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Eutrophication Management in Lake Victoria
Transcript of Eutrophication Management in Lake Victoria
Thijs Groenewegen Eutrophication in the Netherlands Water facts:
16% surface area
Very shallow (<2m)
Huge size variation Intensification since 1950 Freshwater restoration
worldwide Phosphorus The culprit: Management focus: reducing phosphorus 1) Influx reduction Waste water treatment Marginal or no clear effects Hydrological Management Replacing lake water with water from external source
with lower nutrient levels
and rich in Calcium and Carbonate (preferably)
Depends greatly on availability good quality external source
Costly Not popular Dredging Chemical agents Artificial mixing Marginal efficiency
New layer soon saturated again Cheap
Results disappointing Liming Preventing algae from accumulating
No decrease Phosphorus Calcium as Phosphorus buffer
Acidification countermeasure The results:
Promising, but in half of the lakes
the zooplanktivores returned even
more strongly than before their reduction.
Works only with strong
trophic dependencies? Top-down approach Biomanipulation in tropical lakes Lake Victoria Omnivorous species Low trophic dependency
High reproduction rate High fish density Low chance of success Agroforestry Combining agro-cultural and forestry
Reduces run-off Local support Papyrus wetlands Buffer zone
Nutrient removal: harvesting Papyrus
Papyrus as economic product Eutrophication management of Lake Victoria Opposed solutions Total Financing: US$77.6 million
Date: 1996 - 2002
Achieve stable ecosystem in Lake Victoria:
disease free environment
posibilities to fulfill multiple needs Evaluation Hot spots of pollution identified,
but not sufficiently emphasized.
"The eutrophication of the lake is primarily due to atmospheric deposition of the elements N and P."
Artificial wetlands constructed Discussion: How do we solve Eutrophication in Lake Victoria? 3) Biomanipulation 2) In-lake phosphorus:
b. Immobilization What did they do so far? Technique Waste water treatment Hydrological management Agroforestry Papyrus wetlands Dredging top-layer Ferric Chloride solution Artificial mixing Liming Biomanipulation Advantage Disadvantage Point-source solution Fast nutrient dilution Agricultural solution Self-sustainable, economic value Direct decrease P Cheap Cheap Reduced algal bloom Self-sustainable Complexity trophic levels Only point-sources Expensive Depends on local communities Loss agricultural areas Temporary Does not counteract influx No decrease nutrients Management on reducing Phosphorus Does not counteract influx GEF and IW:LEARN database on Lake Victoria Environmental Management Project (a) proposal, (b) summary and (c) evaluation http://www.iwlearn.net/iw-projects/Fsp_112799468783
Goldschmidt, T., Witte, F., Wanink, J., 1993. Cascading Effects of the Introduced Nile Perch on the Detritivorous/Phytoplanktivorous Species in the Sublittoral Areas of Lake Victoria. Conservation Biology 7(3):686-700.
Gulati, R., D., van Donk, E. , 2002. Lakes in the Netherlands, their origin, eutrophication and restoration: state-of-the-art review. Hydrobiologia 478: 73–106.
Lung’ayia, H., Sitoki, L., Kenyanya, M., 2001. The nutrient enrichment of Lake Victoria (Kenyan waters). Hydrobiologia 458: 75–82
Mwanuzia, F., Aalderink, H., Mdamoc, L., 2003. Simulation of pollution buffering capacity of wetlands fringing the Lake Victoria. Environment International 29:95– 103
Scheffer, M., Hosper, S.H., Meijer, M-L., Moss, B., Jeppesen, E., 1993. Alternative Equilibria in Shallow Lakes. Tree 8(8)
Sitoki, L., Gichuki, J., Ezekiel, C., Wanda, F., Mkumbo, O.C., Marshall, B.E., 2010. The Environment of Lake Victoria (East Africa): Current Status and Historical Changes.
Internat. Rev. Hydrobiol. 95(3): 209–223
Smith, V.H., Schindler, D.W., 2009. Eutrophication science: where do we go from here? Trends in Ecology and Evolution 24(4): 201-207
Watershed management research @ ICRAF: Transvic agroforestry project Lake Victoria. http://www.worldagroforestrycentre.org/water/transvic.asp
Witte, F., Wanink, J.H., Kishe-Machumu, M., Mkumbo, O.C., Goudswaard, P.C., Seehausen, O., 2007. Differential decline and recovery of haplochromine trophic groups in the Mwanza Gulf of Lake Victoria. Aquatic Ecosystem Health&Management, 10(4):416–433.
Worldbank Project database on Lake Victoria Environmental Management Project Phase II. References