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INDEX

1.1.1 Introduction 2

1.1.2. Lake use 2

1.1.3 Restoration methodes 3

1.1.4. Why a restoration database 4

1.1.5. What is the lake restoration questionnaire within the “Alplakes” project? 4

1.1.6. Restoration techniques 6

1.1.6.1. Biological procedures 6

1.1.6.2. Chemical procedures 7

1.1.6.3. Physical procedures 10 1.1.7 Description of the Lake Remediation Database of the Alplakes Project 22

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Workpackage 5: Action 7 DATABASE – ALPINE LAKES –

RESTORATION MEASURES AND PROBLEMS

1.1.1. INTRODUCTION Healthy lakes have a natural capacity to cleanse themselves. Each lake is an individual ecosystem with a food web of organisms that assimilate the incoming nutrients. The food web makes nutrients available up from the simplest bacteria, to people catching fish. This natural lake restoration system works very well to conserve lake water quality and keep the ecosystem in balance.

The coherence between nutrients (phosphorus and nitrogen) and primary production is used as base for lake categorization. Nutrient-poor lakes are called oligotrophic and said to have a low concentration of algae that is reflected in high water transparency. Mesotrophic lakes have good clarity and an average level of nutrients and algae biomass. Eutrophic lakes are enriched with nutrients, resulting in good plant growth and possible algal blooms. Hypertrophic lakes are bodies of water that have been excessively enriched with nutrients, which leads to poor clarity and to devastating algal blooms. Excessive nutrient inflow due to anthropogenic activities overruns the ability of the ecosystem to assimilate the nutrients. Once this occurs the aesthetic quality of the lake is affected by stimulating the growth of nuisance algae and macrophytes. Algae blooms of “smelly” floating algae cottons are the consequences.

Due to the nutrients overload and high organic production the oxygen content decreases. As a consequence the natural assimilation of nutrients in the lake ecosystem breaks down. This is why aerobic organisms decompose more efficient organic material than anaerobic organisms. Aerobic organisms feed on organic material contained in the sediments and increase body mass and reproduction. Aerobic conditions at the lake bottom benefit all aspects of the aquatic environment and cause natural lake restoration. Decomposition processes of organic material under anaerobic conditions are slower. While under aerobic situation a reduction of organic sediments takes place, leads anaerobic digestion to an increase of organic sediments. During anaerobic conditions in the depth of the lakes, bacterial enzymes and lack of oxygen make phosphorus stored in sediments soluble. Then the nutrients return to the water column and get available to primary production (algae growth) again. Anaerobic conditions at the lake bottom have a degrading effect on the ecosystem functioning.

1.1.2. LAKE USE Lakes provide humans with services that include water for irrigation, public supply, industry, energy cooling and dilution of pollutants, hydroelectric power, transportation, recreation, fish, and aesthetic enjoyment (POSTEL & CARPENTER 1997). As these purposes increased and lakes degraded scientific studies about the processes of lake ecosystem showed, that lakes must be understood in the landscape context of their catchments (Likens 1984, Wetzel 1990). During the past decades changes in agriculture, riparian land use, forestry, fossil fuel consumption, and demand for ecosystem services (like: use for recreation, eco tourism, natural areas etc.) link lakes to larger social and economic aspects (POSTEL and CARPENTER 1997). Yet sustainable restoration of lakes must address the social and economic responsibility (CARPENTER & COTTINGHAM 1997) beneath the biotic and chemical causes of lake degradation. The most common causes of lake degradation are pollutants from agriculture, demographic, and social changes that link lakes on a large-scale to human systems.

In the past many communities got beware of lakes conditions and saw the coherences between sewage water, watershed and lake ecosystem malfunctioning. The communities

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started to invest in waste water treatment plants and sewage systems to reduce the nutrient loads from catchment areas. This was an important and useful step to start re- oligotrophication processes of lakes. But in some cases (depending on the oxygen free zone and amount of decomposition in the lake sediment) these measures were insufficient by affecting only the upper water body and not the deeper water body, which still stayed rich of nutrients. Mostly these lakes are subjects for remediation measures particularly when these lakes are of public interest for water supply or recreational purposes in order to avoid algae blooms, arising from the nutrient conservation of bottom layers.

1.1.3. RESTORATION METHODES The goal of sustainable restoration is to come up a natural, self-regulating system. That means that the focus lies not only in the treatment of polluted lakes but also of their surroundings (e.g. restoration of riparian, wetland, and vegetation of macrophytes; reduced harvests on native fish; and reduction of phosphorus use for agricultural purposes). Ultimately, these changes are linked to social and economic processes at regional scales with nationwide importance.

In view of the economic benefits of clean lakes, it seems surprising that lakes continue to degrade and that restoration programs are few. The causes for lake degradation are understood, and many useful technologies for lake restoration exist. Why is restoration of lakes still so difficult?

The fundamental problem of lake restoration is an economic mismatch: those who cause the problem do not benefit sufficiently from the remediation. On the other hand, the beneficiaries of lake restoration are not those who caused the degradation. The economic benefits of clean lakes need to be channelled in ways that create incentives to reduce phosphorus use for several purposes. With the water framework directive (WFD) of the European Commission (EC) this incentives get regulated, as it postulates to reach a good ecological status and avoid degradation.

Agriculture and urbanization are able to change water quality of lakes from valuable to degraded states. However, lake degradation is not a necessary consequence of agriculture and urbanization. High-quality lakes can be maintained in developed landscapes. Restoration of lakes requires economic and ecological interventions. Sustainable restoration will link the economic benefits of clean lakes to increase the awareness for environmental protection. Lake and catchment area management is a complex process that is interdisciplinary by nature and involves many factors that make it difficult to know where to start in many cases. Compromises are made between study and action, protection and conservation, restoration and maintenance, and expense and expedience.

Most restoration measures aim at phosphorus reduction to refurbish polluted lakes and reservoirs. To attain this goal biological, chemical or physical procedures can be used:

Biological procedures:

Biomanipulation Primary sedimentation basin Barley straw

Chemical and biochemical procedures:

Reduction of phosphorus

Physical procedures:

Hypolimnetic oxygenation Hypolimnetic withdrawal Sediment dredging Flushing or dilution Harvesting or elimination of algae and macrophytes Sediment capping Primary sedimentation basin Sonication Artificial mixing or destratification

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Physical and chemical and biochemical procedures are time consuming, rich in by products and require expensive equipment and long term maintenance. By comparison biological measures show greater significance considering the costs, maintenance and energy consumption.

1.1.4. WHY A RESTORATION DATABASE? Within the polylingual alpine region huge knowledge about lake management exists at national, regional and institutional levels. Every country has experience in dealing with water management and especially lake water management.

Among the partners many examples for direct interventions on lakes are known. Unfortunately this extensive knowledge is very often documented only for the use at administrative level or is only published at regional level and therefore inaccessible to lake managers. This situation is not satisfying because the access to different experience gained from lake restoration measures is difficult and time consuming.

With the database for restoration measures on lakes in alpine region we hope to set a base for the future by collecting as much information as possible about lake problems, restoration methods, their functioning and sustainability.

The aim of the database is to offer a comprehensive overview of applied restoration methods in alpine lakes. It also collects data of unsolved lake management problems. It helps to find common problems, which need a concerted approach and investigation in order to share and save money.

The database will support Lake Managers in finding contacts, literature, technical equipments, cost and similar lake problems. It will give an overview of restoration methods and their success in solving a specific problem.

For those involved with managing a lake, this database will provide information essential to understanding options and narrowing the choices, but it is not a substitute for competent advice from lake management experts. However, it cannot anticipate and address all possible situations that may arise or every factor that may go into a decision. As there are existing different pathways to refurbish a polluted lake it is important for Lake Managers to know as much as possible about pros and cons. So the more the database gets filled with example the more useful it will become.

1.1.5. WHAT IS THE LAKE RESTORATION QUESTIONNAIRE WITHIN THE “ALPLAKES”-PROJECT?

The database itself is developed to increase with new scientific cognitions, technical methods and experiences. Therefore all lake managers of the alpine space are asked to provide the lake restoration questionnaire with examples for restoration measures and/or unsolved lake problems. Only with this assistance the database can get a useful and practicable instrument in order to support decision makers to take necessary measures.

You can download the questionnaire from the “Alplakes” homepage (www.alplakes.org) under the sector environment; chapter Action 7.

The content of the following pages gives a brief overview of different kinds of lake restoration methods and is linked to the content of the database.

The questionnaire and the database were developed on behalf of the Department 15 – Environment of the provincial government of Carinthia (Liselotte Schulz and Gabriele Wieser) and by the Carinthian Institute for Lake Research (Roswitha Fresner and Andrea Rauter).

References: POSTEL, S., & S.R. CARPENTER. 1997. Freshwater ecosystem services. Pages 195-214 in G. Daily , editor. Nature's services. Island Press, Washington, D.C., USA.

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WETZEL, R.G. 1990. Land-water interfaces: metabolic and limnological regulators. Internationale Vereinigung fur Theoretische und Angewandte Limnology 24: 6-24. LIKENS, G.E. 1984. Beyond the shoreline: a watershed-ecosystem approach. Internationale Vereinigung fur Theoretische und Angewandte Limnology 22: 1-22. CARPENTER, S. R., & K. L. COTTINGHAM. 1997. Resilience and restoration of lakes. Conservation Ecology [online]1(1): 2. Sources: http://www.consecol.org/vol1/iss1/art2/

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1.1.6. RESTORATION TECHNIQUES The content of the following pages gives a brief overview of different kinds of lake restoration methods and is linked to the content of the database.

1.1.6.1. Biological procedures

Biomanipulation

Lake bio manipulation is based on the trophic-cascade/top-down theory, namely the prediction that increased piscivore abundance will result in decreased planktivore abundance and furthermore an increased zooplankton abundance. The increased zooplankton grazing pressure leads to reductions in phytoplankton abundance and improved water clarity.

However, the bio manipulation affects not only the pelagic food chain from fish to algae. It rather serves as a “trigger” for secondary processes, such as establishment of submerged macrophytes, reduced internal loading of nutrients, and reduced resuspension of particles from the sediment.

The type of water body, the trophic structures and dynamics, the time scales of the population responses and the turnover of resources which are invoked have to be taken into account before a food web manipulation is accomplished.

Recent bio manipulations have shown that, correctly performed, the method also achieves results in large, relatively deep and eutrophic lakes, at least in a 5-year perspective. It is a relatively inexpensive and attractive method for management of eutrophic lakes, and in particular as a follow-up measure to reduced nutrient load.

References:

BENNDORF, J. (1990): Conditions for Effective Bio manipulation: Conclusions Derived from Whole- Lake Experiments in Europe. Hydrobiologia. 200/201: p 187-203.

DEMELO, R., FRANCE, R. & D. J. McQueen (1992): Bio manipulation: Hit or myth?. Limnology and Oceanography. 37(1): 192-207.

HANSSON L.-A., ANNADOTTER H., BERGMAN E., HAMRIN S.F., JEPPESEN E., KaireSalo T., LUOKKANEN E., NILSSON P., SØNDERGAARD M. & STRAND J. (2004): Minireview: Biomanipulation as an Application of Food-Chain Theory: Constraints, Synthesis, and Recommendations for Temperate Lakes. Ecosystems. 1(6): 558-574.

REYNOLDS, C.S. (1994): The ecological basis for the successful bio manipulation of aquatic communities. Archiv fur Hydrobiologie. Stuttgart. 130 (1): 1-33.

Primary sedimentation basin

Primary sedimentation basins serve as storm water retention impoundments created by either constructing an embankment or excavating a pit which retains a permanent pool of water used for water quality improvement. The primary sedimentation basin provides for mechanical settling of fine suspended sediments of polluted tributaries or storm water runoffs as well as biological processing and removal of nutrients from the storm water before being discharged by displacement of a subsequent storm event. Pools also protect deposited sediments from resuspension. To maintain water quality (oxygen levels) and prevent stagnation, a sufficient inflow of water is necessary on a regular basis.

Aquatic vegetation plays an important role in the pollutant removal dynamics of the primary sedimentation basin. Soluble pollutants, especially nutrients, are removed through biological assimilation by both phytoplankton and macrophytes. In addition, an organically enriched wetland substrate will provide an ideal environment for bacterial populations to metabolize organic matter and nutrients.

A primary sedimentation basin is an appropriate water quality practice in residential and commercial areas where nutrient loadings are expected to be high.

Sources: www.state.nj.us/dep/watershedmgt/DOCS/BMP_DOCS/chapter5_wet_pond.PDF

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Barley Straw

Rotting barley straw (Hordeum vulgare) produces allelopathic compounds that act as algaecides. This technique is not thoroughly understood or widespread at this time, but the competition for nutrients between heterotrophic decomposers and autotrophic algae appears to favour the heterotrophic organisms after barley straw addition.

Doses of barley straw under well-oxygenated conditions are typically around 2,5 g/m² of pond surface, with doses of 50 g/m² or more necessary where initial algal densities are high or flow is limited. Doses of 100 g/m² may cause oxygen stress in the pond as decomposition proceeds, but this can be avoided by the use of a land-based digester into which straw is deposited and through which water is pumped as the straw decays.

Application of the straw as whole bales or completely loose has been less successful than installation in loose but contained portions.

Sources: http://www.mass.gov/dcr/waterSupply/lakepond/downloads/practical_guide.pdf

1.1.6.2. Chemical procedures

P-elimination by flocculation/floatation with water backflow (PELICON)

The pelicon technique (Phosphate Elimination Container) is based on the drinking water treatment and eliminates the phosphorous of the hyporheic water. The precipitation, flocculation and flotation occur in an phosphate elimination container ashore (Fig. 5). Phosphorous precipitation can be achieved with metal salts like aluminium sulphate, ferric salts (chlorides, sulphates), ferric aluminium sulphate, clay particles and lime (as Ca (OH)2 and as CaCO3).The phosphorous-poor treated water is returned into the lake and stratifies according to its density and temperature in the hypolimnion. No dilution or mixing with the untreated water takes place.

The elimination of phosphorous of the hyporheic water of a lake via a portable pelicon technique implements 10 m³/h to 120 m³/h. Stationary equipment are able to clean much higher volumes.

Figure 1.1.6.2.1: Schematic setting of an Phophate elimination container (PELICON). References: FITSCHEN T. 2002. Pelicon Externe Phosphat-Elimination zur Restaurierung eutropher Gewässer.

Wasser, Luft und Boden – Zeitschrift für Umwelttechnik (9): 1-4.

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KEIL, U. 1995. Phosphat-Elimination zur Restaurierung geschichteter Gewässer. Limnologie Aktuell 8. Gustav Fischer Stuttgart: 115-118.

VIETINGHOFF, H. 2001. Restaurierung des Kleinen Seeiner Sees durch externe Phosphatelimination, UFO – Verlag, Allensbach.

Sources: http://www.strandbad-farmsen.de/Pelicon_Artikel_WLB_2002-09.pdf

Floating phosphorous elimination plant (NESSIE)

A floating phosphorous elimination plant called “NESSIE” on the basis of a filter with porous adsorbing granules with a large specific surface area of 300m²/g has been designed by RICHERT (2002). Lake water is pumped over the filter using a wind-solar hybrid system as energy source (150 Wh). The P-loading capacity under laboratory conditions is about 60 g/kg adsorbent, but may be half as much in situ. The loads adsorbent is suitable to be used as fertilizer.

References:

RICHERT, O. 2002. NESSIE – schwimmende Entphosphatungsanlagen. IGB – Workshop Seentherapie, Blossin, Abstracts.

Phosphorus precipitation

Phosphorus precipitation by chemical complexing removes phosphorus from the water column and can control algal abundance. Inactivation of phosphorus on the surface of lake sediments can greatly reduce the release of phosphorus from those sediments, minimizing the internal load. This technique is most effective after nutrient loading from the watershed is sufficiently reduced, as it acts only on existing phosphorus reserves, not new ones added post-treatment. In-lake treatments are used when studies indicate that the primary source of the phosphorus is internal (recycled from lake sediments). Such nutrient control generally does not reduce macrophytes abundance, but can control algal growths.

The three most common treatments for lakes employ salts of aluminium, iron, or calcium compounds. The typical compounds used include aluminium sulphate (Al2(SO4)3 x H2O), sodium aluminate (Na2Al2O x H2O), iron as a ferric chloride (FeCl3) or ferric sulphate (Fe2(SO4)3), and calcium as lime (Ca(OH)2) or calcium carbonate (CaCO3).

Ferric salts

The “ferrous wheel” (Fig. 1.1.6.2.2) can be amplified by the input of ferric salts. Iron is initially input to lakes from groundwater and streams as Fe3+. As the Fe3+ reaches the oxycline, it is reduced to Fe2+ due to the change in redox potential from the oxidizing surface waters to the reducing bottom waters. The Fe2+ exists as a dissolved species and is therefore controlled by advective-diffusive forces of the bottom waters. When Fe2+ is transported to the upper waters by these forces, it is oxidized back into Fe3+ which then precipitates again as an iron oxide compound and falls back down below the oxycline to be reduced back into Fe2+. A small amount of iron is lost to mineral formation or outflow from the system, but CAMPBELL has shown a residence time for iron of greater than 15 years (CAMPBELL & TORGERSEN 1980).

As phosphate diffuses upward from anoxic bottom waters, it can encounter the iron oxides that form at the oxycline. The phosphate can then adsorb onto the iron oxides and sediments out of the system. The phosphorous bound to the iron oxides is released as the iron oxides dissolve in bottom waters. The phosphorous released diffuses back up in the water column until it reaches more iron oxides above the oxycline, and the cycle continues. This process essentially traps the phosphorous and does not allow it to diffuse up into surface waters where it can become available to phosphorous-limited primary producers.

Ferric salts are effective in precipitating phosphorus, but difficult to handle because of their aggressive acidity. Furthermore, the iron-phosphorus complex is stable only under oxic conditions. Thus application of ferric salts usually requires subsequent continuous aeration to avoid re-dissolution of phosphorus under anoxic conditions. Due to the high mobility of iron ions, addition of iron frequently often has to be repeated at regular intervals. Iron may be a limiting micronutrient in some systems and, in such situations; treatment with ferric salts may actually stimulate growth of cyanobacteria and algae.

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Figure 1.1.6.2.2: The “Ferrous Wheel” adapted from CAMPBELL & TORGERSON (1980). Iron input as Fe3+ falls below the oxycline where it is reduced to Fe2+. The dissolved Fe2+ then diffuses back up through the oxycline and is oxidized back into Fe3+ where is forms iron oxide solids that then fall back below the oxycline. This cycle can trap iron in lakes for years.

Aluminium salts

The effectiveness of aluminium salts application rests on the ability of aluminium to form complexes, chelates, and insoluble precipitates with phosphorus, thereby removing it from the water column and depositing it in the sediment in forms unusable by phytoplankton. Depending on pH, phosphorus concentration, aluminium concentration, and the rate at which additional phosphorus is supplied, aluminium salts can provide long-term inactivation of sediment phosphorus (CONNOR & MARTIN 1989). Because of its ability to continue to bind phosphorus under the widest range of pH and oxygen levels, aluminium is usually the preferred phosphorus inactivator. Furthermore, aluminium has been shown to have no toxicity to aquatic life at the pH and dose necessary for lake restoration (COOKE & KENNEDY 1981). Although not all forms of phosphorus (e.g., dissolved organic phosphates) are removed by aluminium salts application, this methodology has proven to be an effective strategy for phosphorus inactivation in many water-quality-impaired lakes.

The week prior to aluminium salts application, copper sulphate can be applied as an algicide to remove phosphorus tied up in the phytoplankton. Theoretically, this phosphorus could recycle in the lake system for many years (CONNOR & MARTIN 1989). Pilot jar and tank studies should be performed before aluminium salts application to determine the best ratio and dosage of aluminium sulphate and sodium aluminate ratio.

Calcite

Calcite (both Ca (OH)2 and Ca CO3) has been used as an algaecide to coagulate and precipitate phytoplankton cells out of the water column in hard water lakes (Murphy et al., 1990; ZHANG and PREPAS, 1996). It is non-toxic, usually fairly inexpensive, and the pH-shock for the aquatic biota can be minimised by careful dosing over an extended time span. Unlike treatment with copper sulphate, the precipitation of cyanobacterial cells with Ca(OH)2 does not appear to cause cell lysis and toxin release into the water (KENEFICK et al., 1993; LAM et al., 1995).

Lime also functions as a longer-term algal inhibitor, reducing eutrophication by precipitating phosphorus from the water (Murphy et al., 1990). It appears that Ca (OH)2 is more effective than CaCO3 in precipitating phosphorus (Murphy et al., 1990). Calcite may serve as an active barrier material and as sediment capping. To enhance the artificial calcite precipitation the input of Ca (OH)2(CaO) should be combined with an aeration of the water.

The result of the P-binding of different technical products depends on particle size, specific surface-area and on the fine structure of the calcite applied. The coccolithic lime, formed

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several million years ago belongs to those with extremely large specific surface area and good sorption ability.

The inactivators are applied to the surface or subsurface, in either solid or liquid form, normally from a boat or barge. These compounds dissolve and form hydroxides, Al (OH)4, Fe (OH)3, or in the case of calcium, carbonates such as calcite (Ca CO3). These minerals form a flock that can remove particulates, including algae, from the water column within minutes to hours and precipitate reactive phosphates. Reactions continue at the surface-water interface, binding phosphorus that could otherwise be released from the sediment. Because aluminium and iron added as sulfates or chlorides dissolve to form acid anions along with the formation of the desired hydroxide precipitants, the pH will tend to decrease in low alkalinity waters unless basic salts such as sodium aluminates or lime are also added. Conversely, calcium is usually added as carbonates or hydroxides.

The solubility curves of phosphate phases against pH levels are illustrated in figure 1.1.6.2.3.

Figure 1.1.6.2.3: Solubility curves of phosphate phases against pH levels.

References: CONNOR, J.N. & M.R. MARTIN. (1989): An assessment of wetlands management and sediment

phosphorus inactivation, Kezar Lake, New Hampshire. New Hampshire Department of Environmental Services, Water Supply and Pollution Control Division, Staff Report Number 161. 109 pp.

COOKE, G.D. & R.H. KENNEDY. (1981): Precipitation and inactivation of phosphorus as a lake restoration technique. U.S. EPA Ecological Research Series. EPA- 600/3-81-012. U.S. Environmental Protection Agency, Washington, DC.

CAMPBELL, P., & T. TORGERSEN. (1980): Maintenance of iron meromixis by iron redeposition in a rapidly flushed monimolimnion. Can. J. Fish. Aquat. Sci. 37:1303-1313.

1.1.6.3. Physical procedures

Harvesting: Decantation of algal cotton from the surface

Algal cotton can be removed from the surface of water bodies using a weed rake. However, specially designed nets should be used to collect the floating plants. The time needed for cleanup depends on the density and types of plants and the size of the area that has to be cleaned.

Sonication is used to break up algae in samples for better analysis, but it is also a new technique on an application scale for lake management. A floating sonicator is now available commercially, and product literature claims that it will break up algae and cause them to sank

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to the lake bottom over target areas that range from 150 to 15.500 m², depending upon the model installed. Power consumption is a maximum of 45 Watts, and the sonic waves reportedly have no effect on zooplankton or fish. The product literature warns that some algae may float after sonication, but that they will eventually sink. No scientific testes of this apparatus have been reported in the lake management literature, and this product is likely to provide only short-term relief, but it may be a viable option for smaller lakes and ponds. Impacts on non-target organisms bear further investigations. This technique has just been introduced in the USA and in Massachusetts.

Source: http://www.mass.gov/dcr/waterSupply/lakepond/downloads/practical_guide.pdf

Lowering the water level of a lake or reservoir can have a dramatic impact on some aquatic weed problems. Water level drawdown can be used where there is a water control structure that allows the managers of lakes or reservoirs to drop the water level in the water body for extended periods of time. Water level drawdown occurs regularly in reservoirs for power generation, flood control, or irrigation; a side benefit being the control of some aquatic plant species. However, regular draw downs can also make it difficult to establish native aquatic plants for fish, wildlife, and water birds habitat in some reservoirs.

Grass carp (Ctenopharyngodon idella), also known as the white amur, is a vegetarian fish native to the Amur River in Asia. The objective of using grass carp to control submerse macrophytes is to end up with a lake that has about 20 to 40 percent plant cover, not a lake devoid of plants. Grass carp feed from the top of the plant down so that mud is not stirred up. However, in ponds and lakes where grass carp have eliminated all submersed vegetation the water becomes turbid. Hungry fish will eat the organic material out of the sediments. They have definite taste preferences. The type of plants grass carp prefer may also be those most important for habitat and for water birds food. Stocking rates depend on the amount and type of plants in the lake as well as spring and summer water temperatures. Grass carp offer long-term control, but fish need to be restocked about every ten years. Survival rates of the fish will vary depending on factors like presence of otters, birds of prey, or fish disease. To prevent stocked grass carp from migrating out of the lake and into streams and rivers, all inlets and outlets to the pond or lake must be screened. Once grass carp are stocked in a lake, it may take from two to five years for them to control nuisance plants. In many cases control my not occur or all submersed plants may be eliminated. They should be stocked only in water bodies where complete elimination of all submersed plant species can be tolerated. Stocking grass carp may lead to algae blooms. They are a biological alternative to aquatic plant control.

Bottom screen or benthic barrier covers the sediment like a blanket, compressing aquatic plants while reducing or blocking light. An ideal bottom screen should be durable, heavier than water, reduce or block light, prevent plants from growing into and under the fabric, be easy to install and maintain, and should readily allow gases produced by rotting weeds to escape without “ballooning” the fabric upwards. Materials such as burlap, plastics, perforated black Mylar, and woven synthetics can all be used as bottom screens. There is also a commercial bottom screen fabric called “Texel”, a heavy, felt-like polyester material which is specifically designed for aquatic plant control. Bottom screens will control most aquatic plants; however freely-floating species will not be controlled by bottom screens. Some species will send out lateral surface shoots and may canopy over the area that has been screened giving less than adequate control. Advantages of bottom screens are the creation of an immediate open area of water, the easy installation around docks and in swimming areas and the control up to 100 percent of aquatic plants. Disadvantages of this method are the habitat reduction by covering the sediment, the need of regularly inspection, the possible damage or dislodgement of bottom screens, the difficulty to anchor the bottom screen on deep muck sediments, the interference of bottom screens with fish spawning and bottom-dwelling animals and the possible colonisation of the bottom screen by aquatic plants.

Diver dredging (suction dredging) is a method whereby SCUBA divers use hoses attached to small dredges (Often dredges used by miners for mining gold from streams) to suck plant material from the sediment. The purpose of diver dredging is to remove all parts of the plant including the roots. A good operator can accurately remove target plants while leaving native species untouched. The suction hose pumps the plant material and the sediments to the surface where they are deposited into a screened basket. The water and sediment are returned back to the water column and the plant material is retained. The turbid water is

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generally discharged to an area curtained off from the rest of the lake by a silt curtain. The plants are disposed of on shore. Removal rates vary from approximately 1000 m² per day to 4050 m² per day depending on plant density, sediment type, and diver efficiency. Diver dredging is more effective where softer sediment allows easy removal of the entire plants, although water turbidity is increased with softer sediments. Harder sediment may require the use of a knife or tool to help loosen sediment from around the roots. In very hard sediments, some plants tend to break off leaving the roots behind and defeating the purpose of diver dredging. In comparison with other aquatic plant management methods, diver dredging is very expensive. Diver dredging is the recommended method for removing plants around docks and in other difficult to reach areas. Besides it can be used in situations where herbicide use is not an option for aquatic plant management.

Mechanical weed cutters cut submerse macrophytes several feet below the water’s surface. There are two types of underwater weed cutters commercially available, including the portable, boat-mounted cutting units and the specialized barge-like cutting machines. Cutting is generally performed during the summer when plants are near the surface. The advantages of this method are the immediate open areas of water that are created by cutters and the possibility to retain habitat for fish and other organisms if the plants are not cut too short. The disadvantages include the grow back of the plants possibly several times during the growing season; the difficulty of some species to cut; the spread of invasive plants through floating plant fragments; and the decomposing of these fragments that drift onshore.

Mechanical harvesters are large machines which both cut and collect aquatic plants. Cut plants are removed from the water by a conveyor belt system and stored on the harvester until disposal. A barge may be stationed near the harvesting site for temporary plant storage or the harvester carries the cut weeds to shore. The shore station equipment is usually an ashore conveyor that mates to the harvester and lifts the cut plants into a dump truck. Harvested weeds are disposed of in landfills, used as compost, or in reclaiming spent gravel pits or similar sites. Harvesting is usually performed in late spring, summer, and early fall when aquatic plants have reached or are close to the water’s surface. Harvesters can cut and collect several km² per day depending on weed type, plant density, and storage capacity of the equipment. Harvesting speeds for typical machines range from 2.000 m ² to 6.000 m² per hour. Depending on the equipment used, the plants are cut from 1,5 m to 3 m below the water’s surface in a swath 1,8 to 6 m wide. Some modern harvesters can cut plants in a range of water depths. Because of machine size and high costs, harvesting is most efficient in lakes larger than a few km². Harvesting can be an excellent way to create open areas of water for recreation and fishing access. Since the lower part of the plant remains after harvest, habitat for fish and other organisms is not eliminated. However, plant grows back and may need to be harvested several times during the growing season. There is little or no reduction in plant density with mechanical harvesting. Along with plants, harvesters also collect small fish and insects.

Rotovators use underwater rototiller-like blades to uproot watermilfoil plants (Fig. 1). The rotating blades churn 18 to 23 cm deep into the lake bottom to dislodge plant root crowns. The plants and roots may then be removed from the water using a weed rake attachment to the rototiller head or by harvester or manual collection. The usage of rotovators is most effective in the winter and spring when plants have died back. Depending on plant density and sediment type, 8 to 12 km² per day can be rotovated. Because of the size of the equipment and high costs, rotovation is most suitable for use in larger lakes. In some cases, the growth of native aquatic plants appeared to be stimulated by rotovation for watermilfoil removal. Perhaps removing the milfoil canopy allowed light to penetrate so that native plants could develop. Negative side-effects are that rotovation churns up the sediment causing temporary turbidity and nutrients, such as nitrogen and phosphorus, to be released into the water.

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Figure 1.1.6.3.1: Schematic rotovator.

Sources: http://board.erm.tu-cottbus.de/index.php?id=5&no_cache=1&file=166&uid=14

Flushing: Using waters low in nutrient content a “dilution” of the P-content in the lake may be achieved. This method has been applied In Lake Mueggelsee, Berlin, where the River Spree flows during the late summer through the lake, thereby flushing out the nutrients redissolved from sediments. In the cold season the Mueggelsee-passage of the now nutrient –rich Spree can be avoided using a bypass around the lake. The flushing sometimes improves the water quality even if total phosphorus in the flushing water is high due to the low utilizability of the P compounds from erosion for algae growth (KLAPPER, 2003).

If suitable water is available in sufficient quantity, flushing can be a very effective tool for reduction of cyanobacterial proliferation. Successful examples are Veluwemeer in the Netherlands (SAS, 1989) and Moses Lake in the USA (WELCH et al., 1972). However, this measure also implies a relocation of the phosphorus to another water body, and this impact must also be evaluated.

References:

KLAPPER, H. (2003): Technologies for lake restoration. Papers from Bolsena Conference (2002). Residence time in lakes: Science, Management, Education J. Limnol., 62(Suppl. 1): 73-90.

SAS, H. (1989): Lake Restoration by Reduction of Nutrient Loading: Expectations, Experiences, Extrapolations. Academia Vlg. Richarz, 479 pp.

WELCH, E.B., BUCKLEY, J.A. and BUSH, R.M. (1972): Dilution as an algal bloom control. J. Water Poll. Contr. Fed., 44, 2245-2265.

WELCH, E.B. (1981): The Dilution/Flushing technique in Lake Restoration. Corvalllis. Env. Res. Lab., USEPA. EPA-600/3-81-016. 13 p.

Sources: http://www.iii.to.cnr.it/pubblicaz/JL_62_supl/10_Klapper.pdf

Hypolimnetic withdrawal

In deep water bodies during thermal stratification the highest nutrient concentrations which are found in the deepest waters, can be siphoned by the so called Olszewski-tube (Fig. 1.1.6.3.2). The Olszewski-tube consists of a pipe installed along the lake bottom from near the deepest point to the outlet, an aeration of outlet water in case of suboxic, anoxic and/or sulfidic conditions and an external nutrient elimination of siphoned waters to prevent the pollution of downstream waters. The low temperatures of the hypolimnion water may have a

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substantial impact on downstream biological processes, such as fish breeding. Hypolimnetic withdrawal is effective only if enough water flows into the lake. Furthermore, some lowering of the water level may be tolerable, but complete destratification by removal of most of the hypolimnion should be avoided, because increasing the contact area between warm surface water and sediments will enhance phosphorus release due to elevated temperatures. To lessen the chances of destratification it is possible to direct inflow water to the meta-or hypolimnion. Nürnberg (1997) summarized the advantages of hypolimnetic withdrawal to reduce the phosphorous content of a lake during summer stratification. The advantages of the method are:

• It addresses the cause of eutrophication. • It does not add chemicals. • It does not necessarily change the water budget. • It can break the cycle of enhanced sediment accumulation of total phosphorus. • It can flush more phosphorus out of the system than the sediments accumulate each year

In the Swiss Mauensee this technique was applied to successfully reduce the biomass of Planktothrix rubescens (Gächter, 1976).

Figure 1.1.6.3.2: Schematic setting of an “Olszewski tube” in a lake.

: KLAPPER, H.2003. Technologies for lake restoration. Papers from Bolsena Conference (2002).

Residence time in lakes: Science, Management, Education J. Limnol., 62(Suppl. 1): 73-90. NÜRNBERG, G.K. 1997 Coping with water quality problems due to hypolimnetic anoxia in Central Ontaria

Lakes. Wat. Qual. Res. J. Canada, 32, 391-405. TOLOTTI M. & THIES H. 2002. Phytoplankton community and limnochemistry of Piburger See (Tyrol,

Austria). J. Limnol., 61(1): 77-88. OECD (Organization for Economic Co-Operation and Development). 1982. Eutrophication of Waters.

Monitoring, Assessment and Control. 156 pp. Olszewski, P. 1961. Versuch einer Ableitung des hypolimnischen Wassers an einem See. Ergebnisse

des ersten Versuchsjahres. Proc. Int. Assoc. Limnio., 18: 1792-1797. GÄCHTER, R. 1976 Die Tiefenwasserableitung, ein Weg zur Sanierung von Seen. Schweiz. Z.

Hydrolog,. 38, 1-28.

Sources: http://www.iii.to.cnr.it/pubblicaz/JL_62_supl/10_Klapper.pdf

Artificial mixing or destratification

In deep lakes a higher nutrient elimination during the stagnation period can be achieved using artificial mixing or destratification, so that deep waters with high nutrient contents are mixed with the epilimnetic waters, and exported with the outflow at the surface.

The simplest method is artificial destratification where compressed air is injected through perforated pipes or course diffusers located at the bottom of the water column (PASTOROK et al. 1981) Induces mixing from the rising air bubbles produces vertical mixing, thereby inhibiting the formation of thermal stratification. Destratification increases bottom water

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dissolved oxygen (DO) by thermal stratification and by redistributing photo synthetically produced oxygen from surface to bottom waters, as well as increasing contact time between water and the atmosphere. The main drawback of artificial destratification is increased summer temperatures in bottom water.

Other mixing technologies include pumping oxygen-oversaturated water from the surface down to the highest deficit near the sediment (MIXOX). The O2-deficient water may be transported from the depth to the surface using rising pipes (aerohydraulic guns) or modified deep water aerators. The oxygenation of the deeper water takes place partly by the air-lifting, but mainly at the large surface of the lake.

Some destratification methods are illustrated in Figure 1.1.6.3.3.

Destratification by means of linear input of compressed air.

Destratification by means of the circulating pump (Mixox) method.

Entry of surface water inputs of lower density into the deep-water zone. Typical case: Jabeler See. (From Paul and KLAPPER 1985).

Jet-destratification in water reservoirs.

Figure 1.1.6.3.3: Destratification Methods

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Aeration equipment for destratification, adopted at the Weissen See, Berlin

Figure 1.1.6.3.4: Destratification technologies.

References: BEUTEL M. 2005. Improving quality of salmonid habitat in lakes using hypolimnetic oxygenation.

UCOWR Conference 2005: River and Lake Restoration: Changing Landscapes. Portland, ME. Abstracts.

KLAPPER, H.2003. Technologies for lake restoration. Papers from Bolsena Conference (2002). Residence time in lakes: Science, Management, Education J. Limnol., 62(Suppl. 1): 73-90.

PASTOROK, R. A., T. C. Ginn & M. W. LORENZEN. 1981. Evaluation of aeration/circulation as lake restoration technique. EPA 600/3-81-014. SCHARF, B.W. 1995. Seentherapie. Habilitationsschreift. Universität Braunschweig. THOMAS, E.A. 1966. Der Pfäffiker See vor, während und nach der künstlichen Durchmischung. Verh.

Internat. Verein. Limnol. 16: 144-152. VISSER , P.M., IBELINGS, B.W., VEER, B., Van Der KOEDOOD, J. & Mur, L.R. 1996. Artifical mixing

prevents nuisance blooms of the cyanobacterium Microcystis in Lake Nieuwe Meer, The Netherlands. Freshwat. Biol. 36:435-450.

Sources: http://www.ucowr.siu.edu/proceedings/2005%20Proceedings/Conference%20Proceedings/07-14 05%20Thursday%20AM2/Session%2027/27.3.Beutel.pdf http://www.iii.to.cnr.it/pubblicaz/JL_62_supl/10_Klapper.pdf

Hypolimnetic oxygenation

Hypolimnetic oxygenation uses pure oxygen gay to oxygenate the hypolimnion while preserving thermal stratification (MCQUEEN & LEAN, 1986). The technique uses a confined air-lift system where air bubbles are injected at the bottom of an air-lift tube, and oxygen is transferred to the water as the air-water mixture travels up the tube. Aerated water is then redistributed into the hypolimnion. Lake managers have utilized both full-lift systems that raise the water to the surface and partial-lift system that raise water up to around the metalimnion. By maintaining a cool hypolimnion, hypolimnetic aeration avoids many of the problems associated with bottom water warming caused by artificial destratification.

Three main types of hypolimnetic oxygen systems are currently in use:

• bubble plume oxygenation • linear diffuser oxygenation and

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• submerged contact chamber oxygenation

Bubble plume oxygenation works by injecting pure oxygen through an array of diffusers at the lake bottom. Oxygen bubbles dissolve into a surrounding plume of rising water. The oxygenated plume detrains and spreads horizontally below the thermocline. The linear diffuser oxygenation consist of an extensive network of line diffusers that release fine oxygen bubbles that rapidly dissolve into the overlaying water column. The submerged contact chamber system injects oxygen gas and hypolimnetic water into the top of an inverted cone at the bottom of the reservoir (Fig. 1.1.6.3.5). Rising oxygen bubbles within the cone are suspended in the down-flowing water, allowing for nearly complete dissolution of the oxygen. Highly oxygenated water is then discharged horizontally out the bottom of the cone.

Figure 1.1.6.3.5: Schematic of submerged contact chamber oxygenation system. (BEUTEL & HORNE 1999).

Problems associated with hypolimnetic oxygenation are the low oxygen transfer efficiencies of most hypolimnetic aeration techniques (SMITH et al. 1975). Thus aeration units may need to operate at high recirculation rates and (/or multiple units may be required. This leads to elevated levels of turbulence within the hypolimnion which can increase sediment oxygen demand (SMITH et al., 1975; ASHLEY 1983; MOORE et al, 1996; BEUTEL 2002). Or result in accidental destratification (HEINZMANN & CHORUS 1994). The introduction of compressed air which predominantly consists of nitrogen may lead to elevated levels of dissolved nitrogen gas in the hypolimnion and the potential for the formation of gas bubble disease in fish (FAST et al. 1975).

References: ASHLEY, K.A. 1993. Hypolimnetic aeration of a naturally eutrophic lake: physical and chemical effects.

Can. J. Fish. Aquat. Sci. 40:1343-1359. BEUTEL, M.W. 2003. Hypolimnetic anoxia and sediment oxygen demand in California drinking water

reservoirs. Lake and Reservoir Management. 19(3):208-221. BEUTEL M. 2005. Improving quality of salmonid habitat in lakes using hypolimnetic oxygenation.

UCOWR Conference 2005: River and Lake Restoration: Changing Landscapes. Portland, ME. Abstracts.

BEUTEL, M.W. & HORNE A.J. 1999. A review of the effects of hypolimnetic oxygenation on lake and reservoir water quality. Lake and Reservoir Management. 19(3):208-221.

FAST, A. W., W. J. OVERHOLTZ & TUBB R.A. 1975. Hypolimnetic oxygenation using liquid oxygen. Wat. Resour. Res. 11(2)294-299.

HEINZMANN, B. & CHORUS I. 1994. Restoration concept for Lake Tegel, a major drinking and bathing water resource in a densely populated area. Environ. Sci. Technol. 24: 1410-1416.

MCQUEEN, D.J. & LEAN D.R.S. 1986. Hypolimnetic Aeration: An Overview. Wat. Poll. J. Can. 21(2):205-217.

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Moore, B.C., P. H. CHEN, W. H. FUNK & YONGE D. 1996. A model for predicting lake sediment oxygen demand following hypolimnetic aeration. Wat. Resour. Bull. 32(4):1-9.

SMITH, S.A., D. R. KNAUER & WIRTH L. T. 1975. Aeration as a lake management technique. Wisconsin Dept. Nat. Resour., Technical Bulletin No. 87. 39p.

Sources: http://www.ucowr.siu.edu/proceedings/2005%20Proceedings/Conference%20Proceedings/07-14-05%20Thursday%20AM2/Session%2027/27.3.Beutel.pdf

Dredges

Dredges are usually used for removing contaminated sediments from lake or river bottoms. They can also be a tool of lake management to dig up sediments in stratified lakes that are rich in nutrients such as phosphorous.

There are two basic types of dredges: mechanical and hydraulic.

Mechanical dredges use mechanical force to scoop up sediments and load them onto a transportation vehicle or directly into a land-based containment area. The most widely available mechanical dredges are the mechanical clamshell dredges. They are most suitable for removing gravel, sand, and very cohesive sediments like clay, peat, and highly consolidated silt. They can operate in very tight spaces without interfering with shipping.

Two kinds of clamshell dredges are the enclosed bucket dredge (Fig. 1.1.6.3.6) and the cable arm dredge (Fig. 1.1.6.3.7).

Figure 1.1.6.3.6: Enclosed Bucket dredge Figure 1.1.6.3.7: Cable Arm Dredge

Hydraulic dredges work like vacuums, using strong pumps to suck up sediments from the bottom. Generally, hydraulic dredges resuspend less sediment than mechanical dredges as they operate. Some hydraulic dredges use special pumps, called pneumatic pumps. There are four main components to hydraulic and pneumatic dredges: the dredge head, the dredge head support, the suction pump, and the pipeline to transport dredged sediments. Hydraulic dredges tend to be identified by their dredge heads, while pneumatic dredges tend to be identified by the pump they use. Often, the dredge head is fitted with a cutter head that loosens the sediments so that the suction pump can pump them to the transport, treatment, or deposal site.

Hydraulic systems suck in slurry, a combination of sediments and water. Pneumatic systems pull in sediments with very little water in them. Unlike mechanical dredges, hydraulic and pneumatic dredges are closed systems: once the sediments enter them, they have no contact with their environs until they reach the transport, treatment or disposal site. Since both types suck sediments in rather than just dip them up, they resuspend much less than mechanical dredges.

Common hydraulic dredges are the plain suction head dredge and the cutter head dredge (Figure 1.1.6.3.8 and 1.1.6.3.9).

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Figure 1.1.6.3.9: Cutterhead Dredge Figure 1.1.6.3.8: Plain Suction Dredge

Dredges that use a combination of mechanical force to loosen sediment and hydraulic force to pump it up are often referred to as hybrid dredges. The horizontal auger dredge (Fig. 1.1.6.3.10) is a commonly used dredge that has a type of screw, or auger, to break up sediment and carry it to the dredge pump. A retractable mud shield over the auger can control resuspension, but increases the probability that the dredge will clog. Four anchored cable wires hold the dredge in place and move it like a pendulum from side to side.

References:

Figure 1.1.6.3.10: Horizontal Auger Dredge

PETERSON, S. A. 1981. Sediment Removal as a Lake Restoration Technique. Corvallis Env. Res. Lab., USEPA. EPA-600/3-81-013. 56p.

WI DEPARTMENT OF NATURAL RESOURCES. 2001. Digging them up. Hydraulic dredging project. 15. USEPA Great Lakes National Program

KLEEBERG A. & KOHL J. 1999. Assessment of the long-term effectiveness of sediment dredging to reduce benthic phosphorus release in shallow Lake Müggelsee (Germany). Hydrobiologia. 394(0): 153-161.

Sources: www.dredge.com/pdf/sierra_endorsement.pdf

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Sediment oxidation Sediment oxidation in shallow lakes is another method using calcium for phosphorous inactivation. FeCl3, buffered with limestone, and liquid calcium nitrate (Ca (NO3)) are injected into the sediment to stimulate denitrification and oxidation of organic matter (Riplox-method, RIPL 1976). Oxidation of organic matter will enhance greater binding of phosphorus with ferric hydroxide complexes. WILLENBRING et al. (1983) recommend a dose of app. 150 g nitrogen/m² to oxidize sediments to a depth of at least 10 cm and prevent the release of phosphorus. If oxidation depths do not exceed 10 centimetres, non-oxidized sediments could become exposed in the future releasing phosphorus to the water column. COOKE et al. (1993) recommended oxidizing the top 15 to 20 centimetres of sediment. An addition of ferric chloride may be necessary if there is not enough phosphorous present in the sediment. The microbial denitrification can be stimulated by the addition of lime, which causes a raise of pH.

Besides calcium nitrate, hydrogen peroxides are used to oxidise contaminated sediments with PCB’s (polychlorinated biphenyl).

References: COOKE, G.D., E.B. WeLch, A.B. MARTIN, D.G. FULMER, J.B. HYDE & G.D. SCHRIEVE. 1993. Effectiveness

of Al, Ca, and Fe salts for control of internal phosphorus loading in shallow and deep lakes. Hydrobiologia. 253: 323-335.

RIPL, W. 1976. Biochemical oxidation of polluted lake sediment with nitrate. A new restoration method. Ambio. 5:112-135.

WILLENBRING, P., W. WEIDENBACHER and M. MILLER. 1983. Reducing sediment phosphorus release rates in Long Lake through the use of calcium nitrate. Lake and Reservoir Management: Proceedings of Third Annual Conference North American Lake Management Society. Knoxville, TN.

Sediment capping

Sediment capping is basically a technique for remediation of contaminated sediments. In-situ capping (ISC) is a form of containment in-place and refers to placement of a covering or cap over an in-situ deposit of contaminated sediment. This technique can also be used to prevent the resuspension of phosphorous from the sediments of the lake bottom. The benthic biota, however, will be buried by the cap. The cap may be constructed of clean sediments, sand, gravel or may involve a more complex design with geotextiles, liners and multiple layers. A variation on ISC could involve the removal of sediments to some depth, followed by capping the remaining sediments in-place.

Site considerations that can influence equipment selection include water depths and wave/current conditions, bottom topography, stratification of the water columns, etc. For granular cap components, the major consideration in selection of equipment and placement of the cap is the need for controlled, accurate placement and the resulting density and rate of application of capping material. Techniques and equipment for the placement of caps are illustrated in figure 1.1.6.3.11.

For detailed information about the placement techniques for granular cap material see:

Sources: http://www.epa.gov/glnpo/sediment/iscmain/four.html

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Figure 1.1.6.3.11: Techniques and equipment for the placement of caps.

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1.1.7. Description of the Lake Remediation Database of the Alplakes Project

In the start window of the database the user can choose between the options “Problems” and “Methods” to search for lakes in the alpine region where several problems were observed and methods implemented, respectively (Fig.1.1.7.1).

Fig. 1.1.7.1: Start window of the database.

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Searching for lakes with similar problems

If the user clicks on the “problems” button a form opens, that provides the user with several information and additional options (Fig. 1.1.7.2). In the list field “Problems” the user can choose between the problems Algal blooms, Cercarial Dermatitis, Decrease of Reeds, Erosion of banks, Fish, Macrophytes and Other Problems (several problems that did not fit into the categories listed above). When the user has selected one problem in the list field “Implemented Remediation Methods” appears a list with the name of the lakes and their implemented remediation measure according to the chosen problem. Simultaneously in the list field “Lakes” appear morphometric data of the lakes to enable the user to choose one lake that is similar to the one the user has an eutrophication problem with. To gain further information about a specific lake, the user has to click on the lake in the “Lake” list field and to click on one of the buttons below. The buttons with red texts give detailed information about the chosen lake irrespective of the chosen problem. The buttons with the blue text link to reports with detailed information about the occurred chosen problem at the selected lake.

Fig. 1.1.7.2: The Problem form gives the opportunity to select a problem, to choose an interesting lake according to morphometric data and its implemented remediation method and it provides some links to detailed reports.

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Links of buttons with red text Parameter The form „Parameter“ provides the user with some general data about the lake (morphometric data, circulation behaviour, main uses, origin of load, the implementation of a wastewater treatment plant) and there are several register with average, minima and maxima data 5 years before the remediation measure was implemented, during the implementation and 10 after the implementation to quantify the success of the remediation measure. A graph visualises the data. The register include data about secchi depth, water temperature, electric conductivity, 3 mg/l oxygen depth layer, oxygen concentration above the lake ground, sulphate above the lake ground, total phosphorous concentration of the epilimnion, total phosphorous concentration above the ground, nitrate concentration of the epilimnion, ammonium concentration above the ground and the phytoplankton biomass of the epilimnion (Fig 1.1.7.3). In the right upper corner of the form “Parameters” is a button to go back to the form “Problems” and “Methods”, respectively.

Fig. 1.1.7.3: The form “parameter” contains general information about a lake and register about several chemical and physical data before and after the implementation of a remediation measure. The data are visualised in a graph.

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Limnological Development and Literature The button “Limnological Development and Literature” on the form links to a report that contains information about the changes of water quality of the investigated lake and detailed information about the eutrophication problem and the used remediation measures (Fig. 1.1.7.4).

Fig. 1.1.7.4: Report of the limnological development of a lake. The second part of the report contains a list of literature concerning the chosen lake (Fig. 1.1.7.5).

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Fig. 1.1.7.5: The list of literature is the second part of the limnological development report.

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„Details on fish abundance“ and „Organization-Costs-Contact“ Further information about the lake gives the report about the fish standing stock. Beside the English name also the scientific name is listed. The form contains also information about the fish stocking. The costs of the remediation measure and further contact addresses are listed in the report Organization-Costs-Contact. Buttons with blue texts Buttons with blue text link to reports with details of the chosen problem. If the selected lake does not have the problem written on the button, the report does not contain any information. Fig 1.1.7.6 shows the details on the algae bloom problem of Lake Ossiacher See with the name of the algae species, the year and the expansion of the bloom on the lake surface.

Fig. 1.1.7.6: An example for a detailed problem description: algal blooms at Lake Ossiacher See.

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Searching for lakes with certain implemented remediation methods

If the user decides for the “methods” button at the start window of the database (Fig. 1.1.7.1) the form “Methods” will open. This form is similar to the “problem” form and contains a list field with common remediation measures to choose from. If the user selects a method in the field “Lakes” appear all the lakes, where this chosen method was implemented. The field “problems” gives additional information about the lakes and the problems that occurred at these lakes (Fig. 1.1.7.7).

Fig. 1.1.7.7: The form “Methods” enables the user to select a given method and to gain morphometric information about lakes, that had a chosen method implemented and which problems occurred at the lakes. The buttons below the “lake” field with the red and blue texts respectively are the same as in the form “problems”. To open another form or report via a button about a lake, the user has to click on a specific lake first before clicking on a button.

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