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Top-down Biomanipulation and the Restoration of Eutrophied Lakes

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?.

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Top-down Biomanipulation and the Restoration of Eutrophied Lakes

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  1. Top-down Biomanipulationand the Restoration of Eutrophied Lakes Keith D. Gareau ESR 575 Portland State University

  2. Purpose of Research How does top-down biomanipulation turn: this (eutrophic lake) into this (oligotrophic lake) What is the process and is it effective?

  3. What will be discussed • 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?

  4. Eutrophication • 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

  5. Top-down Biomanipulation • 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).

  6. Top-down Biomanipulation algalbiomass planktivorousfish piscivorous fish zooplankton and/or

  7. Why is top-down biomanipulation important in limnology? • A means to restore the water quality of eutrophied lakes • Other remedial techniques • Physico-chemical • ALUM injection • Dredging • Nutrient catchment

  8. Real life top-down biomanipulation researchTwo studies According to Carlson’s Trophic State Index: Transparency = > 2.0 m Total phosphorous (TP) = < 0.024 mgP/L Chl-a = < 0.007 mg/L When is a lake eutrophic?

  9. Peretyatkoet al. (2009) - Total fish removal from eight hypereutrophic phytoplankton dominated ponds in Brussels, Belgium - Manmade ponds with a mean depth 1.5 m and surface areas < 2.3 ha • Removed > 500 kg/ha of plankti-benthivorous fish from each pond • Mainly carp

  10. Peretyatko’s results from total fish removal:

  11. Peretyatko’s results from total fish removal: 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

  12. Heerdt & Hootsman (2007) - 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

  13. Heerdt & Hootsman’s results from total fish removal:

  14. Heerdt & Hootsman’s results from total fish removal: How did this happen? - Reduced planktivorous fish biomass 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 Bosmina Protection for zooplankton “By reducing benthivorous fish sediment resuspension is reduced.”

  15. Conclusion - 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)

  16. Conclusion - Top-down biomanipulation canNOT: - Reduce the trophic state of lakes in terms of TP - Limited affect on reducing TP and only observed to reduce TP when TP is at high concentrations Peretyatko’s experiment Carlson’s Trophic State Index: TP: 0.35 mgP/L 0.23 mgP/L TP = < 0.024 mgP/L to not be eutrophic Heerdt & Hootsman’s experiment TP: 0.071 mgP/L No significant change

  17. Conclusion • 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

  18. Conclusion Therefore, I suggest further research in… … the effectiveness of top-down biomanipulation at different TP concentrations in lakes. …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.

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