INTRODUCTION

Humans, animals, plants and a huge diversity of aquatic species are completely dependent on

adequate and sustainable fresh water sources. Evaporating water from the surface returns as

precipitation, flows across the land thus replenishing aquifers, lakes, ponds, wetlands, streams

and finally discharges into the sea, bringing nutrients to marine life. All life, and all human

economics and cultures are dependent on this cycle. Most fresh water is still bound in ice.

Out of the liquid portion, 99% is in underground aquifers. The amount in lakes and streams is

small, but renewed rapidly, making them the primary source for fresh water in most regions.

In Denmark, however the primary source of drinking water origins from the groundwater.

Lakes in Denmark are mainly used for recreational purposes as is the lake Guldager

Mølledam. Guldager Mølledam is a small, artificial lake north of Esbjerg, close to the

suburban area of Guldager. The outlet is Guldager Møllebæk which runs out into the sea at

Ho Bay. Until 1987 the cleaned wastewater from Guldager was discharged into the stream

leading to Mølledam. In 1987 the discharge of the waste water was cut off, however the

wastewater had already been polluting the lake significantly with phosphorus and metals.

These pollutants were stored within the sediment. Due to the fear of phosphorus leaking out

into the lake water the decision was made to restore the lake by sediment removal. The

sediment removal was performed in 1998/1999 and increased the lake water quality

significantly as well as in the outlet stream, Guldager Møllebæk (Ribe Amt, 1998).

The European Union established the Water Framework Directive in 2000 (2000/60/EC), the

main purpose of the directive was to ensure good quality in freshwaters. The objective is to

prevent or reduce pollution into freshwater basins and to provide tools for the environmental

management of these freshwater sources. By the end of 2015 all water sources within

Member States shall have a good ecological status. The Annex V in the Directive gives

guidelines on how to assess the quality for these water sources, however each Member State

shall provide the EU with a management programme by the end of 2006 on how they will

perform this evaluation. (Water Framework Directive 2000/60/EC.) To ensure the good

quality of lakes in Denmark there are several laws, which aids in the protection against

pollution of lakes and any surface waters. The Danish environmental Protection Act is the

foundation for environmental protection in Denmark. The main objective within the Act

follows the principle of Polluters Pays and Best Available Technology.

2

The aim of the project is to investigate which factors affect the lake water quality and to

assess the water quality in Guldager Mølledam. By looking into the physical properties, the

chemical properties and the biological properties of the lake we are able to assess the

environmental condition of the lake. This is performed by taking water samples from the inlet

stream, the outlet stream and the lake. Some sediment samples are taken from the lake bottom

in order to evaluate the situation in the sediment today, 11 years after the sediment removal.

The flow is measured at the inlet and outlet stream in order to calculate the retention time for

the lake. The analysis of the samples are performed in the laboratory at Aalborg University,

Esbjerg. The results can be compared with the data before the sediment removal.

The stream Guldager Møllebæk is assessed based on the Danish Stream Fauna Index (DSFI).

The DSFI is a standardized method for biological assessment of running waters in Denmark.

The species of the macroinvertabrates found in the stream are defined and based on them the

ecological quality for the stream can be assessed.

This report gives a short introduction to all parameters, which are to be taken into

consideration when assessing lakes, where after it focuses on the methods used in order to

evaluate the parameters. The final part of the report focuses on assessing the results achieved

and comparing them with the data before the restoration.

3

2 LAKES

Lakes are enclosed bodies of water (usually freshwater) totally surrounded by land and with

no direct access to the sea. They satisfy different human requirement such as drinking or

irrigation, navigation, recreation or fisheries (UNESCO/WHO/UNEP 1996). The main

sources from which lakes receive its water are; flow from streams and rivers, direct

precipitation from rainfall, groundwater, runoff from the watershed, and man made sources

from outside the catchment area. Water leaves lakes through groundwater or surface water

flow, evaporation, extraction by humans. Most lakes have an inlet, a drainage basin

(catchment area) and an outlet. The changes in the level of lakes, is controlled by the

difference between the sources of inflow and outflow, compared with the total volume of the

lake (Byrun, S. Et al 2009).

Lakes make up about 0.008% of the total distribution of water on the earth’s surface. They

are useful as a source of water, habitat for aquatic organisms, recreational activities etc. Most

lakes contain freshwater and are continuously supplied from a stream but if the supply of

freshwater is limited, minerals from the bottom of the lake can concentrate the water making

it salty. The Dead sea is an example of a salt lake (Byrun, S. Et al 2009, Sand-Jensen, K. Et al

2006). Lakes can also help protect water quality. Eroded sediments, debris and other

pollutants washed from watersheds are deposited in lakes by inflowing streams so that

outflowing streams often carry less of these pollutants. (Michaud, J.P. 1991)

2.1 Classification of Lakes

There are various ways by which lakes can be classified. These are; based on origin, based on

formation process, based on water source and type of outflow, and based on productivity.

2.1.1 Based on origin

Lakes can be classified in to two broad categories based on origin. These are natural and

artificial lakes. Although this classification is quite broad, the general idea is that some lakes

have been formed as a result of mans activities like the building of dams while others

(majority) are as a result of natural ongoing processes.

4

2.1.2 Based on Water source and type of outflow

Seepage lakes: these are natural lakes which get their water mainly from precipitation,

groundwater and limited runoff. They do not have stream outlets and lose their water mainly

by evaporation.

Groundwater drainage lakes: natural lakes fed mainly by groundwater, precipitation and

limited runoff. They have stream outlets.

Drainage lakes: lakes fed by streams, groundwater, precipitation and runoff and drained by a

stream.

Impoundment lakes: these are manmade lakes created by the building of damns around a

stream. They are also drained by a stream (WAL 2009)

2.1.3 Based on formation process

This classification includes tectonic lakes (formed as a result of movement of the earths

crust), volcanic lakes (formed as a result of volcanic eruptions), glacial lakes (formed as a

result of melting of glaciers) and artificial lakes (formed as a result of human activities).

(Softpedia 2009)

2.1.4 Based on productivity

Lakes can be classified on the basis of their richness in nutrients. Nutrient availability is

important for the quality of a lake as it can influence the state of productivity. Certain aquatic

organisms can be found in high nutrient lakes while other types can be found in low nutrient

lakes. The main nutrients of concern are phosphorus and nitrogen. Using this classification,

lakes can be categorised into four main groups;

Oligotrophic lakes: These are lakes with low primary productivity and low nutrient

concentrations. They are generally clear and tend to be saturated with oxygen throughout the

water column.

Eutrophic lakes: These are lakes with high concentration of nutrients and are associated with

high biomass production, usually with low transparency. If deep enough to thermally stratify,

the bottom waters are devoid of oxygen.

5

Mesotrophic lakes These are lakes which exhibit characteristics between the oligotrophic

and eutrophic lakes.

Hyper-eutrophic lakes: These are lakes with exceedingly high nutrient concentrations and

associated biomass production. Anoxia or complete loss of oxygen occurs in the hypolimnion

during summer stratification. (JPT 2009)

2.2 Lake restoration and factors affecting lake water pollution

2.2.1 Lake restoration

There are a number of methods employed in the restoration of lakes. These include;

Dredging

In this method the lake sediments are removed and dumped in artificial basins where the

particles are allowed to sink. It is then treated with aluminium sulphate or iron chloride to

reduce the phosphorus concentration. The resulting phosphorus-metal complex precipitates

and is removed by mechanical processes. The water can then be returned to the lake.

Sometimes, however, the water can be returned directly before treatment. This method is

suitable mainly in small shallow lakes and ponds due to economic reasons.

The removal of lake sediment, also called dredging, is an effective, but expensive, lake

management technique. It can result in control of both algae and macrophytes. It is frequently

recommended for deepening shallow lakes for biomass control, eliminating contaminated

layers of toxic substances, and controlling nutrient loading by removal of enriched sediment

layer. It has a significant long-term advantage over nutrient inactivation. The disadvantages

are high costs, requiring of dredging material and disposal sites of the sediment (Cooke et

al.,1993).

The Riplox method

In this method the amount of phosphorus that is released from the sediment into the water is

reduced by oxidising the sediment surface while at the same time causing the phosphate to

precipitate in metal complexes. By pumping calcium nitrate (Ca(NO3)2) and adding iron

chloride (FeCl3) into the sediment, both oxygen and iron concentrations are increased. The

oxygen produced, acts as a lid preventing the release of phosphorus from sediment into the

6

water while iron combines with the phosphorus forming phosphate precipitates. The pH is

stabilised by adding calcium hydroxide and, at suitable pH, denitrifying bacteria will convert

the nitrate in the Ca(NO3)2 into N2 which is released into the atmosphere (Cooke et al.,1993).

Biomanipulation

Biomanipulation is the deliberate alteration of an ecosystem by adding or removing species,

particularly predators. The basic idea of this method is to increase the grazing rate on algae in

eutrophicated lakes, thereby decreasing the likelihood of algae blooms. In order to achieve

this, the predation pressure on large zooplanktons (which feed on algae) is reduced by

removing fishes which prey on them. Apart from the zooplanktons feeding on the algae, the

process also allows for increased biomass of submerged macrophytes in the sediment surface.

The submerged macrophytes absorb large amounts of nutrient from the sediment making it

unavailable for phytoplankton and they oxidise the sediment surface, thereby reducing

sediment loading. The removal of the fish is also helpful as it means reduced excretion of

nutrients in the lake water. It is also a removal of large amounts of phosphorus bound to the

bodies of the fish. All of these processes, which help in the treatment of the eutrophicated

lake, are triggered by the removal of fishes (Cooke et al.,1993).

Reduction of the algal biomass will prevent algae bloom and allow for light penetration

which is favourable for good lake quality.

Wetlands construction

This method focuses on reducing the amount of nutrients and sediments flowing into the lake

from an inflowing stream or drainage pipes from farmlands. This is achieved by constructing

a wetland in connection to these output sources. By allowing such incoming water to spread

out on a larger area, such as a wetland, the water flow rate decreases giving time for

suspended particles (some of which are nutrient rich) in the stream to sink to the bottom. In

addition, wetlands are shallow and this allows for high growth rate of macrophytes which

incorporate large amount of nutrients in their tissue. Also the vegetation allows for growth of

denitrifying bacteria which transfer nitrogen from water into the atmosphere. Hence wetlands

remove nutrients by sedimentation, denitrification and direct uptake by plants. (Bronmark

and Hansson 2005)

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2.2.2 Restoration related to problematical algal growth

As a rule, algae are not a health concern, however some “blue-green” algae can produce

endotoxins or exotoxins which can be harmful above certain concentrations. Algae

production occurs rapidly under suitable conditions and can cover streams, lakes and

reservois in large floating blooms. Three species of the blue-green algae, Anabaena flos-

aquae, Microcystis aeruginosa and Aphanizomenon flos-aquae produce exotoxins which have

resulted in illness or death in mammals, birds and fish that have ingested a sufficient dose.

The algal biomass is dependent on the concentration of limiting nutrients in the photic zone.

The primary cause of excess algae is high nutrient concentration from external sources which

should be controlled first. (Measured in cells/ml)

Phosphorous

Internal release of phosphorous may be the most significant source that could delay

improvement of water quality. Sediment phosphorous release can be controlled by the

popular technique of adding aluminum salts to the water column resulting in an aluminium

floc that settles to the sediment surface forming a barrier to further release (Cooke et

al.,1993).

Dilution

The technique of dilution involves the addition of low nutrient water to virtually wash lake

nutrient concentrations out of the lake. While effective, the use of such technique has limited

application due to the availability of large quantities of water with low nutrient level (Cooke

et al.,1993).

Land use modifications

Land-use modifications can be used to control nutrient loss from the watershed from urban

runoff. This method can be used in areas that are already undergoing development. The

hypolimnetic withdrawal of nutrient enriched waters can be achieved through pumping,

siphoning, or selective discharge (through building of dams) instead of low-nutrient surface

waters. This can enhance the phosphorous export, reduce surface phosphorous concentration,

and improve hypolimnetic oxygen content (Cooke et al.,1993).

8

Artificial circulation

Artificial circulation is used to prevent or eliminate thermal stratification through the mixing

column of rising air bubbles. Dissolved oxygen content will increase and reduce iron and

manganese. Furthermore it can cause light to limit algal growth in situations where nutrients

are uncontrollable and can control blue-green algae (Cooke et al.,1993).

Removal of algae

Grazing of algae by large zooplankton can be enhanced by eliminating planktivorous fish

through physical removal. This technique is cheap and effective, but usually for a limited

time (Cooke et al.,1993).

Copper sulphate

Copper sulphate treatment has been commonly used for lakes suffering from algal biomass

and taste and odor problems. The problems of this treatment is the short lasting effect – it can

be considered a detrimental aspect (Cooke et al.,1993).

2.2.3 Problems related to Macrophyte growth

Problems are often associated with eutrophication and increased inputs of sediment. The

reduction of in-lake nutrient concentrations does not affect macrophytes, as their nutrient

demands are largely supplied through root uptake from the sediment. Therefore, more direct

methods are used to deal with excessive biomass.

Macrophyte harvesting

The removal of macrophyte biomass through harvesting is often an effective, sometimes

cosmetic, treatment. Nutrients are physically removed, which in some lakes can be a

significant source of internal loading. It must be ensured though, that the removal of plants

must be performed thoroughly. A quick grow back sometimes results from cutting plant

stems, while grow back can be lowered by cutting the roots. Harvesting can have negative

effects, such as fish removal, sediment phosphorous release and dispersal of plant fragments

to uninfested areas of the lake (Cooke et al.,1993).

9

3 Guldager Mølledam and Guldager Møllebæk

Guldager Mølledam is a small, shallow artificial lake in the community of Esbjerg. The lake

is located around seven kilometres north of Esbjerg, in the close vicinity of the suburban area

Guldager. The inlet source to Guldager Mølledam originates from Guldager. Guldager

Møllebæk is the outlet from the lake and runs out into the North Sea at Ho Bay. Before 1987

the wastewater treatment plant discharged the cleaned wastewater directly into the inlet

channel to Guldager Møledam but in 1987 the discharge was directed to the wastewater

treatment plant Esbjerg Reningsanlæg Vest. Due to this the lake was highly polluted by the

wastewater especially by phosphorus and heavy metals. The phosphorus and heavy metals

settled into the sediment, creating a large storage. The lake was restored in 1998/1999 due to

fear of phosphorus leaking out into the water, thereby polluting the entire lake and Møllebæk.

(Ribe Amt., 1994.)

3.1 Mølledam and Møllebæk before the restauration

There were two inlet flows into Guldager Mølledam, the main inlet source was at the

northeast corner of the lake. The other inlet source was over a larger area and was somewhat

diffuse in the northwest corner of the lake. The wastewater from Guldager was discharged

into the main inlet source until 1987, when it was cut off. The inlet rate has been measured in

1998 to be 10 – 40 l/s at the main inlet source. The outlet source for Guldager Mølledam is

located at the southern end of the lake. The outlet flow measured in 1998 was 20 – 74 l/s.

(Ribe Amt., 1994.) The lakes hydrological and morphological data from 1986 is presented in

Table 1.

Table 1 The morphological and hydrological data for Guldager Mølledam 1987 (Ribe Amt.

1994)

Area (m2) 25,000

Volume (m3) 11,000

Largest depth (m) 0.75

Average depth (m) 0.44

Average inlet flow (l/s) 21.4

Average outlet flow (l/s) 38.6

Average hydrolic retention time (days) 3

10

The average hydrolic retention time was relatively short and therefore the water within the

lake was mixed very well. The water in the lake used to be clear even though the nutrient

load was high. This might be due to short hydrolic retention time since no algae blooming

could occur but also due to the fact that the lake was very shallow. During windy days the

Secchi depth might be reduced since bounded material can be resuspended and thereby

decrease the Secchi depth. (Ribe Amt., 1994)

The area specific runoff from the lake was 5.57 l/s/km2 when the average inlet flow of 21.4

l/s and the catchment area of 3.85 km2 were taken into consideration. The catchment area for

the inlet source to the lake had an area of 3.30 ha and the residual catchment area was 0.55

ha. The annual runoff from the inlet catchment area was 579 million litres, from the residual

catchment area 97 million litres, from groundwater 543 million litres and from the lake 1218

million litres. (Ribe Amt., 1994)

Nutrient and pollution into Guldager Mølledam

Until 1987 the cleaned wastewater from Guldager was directly discharged into the stream

leading to the lake. In 1987 the wastewater was diverted to Esbjerg Rensningsalæg Vest. As a

result of this the water quality in the inlet stream improved significantly, however the

phosphorus and heavy metals that originated from the wastewater was stored in the sediment

of Mølledam. The phosphorus in the sediment was released into the lakewater and thereby

continuously polluted the water quality. Since the wastewater from Guldager was cut off

there aren’t any known pollution sources, however even if the nutrient input from the

surrounding agricultural areas are a reality, they are of no significant importance compared to

the pollution stored in the sediment. (Ribe Amt., 1994)

In the tables below the data from the analysed samples taken in 1987 and 1990 are presented.

The data is average results from water samples taken from the lake, the inlet and the outlet

source. The last table presents the results from sediment samples taken from the lake. (Ribe

Amt., 1994)

11

Table 2 Data from inlet and outlet streams at Guldager Mølledam. (Modified Ribe Amt.,

1994)

Parameters Inlet Stream Outlet Stream

Total N (mg/l) 10.53 5.91

NH4 (mg/l) 0.11 0.24

NO2 + NO3 (mg/l) 8.92 4.87

Total P (mg/l) 0.12 0.25

Ortho P (mg/l) 0.09 0.19

pH 6.28 7.11

Q (l/s) 18.72 38.0

The data was collected during one year, taking samples every month. The results are shown

as averages, however it is significant to remember that many of the parameters are influenced

by temperature and season. The results are from samples taken in 1987. (Ribe Amt., 1994.)

Table 3 Results from water samples taken in Guldager Mølledam (Ribe Amt., 1994)

Parameters Mølledam

Total N (mg/l) 4.95

NH4-N (mg/l) 0.22

NO2 + NO3 (mg/l) 4.06

Total P (mg/l) 0.22

Ortho P (mg/l) 0.19

pH 7.24

Conductivity (mS/m) 29.38

Alkalinity 0.94

Silicates 7.49

Chlorophyll a 2.23

The data was collected during an eight month period, from April to November. The samples

were taken once a month. The results presented are averages based on the single data

acquired. Many of the parameters are influenced by temperature and season, which has to be

taken into consideration when evaluating the results. The samples were taken in 1987. (Ribe

Amt., 1994)

12

Table 4 Results from sediment samples, in g/kg dry stuff, taken in Guldager Mølledam (Ribe

Amt., 1994)

The samples were taken in 1989. The data represents the average between depths ranging

from 0 – 50 cm. The sampling points were all in Mølledam, the inlet represents the sample

taken close to the inlet source and the outlet represents the sample take close to the outlet

source. (Ribe Amt., 1994)

Table 5 Concentration of metals analysed in the sediment samples. (Modified Ribe Amt.,

1994)

The analyses were performed on the sediment samples representing 0 – 30 cm in depth. The

samples were taken in 1989.

3.2 Guldager Mølledam and Møllebæk today

After the restoration of the lake, the water quality of the lake improved significantly. The

depth of the lake increased since almost 22.000 tons of sediment was removed. Today the

surroundings and quality of the lake has changed significantly since the evaluation done in

1994. The catchment area of Guldager Mølledam is 389 ha of which the lake itself covers 2,5

ha. The surrounding area is mainly covered by agriculture and suburban area. There are a few

hectares of forests and lakes. In the close vicinity of the lake there are grasslands to the north

and east of the lake, on the southeast side there is vegetation of alder and some scirpus. On

the west side there are trees growing all the way down to the lake and also some scirpus.

Today the lake is mainly used for recreational purposes. (Ribe Amt., 2002.)

Parameters Inlet Middle Outlet

Easily absorbed P 0.11 0.08 0.01

Iron-P 0.84 2.38 3.74

Ca-P 0.09 0.18 0.33

Residual P 0.94 1.13 1.83

Total P 2.51 2.01 5.58

Total Fe 28.8 26.4 44.0

Parameters Amount

Cadmium (mg/kg dry stuff) 6.9

Mercury (mg/kg dry stuff) 0.227

Lead (mg/kg dry stuff) 60

Nickel (mg/kg dry stuff) 46

Dry stuff (%) 11.4

13

The following figure gives an overview of the lake location, the estimated catchment area due

to slope and road boundaries.

Figure 1 Location of Guldager Mølledam with catchment estimation.

According to the measurements done in 1999 the retention time had increased to 8,5 days.

The deepest point in the lake is 2,75 meters and the average depth is 1,14. The Secchi depth

was measured in February and was 1,93 metres. After the restoration the volume increased

significantly and was, in 1999, 30.000 m3. The amount of total phosphorus input was 0,034

mg/l and 0,074 mg/l for the outlet, and in the lake 0,086 mg/l. The amount of total

phosphorus is still higher in the outlet, which suggests that there is still phosphorus stored in

the sediment. The concentration of total nitrogen was 8,71 mg/l in the inlet and 7,56 mg/l in

the outlet, and in the lake water 7,1 mg/l. The amount of nitrogen in the lake is higher in

comparison with similar lakes in Denmark. The groundwater plays a significant role in the

nutrient input to the lake, and it has been calculated that there is a 5 mg N/l and 0,07 mg P/l

input into the lake from groundwater. The amount of Chlorophyll α was 15 – 150 µg/l

depending on the season. The iron concentration in Guldager Mølledam was 0,4 mg/l. (Ribe

Amt., 2002.)

The amount of total phosphorus in the sediment was measured in 1992 and the phosphorus

content was high, 0,5 – 7,3 g P/kg DS, the iron content was low during that time, only 10 –

60 g/kg DS. A survey of heavy metals in the sediment was done in 2000, which showed that

the cadmium content was still high even after the restoration. (Ribe Amt., 2002.)

14

3.3 Legislation

3.3.1 European legislation

On the 23rd

October in 2000, the European Union established the Water Framework Directive

(WFD) 2000/60/EC formally known as “Directive 2000/60/EC of the European Parliament

and of the Council of 23 October 2000 Establishing a framework for Community action in the

field of water policy”. The Directive entered into force on the 22nd

of December 2000. The

aim of the WFD is to provide Member States with a framework for water protection and

management in order to prevent and reduce pollution of inland surface waters, groundwater,

transitional waters as well as coastal waters. The WFD also gives guidelines to promote

sustainable water use, protect the aquatic environment, to improve the status of aquatic

ecosystems and to lessen the effects from floods and droughts. (Water Framework Directive

Information Center; European Communities, Water Framework Directive.)

All Member States shall have achieved a good status for all surface waters and groundwater

shall have a good status in both quantity and chemical quality within 15 years after the

enforcement of the WFD. The status qualification focuses on the impacts from human

activities where a water body with a good status has few impacts from human activities. All

Member States shall have established an integrated monitoring programme by December

2006. The monitoring programme shall contain physical, chemical and biological data. The

monitoring programme is essential for assessing the status of surface and groundwater

bodies. (Article 8, Water Framework Directive.)

Annex V in the WFD provides guidelines on how to design the programme, what are the

parameters that are to be monitored and how the results are to be presented. For classifying

the ecological status for rivers and lakes several parameters within the biological,

hydromorphological, morphological as well as chemical and physico-chemical elements has

to be evaluated. A complete list of these parameters is presented in Appendix 1 (Annex V,

Water Framework Directive).

The waters are classified based on these parameters as waters with a high, good or moderate

ecological status. Waters that do not meet the requirements for moderate status are classified

as poor or bad.

Until 2015 there are, however, still some other Directives in force regarding water protection.

The Council Directive on the quality of water intended for human consumption (98/83/EC),

15

defines the quality standards for drinking water. In Directive 76/160/EEC, Council Directive

of 8 December 1975 concerning the quality of bathing water, the European Union sets

requirements on the quality of bathing water. The Directive was repealed by Directive

2006/7/EC. The Council Directive 91/27/EEC gives guidelines in reducing water pollution

from urban waste water. The Directive on the quality of fresh waters needing protection or

improvement in order to support fish life (2006/44/EC) is constructed for the protection of

fresh waters where certain fish species lives. Directive 2006/113/EC states the quality

requirements for shellfish waters.

3.3.2 Danish legislation

The Danish Environmental Protection Act, which entered into force in 1974, is the

foundation for environmental protection in Denmark. The Act has been amended several

times during the years. The early focus of the Act was on pollution prevention for

groundwater and surface water. Today the focus is on any pollution activity such as noise, air

pollution, vibrations etc. The main objective when administrating the Act is on the principle

Polluters Pays and Best Available Technology.

The main environmental law regulating the environmental protection is the Protection of

Nature Act. The law was established on January the 3rd

in 1992 and was consolidated in

August the 18th

in 2004. The aim of the Protection of Nature Act is to provide means on how

to conserve resources in nature and its fauna and flora as well as to protect natural and

cultural monuments. The Act is divided into 14 chapters and chapter 2 focuses on the

protection of i.e. lakes and watercourses. §16 set a minimum distance, 150 meters to the

watercourse that shall be left untouched. Within these protection zones no buildings can be

set up nor can the environment be altered. These regulations are, however, only for lakes with

a size over 100 m2.

The Planning Act is of significant importance considering protection of lakes. The protection

of watercourses is to be taken into consideration in the land use plan which each county are

obliged to make. In 1998 the Action Plan for the Aquatic Environment II came into force.

This was a result of the EU Nitrates Directive, and its objective is to reduce discharged of

nitrates into the aquatic environment. The Environmental Objectives Act is the national

implementation of the Water Framework Directive into Danish legislation. The Act came into

force in 2003.

16

Natura 2000 is an European network of protected sites. These sites have the highest value of

natural habitats and species and animals which are rare, endangered or vulnerable. Natura

2000 applies to birds sites, habitat sites and marine environment. Areas within the Natura

2000 network are more stringly protected. In 2006, Denmark had 254 sites of Community

Importance, 113 sites of Special Protection Areas and 27 Ramsar Sites. All of these are

included in the Natura 2000 network. (Miljøministeriet, Danish Natura 2000).

17

4 FACTORS AFFECTING LAKES AND THEIR INTERACTIONS

There are a number of physical, chemical and biological factors which affect lakes and their

entire aquatic ecosystem. These factors and their interactions are referred to as the abiotic and

biotic frame. Variations and temporal fluctuations in this frame within lakes play major role

in determining the variety of habitats and organisms contained in them. Examples of these

factors are sediment conditions, nutrient concentrations, light availability, pH, temperature,

oxygen content, photosynthesis etc. Some of these factors and their interactions are discussed

below.

4.1 Light, Primary production and Respiration

Light is a major factor that influences lake condition. Energy from sunlight provides the

major energy input into lakes. This is transformed into potential energy by biochemical

processes such as photosynthesis and to heat by absorption by particles, dissolved substances

and by water itself. Light intensity at the lake surface varies seasonally with cloud cover and

decreases with depth down the water column. The rate at which light decreases with depth

depends upon the amount of light-absorbing dissolved substances and the amount of

absorption and scattering caused by suspended substances in the water.

Light is necessary for photosynthesis i.e. the process by which green plants convert carbon

dioxide and water into sugar and oxygen. It supplies the energy used by organisms like

algae (phytoplankton), algae attached to surfaces (periphyton), and vascular aquatic plants

(macrophytes) in this conversion process. The more the amount of light the more

photosynthesis can occur and thus the deeper into the water column light can penetrate the

lower the depth at which photosynthesis can occur (Bronmark and Hansson 2006).

6CO2 + 6H2O + Light C6H12O6 + 6O2

Photosynthesis is vital process in lakes as it is a source of dissolved oxygen. Based on this

relationship between light, photosynthesis and respiration, lakes can be divided into three

zones. That portion of the water column supplied with enough light so that photosynthesis

(primary production) exceeds respiration (P > R) is the Photic zone. Solar radiation reaching

this zone is high hence leading to high a rate of photosynthesis in this zone. The underlying

18

water is part of the Aphotic zone which receives very little or no solar radiation and as such

primary production in this zone is less than respiration (P < R). The Compensation zone is

the transition between the Photic and Aphotic zones. This zone marks the Compensation

depth which is the depth at which only 1% of the surface light remains. It is the maximum

depth, where photosynthesis process can occur and thus here primary production equals

respiration (P = R) (Dodds, 2002).

4.2 Dissolved Oxygen (DO)

Dissolved oxygen (DO) is a measure of the amount of gaseous oxygen O2, dissolved in lakes

and ponds at a particular pressure and temperature. It is essential particularly for respiration

of aquatic life and is utilised in other activities such as in the decomposition of organic matter

(Bronmark & Hansson, 2005). Changes in the amount available in the lake could have

significant impact on the behavior and existence of organisms which could lead to death in

extreme deficiency.

When dissolved oxygen is sufficiently present in a water body, organic materials and wastes

are degraded effectively. Under such conditions, nutrients such as, phosphorus is converted to

phosphate (PO4) and nitrogen forms ammonia and nitrates. On the other hand, when the DO

is limited or insufficient to support microbial activity, methane is released from carbon,

odorous amines result from nitrogen and the foul-smelling H2S gas from sulphur.

Oxygen in the aquatic environment mainly comes from the atmosphere by direct diffusion

and photosynthesis by aquatic plant and algae. Oxygen uptake from the atmosphere depends

on factors such as temperature, pressure, salinity and area of exchange surface.

Temperature: Cold water can hold more dissolved oxygen while warm water gets

saturated easily with oxygen. So cool temperature enhances oxygen uptake.

Salinity: This is the amount of salts in the lake. The amount of dissolved oxygen

decreases as salinity increases.

Pressure: The amount of dissolved oxygen increases with increasing water pressure.

Wind: more oxygen dissolves into water when wind stirs the water, as the waves

create more surface area, more diffusion can occur.

19

Figure 2 Solubility of oxygen in water. (JPT, 2009)

The amount of dissolved oxygen in lakes is strongly affected by the rates of photosynthesis

and respiration. Oxygen is produced during photosynthesis and consumed during respiration

and decomposition of dead organic matter. Photosynthesis occurs only in daytime as the

process requires light where as respiration occurs all day. Thus amount of dissolved oxygen

varies at different times of the day. The organic matter content can also affect the level of

dissolved oxygen. Polluted lakes generally have low DO while clean lakes have relatively

high amounts of DO. In essence factors like light (e.g day and night), temperature changes

(seasons, night and day), plant and animal population can lead to significant increase or

reduction depending on the direction of change (Bronmark & Hansson, 2005, JPT 2009).

4.3 Temperature, density and seasonal changes

Processes in lakes are strongly determined by the temperature profile, which in turn depends

on climate (solar radiation), wind, and also on the lake depth. Thus, lakes undergo seasonal

changes with regard to their temperature-density profiles which directly influence various

characteristics of the lake.

The temperature-density relationship for water reflects upon the premise that as water

increases in temperature, it becomes less dense and as its temperature decreases, it becomes

more dense. The exception to this rules however, is that water reaches its maximum density

at approximately 40C. As water cools below 4°C, the number of water molecules joined by

0

2

4

6

8

10

12

14

16

0 5 10 15 20 25 30

Solubility of Oxygen in water

Ox

yg

en(m

g/L

)

Temperature (˚C)

20

hydrogen bonds to form loose clusters, increases. Thus below 40C, water actually becomes

less dense as it cools because of the formation of these structured aggregates.

4.4 Thermal stratification in lakes

Lakes undergo seasonal changes with regard to their temperature-density profiles and these

changes in temperature profile with depth can result in thermal stratification. This is a

phenomenon whereby lakes show a clear physical separation of the water masses of different

densities, usually into three defined strata’s namely: (i) the epilimnion or surface waters of

constant temperature (usually warm mixed throughout by wind and wave circulation, (ii) the

hypolimnion or deeper high density water (this is usually much colder except in tropical

lakes), (iii) a fairly sharp graduation zone between the two which is defined as the

metalimnion.

Figure 3 Various strata’s in a stratified lake (JPT, 2009)

This profile however changes from one season to the next in temperate regions and creates a

cyclic pattern that is repeated from year to year expressing seasonal circulation of water.

With the beginning of spring as shown in figure 3, the ice melts on a lake and the lake water

is generally of the same temperature from the surface to the bottom. Wind allows circulation

and mixing of the lake water and as such surface water can be pushed to the lake bottom and

bottom water can rise to the surface. This is called Spring overturn. This circulation pattern

is very important in that it allows relatively large amounts of oxygen to reach the bottom of

the lake.

21

As spring proceeds into summer, water temperatures will increase with the intensity of solar

radiation. The amount of solar radiation absorbed decreases with depth, thus the lake heats

from the surface down.

Figure 4 Seasonal temperature cycles in stratified lakes (Encyclopaedia Britannica, 1996)

The warm water is less dense than the cold water below resulting in a layer of warm water

that floats over the cold water. Thus Summer stratification occurs with a layer of warm

water at the surface of the lake (epilimnion) and the cold layer (hypolimnion) below the

epilimnion, both separated by a layer of water (metalimnion) which rapidly changes

temperature with depth. During the summer, there is limited supply of oxygen at the lake

bottom (hypolimnium). This is because there is no mixing to provide oxygen and inadequate

light for photosynthesis due to the stratification. The available oxygen is thus depleted during

respiration. Oxygen is further used up by aerobic bacteria for the decomposition of algae

which die during this time. This is known as summer stagnation. Anaerobic bacteria will then

begin to decompose the dead algae which gradually accumulate at the bottom of the lake. The

anaerobic bacteria produce H2S, thereby emitting a “rotten egg” smell. Some of the sulphur in

the H2S may combine with iron to form pyrite (FeS2) known as “fools gold”.

As autumn approaches temperatures decreases and the epilimnion begins to decrease in

depth. Eventually the epilimnion gets so shallow and the lake loses its stratification. Thus as

22

in the spring, the lake water in the autumn has generally uniform temperatures and wind can

once again thoroughly mix the lake water. This is known as the Autumn or Fall overturn.

In addition, surface water, which is in direct contact with the cold air, gets cooled faster than

the water below. This cold, dense water sinks and further helps to mix the lake, and once

more oxygen and nutrients are replenished throughout the lake.

The surface water is eventually cooled below 4° C as winter approaches. At this point, the

water no longer sinks. The water temperature at the surface reaches 0°C and ice begins to

cover the surface of the lake. During the winter, ice cover prevents wind from mixing the

lake water. Thus Winter inverse stratification occurs with a layer of low density water

colder than 40C, but warmer than 0

0C forms just under the ice. Below this water, the

remainder of the lake water is usually near 40C. As spring approaches, the seasonal cycle

begins again (JPT, 2009; GVHU; Encyclopaedia Britannica, 1996).

4.5 Nutrient loading and primary production

Nutrient loading refers to the enrichment of a lake by nutrients (especially nitrogen and

phosphorus compounds, but also other organic matter). This increase in nutrients can occur

under natural or anthropogenic conditions which include nutrient inputs from sewage

discharges, increase usage of nutrient based fertilizers on farm land, changes in land use

causing erosion and weathering.

The increase in the concentration of nutrients in lakes can trigger a chain of events starting

with massive increase in primary producers since they are generally growth-limited by

nutrients especially phosphorus in freshwater ecosystem. Thus there is a planktonic algae

proliferation in the photic (surface layer) zone of lakes which is the productive layer. This

proliferation of algae in the photic zone can prevent the penetration of sunlight into the lake

which can in turn disrupt the production of oxygen. This whole situation leads to an

imbalance in the nutrient and material cycling process in the lake. Consequences derived

from the eutrophication process often affect most of the vital uses of the water. These

consequences in some cases are appearance of abnormal colours, bad smells, depletion in fish

diversity and changes in the composition of the populations of organisms (reduced

biodiversity). Lakes can be classified based on nutrient loading into oligotrophic lakes,

mesotrophic lakes, eutrophic and hyper-eutrophic lakes.

23

4.6 Limiting factor for lakes

These are factors which determine the level of production in water bodies i.e the nutrient

whose absence reduces or stops production. In lakes, the limiting factor is usually phosphorus

while in seas nitrogen becomes the limiting factor. This situation changes when the limiting

factor is in abundant supply e.g if the concentration of phosphorus is very high in lakes,

nitrogen becomes the limiting factor.

In lakes, the rule of thumb for limiting factors is given below;

Rule 1

P is most often limiting when [NTotal] / [PTotal] > 12-15. Here there is abundance of

nitrogen and less phosphorus.

N is most often limiting when [NTotal] / [PTotal] < 9-10. Here the concentration of

phosphorus is not very high.

Rule 2

P is limiting when [PTotal] < 0.05 mg/l

N is limiting when [PTotal] > 0.1 mg/l

“In lakes with P- limitation, ortho-phosphate concentration under production maximum will

be approximately zero”. This is because ortho-phosphate is usually the form that is used for

productions. Therefore, it would be used up at maximum production (Jens Peter 2009).

24

5 PARAMETERS FOR LAKE QUALITY ASSESSMENT

This chapter introduces the parameters which are to be taken into consideration when

assessing lakes. The subchapters will give a short description on what the parameters present

and why they are vital for lake water quality assessments. The first subchapter regards the

physical parameters, the second the chemical parameters and the third presents the biological

parameters.

5.1 Physical properties

5.1.1 Temperature

The temperature of water is considered as one of the main factors for the ecosystem which

can affect behaviour, metabolic rates and distribution patterns of organisms. Seasonal and

vertical changes of water temperature are the main determinant for behaviour of organisms,

as most of them adapt their body temperature to changes in water temperature (Cooke et

al.,1993).The main source of heat for lakes is solar radiation, which results mostly in seasonal

but also daily changes of temperature. The so called thermal stratification of lakes is a result

of solar radiation heating up the upper layer of a lake, whereas the lower layer does not

experience light, due to absorption of most light during the first meters. High density, low

temperature water settles, while water with higher temperature and lower density will remain

on the surface. These two layers occur during summer and winter months. During the autumn

and spring, the water temperature distribution is relatively equal, and the lake can be assumed

to be well mixed if no thermal difference is detected. Temperature should be determined at 1

m intervals with depth, but usually one profile at the deepest point is adequate if the water

body is small (Cooke et al.,1993).

The following graph presents one example of temperature and oxygen changes in a deep lake

(not Mølledam). With increasing water depth, the level of dissolved oxygen gradually

decreases, simultaneously to the temperature (Cooke et al.,1993).

25

Figure 5 Distribution of temperature and dissolved oxygen during summer thermal

stratification of an eutrophic lake (Cooke, et al., 1993).

5.1.2 pH

pH is defined as the negative logarithm of hydrogen ions concentration. It is an indication of

the acidity, alkalinity or neutral state of a substance. The pH scale ranges from 0 to 14.

Acidity decreases from 7 to 0, a neutral substance has a pH of 7 whereas alkalinity increases

from 7 to 14. pH is an important parameter for chemical and biological processes. For

instance pH determines the solubility of heavy metals in lakes and heavy metals can be quite

toxic to aquatic life especially when very soluble in water. Metals tend to be more soluble at

low pH. pH can also affect the form in which phosphorus is most abundant as well as

determine whether aquatic life can use it. It is thus a good indicator of water quality.

The pH values of lakes and ponds show regional differences and this can be due to variables

such as geological structure of catchment area, input of chemical substances from inlet, acid

rain and anthropogenic carbon dioxide. However, most lakes and ponds on earth have a pH

range of 6.0 to 9.0 (Bronmark & Hansson, 2005). This range is favourable for the life of

aquatic organisms and deviation can significantly affect aquatic life and may even lead to

0

5

10

15

20

25

0 5 10 15 20 25 30

Dep

th (

m)

Water temp°(C)

Temperature and Dissolved Oxygen (DO) in

eutrophicated stratified lakes.

DO (mg)

Temp (°C)

26

death. High pH changes in particular areas can be due to the presence of acidic or alkalinic

chemicals etc. (Michaud J 1991, Bronmark & Hansson, 2005).

5.1.3 Turbidity and transparency

The turbidity of lakes and water in general is affected by particles in water. Such water with

high turbidity is cloudy, i.e. has a high concentration of particles shielding the penetration of

light into the water. For lakes, this has a negative effect on plant and fish life, as life is mostly

depending on the availability of light. Water with low turbidity, such as clear mountain lakes,

is considered to be favored by human. Water containing high turbidity, such as the yellow

river in China, has a high density of solid particles. This should not be confused with

pollution, as sand particles, for example, are not pollutants in water. Suspended sediments

often come from sources such as resuspension from the lake bottom, construction sites,

agricultural fields, and urban storm runoff. Turbidity and transparency are indicators of the

impact of human activity on the land surrounding the lake. Transparency can be measured in

the field to indicate the level of biological activity; the estimation of such light penetration is

determined with the secchi disk. (Carlson, Simpson. 1996)

5.1.4 Secchi-depth

The determination of water transparency with a Secchi disk is one of the most reliable,

frequently used and meaningful indicators of lake quality. The Secchi depth is measured

insitu and immediately tells about the quality of the lake water. The depth of transparency is

the path length in Beer´s law equation trough which light is scattered and absorbed as a

function of particle concentration in the water. As the concentration increases, transparency

depth decreases exponentially. In essence, the light entering the water will be either absorbed

or scattered by particles, dissolved colored matter, and the water itself. However,

transparency can be intermitted through particles from algae and other suspended solids. The

higher the visible depth, the better state of lake can usually be expected. The secchi disk is a

white disk with a diameter of about 20 cm, which is lowered into the water of a lake until it

can be no longer seen by the observer. It can be expected, that light can penetrate about 1.7

times the secchi disk depth until it can no longer be seen. (Carlson, Simpson. 1996)

27

.

Figure 6 Secchi disk depth measurement

5.1.5 Conductivity

Conductivity is a measure of the ability of water to conduct an electrical current. The current

is conducted by moving ions which mainly come from dissociation of inorganic compunds.

Therefore conductivity measurements show the concentration of dissolved salts/solids in

water and other ions (Centre for Educational Technology 2004). Other factors that determine

conductivity are temperature, oxidation state and mobility of the ions. Organic compounds

and colloidal silica do not conduct electric current. The unit of conductivity is microsiemens

per centimeter (μS/ cm). Conductivity in fresh water ranges from 10μS/ cm to 1000 μS/ cm,

but may by higher in polluted water bodies, especially those polluted by sewage or fertilizers

(UNESCO/WHO/UNEP 1996).

5.1.6 Total solids

This is the total amount of the dissolved and suspended solids in water. Dissolved solids

include ions like calcium, iron, bicarbonate, phosphorus etc. that are dissolved in the water

and cannot be separated by filtration. Some of these ions are essential for aquatic life as cells

also depend on the density of total solids to determine the amount of water that flows in and

out of the cell. Suspended solids consist of such substances as clay, silt and various particles

which are suspended in the water and not dissolved. Suspended solids can affect the turbidity

and light penetration in a lake and hence affect the rate of photosynthesis. Dissolved solids

are able to pass through filter with 2μm pores while suspended solids cannot.

Total Solids (TS) = Total dissolved solids (TDS) + Total suspended solids (TSS)

28

The level of total solids in a lake can serve as an indication of the state of health of the lake in

that the total solids will support life either positively or negatively depending on its quantity

and quality. In addition, by comparing the total solid values at the inlet and the outlet,

information about the stocking of sediments and particles in the lake can be obtained.

Particles are usually introduced into lakes through the inlet stream and while some of these

solids may flow out at the outlet stream some may remain in the lake and eventually settle at

the bottom. The difference between the total solid at the inlet and the outlet can be used to

estimate how much particles are deposited in the lake. According to (APHA et al 1992) the

Total dissolved solids (TDS) can be calculated theoretically by multiplying the conductivity

of the lake by a factor (ranging between 0.55-0.9, depending on the water body). The total

suspended solids (TSS) can then be derived by subtracting the product from the amount of

total solids in the lake.

The total solid (also referred to as total residue) of a water sample can be determined by

evaporation and drying of that water sample and is measured in mg/L.

5.1.7 Alkalinity

The capacity of water to neutralize acid is known as alkalinity. It is the buffering capacity of

the water body (Bronmark and Hasson 2005). It is the sum of all the bases that can be titrated.

Alkalinity in water is due to the presence of different compounds. In many surface waters,

alkalinity is mainly a function of carbonate (CO3−2

), bicarbonate (HCO3−) and hydroxide

(OH−) content and it gives an indication of the concentration of these components. However,

if borates, silicates, phosphates, or other bases are present, the measured value may include

contributions from them. Forms of inorganic carbon at different pH levels are shown in

Figure 7.

29

Figure 7 Forms of inorganic carbon at different pH levels (COTF).

Another source of alkalinity is chemical composition of the soil. Water bodies are more

alkaline when the surrounding soil contains calcium carbonate (CaCO3, Limestone), while

granite or quartz bedrock leads to lower alkalinity (Addy et al., 2004).

Alkalinity is important in lake water because it protects fish and other aquatic life against

sudden pH changes. Living organisms, especially aquatic organisms function best in a pH

range of 6-9. Water with higher alkalinity is more resistant to pH changes as it has higher

buffering capacity for acid input, (acid rain, acidic wastes). Water with pH lower than 4.6

does not have the ability to neutralize strong acids as they are acidic and do not contain

HCO3− and CO3

−2. In well buffered lakes, daily fluctuations of CO2 concentration cause only

small changes in pH value (Addy et al., 2004). For protection of aquatic life, alkalinity should

not be lower than 20mg/l of CaCO3 (Greenberg et al., 1992).

Table 6 Classification of lakes and ponds based on alkalinity (URI, 2009).

30

5.2 Chemical properties

5.2.1 Dissolved Oxygen

The concentration of dissolved oxygen is a good indicator of the quality of water in the lake

and its ability to support aquatic life. Dissolved oxygen (DO) is a measure of the amount of

gaseous oxygen O2, dissolved in lakes and ponds at a particular pressure and temperature. It is

essential particularly for respiration of aquatic life and is utilised in other activities such as in

the decomposition of organic matter (Bronmark & Hansson, 2005). Changes in the amount

available in the lake could have significant impact on the behaviour and existence of

organisms which could lead to death in extreme deficiency. DO can be measured using a

probe meter or by nitration method in the laboratory. It is measured in mg/L.

5.2.2 Organic matter

Organic matter content in a lake can be used as an indication of the level of pollution in a

lake. High organic content may be an indication of water pollution. The sources of organic

matter in a lake can be natural or anthropogenic. The primary source of organic matter to

lake sediments is the plants in and around the lake (Meyers and Teranes 2002). Natural

substances include: humic acids, proteins, carbohydrates, starch, chlorophyll and other

compounds synthesized by aquatic organisms. Other organic substances may be introduced

into lakes as a result of anthropogenic activities like agriculture, wastewater effluents, acid

rain etc.

Organic matter within sediment samples can be quantified by burning a known amount of the

sediment at 550°C for one hour and then recording the decrease in weight.

5.2.3 Nutrients

The main nutrients of concern in lakes and stream are nitrogen and phosphorus. They are

indicators of water quality as excessive amounts usually result in eutrophication and algae

blooms. The main source of these nutrients for water bodies includes leaching fertilizers,

pesticides, animal manure from agricultural land, untreated waste water from industries,

municipal and sewer.

31

Total phosphorus

Phosphorus is one of the key nutrients required by all organisms for existence. Phosphorus is

essential for all organisms as it is needed for synthesis of enzymes, organic material (DNA,

RNA) and highly energetic molecules of adenosine triophosphate (ATP). Its presence and

that of other elements provide adequate environments for productions in lakes and other

water bodies. It occurs in water bodies both in organic and inorganic forms. The aggregation

of all phosphorus present in water is what is referred to as total phosphorus. It exists in

organic forms as part of the organism and in inorganic form as metaphosphates,

polyphosphates and orthophosphates (PO43-

) which is the form that is essential for organisms

(Bronmark & Hansson, 2005).

Phosphorus compounds enter the surface waters by weathering of rocks, decomposition of

organic matter, run-offs from agriculture, municipal and industrial wastewater. Under aerobic

conditions phosphates form insoluble compounds with iron Fe3+

and aluminium Al3+

ions

under acidic conditions and with calcium Ca2+

ions under alkaline conditions, and

precipitates. It then accumulates at bottom sediments where it is not available for

phytoplankton. However leaching of phosphorus from sediment is possible depending on pH

and dissolved oxygen (Loon and Duffy 2000) (Shaw et al, 2004).

Overloading of lakes with phosphorus leads to high productivity and this results to high level

of eutrophication. This eutrophication prevents the penetration of sunlight to deeper parts of

the lake resulting in low activity. When the plants die, their decomposition by aerobic

microorganisms leads to a high oxygen demand creating a low concentration of dissolved

oxygen in the bottom region of the lake.

Total phosphorus can thus be used to assess the quality of a lake and this is tied to nutrient

load and production. A high production corresponds to high nutrient load which in turn

relates to a high phosphorus concentration (Shaw et al, 2004).

Total nitrogen

This is the sum of the nitrogen present, in all the forms (organic and inorganic), in the lake or

stream. Naturally, nitrogen finds it way in lakes through precipitation, nitrogen fixation and

from surface and ground water drainage (Bronmark & Hansson, 2005). Anthropogenic

sources are mainly fertilizers from agricultural activities which leach during rainfall and other

32

activities into the lakes (Alma & Etheridge, 1993). It also occurs in organic forms during the

decay of plant and animal proteins from water organisms and waste water.

Like phosphorus, nitrogen is an essential nutrient for the growth and development of aquatic

organisms especially plants (as core element in DNA formation). Thus, high load leads to

high level of production in the lake like algae blooms. It is important to note that the effect of

nitrogen load depends on the concentration of phosphorus (limiting factor) i.e high nitrogen

load might not necessarily lead to eutrophication in the absence of phosphorus (Bronmark &

Hansson, 2005). However, this situation reverses in many polluted lakes where nitrogen

becomes the limiting factor.

Nitrogen content can be measured as total nitrogen or in the various forms in which it exists

in water. These forms are listed below;

Nitrates (NO3-) - This is the dominant form of nitrogen in water at normal concentration of

dissolved oxygen (Environment Canada, 2005) and it is the form of nitrogen that is readily

taken up by plants. Determination of its concentration gives an indication of the nutrient level

in the lake. Typical NO3- values range from between less than 1mg/L for unpollutet waters to

5mg/L for waters influenced by human activities. Natural concentrations of NO3- seldom

exceed 0.1mg/L. Extreme pollutions may lead to levels up to 200mg/L.

(UNESCO/WHO/UNEP 1996).

Nitrites (NO2-) - This the product of a nitrification process which is eventually converted to

nitrates for plant uptake.

Ammonia (NH3) – Ammonia in lakes is a product of the decomposition of organic materials

by heterotrophic bacteria especially in the low oxygen zones. It exists primarily in water as

ammonium ion (NH4+) and also as undissociated ammonium hydroxide (NH4OH) which is

toxic to aquatic life. The concentration of ammonia is an indication of the level of toxicity of

the lake.

5.2.4 Iron

One of the main chemical process affecting the flux of phosphorus at the sediment-water

interface is the complex binding of phosphate with iron in the presence of oxygen and the

released of phosphorus during anoxic conditions. (Bostrom et al. 1982). A chemical process

where electrons are lost is called oxidation and the opposite process where electrons are

33

gained, is called reduction. A reduction is always coupled with an oxidation and are together

called a reduction-oxidation reaction, or a redox reaction. A high redox potential is related to

well oxygenated environments (Bronmark and Hasson 2005).

At low oxygen concentration (low redox potential), iron occurs as Fe2+

which is soluble in

water. If the oxygen concentration increases (the redox potential increases), the chemical

equilibrium of the redox reaction is forced to the right and iron is oxidised to Fe3+

Fe2+

⇌ Fe3+

+ e−

Fe3+

which is not soluble in water but forms complexes with other molecules, precipitates and

sinks to the bottom of the lake. Phosphate, which is the main actor in the eutrophication

process, has a high affinity for forming such precipitates. This makes phosphate less

bioavailable for phytoplankton. However, as the oxygen concentration declines, iron will

transform to its reduced, soluble form (Fe2+

) and release its phosphate, again making it

available for phytoplankton growth in a process called internal loading (Burns and Ross

1971).

5.2.5 Biochemical Oxygen Demand (BOD5)

The BOD5 is one of the most common determinations of water quality in regards of bacterial

activity and organic material available for bacteria digestion. Bacteria consume oxygen

during digestion of the organic material available, which can be measured in respect of their

activity. The BOD5 determines the amount of oxygen consumed by the mater matrix after 5

days at 20°C storage. The higher the value, the more biological available the water sample.

Typical values of BOD are given in mg/L and range between 1mg/L for drinking water, 200-

300mg/L in domestic waste water to several thousand mg/L in pure manure from cattle.

(Bank, 1994)

The value is determined every 24 hours after the test is started and should increase with time.

For example, the BOD of 500mg/L indicates that a sample of one litre water consumed

500mg of pure oxygen within 5 days at 20°C.

34

5.3 Biological properties

5.3.1 Aquatic macrophytes

Aquatic macrophytes are plants, growing in water or in wet areas which are visible to the eye.

Examples are mosses, macroalgae, ferns angiosperms etc. They are of great benefit as they

serve as a source of oxygen and food for the macroinvertebrates (US EPA, 2008a). They

occur in three main different forms:

Emergent Macrophytes (when the plants are rooted in the sediments and protrude up

above the surface of the water),

Submergent Macrophytes (when they grow completely below the surface),

Floating and Free floating Macrophytes (floating when the plants are rooted to the

bottom with leaves floating on the surface of the water or free-floating when they are

not rooted to the bottom but their leaves are still floating on the surface).

Macrophytes are excellent indicators of water quality because of

their noticeable response to toxic chemicals, metals and conditions like nutrient

loading and turbidity

the ease in sampling using aerial photography or transects

Overabundance of macrophytes may interfere with lake processing and recreational activities.

(US Environmental Protection Agency, 2008a; Kesab Website).

35

Figure 8 Macrophytes in a lake

5.3.2 Phytoplankton

Phytoplankton are small microscopic plants which float in the water body. They are the

autotrophic part of plankton and thus are primary producers (photosynthetic) in the aquatic

food chain fixing large amount of carbon and producing oxygen. Phytoplankton are very

small (microscopic) but when appearing in big numbers they can be seen as green coloration

in the water due to the presence of chlorophyl within their cells. The size of phytoplankton is

about 0.002 mm to 1 mm. They include diatoms, dinoflagellates, cyanobacteria and ciliata.

They depend on light since they are photosynthetic and so they have to live in the surface

layer (photic zone) of the water body.

Figure 9 Phytoplankton

The growth or decline in the population of certain species of phytoplankton can be an

indication of water quality as their population can correspond to the enrichment or reduction

of certain minerals like phosphates and nitrates. For example a high population of the

chlamydomonas sp (algae bloom) in a lake or stream is an indication of a eutrophication

36

while a low population may indicate low contamination. Regular monitoring of Diatoms

enforces environmental legislation in some countries of Europe. Diatoms contain silica on

their body and presence of Diatoms relates the Silicate in the lake water. Trophic Diatom

Index for Lakes (TDIL) can be used to assess the ecological lakes (Csilla et al., 2007).

5.3.3 Zooplankton

These are tiny animals classified as flagellates and protozoans which are able to float, drift or

partially swim in water bodies. They are dependent on water current to move any distance.

Most of them are too small to be seen with the naked eyes. There are two kind of

zooplankton: holoplanktonic organisms which spend their complete life cycle as a part of

plankton, and meroplanktonic organisms which spend a larval or reproductive stage in the

plankton. Zooplanktons are mainly heterotrophic, feeding on the phytoplankton population.

They also serve as food for consumers on higher trophic level (Michaud 1991, ETE 2004).

Their increase is an indication of high nutrient activity which could be due to human

activities like agriculture.

Figure 10 Some species of Zooplankton (Wikipedia, 2009)

5.3.4 Chlorophyll α

Chlorophyll a is the green pigment that allows plants to convert sunlight into organic

compounds through the process of photosynthesis. It is the most common of the five

37

photosynthetic pigments present in every plant that performs photosynthesis and is a useful

parameter for determining the biological productivity of a water body. An excessive amount

of chlorophyll a is a sign of excessive nutrient load, which subsequently reduces the amount

of dissolved oxygen. This can eventually result in eutrophication. This unusually high

concentration of chlorophyll a is more often than not attributed to anthropogenic sources.

Chlorophyll is a measure of all green pigments whether they are active (alive) or inactive

(dead) and is a measure of the portion of the pigment that is still active i.e, the portion that

was still actively respiring and photosynthesizing at the time of sampling”. It is measured in

μg/L. The chlorophyll-a concentration is associated with high algae population. Therefore, it

also has influence on dissolved oxygen, nutrients, pH changes in the lake. High algae

concentration may also cause aesthetic problems. The algae of concern in this case are a

group called the “blue-greens” – named after their particular pigment colour.

Figure 11 Structure of Blue green algae (Left) (Michaud 1991) and

Algae bloom (Right) (Nature Report,2008)

5.3.5 Macroinvertebrates

Macro-invertebrates are the animals without backbone (invertebrates) and are visible to the

eyes. These include insects like the stoneflies (plecoptera), mayflies (ephemeroptera),

crustaceans like the crayfish (parastocoidea), molluscs like snails and clamps, worms

(annelids) etc all of which live in a river channel, pond, lake, wetland or ocean. These aquatic

organisms particularly those live in bottom part of the lakes (benthic macroinvertebrates) are

38

usefull as water quality indicators. This is because they are sensitive to pollution, and also

since they have limited mobility they mainly stay in areas that will encourage their survival.

Their presence in waters can thus be an indication of the present state of stream or lake. They

are also easy to collect and identify. The orders Ephemeroptera, Plecoptera, and Trichoptera

are very important and sensitive to pollution and thus they are used as unpolluted water

quality indicators (ETE 2004).

5.4 Danish Stream Fauna Index (DSFI)

The Danish Stream Fauna Index (DSFI) is a standardised method for biological assessment

(biomonitoring) of running waters in Denmark. The DSFI has been developed primarily to

detect the impact of organic pollution using microinvertebrate taxa. It was introduced in

1998 and is currently used yearly at 1051 stations in the National Monitoring Programme for

the Aquatic Environment NOVA. It is also widely used by regional water authorities.

In the DSFI the ecological quality in running waters is described by index values ranging

from 1 to 7, with the highest number representing the best ecological quality. The table

showing the values and taxas of the DSFI can be found in the appendix. (DSFI 2009)

39

6 SAMPLING AND ANALYSIS OF SAMPLES

The samples were taken together with the other MET groups. The workload was shared

between both groups and the aim was to have one group member from each group

performing the different sampling. The samples were not taken according to any standards

nor were the samplers accredited samplers. This has to be taken into consideration when

evaluating the sampling methods used and when evaluating the analysis results.

The macro invertebrate samples were taken on the 7th

October 2009. Water and sediment

samples were taken on the 16th

October. In this chapter the sampling method, the sampling

locations and method of analysis are presented. The parameters that were measured are

reported under the subchapters: in-situ measurements, water sample measurements, sediment

sample measurements and biological measurements.

6.1 In-situ measurements

The parameters that were measured in-situ are; dissolved oxygen, temperature, pH,

conductivity and flow rate.

Dissolved oxygen, Temperature, pH and Conductivity

Dissolved oxygen, temperature, pH and conductivity were measured in-situ using a dissolved

oxygen and temperature meter, pH meter and a digital conductivity meter respectively. Water

samples were collected into water bottles and the parameters were measured by dipping the

above mentioned measuring instruments into the bottles. Their values were recorded.

Measuring these parameters on site will give more reliable results since transportation and

storage time will affect these parameters.

The Secchi-depth was also measured at the lake by using Secchi-disk. The Secchi disk is a

20cm disk, which was lowered into the water of the lake until it was no longer seen.

40

Figure 12 Field analyzers used for the in-situ measurements: Secchi disk (Left); and pH and

Conductivity meter (Right)

Flow rate

In order to determine the input and output of water and nutrients to and from the lake, the

flow of the inlet and the outlet stream are measured. For this measurement, a current meter

equipped with an electric counter, as shown in the figure below, was used.

Figure 13 Current meter as used in the flow measurement

Principle (Flow measurement)

The principle relies on the current of the water which causes a small propeller to rotate. The

rotation is electronically counted for a period of 50 seconds at different positions along the

stream’s transect. Therefore, the profile is divided into different sections and the flow is

measured each at different depths just below the water surface. Based on the rotation

measurements, the flow velocities and the areas of different depths - the volume flows can be

calculated by means of a mathematical algorithm. Subsequently, the retention time of water

in the lake (turnover time) can be determined by dividing the lake’s volume by its output

flow. Moreover, if the volume flow [l/s] and the nutrient concentrations [mg/l] are known, it

41

is possible to determine the annual input and output of nutrients to and from the lake caused

by the runlets.

Inlet

The survey of Guldager Mølledam revealed that there is one inlet at the north shore of the

lake. The Inlet had a shallow, very slow flow and relatively wide profile embedded with a lot

of organic deposits. Two flow measurements were undertaken which is a representative of the

Inlet stream flow. Based on the wide cross-sectional area and the flow velocity, which was

determined by means of a current meter and formula provided by the measurement

equipment, the flow had been determined. For each of the sub-areas the flow velocity was

measured separately and the total inlet flow equal the sum of the partial flows.

Outlet

Guldager Møllebæk is the only outlet of the lake and is much larger than the inlet runlet. As it

flows through a pipe below a bridge providing defined geometric dimensions, the hydraulic

profile can be divided into sub-areas as shown in the diagram. For each of the sub-areas the

flow velocity was measured separately and the total outlet flow equal the sum of the partial

flows.

6.2 Water sample measurements

6.2.1 Sampling

The water samples were taken on the 16th

October. The water sample from the outlet stream

was taken from the other side of the road, close to the road drum. The location is presented in

figure 13. Five litres of water was taken and placed into plastic flasks with a lid. The water

sample from the inlet stream was taken approximately 20 metres upstream from the lake. It

was not possible to take the sample closer to the lake due to dense vegetation. Five litres of

water was taken.

Temperature was measured at several points in the lake as well as depth in order to establish

that the lake water was well mixed. Since the temperature difference between the points were

not significant, the decision was made to take three water samples from one sampling point.

The purpose of taking three samples was to be able to calculate that the samples were

statistically representative for the lake water. The samples were taken in the middle of the

42

lake and will represent the water quality in the entire lake. From the same sampling point the

Secchi-depth, water temperature and water depth was measured. Five litres of water sample

was taken and also one one-litre sample to measure the alkalinity.

Figure 14 Lake water sampling

6.2.2 Analysis of water samples

The parameters that were analysed from the water samples include: alkalinity, BOD5, total

solids, total nitrogen, total phosphorus and orthophosphate, iron, chlorophyll a.

Alkalinity

Alkalinity was determined using Radiometer Analytical. Alkalinity of water was determined

by end point titration with a strong acid solution. Phenolphtalein alkalinity corresponds to

titrable alkalinity at pH 8.3 and total alkalinity corresponds to titratable alkalinity at pH 4.5.

This application note is an application of international standard ISO 9963-1.

We calibrated the electrode with pH 4.005 and pH 10.012 IUPAC Series pH standards and

pipetted 100ml of water into a flask. The electrode was dipped and delivered tipped in the

sample. The method was started by pressing the RUN key on the Radiometer Analytical and

the results were provided.

43

Figure 15 Radiometer Analytical

BOD5

Water samples collected for BOD measurement must not contain any added preservatives and

must be stored in glass bottles. Ideally the sample should be tested immediately since any

form of storage at room temperature can cause changes in the BOD (increase or decrease

depending on the character of the sample) by as much as 40 per cent. Storage should be at 5°

C and only when absolutely necessary. The determination was performed through the

OXITOP measurement.

Figure 16 Oxitop BOD5 determination flasks. (ENVCO)

44

Total solids

Dry and empty beakers were weighed on the electronic weighing balance and their

measurements taken. 50 ml of the water samples (inlet and outlet) were then measured into

the beakers using a pipette after which the beakers were placed on the heater and the samples

evaporated to dryness. The weight of the beakers was then measured on the weighing

balance. The difference in weight of the empty beakers after heating and before heating

represents the total solids.

Calculation : Total solids (mg/L) = mlvolumesample

BA

,

1000)(

Where: A = weight of dried residue + beaker (after evaporating and drying)

B = weight of empty and dry beaker (before evaporating and drying)

Measurements for total solids were not taken at the middle of the lake but it can be expected

that the value for the amount of totals solids at the middle of the lake should be between the

results for the inlet and outlet.

Total Nitrogen

The determination of nitrogen was divided into two parameters, the total nitrogen asessment

and the subconsequent nitrate. The analytics were performed through the FIA STAR 5000, 2

weeks after the water samples were taken. The total amount of nitrogen in the sediment

samples was analysed with FIASTAR 5000.

The total nitrogen assessment and the subsequent nitrate were performed during this project

work. Theoretically, samples taken for the determination of total nitrogen, nitrate and nitrite

should be collected in glass or polyethylene bottles and filtered and analysed immediately.

According to the literature, if this is not possible, 2-4 ml of chloroform per litre can be added

to the sample to retard bacterial decomposition. The sample can then be stored at 3-4° C.

45

Figure 17 FIASTAR 5000

Total Phosphorus and Orthophosphate

Total phosphorus was measured in the water samples using FIASTAR 5000 Analyzer, each

sample was analyzed twice. The concentrations obtained were very low, approximately to

zero. We were then advised by the Laboratory Technician to analyse for orthophosphate in

the water samples at a lower calibration curve which will be approximately the same as the

concentration for total phosphorus. The analysis was carried out two weeks after collection of

the sample. Samples from the lake, inlet and outlet stream were analyzed without the

treatment of autoclave. The samples were filtered through 0.45 m membrane filters for the

analysis.

Iron

Iron in the water samples was measured with Atomic Absorption Spectrometry (AAS). AAS

is used for the determination of trace elements in water samples and in acid digests of

sediment. The water samples were pre-treated by taking 40-ml of sample, adding 10-ml

concentrated nitric acid and put into the autoclave for 30 minutes. Standards were prepared

with the concentrations of; 1 ml/l, 5 ml/l and 10 ml/l. The standards were run through the

AAS in order to obtain a calibration curve, where after the samples were analyzed.

46

Chlorophyll a

The amount of chlorophyll a in the samples was measured following a protocol obtained from

a Danish standard for water and environment (DS2201). The following steps were undertaken

(for every sample in duplicate):

a. 400ml of each sample was filtered through Whatman GF/C filter paper (4.7cm)

making use of a vacuum pump.

b. Each filter paper was transferred to a 10ml centrifuge tubes and stored in the fridge at

–80 C for one day

c. The centrifuge tubes were filled with 96% ethanol, wrapped in aluminium foil and

kept for 20 hours

d. The samples were centrifuged at 10000rpm for 10 minutes

e. The volume of ethanol was filled up to 10ml

f. The samples were analysed with a spectrometer at two different wavelenght namely

665 nm and 750 nm. Plastic cuvettes were used.

The concentration of chlorophyll a in g/L was then calculated based on the results.

6.3 Sediment sample measurements

6.3.1 Sampling

Sediment samples were taken from three sampling points, one in the middle of the lake, one

close to the inlet stream and one close to the outlet stream. The location of the sampling

points for the sediment samples together with the approximate distance from the shore is

presented in figure 18.

47

Figure 18 Location of sampling points for sediment samples and lake depths

The purpose of the locations for the sediment samples was to be able to compare the

distribution of substances in the lake sediment. The sampling points were given a number

where 1 is the middle of the lake, 2 is close to the inlet, and 3 is close to the outlet.

6.3.2 Analysis of sediment samples

The parameters analyzed in the sediment samples are: metals and phosphorus, iron, nitrogen

and organic matter.

Metals and Phosphorus

The amount of metals and phosphorus in the sediment samples were measured with Perkin

Elmer Optima 3000DV. Inductively coupled plasma atomic emission spectrometry (ICP

AES) is used for qualitative and quantitative measurements of elemental composition in

samples. The samples, for the metal analysis, were pretreated and diluted to 50-ml. Standards

were prepared with the concentration, 1 ml/l, 2 ml/l and 10 ml/l. A calibration curve was

made and the samples were analyzed.

The samples for phosphorus analysis needed different standards than for the metals. The

standards had concentrations of 1 m/l, 5 ml/l, 10 ml/l and 20 ml/l. When measuring

phosphorus with ICP AES, a higher pearch has to be used since the measurements are

performed in low range. This is done by inserting N2-gas that eliminates any air in the

samples.

48

Figure 19 Location of sampling points for sediment samples and lake depths

Iron

The amount of iron in the sediment was measured using Atomic absorption

spectrophotometry (AAS). The same samples were used as for the ICP analyses, however

they had to be diluted one more time by taking 1-ml of sample and diluting it up to 100-ml.

Standards with concentrations of 1 ml/l, 5 ml/l and 10 ml/l were made. The standards were

run through the AAS apparatus, where after the samples were analysed.

Figure 20 Atomic Absorption Spectrometer

49

Nitrogen

The total amount of nitrogen in the sediment samples was analysed with FIASTAR 5000.

The samples were pre-treated and then analysed at the same time the as the water samples.

The sediment samples were treated in the same manner as the water samples.

Organic matter

The furnace was turned on and set to 500°C and allowed to heat up for about an hour.

Defined amounts of each sample, was then transferred into dry and empty crucibles. The

weights of the sample and crucibles were measured on the weighing balance after which they

were transferred into the furnace. The samples were left to heat in the furnace for three hours

after which the furnace was turned off. The samples were then left in the furnace overnight.

The next day the crucibles were removed from the furnace and their weights were

determined. Organic matter content was determined as the loss in weight.

6.4 Biological measurements

The following biological parameters were analysed in this study: phytoplankton and

macro-invertebrates.

Phytoplankton

Sampling

Plankton was sampled in duplicate very close to the outlet of the lake. A cone-shaped sieve

was moved along the surface of the lake and filled with water. The ventil was closed, and the

water was allowed to filter out of the sides, to obtain a concentration of the plankton

concentrated in the small plastic funnel. Then the ventil was opened, and the sample poured

into a bottle. This process was repeated until the bottle was full. Figure 21 shows the plankton

net used for collecting plankton from the lake.

50

Figure 21 Net for collecting phytoplankton

Analysis of phytoplankton

In the laboratory, 3 drops of the sample collected were mounted on a microscope slide and

covered with a cover slip. The specimen was examined under an Olympus 249113

microscope and different magnifications (10x – 40x) and light intensities were used. Pictures

of these micro-organisms were taken and compared to a reference key (Tavlerne Fra Dansk

Planteplankton by Gunnar Nygaard) which were then identified accordingly.

This set up is shown below:

Figure 22 Olympus 249113 Microscope used for identification of plankton

Macro-invertebrates (DSFI Methodology)

The macro-invertebrates were collected and analysed based on the method in the Danish

Stream Fauna Index (DSFI). The biological organisms were collected at the outlet stream,

51

around 50 metres downstream from the lake. The biological samples were obtained by

applying the kick-sampling method and pick sampling. The samples are taken to the

laboratory where the organisms are killed by adding ethanol. When the organisms are dead

they can easily be selected out from the unnecessary debris and placed into the refrigerator

until they are to be evaluated.

Kick sampling

Three transect points approximately 10 metres apart were marked along the stream, and from

each of these transect points, four kick samples were collected. The sampling was done from

downstream to upstream to prevent disturbance of sediment due to water flow. Samples were

then collected by putting the hand net on the stream bed, placing the foot in front and then

moving the foot backward against the current. By this movement animals and sediment are

collected into the net. The animals were then selected from the sediment and put in trays.

Figure 23 Kick sampling

52

Pick sampling

Stones were collected from an undisturbed part of the stream, and from these stones animals

were picked into a dish within 5 minutes. These samples are later on pooled together to get a

composite (a more representative) sample which is then used for analysis.

Laboratory analysis

In the laboratory, the animals were properly selected from the sediments and placed in

ethanol in order to kill and preserve them. They were then stored in the refridgerator

overnight.

Figure 24 Microscope for Macro-invertebrate analysis

Following this, the animals were visually observed using a microscope and identified by their

individual taxa according to literature (Macan, and Quigley). After which, the samples were

then sorted according to their indicator group (IG) and diversity groups as described in the

DSFI methodology and the calculation of the DSFI index value was done. Those with no

classification were disregarded.

53

7 RESULTS

In this chapter the results from the analysis are presented and the reliability of the results is

discussed. The results of the parameters measured are presented under the sub-chapters:

results of in-situ measurements, results of water sample measurements, results of sediment

sample measurements and results of biological measurements.

7.1 Results of In-situ measurements

The average depth measured of the lake was 1,47 m and the highest depth was 1,78 m. The

results of Secchi-depth for the three measured points are 1.5 m, 1.60 m and 1.78 m. The

results of the remaining in-situ measurements are presented in table 7.

Table 7 The average results from in-situ measurements

Sampling

Points

Temperature

(°C) pH

Conductivity

(μS/m)

Dissolved Oxygen

(mg/l)

Inlet 7.0 6.92 402.0 8.65

Middle 7.2 6.85 400.0 10.97

Outlet 7.7 6.91 393.0 11.00

Flow rate

The detailed calculations of the flow including all formulae are presented in the appendix of

the project.

n- Revolution per second

For: 0.52 s−1

≤ n ≤ 1.26 s−1

v = 0.2303.n + 0.040

For: n ≥ 1.26 s−1

v = 0.2485.n + 0.017

Flow: Q = v*A

54

Inlet

Table 8 The flow measurements for the inlet

Sampling Points Point A Point B

Profile (m2) 0.062 0.124

Velocity (rps) 0.440 0.580

Velocity (m/s) 0.141 0.174

Flow (l/s) 8.74 21.56

The calculations for the flow measurements are presented below.

Total Inlet

Flow: Q inlet, total = QA + QB

= 30.3 m3/s

Q inlet, total = 0.0303 m3/s = 30.3 l/s

NO3/NO2: mInput, NO3/NO2 = Q inlet, total × c NO3/NO2

= 30.3 l/s × 8.136 mg/l = 247mg/s

Outlet

Table 9 Flow measurements for outlet

Sampling Points Outlet A Outlet B Outlet C Outlet D Outlet E

Profile (m2) 0.0294 0.036 0.036 0.0262 0.0294

Velocity (rps) 0.98 0.94 0.78 0.76 0.72

Velocity (m/s) 0.266 0.256 0.224 0.215 0.206

Flow (l/s) 7.8 9.22 8.1 5.6 6.1

55

Total Outlet

Flow: Q outlet, total = QA + QB+ QC+ QD+ QE

= 0.0078 m3/s + 0.00922 m

3/s + 0.0081 m

3/s+ 0.0056 m

3/s + 0.0061 m

3/s

Q outlet, total = 0.03682 m3/s = 36.82 l/s

NO3/NO2: mOutput, NO3/NO2 = Q outlet, total × c NO3/NO2

= 36.82 l/s × 5.68 mg/l = 209 mg/s

Turnover time

After calculating the flow, we were able to count the hydraulic turnover time in Guldager

Mølledam in which the entire water masses are exchanged once. The way of calculating and

the results are presented in the following.

Approximate length of lake: 207 m

Approximate width of lake: 80 m

Average lake depth: 1.3 m

Average volume of Guldager Mølledam:

V = length × width × depth

= 207m × 80m × 1.3m = 21,528 m3

Hydraulic turnover time(τ) = V

Q outlet, total

= 21,528 m3

1,161,155 m3/a

= 0.01854016a

Therefore the turnover time of Guldager Mølledam is approximately 6.7 days.

56

7.2 Results of water sample measurements

Alkalinity

The results for the alkalinity measurements are presented in the table below.

Table 10 Results from alkalinity measurements

Number of Sample Alkalinity

(mg CaCO3/l)

1 50.10

2 63.36

3 51.88

4 49.68

5 54.39

Average 53.88

Alkalinity was measured in five water samples. The alkalinity of a water body indicates its

capacity to neutralize acids, which protects and buffers against rapid changes of pH.

BOD5

The BOD5 determination was started one day after the sample was taken from the lake. The

method of measurement was done with OXITOP bottles. The figure below presents the

results of the BOD5 measurement; all values are given in mg/L O2.

Figure 25 BOD5 Results

2 2 2

1 1

0

1

2

3

4

5

mg/l

O2

BOD5 (mg/l)

Inlet1 Inlet2 Middle1 Middle2 Outlet1 Outlet2

After 24

hours48 hours 3 days

4 days 5 days

57

The overall results indicated a very low consumption of oxygen. This suggests low amount of

biodegradable organic matter and thus more available oxygen. This is reflected in the high

amount of dissolved oxygen in the lake. The highest value of 5mg/l can still be considered

with high water quality. The values were close to the detection limit and can therefore show

variations in BOD levels which are virtually impossible to obtain; e.g. the value of inlet 1.

Total Solids

Table 11 Total Solids results

Sample

Wt. of Beaker

and sample

(g)

Wt. of Beaker

(g)

Wt. Of

residue (g)

Total

Solids

(mg/l)

Average

Outlet 1 46.6878 46.6981 0.01030 206 209

Outlet 2 50.6209 50.6315 0.01060 212

Inlet 1 47.9775 47.9915 0.01400 280 293

Inlet 2 43.1152 43.1305 0.01530 306

The difference in the total solids at the inlet and outlet as seen in table 11 is an indication that

particles are being deposited or utilised in the lake. This suggests that the lake acts as a sink

which collects particles from the inflowing stream thereby improving the water quality. The

amount of solids deposited in the lake is calculated by multiplying the total solids at inlet and

outlet with their respective flow rate values and then finding the difference. The results are

given below.

𝐴𝑚𝑜𝑢𝑛𝑡 𝑜𝑓 𝑠𝑜𝑙𝑖𝑑𝑠 𝑔𝑜𝑖𝑛𝑔 𝑖𝑛 𝑙𝑎𝑘𝑒 = 𝑓𝑙𝑜𝑤 𝑟𝑎𝑡𝑒 𝑎𝑡 𝑖𝑛𝑙𝑒𝑡 × 𝑇𝑜𝑡𝑎𝑙 𝑠𝑜𝑙𝑖𝑑𝑠 𝑎𝑡 𝑖𝑛𝑙𝑒𝑡

30.3 𝐿/𝑠 × 293 𝑚𝑔/𝐿 = 8877.9 𝑚𝑔/𝑠

𝐴𝑚𝑜𝑢𝑛𝑡 𝑜𝑓 𝑠𝑜𝑙𝑖𝑑𝑠 𝑔𝑜𝑖𝑛𝑔 𝑜𝑢𝑡 = 𝑓𝑙𝑜𝑤 𝑟𝑎𝑡𝑒 𝑎𝑡 𝑜𝑢𝑡𝑙𝑒𝑡 × 𝑇𝑜𝑡𝑎𝑙 𝑠𝑜𝑙𝑖𝑑𝑠 𝑎𝑡 𝑜𝑢𝑡𝑙𝑒𝑡

36.82 𝐿/𝑠 × 209 mg/L = 7695.38 𝑚𝑔/𝑠

𝐷𝑖𝑓𝑓𝑒𝑟𝑒𝑛𝑐𝑒 𝑖𝑛 𝑡𝑕𝑒 𝑡𝑤𝑜 𝑣𝑎𝑙𝑢𝑒𝑠 𝑖𝑠 8877.9 𝑚𝑔/𝑠 − 7695 𝑚𝑔/𝑠 = 1182.52 𝑚𝑔/𝑠

Therefore the amount deposited in the lake per second is 1182.52 mg/s

58

Total Nitrogen and Nitrogen Oxides

The storage time for our samples was consequently not suitable for any reliable result. The

following graphs present total nitrogen (TN) and nitrate (NO) concentrations from inlet,

outlet and lake middle sampling.

Figure 26 Total Nitrogen (mg/l) results

The results indicate a higher load of nutrients from the inlet of the lake. The nitrogen

compounds decrease during the retention time inside the lake and eventually leave the outlet

with reduced concentration. This indicates a nutrient fixation of nitrogen inside the lake.

Typical nitrogen concentrations vary from a few micrograms per litre in some lakes to more

than 20 mg/l in raw sewage.

8,1361

6,1436 5,8687

0

1

2

3

4

5

6

7

8

9

Inlet Middle Outlet

Total Nitrogen (mg/l)

59

Figure 27 Nitrogen Oxides (mg/l) results

The determination of nitrate should indicate lower concentrations than the total nitrogen, due

to the fact that nitrate is one of the compounds evaluated with TN. As can be seen from the

graph, this is the case, but most of the TN found in the lake is available in the form of nitrate.

Total Phosphorus and Ortho-Phosphate

In the tables below the measured concentrations of total phosphorus and ortho-phosphate are

presented. The measurements for total phosphorus were below the calibration curve,

however, the advice was given that the concentration of ortho-phosphate will be almost the

same as for total phosphorus.

Table 12 Total phosphorus in the Inlet, Lake and Outlet

INLET MIDDLE OUTLET

Total osphorus

PO4-P

(mg/l)

0.941 0.061 -0.100

0.939 0.088 -0.103

-0.107 0.065 -0.098

-0.108 0.061 -0.094

-0.090 0.060 -0.110

-0.093 0.058 -0.112

Average (mg/l) 0.247 0.036 -0.103

Dilution Factor (0.8) 0.8 0.8 0.8

Total Phosphorus

PO4-P

(mg/l)

0.1976 0.0288 -0.0822

7,9085

4,9895 5,0195

0

1

2

3

4

5

6

7

8

9

Inlet Middle Outlet

NO3- (Nitrate, mg/l)

60

Table 13 Ortho-phosphate in the Inlet, Lake and Outlet

Trial INLET MIDDLE OUTLET

Total Phosphate

PO4-P

(μg/l)

1 10.490 12.539 12.873

2 10.179 11.831 12.704

3 8.878 11.642 12.597

Average (μg/l) 9.849 12.004 12.725

Standard Deviation 0.855 0.473 0.139

Iron

The results from the iron analysis in the water samples are presented in table below.

Table 14 Iron content results

Sample

Point Fe (mg/) measured Fe (mg/l) final

Lake (1) 0.39 0.48

Lake (2) 0.37 0.46

Lake (3) 0.33 0.42

Inlet 0.29 0.37

Outlet 0.34 0.42

The average amount of iron in the lake is 0.45 mg/l. The content of iron is based on

calculations from the measured amount times the dilution factor.

Chlorophyll a

The chlorophyll a concentration in the water samples are presented in Table 15.

Table 15 Chlorophyll a results

Sample

Point Abs 665 Abs 750 A665-A750

Chlorophyll

Concentration

(μg/l)

Average

(μg/l)

Middle (1) 0.0744 0.0253 0.0491 14.49 15.36

Middle (2) 0.0531 0.0002 0.0529 15.93

Middle (3) 0.0910 0.0880 0.0030 0.900 6.79

Middle (4) 0.0603 0.0182 0.0421 12.68

Average 11.08

61

Chlorophyll a is a measure of all green pigments whether they are active (alive) or inactive

(dead). Chlorophyll a is a measure of the portion of the pigment that is still active; that is, the

portion that was still actively respiring and photosynthesizing at the time of sampling.

CALCULATION:

For Sample 1.1: 104 . e. A(665K)

83. v. l

C = 104 . 10ml. 0.0491

83 1 . 4l. 1cm

g.cm

C = 14.79 g/L

Where:

C = concentration of chlorophyll in g/L

e = volume of ethanol in which the sample was diluted (10 ml)

83 = absorption coefficient of 96% ethanol in 1*g−1

*cm−1

I = volume of sample that was filtered (400ml)

V = lenght of the cuvette (10mm)

A(665K) = A(665) – A(750)

7.3 Results of sediment sample measurements

Heavy metals, iron and phosphorus

The results from the sediment analysis are presented in table 16.

Table 16 Sediment analysis results

Sample

Point

Ni

(mg/kg DS)

Pb

(mg/kg DS)

Cd

(mg/kg DS)

Fe

(mg/kg DS)

P

(mg/kg DS)

N

(mg/kg DS)

Middle 29.41 59.14 -1.70 24.69 1.72 0.40

6.55 47.73 -4.30 45.69 0.34 0.34

Inlet 26.26 26.35 -3.25 15.28 0.31 0.43

0.60 10.47 -3.99 0.94 -0.03 0.16

Outlet 28.39 32.44 -2.60 17.56 1.23 0.48

62

25.51 58.13 -3.10 34.65 2.53 0.37

Average 19.45 37.38 -3.16 23.13 1.02 0.36

The results for cadmium were all under the detection limit and therefore negative results are

shown. The cadmium results are not to be considered since they do not represent the actual

situation. The results for the samples from the inlet are not representative since they differ

significantly from other results. The reason for the difference might be due to errors

occurring when pre-treating the sample or dilution of the sample. Even in the reference

sample which was made the same pattern could be followed. The sediment in the bottom

layer at inlet was sandy and smelled of sulphur. This might be the reason to poor results, the

method used is more suitable for soil types with a smaller grain size.

Organic matter

The results for the organic matter analysis are given in the table below.

Figure 28 Organic Matter in Sediment samples

The results show that organic matter is highest at the middle of the lake. The values for both

the upper and lower layer samples at that point are higher than the values from the inlet and

outlet. This suggests that organic matter is being deposited at the bottom point of the middle

of the lake.

0.11

0.1580.137

0.035

0.404

0.14

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

INLET MIDDLE OUTLET

TOP

BOTTOM

63

7.4 Results of biological measurements

Phytoplankton

The microscopic examination indicates the presence of both phytoplankton and zooplankton.

The phytoplankton species belong to the groups of greenalgae, diatoms, euglenoids, and blue-

green algae.

S1.Phacus sueicicus Llemmerman S2.Synedra acus Kützing

Hyalotheca mucosa Ehrenberg

S3.Fragilaria capunica Desmazieres S4.Synedra ulna Ehrenberg

S5. Chlamydocapsa planctonica Fott S6.Tetraedron limneticum Borge

64

S7. Peridinum aciculiferum Lemmerman S8. Diatoma Elongata Agardh

S9. Mallomonas Caudata Iwanoff S10. Mallomonas Teilingii Conrad

S11. Asterionella formosa Hassall S12.Pleurotaenium trabecula Ehrenberg

65

S13. Perinidium palatinum Lauterborn S14. Chlamydocapsa planctonica Fott

Westella botryoides Wildermann

Figure 29 Various species of Phytoplanktons

The processes of photosynthesis and respiration caused by algae ehance changes in lake pH,

and the presence of algae in the water column is the main factor affecting Secchi disk

readings. Algae cause aesthic problems in a lake; a green `Scum,` swimmers itch, and rotting

scent are common problems associated with high algae concentrations.

Macro- invertabrates

The individual macro-invertebrates collected during the sampling, their taxonomy, number,

pictures and diversity groupings are given in the table below.

Table 17 Macro-invertebrates in Guldager Møllebæk

Organism Kick

sample

Pick

sample Image

Diversity

Groups

Common name: Gammarus

pulex

Class: Crustacea

Order: Amphipoda

Family: Gammarus

> 10

4

Positive

(Gammarus)

66

Common name: Hydropsyche

sp.

Class: insectae-larvae

Order: Trichoptera

Family: Hydropsychidae

> 6

> 10

Nil

(non-case

bearing

member of

Trichoptera)

Common name: Dicranota sp.

Class: Insecta-larvae

Order: Diptera

Family: Tipulidae

> 10

-

Nil

Common name: Baetis rhodani

Class: Insecta-Nymphs

Order: Ephemeroptera

Family: Baetidae

3

-

Positive

(Every family

of

Ephemeropte

ra)

Common name:

Class:

Order: Oligochaeta

Family: Tubificidae

< 100

8

Nil

(Negative

only if ≥100)

Common name:

Class: Insecta

Order: Coleoptera

Family: Helodidae

3

-

Nil

Specie: Erpobdella octoculata

Class: Hirudinea

Family: Erpobdellidae

2

-

Negative

(Erpobdella)

Specie: Lymanae auricolata

Class: Gastropoda

Order: Pulmonata

Family: Planorbiidae

5

1

Negative

(Lymnae)

Specie:

Class: Insecta-Nymphs

Order: Ephemeroptera

Family: Ephermerellidae

13

-

Positive

(Every family

of the

Ephemeropte

ra)

67

Number of Diversity groups (Total positive – Total negative): 3 – 2 = 1

Analyses of the indicator taxa of the animals show they belong to Indicator Group 2 (IG 2)

due to the taxon (Ephemerellidae).

The index value (fauna class) is the value on the DSFI-table where the diversity group and

indicator group intersect. In this case the Index value is 4.

With an index value of 4 can be said to have a good environmental state as at time of

sampling.

Macrophytes

The analysis for macrophytes was done by visual observation. The results showed the

presence of emergent, floating and submerged macrophytes which is indicative of reasonable

sunlight penetration. It also suggests the presence of oxygen and production at that depth in

the lake.

Figure 30 Macrophytes at Guldager Mølledam

68

8 DISCUSSION OF RESULTS

8.1 In-situ measurements

Temperature, pH, Conductivity and dissolved oxygen

All the in situ measurements were taken at different points at the surface, below the surface

and close to the bottom of the lake determine an average value.

Temperature measurements at different points were relatively close in value indicating that

the lake was well mixed and there was no stratification. The average temperature of the lake

was 7.2°C. This value is below the maximum temperature given in the EU Council Directive

2006/44/EC for Salmonoid and Cyprinid waters.

The pH value for Guldager Mølledam was 6,85. This value is close to neutral pH. According

to Bronmark and Hanson (1996) the pH that is conducive for aquatic life in normal natural

waters ranges from 6 to 8. This indicates that the lake has a good and normal pH level.

The average Conductivity of the Lake Guldager Mølledam was 400 µS/cm. According to

UNESCO/WHO/UNEP (1996) Conductivities of most fresh waters range from 10-1,000

µS/cm while that of polluted waters or waters receiving large quantities of land run-off may

have conductivities in excess of 1,000 µS/cm. Thus the conductivity of Guldager Mølledam

falls within the range of most fresh water according to these range values.

The results for dissolved oxygen measurements show that the lake has a value of 10.97 mg/L.

According to UNESCO/WHO/UNEP (1996), dissolved oxygen values in unpolluted waters

are usually close to 10 mg/L. This results therefore indicates an unpolluted state of the lake.

Secchi depth

The secchi depth measurement showed a value of 1.78 m (it was visible all the way down the

bottom). This result is indicative of the presence of few algae and suspended particles. The

trophic state index (TSI) for a lake can be calculated based on the measured Secchi depth

(Michaud 1991) using the formular;

TSI = 60-14.41 (ln SD), where (In SD) stands for the natural log of the secchi depth.

69

natural log of 1.78 = 0.5766

therefore TSI = 60 – 14.41 (0.5766) = 51.69

The results showed that the trophic state for Guldager Mølledam is mesotrophic.

According to Michaud (1991), the transparency of the lake can be calculated by multiplying

the secchi depth by a factor of 1.7. In this case the transparency results in 3.026 meters for the

penetration of sunlight. This implies that light will penetrate up to the bottom of the lake.

Flow and turnover time of lake

Input and Output of Water

The flow measurement in the inlet and outlet stream revealed that about 955,000 thousand m³

of water are entering Guldager Mølledam each year and approximately 1.2 million m³ are

leaving the lake. The data given, based on the flow measurements indicate that the water

level should be decreasing, which in contrast is not the same. The flow measurement provides

just a rough estimation of the real situation and there are various factors which should be

taken into account.

The flow measurement was taken on one day and then was projected to the annual in- and

output of water. Moreover, the inlet and outlet stream are not the only factors responsible for

the input and output of water to and from lake. If there is heavy precipitation there might be

additional temporary inlets supplying water to the lake which were not visible at the date of

examination and thus, precipitation and evaporation also should be taken into consideration.

In addition, there is no information available concerning the hydrogeological situation around

Guldager Mølledam. Hence, it is also possible that the lake might be receiving groundwater

from a closed by ground aquifer.

Furthermore, the flow measurement of the outlet, Guldager Møllebæk, seems to be precise

because it was carried out directly in the concrete tube or pipe at the outlet below a bridge

providing ideal geometric shapes in which the flow was measured in five sub-areas.

Turnover Time

The turnover time was attained by dividing the volume of Guldager Mølledam by the output

flow, a turnover time of 6.7 days has been determined. The turnover time might not be

70

precise because since some factors might contribute in the supplying of water to the lake and

it might be slightly different because of these contributing factors, it can be definitely stated

that the complete exchange of the lake water is very short. This shows that a possible

pollution in the inlet will not affect Guldager Mølledam for long term because the complete

exchange of the lake water is within a few days.

8.2 Water sample measurements

Alkalinity

The alkalinity of Lake Guldager Mølledam is 53.88 mgCaCO3/L. According to (Bronmark

and Hanson 2005) lakes with alkalinity above 25 mgCaCO3/L can be said to have good

buffering capacity and thereby have a low risk of acidification. Since the alkalinity of the

Lake Guldager Mølledam is much higher than this limit, the aquatic organisms are less

affected by pH fluxes. Organisms vulnerable to fluxes in pH have good conditions to live in

this lake based on its alkalinity.

Total Nitrogen and Nitrogen Oxides

The results of nitrogen measurements show nitrate (NO3-) concentrations in lake mølledam of

around 5 mg/L. According to UNESCO/WHO/UNEP (1996), this might be an indication of

human influences on the lake. The catchment includes some areas for agriculture, which are

likely expected to be a reason for this rather high load of nitrogen in the inlet, but also in the

lake itself.

Total Phosphorus and Orthophosphorus

Results obtained from the lower calibration curve using FIAstar 5000 confirmed the

concentration of Orthophosphate in the lake Guldager Mølledam was 12.004µg P- PO4/l.

Moreover, comparing with the inlet stream water which is 9.849µgP- PO4/l and that of outlet

stream water which is 12.725µg P- PO4/l, a significant difference could be observed in the

concentrations of Orthophosphate. This indicates that less amount of Orthophosphates is

coming in from the inlet stream high amount of orthophosphorus is released from the lake

into the outlet stream. Relatively, some of the orthophosphate is released from the sediments

of the lake. This situation could indicate that phosphorus is deposited in the sediments of

71

Lake Guldager Mølledam and this phosphorus released into the outlet stream can be

attributed to internal loading of phosphorus in the sediments. This can also explain the high

concentration of phytoplankton and reeds around the lake.

Based on the concentration of the dissolved phosphorus and according to the division of

trophic levels reflecting the degree of eutrophication Lake Guldager Mølledam should be

classified as Mesotrophic (refer to literature).

Iron content

The amount of iron in lake water influences the freedom of phosphorus. When the oxygen

level is sufficient the phosphorus wil stay chemically bound to iron compounds. The average

amount of iron in the inlet was 0,37 mg/l and in the lake 0,45 mg/l. Since the amount of iron

measured in the outlet was 0,42 mg/l, it can be evaluated that some of the iron in the outlet

samples originate from the sediment. A reduction of iron content in the lake should be seen

over a longer time period.

Chlorophyll a

Chloropyll a concentration in lake water was 11.08g/L. Chlorophyll a concentration gives

an indication of the algal biomass in the lake water, and thus the degree of eutrophication.

Decompostion of algae also causes the release of nutrients to the lake, which may allow algae

to grow. Their processes of photosynthesis and respiration cause changes in lake pH, and the

presence of algae in the water column is the main factor affecting Secchi disk readings. When

decomposition processes predominate, dissolved oxygen levels are considerably reduced in

stratified lakes.

Chlorophyll a concentrations can be used to determine a lake’s trophic status in relation to

lake’s productivity state. According to this, and the result obtained, it can be inferred that

Lake Guldager Mølledam is mesotrophic.

8.3 Sediment sample measurements

Phosphorus

72

Sediment in shallow lakes play a significant role in the overall nutrient dynamic. Phosphorus

in the sediment is chemically bound to iron compounds or fixed in organic forms. If the

oxygen level close to the sediment surface is very low or close to zero, the bound phosphorus

can be released into the water, thereby decreasing the water quality. The amount of

phosphorus bound into the sediment is also dependent on the pH. If pH is below 8, the

phosphate binding to metals is strong. In Guldager Mølledam the pH was 6,85 and the

oxygen content was close to 11 mg/l, this indicates that there will not be a significant release

of phosphorus into the lake water. The relation between iron and phosphorus content is high

(23:1) which supports the statement that phosphorus will be bound to the sediment (Ribe

Amt. 1998).

8.4 Biological measurements

Phytoplankton

The processes of photosynthesis and respiration caused by algae ehance changes in lake pH,

and the presence of algae in the water column is the main factor affecting Secchi disk

readings. Algae cause aesthic problems in a lake; a green `Scum,` swimmers itch, and rotting

scent are common problems associated with high algae concentrations.

8.5 Comparison with legislation

The lake has been classified as B “Naturligt og alsidigt plante- og dyreliv” by Ribe Amt in

2000. The translation of the classification would be “Natural and versatile plant and animal

occurrence”. The classification is mainly based on types of plants and animals living in the

lake. One of the parameters which affect this classification is also Secchi depth. The Secchi

depth for a B classified lake shall be 1 – 3 meters, which our results confirm. Our assessment

did not include investigations on plant- and animal life in the lake and therefore nothing can

be determined in regards to them.

According to the Water Framework Directive (2000/60/EC) all lakes in Member States shall

have a “good ecological status” by the end of 2015. Investigations in Denmark has shown

that the total phosphorus concentration regulates the ecological state in lakes. It has therefore

been suggested that the concentration of total phosphorus shall be used when assessing

ecological quality for lakes. There are different limit values for shallow lakes (< 3 m) and

deep lakes (> 3 m). (Nielsen et al. 2005)

73

Table 18 shows the limit values of total phosphorus content (µg P/l) for shallow and deep

lakes are presented. Based on these values an ecological status can be given for the lake.

Table 18 Limit values for total phosphorus concentration (µg P/l) in shallow and deep lakes.

(Modified from Nielsen et. al, 2005)

High Good Moderate Fair Poor

Shallow < 25 < 50 < 100 < 200 > 200

Deep < 12.5 < 25 < 50 < 100 > 100

Our measurements for total phosphorus were below the detection limit, however the amount

of ortho-phosphate was measured. The concentration of ortho-phosphate should be in the

same range as total phosphorus. The concentration of ortho-phosphate in Guldager Mølledam

was 12,004 µg P-PO4/l. One could suspect that the concentration of total phosphorus would

be below the limit value for high ecological status in shallow lakes. The measured

concentration for total phosphorus in 1999 was 0,086 mg/l and according to the requirements

for this classification system the lake should be classified as moderate.

The European Directive (2006/44/EC) gives classification parameters for supporting fish life

in lakes. The parameters vary for salmonoid and cyprinid waters. In table 19 a comparison

between the limit values and our values are presented.

Table 19 Comparison of limit values and our measurements. (2006/44/EC, Annex 1)

Properties Salmonid Water

Cyprinid

Water Inlet Lake Outlet

G I G I

Temperature (°C) --- 21.5 (10) --- 28

(10) 7 7.2 7.7

Dissolved O2 (mg/l) 50% ≥ 9 50% ≥ 9 50% ≥ 8 50% ≥

7 8.65 10.97 11

100% ≥7 100% ≥5

pH --- 6 – 9 --- 6 - 9 6.92 6.85 6.91

BOD5 (mg/l O2) ≤ 3 --- --- ≤ 6 2 4.5 3

The letter G stands for guideline value and I for mandatory value. The temperature in

parenthesis are the limit value for breeding season for these fish species. Based on these

compared parameters the inlet stream, Guldager Mølledam, and Guldager Møllebæk have

74

sufficient water quality for supporting Cyprinidae. Only the inlet stream fulfils the

requirements for Salmonid waters. The list in Annex 1 (2006/44/EC) contains several more

parameters, however these were not analysed in our project. The result might vary if all of

those parameters are taken into consideration.

8.6 Comparison with previously performed assessments

After the restoration of the lake in 1998/1999, Ribe Amt performed an assessment of the

environmental state of the lake. In the table below the results from the assessment performed

in 1987, 1999/2000 and 2009 (performed by our group) are presented. A sediment

investigation was performed by Ribe Amt in 1990.

Table 20 Comparison of results

Sample Point Parameter 1987 1999/2000 2009

INLET Total Phosphorus (mg/l) 0.12 --- 0.20

Nitrogen (mg/l) 10.53 --- 6.75

LAKE

Depth (m) 0.44 1.14 1.47

Secchi depth (m) 0.4 – 0.7 1.93 1.5 – 1.7

Total Phosphorus (mg/l) 0.22 0.086 0.03

Total Nitrogen (mg/l) 4.95 7.1 5.23

Chlorophyll a (µg/l) 2.23 15 – 150 11.08

Iron (mg/l) --- 0.4 0.45

OUTLET Total Phosphorus (mg/l) 0.25 --- -0.03

Nitrogen (mg/l) 5.91 --- 4.87

Sample Point Parameter 1990 1999/2000 2009

SEDIMENT

Iron (mg/l) 26.4 --- 23.13

Phosphorus (mg/l) 0.5 – 7.3 1.8 1.02

Lead (mg/kg DS) 60 --- 37.38

Nickel (mg/kg DS) 46 --- 19.45

Cadmium (mg/kg DS) 6.9 1.5 -3.16

After the sediment removal the depth of the lake increased significantly. The variation in the

results from 1999/2000 and our measurements in 2009 is likely a result from difference in

measurement locations. This also explains the variations in Secchi depth.

The amount of total phosphorus in the lake between 1987 and 1999/2000 was expected since

the sediment was removed and the phosphor input from the sediment was thereby removed.

The measurements for total phosphorus in 2009 were all under the detection limit and cannot

75

be compared with previous results. The amount of ortho-phosphate was measured and the

results indicate low content of ortho-posphate.

A decrease in total nitrogen content during autumn and winter is normal and this explains the

variations between the results from 1999/2000 and 2009. The amount of nitrogen input

increases during spring/summer since agriculture is the main contributor. The measurements

from 2009 only represent only the situation in October while the other results are expressed

in annual averages. The content of total nitrogen can vary depending on rainfall and

groundwater input. If the amount of rainfall has been high, the runoff from the catchment

area will contain high amounts of nitrogen compounds.

An increase in the amount of chlorophyll α can be seen from 1987 to 1999/2000. This is due

to improved lake water quality after the restoration. The low concentration in 2009 is due to

seasonal variation. During autumn the content of chlorophyll α will normally be lower than

during late summer.

The iron content in the lake water was not measured in 1987. The results from 1999/2000 and

2009 show that the iron content has not changed significantly during the years.

The sediment investigation before the restoration was done in 1990. The iron content as

measured to be low (0,5 – 7,3 g P/kg DS) but the phosphorus content was high. The relation

between iron and phosphorus was low, indicating that there is a possibility of phosphorus

exchange from the sediment into the lake water. In 1999/2000 the results from measurements

during the summer indicate that the same feature can possibly occur, however only in some

parts of the lake. Our measurements from 2009 indicate that the iron and phosphorus relation

is around 23:1, which indicate good binding of phosphorus to the sediment.

The amount of lead and nickel has decreased significantly since 1990 to around half of the

amount. Since our measurements of cadmium content are unreliable, a comparison with

earlier measurements cannot be done. A reduction in cadmium content can be seen from 1990

to 1999/2000, however the cadmium content was still high in 1999/2000 in comparison to the

limit value of 0,8 mg/kg DS.

The comparison of our results with previous analyses shall not be taken too seriously. There

are many factors that affect the results; sampling procedure, samplers and laboratory analysis

are only a few. When Ribe Amt performs assessments for lakes there are experienced

samplers performing the sampling and the analysis are performed by accredited laboratories.

76

The storage time for our samples was too long and this might also influence the accuracy of

the results.

77

9 CONCLUSION

The purpose of our project was to investigate the environmental state for the water quality in

Guldager Mølledam and Guldager Møllebæk. The parameters measured in assessing the

environmental state has been shortly described as well as their influence on the water quality.

The methods used to assess the lake and the stream has been discussed.

Guldager Mølledam used to be polluted with wastewater coming from the suburban area

Guldager. In 1987 the wastewater input was cut off and an environmental assessment of the

lake was performed. The results showed that the lake contained high amount of phosphorus

and heavy metals in the sediment, which resulted in the decision to restore the lake by

sediment removal. This restoration was performed in 1998/1999 and a new assessment was

done in 1999/2000. The results showed an improvement in the environmental state.

Based on the results achieved from our investigations, we have drawn the conclusion that the

environmental state of Guldager Mølledam has improved significantly. The amount of

phosphorus in the sediment is low and is mainly bound to iron. The cholorophyll α content in

the lake suggests that the trophic state of Guldager Mølledam is mesotrophic, and the results

from the Secchi depth as well as dissolved phosphorus indicates the same.

The environmental state of Guldager Mølledam has improved since 1999/2000. In 1999 the

amount of phosphorus in the sediment was still high in relation to the iron content, therefore

there was still a possibility of phosphorus leakage into the lake water. Our research showed

that the relationship between iron and phosphorus has improved significantly and if there are

no fluctuations in pH and oxygen content near the sediment surface, the phosphorus will stay

bound to the sediment.

The amount of total phosphorus can be used to assess the quality of the lake in accordance to

the Water Framework Directive. Our results for total phosphorus are not reliable, but if the

amount of ortho-phosphate is used, the ecological state of the lake can be considered as high.

The aim within the Water Framework Directive is that all lakes within Member States should

have a good ecological state before 2015.

The environmental state of Guldager Møllebæk was based on the Danish Stream Fauna

Index. The environmental state for the stream was assessed as good based on that the stream

had an index value of 4.

78

The results from our study only represents the time when it was performed, October 2009. In

order to make a more describing assessment of the environmental state for Guldager

Mølledam and Møllebæk, investigations should be made that covers the annual fluctuations.

This requires sampling throughout the year. The reliability of the results can be improved by

using standardized sampling methods, samplers as well as laboratory analysis.

79

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85

APPENDIX 1 1/2

Directive 2000/60/EC of the European Parliament and of the Council of 23 October 2000

Establishing a framework for Community action in the field of water policy, Annex V p. 42 –

43

86

APPENDIX 1 2/2

87

APPENDIX 2 1/3

MEASURING METAL AND PHOSPHOR CONCENTRATIONS IN SEDIMENT

USING ICP

Inductively coupled plasma atomic emission spectrometry (ICP AES) is used for qualitative

and quantitative measurements of elemental composition in samples. A plasma source is used

to excite atoms or ions in the sample to a higher energy level. When the atoms or ions return

back to their ground state they emit photons at a certain wavelength dependent on the

element. The light is recorded and based on that the content of the element in the sample is

calculated. The elements measured with the ICP AES in the sediment samples were: nickel,

cadmium, lead and phosphorus. The wavelengths used for Ni, Cd and Pb elements were:

231,604 nm, 228,802 nm and 283,306 nm respectively.

Pretreatment of samples

The samples were pretreated by taking approximately 1 gram of dry, grinded sample and

added into a 100 mL autoclave flask. There were altogether 12 samples. 20 mL of 7 M Nitric

acid was added. A blank sample was made that contained only 20 mL of 7 M Nitric acid. The

pre-treated samples together with the blank were put into the autoclave for 30 minutes at 200

kPa (120°C).

Preparation and analysis of samples and standards

The samples were then filtrated and diluted up to 50 mL. Standards for measuring the metals

were made by adding a stock solution, Multi-Element Standard. The concentration of the

standards were 1 ml/L, 2 mL/L and 10 mL/L. The blank contained 1% HNO3.The standards

were run through the ICP in order to make a calibration curve. When the calibration curve

was made, the samples were run through the ICP.

For measuring the amount of total phosphorus with the ICP, different standards has to be

made. The concentration for the standards were; 1 mg/L, 5 mg/L, 10 mg/L and 20 mg/L. The

standards were made with a stock solution containing 100 mg/L phosphors. Measuring

phosphorus with ICP requires a higher a high pearch. High pearch essentially means that

gaseous nitrogen is inserted to remove air that is contaminating measurements in low range.

The standards were first run through the ICP in order to make a calibration curve, afterwards

the samples were run through the ICP.

88

APPENDIX 2 2/3

Samples 1 A, 1 AA, 3 A, 3 AA, 3B and 3BB needed to be diluted since the measured results

were above the calibration curve. The samples were diluted by taking 1 mL of sample and

adding 5 mL of water.

Results

The results are presented in the table 1. Samples marked with a star (*) have been diluted an

additional time.

Table 1. Measurement results

Weight of P (mg/L) Amount of P

Sample ID sample (g) measured in g/kg dry stuff

Blank - 0,000 -

Std. 1 (1mg/L) - 1,000 -

Std. 2 (5mg/L) - 5,000 -

Std. 3 (10 mg/L) - 10,000 -

Std. 4 (20mg/L) - 20,000 -

Blank sample 0 -0,142 -

1A 1,0011 29,830 1,490

1AA 1,0019 27,990 1,397

*1A 1,0011 6,080 1,822

*1AA 1,0019 5,402 1,618

1B 0,9999 6,900 0,345

1BB 1,0009 6,903 0,345

2A 1,0035 6,266 0,312

2AA 1,0092 6,244 0,309

2B 1,0023 -1,832 -0,091

2BB 1,0024 0,490 0,024

3A 1,0005 20,580 1,028

3AA 1,0004 20,910 1,045

*3A 1,0005 4,029 1,208

*3AA 1,0004 4,159 1,247

3B 1,0006 43,990 2,198

3BB 1,0009 42,860 2,141

*3B 1,0006 8,577 2,572

*3BB 1,0009 8,294 2,486

89

APPENDIX 2 3/3

The letter A stands for the upper layer of the sediment and B for the bottom layer, AA and BB

are reference samples. The number 1 are samples taken from the middle of the lake, number 2

close to the inlet, and number 3 close to the outlet.

Discussion and Conclusion

The results obtained were fairly accurate and the procedure was easy to perform. The results

might be affected by the fact that the samples had been stored in an exicator with an open lid.

The reason why the lid had to be open was because the samples were hot when they were put

into the exicator. If the lid was not open it would have been impossible to take the samples

out without breaking the exicator. Due to this the samples might have been contaminated with

humidity in the air. The result from sample 2BB is not reliable since in every analyses that we

did there was something wrong with 2BB. 2BB is a reference sample of the bottom layer and

since the results are more reliable of 2B, the results from that shall be used.

90

APPENDIX 3 1/3

MEASURING METAL AND IRON CONCENTRATIONS IN SEDIMENT AND

WATER SAMPLES USING AAS

Atomic absorption spectrophotometry (AAS) is used for the determination of trace elements

in water samples and in acid digests of sediment. AAS determines mainly the presence of

metals in liquid samples such as iron, copper, aluminium, lead etc. In their elemental state,

metals will absorb ultraviolet light at a certain wavelength dependent on the metal. The

sample is aspirated into a flame and lightbeam with a certain wavelength goes through the

flame. The light passes the flame and goes into a monochrometer whereafter it goes onto a

detector. The detector measures the amount of light and based on that calculates the amount

absorbed by the sample. The content of iron was measured in the sediment and water samples.

The specific wavelength for iron was 248,3 nm.

Pretreatment of samples

Sediment samples

The samples were pretreated by taking approximately 1 gram of dry, grinded sample and

added into a 100 mL autoclave flask. There were altogether 12 samples. 20 mL of 7 M Nitric

acid was added. A blank sample was made that contained only 20 mL of 7 M Nitric acid. The

pre-treated samples together with the blank were put into the autoclave for 30 minutes at 200

kPa (120°C).

Water samples

The water samples from the lake, inlet and outlet stream were pretreated by taking 40-ml of

sample and inserting them into 100-ml autoclave bottles. 10-ml of concentrated Nitric acid

was added. The bottles were put into the autoclave for 30 minutes at 200 kPa in 120°C.

Preparation and analysis of samples and standards

Sediment samples

The same samples that were used for measuring with ICP were used, the ones that were

filtered and diluted up to 50 mL. Standards were made, having the concentrations 1mg/L, 5

mg/L and 10 mg/L. The stock solution for the standards was a standard iron solution

containing 1000 mg iron/L. The standards were run through the AAS in order to achieve a

91

APPENDIX 3 2/3

calibration curve. One sample was measured and the result was not within the calibration

curve, therefore was all samples diluted by taking 1 mL of sample and dilutes it up to 100 mL.

Water samples

The pretreated samples were directly analysed. Before analyzing the samples standards were

made having the concentrations of 1 mg/l, 5 mg/l and 10 mg/l. The standards were run

through the AAS and a calibration curve was obtained. The samples were then analysed by

the AAS.

Results

The results are presented in the table 1. The letter A stands for the upper layer in the sediment

and B for the bottom layer. The double letter combination represents the reference sample.

The sample ID number describes from where the sediment samples were taken, where 1 is at

the middle of the lake, 2 is close to the inlet, and 3 is close to the outlet.

Table 1. Measurement results for sediment samples

Table 2. Measurement results for water samples

Sample Weight of Fe (mg/l) Fe

ID sample (g) measured (g/kg DS)

1A 1,0011 5,22 26,06

1AA 1,0019 4,67 23,32

1B 0,9999 9,09 45,46

1BB 1,0009 9,19 45,92

2A 1,0035 3,02 15,06

2AA 1,0092 3,13 15,49

2B 1,0023 0,03 0,16

2BB 1,0024 0,34 1,72

3A 1,0005 4,74 23,67

3AA 1,0004 2,29 11,46

3B 1,0006 5,61 28,02

3BB 1,0009 8,26 41,27

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APPENDIX 3 3/3

The values for the actual amount of iron was obtained by multiplying the measured value with

the dilution factor 1,25.

Discussion and Conclusion

The results obtained from the analysis seem to be rather accurate and the procedure for

analyzing the water samples was much easier than for the sediment samples. The sediment

samples needed to be diluted further whereas the water samples could be directly analyzed.

The sediment sample 2 shows deviating results compared to the rest of the samples, however

this was found in other analyses performed on the sediment samples. Sediment sample 2 had

very sandy soil and smelled of sulphur. The reason for deviating results might be due to the

grain size of the sample, perhaps the method used require finer grain size.

Sample Fe (mg/l) Fe

ID measured mg/l

Blank sample 0,22 0,28

Lake 1 0,39 0,48

Lake 2 0,37 0,46

Lake 3 0,33 0,42

Inlet 0,29 0,37

Outlet 0,34 0,42

93

APPENDIX 4 1/5

DIRECTIVE 2006/44/EC OF THE EUROPEAN PARLIAMENT AND OF THE COUNCIL

of 6 September 2006 on the quality of fresh waters needing protection or improvement in

order to support fish life

94

APPENDIX 4 2/5

95

APPENDIX 4 3/5

96

APPENDIX 4 4/5

97

APPENDIX 4 5/5

98

APPENDIX 5 1/4

Acute toxicity test with marine Acartia Tonsa

Introduction

The experiment was performed on Acartia Tonsa which represents marine zooplankton. The

organism is well represented in Danish coastal waters and feeds on algal plankton. The

organisms are born and grown in the laboratory. Organisms older than ten days are applicable

for toxicity testing. The organisms are placed in seawater with different concentrations of

cupper. The lethal concentration (LC50) is evaluated by counting the amount of alive

organisms after 24 and 48 hours. The LC50 is then calculated based on this data.

Methodology

Preliminary testing

Preliminary testing is important in order to find the concentration range which is to be used in

the definitive test.

Four control samples was made that contained only 25 mL of seawater. Into each control

sample 5 organisms was added, making a total of 20 organisms in the control samples.

The concentration of cupper containing samples were; 0,3 mg/L, 0,6 mg/L, 0,9 mg/L and 1,2

mg/L. Two samples of each concentration were made. The concentration of the standard

solution used was 100 mg/L. The toxicant containing water was diluted to 50 mL for each

concentration. The concentration of the solution was achieved by performing the following;

0,3 mg/L: 0,3 mL of Cupper solution added into volumetric flask and diluted to 50

mL with seawater.

0,6 mg/L: 0,6 mL of Cupper solution added into volumetric flask and diluted to 50

mL with seawater.

0,9 mg/L: 0,9 mL of Cupper solution added into volumetric flask and diluted to 50

mL with seawater.

1,2 mg/L: 1,2 mL of Cupper solution added into volumetric flask and diluted to 50

mL with seawater.

25 mL of solution was added into plastic cups and the cups were marked according to

concentration. The pH and Oxygen content was measured in the lowest and highest

99

APPENDIX 5 2/4

concentrations. In order to continue with the test the pH had to be 7,8 ± 0,2 and the Oxygen

content had to be ≥ 7 mg/L. The values for pH and Oxygen in the lowest and highest

concentrations were 7,91 and 8,4 mg/L, 7,90 and 8,4 mg/L respectively.

Into each sample five organisms were added by using a small net in order to catch them, care

had to be taken since the animals are very fragile and if a body part breaks they might die.

There were altogether ten animals representing each concentration. The samples were placed

in a well ventilated cabin at 20°C. The organisms were counted after 24 and 48 hours.

Table 1. Results from the preliminary test.

The total amount of dead organisms in the control samples could not be above 2, therefore

were the results from the preliminary test not good. The reason for the dead animals in the

control samples might be due to careless handling of the animals. However based on these

results the concentration range for the definitive test was selected.

Definitive test

The concentration range for the definitive test was selected to be 0,1 mg/L, 0,2 mg/L, 0,3

mg/L and 0,5 mg/L. The samples were prepared in the same manner as for the preliminary

test, however in the definitive test four samples representing each concentration was made.

Concentration of Cu 24 h 48 h

Control A 4 3

Control B 4 3

Control C 4 4

Control D 4 4

0,3 A 1 0

0,3 B 2 0

0,6 A 0 0

0,6 B 0 0

0,9 A 0 0

0,9 B 0 0

1,2 A 0 0

1,2 B 0 0

Amount of alive

100

APPENDIX 5 3/4

Also four control samples were made containing only 25 mL of sea water. The concentrations

were prepared in the following manner;

0,1 mg/L: 0,1 mL of 100 mg/L Cu-standard diluted to 100 mL

0,2 mg/L: 0,2 mL of 100 mg/L Cu-standard diluted to 100 mL

0,3 mg/L: 0,3 mL of 100 mg/L Cu-standard diluted to 100 mL, and

0,5 mg/L: 0,5 mL of 100 mg/L Cu-standard diluted to 100 mL

25 mL of each concentration were added into plastic cups, the pH and oxygen was measured

in the lowest and highest concentrations. The pH value for the lowest concentration was 8,06

and oxygen content 8,3 mg/L. In the highest concentration the pH was 8,08 and the oxygen

content 8,3 mg/L. Five organisms of Acartia Tonsa was added into each sample, where 20

animals represented one concentration, five organisms were added into each control sample.

Results

The amount of survived animals was counted after 24 and 48 hours. The amount of alive

animals is shown in Table 2.

Table 2. Results after 24 and 48 hours.

The logarithmic curve drawn based on these results can be seen below. Based on the curve the

LC50 was calculated. The concentration for LC50 after 24 hours could be found at the

Time Concentration T P

h mg/L 1 2 3 4 %

24 0 5 5 5 5 20 0

0,1 4 5 5 5 19 5

0,2 4 1 2 3 10 50

0,3 3 2 2 2 9 55

0,5 1 1 2 1 5 75

48 0 4 4 5 5 18 10

0,1 3 5 3 5 16 20

0,2 2 1 0 1 4 80

0,3 1 1 2 2 6 70

0,5 0 0 0 0 0 100

Number of suvivors

101

APPENDIX 5 4/4

concentration 0,25 mg/L. The concentrations for LC50 after 48 hours was approximately 0,15

mg/L.

Figure 1. Curve drawn based on the results.

Discussion and Conclusions

The test results are not reliable since definitive test was based on the preliminary test. The

preliminary test was not reliable since more than 10 % of the organisms died after 48 hours,

however the concentrations that caused 100 % of the organisms to die could be seen from the

preliminary test. The explanation for the death of the organisms in the control samples could

be careless handling of the organisms when transporting them to the sample cups.

The definitive test showed more reliable results since the control samples were valid. The

reason why after 48 hours there was a decrease in the percentage of dead organisms between

concentrations 0,2 mg/L and 0,3 mg/L is a mystery. It might be explained by human error.

The test organisms are very small and not easy to distinguish in the sample cups therefore

there might have been a counting error. Since more than 50 % of the organisms had already

died the counting error does not effect the results for LC50.

102

Appendix 6 1/4

Calculations on Flow Measurements

Inlet

Assumed Profile of Guldager Møllebæk (cm)

Area A

Profile A: triangular (a=0.40m, h=0.31m)

= 0.40m. 0.31m = 0.062 m2 2 Velocity A: 22 revolutions per 50s. nA = 22 = 0.44 s−1

50 VA = 0.2303. nA + 0.040 = 0.141 m/s

Flow: QA = VA . AA = 0.141 m/s . 0.062 m2 = 0.0087 m

3/s ↔ 8.74 l/s

Area B

Profile B: triangular (a=0.80m, h=0.31m)

= 0.80m. 0.31m = 0.124 m2 2 Velocity B: 29 revolutions per 50s. nB = 29 = 0.58 s−1

50 VB = 0.2303. nB + 0.040 = 0.174 m/s

Flow: QB = VB . AB = 0.174 m/s . 0.124 m2 = 0.02156 m

3/s ↔ 21.56 l/s

103

Appendix 6 2/4

Outlet

Defined profile of Guldager Møllebæk (cm)

Area Calculation:

Aflow, total:

AFLOW: = 𝑎𝑟𝑐𝑐𝑜𝑠 1 −𝑕

𝑟 . 𝑟2 − 𝑕. 2𝑟 − 𝑕 . 𝑟 − 𝑕

AFLOW:= 𝑎𝑟𝑐𝑐𝑜𝑠 1 −0.28𝑚

0.40𝑚 . 0.40𝑚2 − 0.28𝑚. 2 . 0.40𝑚 − 0.28𝑚 . 0.40𝑚− 0.28𝑚

AFLOW: = 0.1568𝑚2

A2=A3:

A2=A3= a.b= 0.36𝑚 .0.10𝑚 = 0.036𝑚2

A4 = 𝑎𝑟𝑐𝑐𝑜𝑠 1 −𝑕

𝑟 . 𝑟2 − 𝑕. 2𝑟 − 𝑕 . 𝑟 − 𝑕

A4 = 𝑎𝑟𝑐𝑐𝑜𝑠 1 −0.08𝑚

0.40𝑚 . 0.40𝑚2 − 0.08𝑚 . 2 .0.40𝑚 − 0.08𝑚 . 0.40𝑚 − 0.08𝑚

A4 = 0.0262𝑚2

104

Appendix 6 3/4

A1 = A5 = 𝐴𝑓𝑙𝑜𝑤 ,𝑡𝑜𝑡𝑎𝑙 –𝐴2− 𝐴3−𝐴4

2 =

0.1568 –0.036− 0.036−0,0262

2 = 0.0294𝑚2

Flow:

Velocity 1: 49 revolutions per 50 seconds. → 𝑛1 = 49

50𝑠= 0.98𝑠−1

𝑣1 = 0.2303 .𝑛1 + 0.040

𝑣1 = 0.2303 . 0.98 + 0.040 = 0.266 𝑚/𝑠

Flow 1: 𝑄1 = 𝑣1 .𝐴1 = 0.266𝑚

𝑠. 0.0294𝑚2 = 0.0078

𝑚3

𝑠= 7.8 𝑙/𝑠

Velocity 2: 47 revolutions per 50 seconds. → 𝑛2 = 47

50𝑠= 0.94𝑠−1

𝑣2 = 0.2303 .𝑛2 + 0.040

𝑣2 = 0.2303 . 0.94 + 0.040 = 0.256 𝑚/𝑠

Flow 2: 𝑄2 = 𝑣2 .𝐴2 = 0.256𝑚

𝑠. 0.036𝑚2 = 0.009216

𝑚3

𝑠= 9.22 𝑙/𝑠

Velocity 3: 39 revolutions per 50 seconds. → 𝑛3 = 39

50𝑠= 0.78𝑠−1

𝑣3 = 0.2303 .𝑛3 + 0.040

𝑣3 = 0.2303 . 0.78 + 0.040 = 0.224 𝑚/𝑠

Flow 3: 𝑄3 = 𝑣3 .𝐴3 = 0.244𝑚

𝑠. 0.036 𝑚2 = 0.0081

𝑚3

𝑠= 𝑙/𝑠

105

Appendix 6 4/4

Velocity 4: 38 revolutions per 50 seconds. → 𝑛4 = 39

50𝑠= 0.76𝑠−1

𝑣4 = 0.2303 . 0.76 + 0.040

𝑣4 = 0.2303 . 0.76 + 0.040 = 0.215 𝑚/𝑠

Flow 4: 𝑄4 = 𝑣4 .𝐴4 = 0.215𝑚

𝑠. 0.0262𝑚2 = 0.056

𝑚3

𝑠= 5.6 𝑙/𝑠

Velocity 5: 36 revolutions per 50 seconds. → 𝑛5 = 36

50𝑠= 0.72𝑠−1

𝑣5 = 0.2303 .𝑛5 + 0.040

𝑣5 = 0.2303 . 0.72 + 0.040 = 0.206 𝑚/𝑠

Flow 5: 𝑄5 = 𝑣5 .𝐴5 = 0.206𝑚

𝑠. 0.0294𝑚2 = 0.0061

𝑚3

𝑠= 6.1 𝑙/𝑠

106

Appendix 7 1/4

DETERMINATION OF TOTAL PHOSPHOSPHORUS AND ORTHO-PHOSPHATE

IN WATER BY FIASTAR 5000

This application note describes a method for determination of total Phosphorus and

orthophosphate in various types of water in the following ranges:

0.01-1 mg/l PO4-P (400 l loop), linear calibration

0.5-5 mg/l PO4-P (40 l loop), linear calibration

The Orthophosphate present in the digested sample reacts with Ammonium Molybdate to

form heteropoly Molybdophosphoric acid which is reduced in a second step to

Phosphomolybdenum blue by Stannous Chloride in a Sulphuric acid medium. The heteropoly

compound formed has anintensive blue colour which is measured at 720 nm

Reagents

. Potassium Dihydrogen Phosphate, KH2PO4

. Sulphuric acid, conc. (H2SO4), =1.84 g/ml

. Ammonium Molybdate, (NH4)6Mo7O24 x 4 H2O

. Hydrazinium Sulphate, N2H6SO4 or

. DEHA (N,N-diethylhydroxylamine), C4H11NO, 97%

.Stannous Chloride, SnCl2 x 2 H2O

. Potassium persulphate, K2S2O8

. Sodium hydroxide, NaOH

. Disodium ethylene diamine tetra-acetic acid, Na2-EDTA, C10H12O8N2Na2

107

Appendix 7 2/4

other reagents prepared include

. Carrier solution 0.09 M Sulphuric acid

. Ammonium Molybdate reagent

. Stannous Chloride reagent

Digestion solution

. Sulphuric acid, 4M

. Stock standard solution, 100 mg/l PO4-P (stock A)

. Interim stock standard solution, 1 mg/l PO4-P (stock B)

. Calibrating solutions

The calibrating solutions were prepared for each working range, by diluting stock A and B as

shown in Table 1 and 2 respectively.

Table 1- Calibration Standard for working range 0.01-1 mg/l PO4-P

PO4-P concentration

(mg/l)

Volume interim

standard (Stock B)

(ml)

Volume stock

standard (Stock A)

(ml)

Final

Volume

(ml)

0 0 - 100

10 1 - 100

50 5 - 100

100 10 - 100

500 - 0.5 100

1000 - 1 100

108

Appendix 7 3/4

Table 2- Calibration Standard for working range 0.5-5 mg/l

PO4-P concentration

(mg/l)

Volume stock standard (Stock A)

(ml)

Final volume (ml)

0 0 100

0.5 0.5 100

1 1 100

2 2 100

3 3 100

5 5 100

The volume defined above were measured by pipette 100ml volumetric flasks and diluted to

volume with distilled water. The calibrating solutions were prepared fresh. All standards were

digested according to the digestion procedure.

Solution

65 g of sodium hydroxide, NaOH, and 6 g of Na2-EDTA C10H12O8N2Na4, were dissolved in

1000ml of water.

Apparatus

. Usual laboratory apparatus and

. FIAstar 5000 Analyzer unit

. Method cassette P with interference filters 720 nm and 1000 nm.

. Pipettes of nominal capacity 0.5-10 ml

. Autoclave

. Teflon digestion tubes, 50 ml

109

Appendix 7 4/4

Procedure

Sampling and sample preparation

The analysis was carried out a week after collection of sample. Phosphate is readily adsorbed

onto plastic surface. For this reason good quality borosilicate glass were used. All glassware

were cleaned and allowed to stand overnight with sulphuric acid, the rinsed with distilled

water and stored filled with distilled water.

Usually a distinction is made between total phosphorus and dissolved phosphorus, by using a

filtration step with a 0.45 m membrane filter.

The analysis was carried out two weeks after collection of the sample. Samples from the lake,

inlet and outlet stream were analyzed without the treatment of autoclave.The samples were

filtered through 0.45 m membrane filters for the analysis.

Digestion procedure

Using a pipette 15.0 ml sample or standard was measured into a digestion tube. 3 ml digestion

solution and 0.15 ml 4 M sulphuric acid were added. The solution was heated for 30 minutes

in an autoclave or boiled under pressure at 150-200 kPa, after which it was allowed to cool

and analyzed in the FIAstar analyzer unit. A blank solution (15ml of distilled water) was also

digested.

110

APPENDIX 8 1/1

Table 1: Water sampling from the boat. Lake middle and lake inlet sampling results.

Sample No Temp (°C) pH Conductivity (µS) Dissolved oxygen (mg/l)

Middle Mix 1 7.0 6.85 400 11

Middle Mix 2 7.5 6.9 401 10.9

Middle Mix 3 7.0 6.8 400 11

Lake inlet 1 6.9 6.92 400 8.4

Lake inlet 2 7.1 6.93 404 8.9

111

APPENDIX 9 1/3

DETERMINATION OF TOTAL NITROGEN AND NITRATE IN WATER BY

FIASTAR 5000

This application note describes the method for determination of total nitrogen and nitrate in

various types of water in the following ranges:

Range of calibration:

Total nitrogen: 0.1-5 mg/l N. (40 l loop), linear calibration.

Nitrate: 0.1-5 mg/l NO3-N (40 µl loop), linear calibration.

Method for total nitrogen determination:

The digested sample was mixed with a buffer solution. Nitrate was reduced to Nitrite in a

cadmium reductor. On the addition of an acidic Sulphanilamide solution, Nitrite formed from

reduction of Nitrate forms a diazo compound. This compound is coupled with N-(1-naphtyl)-

Ethylene Diamine Dihydrochloride (NED) to form a purple azo dye. This azo dye was

measured at 540 nm.

Method for nitrate determination:

The sample containing Nitrite/Nitrate was mixed with a buffer solution. Nitrate in the sample

was reduced to Nitrite in a cadmium reductor. On the addition of an acidic Sulphanilamide

solution, Nitrite initially present and Nitrite formed from reduction of Nitrate formed a diazo

compound. This compound is coupled with N-(1-naphtyl)-Ethylene Diamine Dihydrochloride

(NED) to form a purple azo dye. This azo dye was measured at 540 nm.

Reagents for nitrate:

Only reagents of recognized analytical grade and water according to grade 1 of ISO 3696

were used.

Sulphanilamide (4-aminobenzenesulfonamide), C6H8N2O2S

N-(1-naphtyl)-Ethylene Diamine Dihydrochloride , C12H14N2 x 2 HCl

Hydrochloric acid; HCl, 37%

112

APPENDIX 9 2/3

Sodium Nitrite, NaNO2, dried to constant mass at 150 °C

Sodium Nitrate, NaNO3, dried to constant mass at 105 °C

Ammonium Chloride, NH4Cl, dried to constant mass at 105 °C

Ammonia, NH4OH

Reagents for total nitrogen:

Only reagents of recognized analytical grade and water according to grade 1 of ISO 3696

were used.

Sulphanilamide (4-aminobenzenesulfonamide), C6H8N2O2S

N-(1-naphtyl)-Ethylene Diamine Dihydrochloride , C12H14N2 x 2 HCl

Hydrochloric acid; HCl , 37%

Sodium Nitrite, NaNO2, dried to constant mass at 150 °C

Sodium Nitrate, NaNO3, dried to constant mass at 105 °C

Ammonium Chloride, NH4Cl, dried to constant mass at 105 °C

Ammonia, NH4OH

Sulphuric acid, H2SO4

Sodium Hydroxide, NaOH

Potassium peroxodisulphate, K2S2O8, Analytical reagent grade. Containing not more

than 0.001% (m/m) nitrogen as impurity.

Boric acid, H3BO3

Glycine, H2NCH2COOH

Calibrating solutions for nitrate and total nitrogen

Table 1: Working range 0.1-5 mg/l NO3-N

NO3-N concentration (mg/l) Volume interim standard (ml) Final volume (ml)

0 - 100

0.1 0.5 100

0.5 2.5 100

1 5 100

2 10 100

5 25 100

113

APPENDIX 9 3/3

The calibrating solutions were prepared fresh:

Glycine solution, 200 mg/l expressed as N.

1.072 g of glycine (H2NCH2COOH), were dissolved in 800 ml distilled water in a

calibrated flask. This mixture was diluted to one litre with distilled water.

Glycine solution, 2 mg/l expressed as N.

We transferred 10 ml of glycine solution and diluted to 1000 ml. This reagent was

prepared fresh.

Apparatus for both, total nitrogen and nitrate determination.

FIAstar 5000 Analyzer unit.

Method cassette NO2/NO3 +interference filters M=540 nm and R=720 nm.

Prepacked reduction columns, part no. 5000 3139

Volumetric flasks, of nominal capacity 100 ml, 500 ml and 1000 ml.

Pipettes of nominal capacity 0.5-25 ml

pH electrode

Procedure

Sample aliquots used for analysis should be free from turbidity; consequently, we had

to filter it through a 0.45 m membrane filter.

Acidification of the samples with hydrochloric acid to approximately pH 2. Storage at

2-5 C for not more than 24 hours.

Starting of FIA 5000, PC and Software.

Verification that correct method cassettes and corresponding detector filters were

installed.

Start of pump/s and pumping of distilled water through each unit and check the flow.

Start of pumping the reagents. The method selector was in the NO2 position for both

measurements.

When the system was filled with liquid, we turned the method selector to NO2+NO3.

Pumped until all the air in the by-pass tube was gone, stopped the pumps and removed

the by-pass tube.

Installation of the Cadmium reductor and starting of the pumps.

Loading of the method in the software; verification that the correct sample loop was

installed.

Loading the Sampler with the samples and drawing Sample List in the Software.

We loaded the calibration standard/s on the Sampler and made a few Test Injections of

one of the standards to verify that the system was equilibrated. Furthermore, we

checked the efficiency of the cadmium redactor.

Finally, the calibration was checked and the sample list started.