top-down biomanipulation and the restoration of eutrophied lakes

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Keith D. Gareau ESR 575 Portland State University

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Top-down Biomanipulation and the Restoration of Eutrophied Lakes. Keith D. Gareau ESR 575 Portland State University. Purpose of Research. How does top-down biomanipulation turn:. this (eutrophic lake). into. this ( oligotrophic lake). What is the process and is it effective?. - PowerPoint PPT Presentation

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Page 1: Top-down  Biomanipulation and the  Restoration of  Eutrophied  Lakes

Keith D. GareauESR 575

Portland State University

Page 2: Top-down  Biomanipulation and the  Restoration of  Eutrophied  Lakes

How does top-down biomanipulation turn:

this (eutrophic lake) into this (oligotrophic lake)

What is the process and is it effective?

Page 3: Top-down  Biomanipulation and the  Restoration of  Eutrophied  Lakes

Background◦ Eutrophication◦ Top-down biomanipulation

Why top-down biomanipulation is important to limnology Present two real-life examples of top-down

biomanipulation Summary of research

◦ What is the take home message?

Page 4: Top-down  Biomanipulation and the  Restoration of  Eutrophied  Lakes

Eutrophication is the enrichment of the nutrients nitrogen and phosphorus to a lake◦ Phosphorous is primary concern in lakes

Negative effects:◦ Phytoplanckton-dominated system

Reduces biodiversity in lake◦ Increase lake odor and turbidity◦ Potentiality of cyanobacteria blooms

Release of neurotoxins Liver damage, promotion of tumor growth, hepatitis,

renal malfunctioning, and hemorrhaging

Page 5: Top-down  Biomanipulation and the  Restoration of  Eutrophied  Lakes

A remedial technique used to restore the natural state of a lakes prior to human induced enrichment through means of high trophic food web manipulation.◦ “…top-down biomanipulation involves increase of

piscivorous fish biomass and/or decrease of planktivorous fish biomass which leads to increase of zooplankton biomass and reduction of cyanobacteria concentration respectively” (Prokopkin et al, 2006).

Page 6: Top-down  Biomanipulation and the  Restoration of  Eutrophied  Lakes

planktivorous fish

and/or piscivorous fish

zooplanktonalgal

biomass

Page 7: Top-down  Biomanipulation and the  Restoration of  Eutrophied  Lakes

A means to restore the water quality of eutrophied lakes

Other remedial techniques◦ Physico-chemical

ALUM injection◦ Dredging◦ Nutrient catchment

Page 8: Top-down  Biomanipulation and the  Restoration of  Eutrophied  Lakes

When is a lake eutrophic?According to Carlson’s Trophic State Index:

Transparency = > 2.0 m

Total phosphorous (TP) = < 0.024 mgP/L

Chl-a = < 0.007 mg/L

Page 9: Top-down  Biomanipulation and the  Restoration of  Eutrophied  Lakes

- Total fish removal from eight hypereutrophic phytoplankton dominated ponds in Brussels, Belgium

- Removed > 500 kg/ha of plankti-benthivorous fish from each pond

-Mainly carp

- Manmade ponds with a mean depth 1.5 m and surface areas < 2.3 ha

Page 10: Top-down  Biomanipulation and the  Restoration of  Eutrophied  Lakes

Peretyatko et al (2009) Experiment

Time Mean Secchi Depth (m) Chl-a (mg/L) Mean TP (mgP/L) Macrophyte cover (%)

Before biomanipulation 0.55 ± 0.20 0.16 ± 0.17 0.35 ± 0.17 0%

1.0 yr. after bimanipulation Bottom ± 0.0 0.017 ± 0.01 0.24 ± 0.13 25 ± 26

Page 11: Top-down  Biomanipulation and the  Restoration of  Eutrophied  Lakes

How did this happen?

- “The main factor responsible for this shift (from eutrophic to clear-water) is undoubtedly phytoplankton grazing by large Cladocerans.”

- No fish predation on zooplankton, therefore, larger individuals and populations of zooplankton occurred

Causing an effect of zooplankton to consume phytoplankton faster than phytoplankton can reproduce

Ultimately, reducing turbidity and algal blooms in the lakes

More light for macrophyte growth

Page 12: Top-down  Biomanipulation and the  Restoration of  Eutrophied  Lakes

- Reduced planktiviorous and benthivorous fish biomass from Lake Terra Nova in the Netherlands

- Shallow lake with mean depth of 2 m and area of 85 ha

Heerdt & Hootsman (2007)

Time benthivorous fish biomass (kg/ha)

plankiviorous fish biomass (kg/ha)

Before biomanipulation 134 80

0.5 yr. after biomanipulation <25 <15

Page 13: Top-down  Biomanipulation and the  Restoration of  Eutrophied  Lakes

Heerdt & Hootsman (2007)

Time Mean Secchi Depth (m) Mean TP (mg/L) Kd Macrophyte cover

Before biomanipulation 0.35 0.071 3.1 0%

0.5 yr. after biomanipulation Bottom 0.079 1.58 30%

Page 14: Top-down  Biomanipulation and the  Restoration of  Eutrophied  Lakes

How did this happen?

Causing an effect of zooplankton to consume phytoplankton faster than phytoplankton can reproduce

Ultimately, reducing turbidity and algal blooms in the lakes

More light for macrophyte growth

Protection for zooplankton

- Reduced planktivorous fish biomass

“By reducing benthivorous fish sediment resuspension is reduced.”

Bosmina

Page 15: Top-down  Biomanipulation and the  Restoration of  Eutrophied  Lakes

- Top-down biomanipulation can:

- Reduce lake turbidity from eutrophied to a clear-water state

Peretyatko’s experiment

Transparency: 0.55 m Bottom (1.5 m)

Heerdt & Hootsman’s experiment

Transparency: 0.35 m Bottom (2.0 m)

Page 16: Top-down  Biomanipulation and the  Restoration of  Eutrophied  Lakes

- Limited affect on reducing TP and only observed to reduce TP when TP is at high concentrations

- Top-down biomanipulation canNOT:

- Reduce the trophic state of lakes in terms of TP

Peretyatko’s experiment

Heerdt & Hootsman’s experiment

TP: 0.35 mgP/L 0.23 mgP/L

TP: 0.071 mgP/L No significant change

TP = < 0.024 mgP/Lto not be eutrophic

Carlson’s Trophic State Index:

Page 17: Top-down  Biomanipulation and the  Restoration of  Eutrophied  Lakes

- Top-down biomanipulation is effective in reducing a lakes turbidity, however, it is not effective in TP reduction

- Based on these two experiment it appears that top-down biomanipulation can only slightly reduce TP when TP is at high concentrations

Page 18: Top-down  Biomanipulation and the  Restoration of  Eutrophied  Lakes

Therefore, I suggest further research in…

…using top-down biomanipulation in conjunction with other remedial techniques in order to fully explore the possibilities and outcomes of the effectiveness of top-down biomanipulation for the restoration of eutrophied lakes.

… the effectiveness of top-down biomanipulation at different TP concentrations in lakes.