Top-down Biomanipulation and the Restoration of Eutrophied Lakes
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Transcript of Top-down Biomanipulation and the Restoration of Eutrophied Lakes
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Keith D. GareauESR 575
Portland State University
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How does top-down biomanipulation turn:
this (eutrophic lake) into this (oligotrophic lake)
What is the process and is it effective?
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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?
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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
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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).
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planktivorous fish
and/or piscivorous fish
zooplanktonalgal
biomass
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A means to restore the water quality of eutrophied lakes
Other remedial techniques◦ Physico-chemical
ALUM injection◦ Dredging◦ Nutrient catchment
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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
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- 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
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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
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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
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- 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
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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%
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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
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- 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)
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- 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:
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- 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
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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.