Nutrients Load As a Risks Factor

in Freshwater Sediments: Assessment, Effects and Reduction

J. Hejzlar, J. Borovec and J. Kopáček

Hydrobiological Institute AS CR and Faculty of Biological Sciences USB,

České Budějovice, Czech RepublicISSA Workshop, February 10 - 12, 2005, Hotel Santon, Brno

Hydrobiological Institute of the Academy of Sciences CR Na Sádkách 7, 370 05 České Budějovice, Czech Republic www.hbu.cas.cz

Outline:

1. Risks of increased nutrient loading for sediments

2. Internal loading of P and its assessment

3. Measures to decrease internal loading of P

4. Designing a lake restoration program

5. Example – Jordán Reservoir

1. Risks of increased nutrient loading

• increase in sedimentation rate – danger of siltation

• change of physical characteristics – water and organic content,

porosity

• change of chemistry

– increased use of electron acceptors (O2, NO3-, SO4

2-), decrease in

pE

– change of pH (CO2 and alkalinity production, H+ consumption)

– accumulation of reduced species (Mn, Fe, Co, Hg, S2-...)

• deterioration of biological quality

– toxicity (H2S, NH3, MeHg)

– loss of habitat

• water-sediment interactions

– release of reduced species in water (Mn, Fe, DOC, NH3, CH4, H2S...)

– release of PO4-P; internal P loading

2. Internal loading of P and its assessment

Internal loading = Release from sedimentINPUT OUTPUT

RELEASESEDIMENTATION

Net retention: Sedimentation > Release

Net release: Sedimentation < Release

Internal loading – one part of cycling between sediment and

water

– high in shallow, polymictic water bodies

– unimportant when HRT is short (<1 yr)

– depends on a ration of P-loading : P-binding

capacity

of mineral component of sediment

– influenced by physics, chemistry, and biology of

sediments

Assessment of internal P loading:

i. Apparent release rate (real in-lake conditions)

a) “input – output – in-lake change” balance (net release only)

b) accumulation of P in hypolimnion (release+mineralization in

water)

c) experimental incubations / sediment pore-water profiling

(release)INPUT OUTPUT

RELEASESEDIMENTATION

a) b) c)input - hypominion experiments output accumulation balance

10

10 5

5

- 5 >5 5

ii. P-release potential evaluation (all releasable species under any conditions)

a) changes in sediment P-concentration profile

soft-water reservoir

2%

27%

3%6%

62%

H2O

BD

NaOH-25°C

HCl

NaOH-85°C

acidified lake

5%2%3%

1%

89%

hard-water lake

11%

67%

15% 3% 4%

b) chemical extraction methods

Fractions (e.g., Psenner & Pucsko 1988)

1. loosely bound (H2O), 2. redox labile (BD), 3. metal hydroxyoxides bound (NaOH20°C),

4. apatite bound (HCl), 5. refractory-organics bound (NaOH85°C)

0 1 2 3

1

5

9

13

17

21

25

29

33

37

H, c

m

P, mg/g

“R

ELEA

SA

BLE“

P

iii. P-retention/release mechanism (for real in-lake conditions)

a) major binding compounds:

Fe (lowland, soft waters), Al (acidified catchments), Ca (hard waters)

b) retention processes:

sedimentation, mineralization + adsorption/precipitation

c) release mechanisms:

mineralization, pH-pE dependent dissolution/desorption,

resuspension, bioturbation

water

benthicboundarylayer

active sediment

inactive sediment

modified from Schauser et al. 2004

Diagenetic transformations of P-forms in sediments

refractory organic P

refractory organic P

labile organic P

labile organic P

dissolved inorganic P

dissolved inorganic P

exchangeable inorganic P

stable inorganic P

exchangeable inorganic P

stable inorganic P

Bu Bu D Bu Bu

Prec

So

So

S,Re

S,ReS,Re S,Re D,Re

M,U

M,U

Bu,Bi,Re

D,Bi,Re

Bu,Bi,Re Bu,Bi

,Re

Prec

Bu

Bi – bioturbation, Bu – burial, D – diffusion, M – mineralization, Prec – precipitation, U – uptake, Re – resuspention, S – sedimentation, So – sorption,

Bu,Bi,Re

d) Indicators of P-release mechanisms:

No release if:

P in Settling-seston NVSS : P in Sediment NVSS < 1

Fe:P in sediment > 15 (Jensen et al. 1992)

Fe(II):Pdiss in pore water > 1 (Phillips et al. 1994)

Al(OH)3:Fe(OH)x in sediment > 3

or

Al(OH)3:Fe(OH)x in sediment < 3, but

Al(OH)3:PH2O+BD in sediment > 25 (Kopáček et al.

submitted)

Measure Controlling factor Effectiveness Duration

Oxidation with Redox potential Low Short-term

NO3- or O2

Precipitation with Al P-binding compound High Short to long-term

Precipitation with Fe P-binding compound Low to high Short-term

Co-precipitation P-binding compound Low to high Short to long-termwith calcite

Capping P-binding compound Depends on Short to long-term and porosity P-binding

Dredging P content Low to high Short-term

Hypolimnetic P-concentration in Low Long-termwithdrawal the hypolimnion

3. Measures to decrease internal loading of P

4. Designing a lake restoration program by control of nutrient release from sediments

DECISION SUPPORT TOOL (Schauser et al. 2003)

Flow diagram of the decision support

PREREQUISITES: 1. Is a control by P limitation useful for the lake and targets?

2. Is the target trophic state realistic? 3. Is a further reduction of the external load impossible?

All yes: decision support is suitable

DECISION SUPPORTA. Preselection: Exclude unsuitable measures by checking each measure in regard to suitability classes • current and critical external load • time characteristics of the lake – HRT, adaptation time, duration of effect • morphological structure of the lake – depth, stratificationFixed assessment by means of importance and

suitability

Suitable measures

Unsuitable measures

Assessment by experts

B. Selection: Select the most suitable measure by cost/efficiency criteria

5. Example – Jordán Reservoir(hyper-eutrophic conditions due to long-

lasting sewage discharges and diffuse pollution)

Lake parameter Value*

Area 0.43 km2

Volume 2.2 mil. m3

Maximum/Mean depth 11 m/5.1 m

Water retention time 0.25 yr

External P load 2.1 g m-2 yr-1

Inflow P 102 mg m-3

Outflow P 94 mg m-3

In-lake P 104 mg m-3

Chlorophyll a 20 mg m-3

Outlets surface

* average 2000, 2001, 2003

Tábor, South Bohemia, CR

cyanobacterial water bloom in summer 2000

cyanobacterial water bloom in summer 2000

organic sediments at sewage outlet

Longitudinal profile of water chemistry

September 4, 2000

Tem perature, °C

414

416

418

420

422

DO, m g/l

414

416

418

420

422

Alt

itu

de,

m a

.s.l.

DRP, µg/l

Total P, µg/l

2.0 2.5 3.0 3.5 4.0 4.5

River km

NH4-N, mg/l

2.0 2.5 3.0 3.5 4.0 4.5

River km

SO4, mg/l

414

416

418

420

422

0.00

0.05

0.10

0.15

0.20

I.00

IV.0

0V

II.0

X.0

0I.0

1IV

.01

VII.

0X

.01

I.02

IV.0

2IV

.03

VII.

0X

.03

I.04

TP, m

g/l

inflow

outflow

0

0.04

0.08

0.12

0.16

I.00

IV.0

0V

II.0

X.0

0I.0

1IV

.01

VII.

0X

.01

I.02

IV.0

2IV

.03

VII.

0X

.03

I.04

DR

P, m

g/l

inflow

outflow

Inflow-outflow changes of P concentrations

Total P Dissolved reactive P summer

stratification - P deposition

non-vegetation period – mineralization and release

-300

-150

0

150

300

450

600

2000 2001 2003

Tota

l P ,

kg

Input, kg Ret.IV-IX, kg

Ret.X-III, kg Ret., kg1570

Input-output balance: Retention = Pin – Pout - Paccum

Ret.X-III ≈ Release

Year Release [kg] [% Ret.IV-IX]

2000 73 38

2001 238 60

2003 33 35

38%

60%

35%

Seasonal changes in sediment composition

DM, % TOC, mg/g TON, mg/g TP, mg/g Fe, mg/g

Inflow part - rapid turnover of settled sestonStratified lacustrine part – seasonal cycle of sedimentation-release

Pore water – seasonal changes of P concentration (peeper technique)

0 1 2 3 4-10

-5

0

5

DRP (mg l-1)

dept

h (c

m)

0 1 2 3 4 5 6

9.7.29.10.17.1.

10.4.

DRP (mg l-1)

Inflow part

Jo-B

Dam part

April

JuneOctoberJanuary

January

October

April

June

Jo-A

January 3, 2002

releaseno release

Sediment composition assessment

dam3%

18%

36%

39%

4%

H2O

BD

NaOH-25°C

HCl

NaOH-85°C

inflow

2%

24%

27%

10%

37%

Phosphorus fractions (Psenner & Pucsko 1988)

Indicators of P-release mechanisms no-

release value

P in Seston NVSS (9.3 mg g-1) : P in Sediment NVSS (2.8 mg g-1) = 3.5 < 1

Fe:P in sediment = 13.5 >

15

Fe(II):Pdiss in pore water = 0.7 (dam part), 7 (inflow part) > 1

Al(OH)3:Fe(OH)x in sediment = 4 (dam part), 0.5 (inflow part) >

3

or

Al(OH)3:Fe(OH)x in sediment < 3, but

Al(OH)3:PH2O+BD in sediment = 90 (dam part), 26 (inflow part) >

25

Low potential of P release from sediment

!

High potential of P release from seston !

Basic information pro selection of internal measures in Jordán Reservoir

Parameter Value

Contemporary external load 2.1 g m2

yr-1

(Pin-lake = 104 mg m-3)

Critical external load 0.6 g m2 yr-1

(Ptarget = 20 mg m-3)

Adaptation time 0.75 yr

Duration of effect for a single measure 0.9 yr

Release rate 0.3 g m2 yr-1

Release potential (from a 30-cm layer) 0.8 g m2

Stratification dimictic

Depth of resuspention 2 to 5 m

High external P-load is the main cause of hypertrophy

Rapid response to decrease in external P-load

Single measures not durable

Al-treatment suitable only in the dam part

Highly improbable lasting effect of internal P-loading after drop in external P-load

Effective types of measures - continuous P-binding compound addition

- hypolimnetic withdrawal (partly)

Conclusions

Sediment with Polygonum amphibium a Limosella aqautica in mesotrophic Nýrsko Reservoir, Czech Republic

1. Excessive nutrient loading in lakes affects composition of sediments and impacts biota and water quality

2. Sediments are a dynamic component of aquatic ecosystem: - coupled with water chemistry - with time response related to water residence time

3. Assessment of sediments as a source of internal P-loading can be reliably done by chemical analysis and mass-balance studies

4. Measures to treat internal P-loading can be optimised based on functional suitability / cost criteria Thank you for your

attention !