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Phosphorus eutrophication in an inter-drumlin lake: causes and effects Lucy Crockford Walsh Fellow Trinity College Dublin What’s impeding this lake’s recovery?
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Phosphorus eutrophication in an inter-drumlin lake: causes and effects

Feb 24, 2016

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Phosphorus eutrophication in an inter-drumlin lake: causes and effects. What’s impeding this lake’s recovery?. Lucy Crockford Walsh Fellow Trinity College Dublin. Outline. Policy Pollution sources and eutrophication Work on the lake Results so far Interpretation. Policy. SI 272 2009. - PowerPoint PPT Presentation
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Page 1: Phosphorus eutrophication in an inter-drumlin lake: causes and effects

Phosphorus eutrophication in an inter-drumlin lake: causes and

effects

Lucy CrockfordWalsh Fellow

Trinity College Dublin

What’s impeding this lake’s recovery?

Page 2: Phosphorus eutrophication in an inter-drumlin lake: causes and effects

Outline

• Policy• Pollution sources and eutrophication• Work on the lake• Results so far• Interpretation

Page 3: Phosphorus eutrophication in an inter-drumlin lake: causes and effects

Policy

Water Framework

Directive2000

Nitrates Directive 1991

Urban Wastewater

Directive1991

Surface Water Objectives 2009

Good Agricultural

Practices2006

(Revised in 2009)

OECD and Tierney, 2008

SI 272 2009

Page 4: Phosphorus eutrophication in an inter-drumlin lake: causes and effects

Pollution Sources in Rural Catchments

DiffusePointUnknown

Page 5: Phosphorus eutrophication in an inter-drumlin lake: causes and effects

Project Objective:

To determine the main processes that are contributing to the increased P concentrations1. External P loads2. Internal P loads3. Wind induced resuspension in shallow areas

Research Questions

4. What are the main contributors of P?5. Which contributors are the primary factor in the impediment of lake

recovery despite source recovery?6. How are the dynamics of the lake contributing to the P concentrations –

biological, chemical, morphological, catchment use etc.?7. How can high frequency monitoring improve our understanding of lake

dynamics particularly the impact of episodic events, DO fluctuations, and the signal of the Chl a sensor?

Internal Lake Sources

Source: SØNdergaard et al., 2001

Page 6: Phosphorus eutrophication in an inter-drumlin lake: causes and effects

Work on the LakeBuoys

Data Sondes – Chlorophyll a, conductivity, dissolved oxygen, temperature, redox, pH - hourly

Manual sampling – P fractions, phytoplankton, zooplanktonBi-monthly

Page 7: Phosphorus eutrophication in an inter-drumlin lake: causes and effects

Cross Section of the Lake

Page 8: Phosphorus eutrophication in an inter-drumlin lake: causes and effects

Neighbouring Catchment

Page 9: Phosphorus eutrophication in an inter-drumlin lake: causes and effects

Results so Far

Weather and external loading

Page 10: Phosphorus eutrophication in an inter-drumlin lake: causes and effects
Page 11: Phosphorus eutrophication in an inter-drumlin lake: causes and effects

Manual Sampling

P fractions, Nitrate and Chl a

Page 12: Phosphorus eutrophication in an inter-drumlin lake: causes and effects

Surface Sondes Chl aDeep Sonde DO

Page 13: Phosphorus eutrophication in an inter-drumlin lake: causes and effects

Summary Statistics Water Year Oct 2010 to Sept 2011

Page 14: Phosphorus eutrophication in an inter-drumlin lake: causes and effects

Conclusions• Lake is switching between meso and eutrophic

status.• The external load of P is low - inline with

source reduction?• Internal loading is occurring in anoxic water.• The lake suddenly mixing fertilises photic zone

– May 2011• Wind factor seems to not be increasing P

concentrations at eastern end.

Page 15: Phosphorus eutrophication in an inter-drumlin lake: causes and effects

Future Work•Chl a crash in spring not determined yet...•Lack of Chl a response to high nutrients at end of summer during fine weather also not determined•Quantify P loads and signal from sondes wrt chlorophyll a•Draw conclusions on the factors impeding lake recovery.

Page 16: Phosphorus eutrophication in an inter-drumlin lake: causes and effects

Algal BloomJuly 2011

Page 17: Phosphorus eutrophication in an inter-drumlin lake: causes and effects

References• SØNdergaard M, Jensen JP, Jeppesen E. Retention and internal loading of

phosphorus in shallow, eutrophic lakes. TheScientificWorld 2001; 1: 427-442.

• Tierney D. Water Quality of Lakes. State of the Environment in Ireland. Environmental Protection Agency, Johnstown Castle, Wexford, 2008.

Acknowledgements• The Agricultural Catchments Programme, Teagasc• Profs Philip Jordan and David Taylor• Drs Alice Melland and Per-Erik Mellander• Mr John Kennedy• GLEON technical group

Page 18: Phosphorus eutrophication in an inter-drumlin lake: causes and effects

Questions?

Page 19: Phosphorus eutrophication in an inter-drumlin lake: causes and effects

Hypotheses – Spring Chl a crash

1. Grazing pressure.2. Lake overturning and “diluting” the

Chlorophyll a concentration.3. Reduction in available nutrients so

population could not be sustained.

Page 20: Phosphorus eutrophication in an inter-drumlin lake: causes and effects

Hypotheses – Increased Deep Water SRP concentrations

1. Release from sediments aka internal loading.2. External inputs from the catchment.3. Wind induced resuspension of sediments.

Page 21: Phosphorus eutrophication in an inter-drumlin lake: causes and effects

Hypotheses – Increased Surface SRP concentrations at end of Summer

1. Lake overturning due to poor weather.2. External loading from the catchment.3. Wind induced resuspension.

Page 22: Phosphorus eutrophication in an inter-drumlin lake: causes and effects

1 m Data Sonde

9 m Data Sonde

1 m Data Sonde

Lake Sediment

WEST EAST

Abstraction(245684 m3yr-1)

Lake Volume1223389 m3

Thermocline (6-7m)

Statistical Significance Testing

N = 11

Independent T testP = 0.9243Difference in annual means is not statistically significant

Page 23: Phosphorus eutrophication in an inter-drumlin lake: causes and effects

1 m Data Sonde

9 m Data Sonde

1 m Data Sonde

Lake Sediment

WEST EAST

Abstraction(245684 m3yr-1)

Lake Volume1223389 m3

Thermocline (6-7m)

N = 11

Independent T testP = 0.9609Difference in annual means is not statistically significant

Statistical Significance Testing

Page 24: Phosphorus eutrophication in an inter-drumlin lake: causes and effects

1 m Data Sonde

9 m Data Sonde

1 m Data Sonde

Lake Sediment

WEST EAST

Abstraction(245684 m3yr-1)

Lake Volume1223389 m3

Thermocline (6-7m)

N = 11

Independent T testP = 0.9362Difference in annual means is not statistically significant

Statistical Significance Testing

Page 25: Phosphorus eutrophication in an inter-drumlin lake: causes and effects

1 m Data Sonde

9 m Data Sonde

1 m Data Sonde

Lake Sediment

WEST EAST

Abstraction(245684 m3yr-1)

Lake Volume1223389 m3

Thermocline (6-7m)

N = 11

Independent T testP = 0.1752Difference in annual means is not statistically significant – but p value much lower than other sample combinations

Statistical Significance Testing

Page 26: Phosphorus eutrophication in an inter-drumlin lake: causes and effects

High Frequency Turbidity