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RESEARCH PRODUCT

Biomanipulating the drinking water reservoir of Estonia's capital city: Prospects for success

subject

description

The possibility of utilizing biomanipulation to improve the water quality of Tallinn's drinking water reservoir (Lake Ulemiste) was analysed on the basis of water quality data, test fishing by different methods, and earlier studies on aquatic plants, light climate and sediments. Eutrophic, polymictic Lake Ulemiste is characterized by a prevalence of high filamentous cyanobacteria biomass, rotifers in the zooplankton community, mature bream in the fish biomass, and a high density of planktivores (YOY perch). Several prerequisites for being a potential target for biomanipulation were identified, including (i) decreased external total phosphorus (TP) loading; and (ii) a sufficient stock of piscivorous fish in the lake. Prohibition of fishing should favour biomanipulation efforts. The potential for recolonization of macrophytes and large Daphnia species in Lake Ulemiste could be judged from historical data. The in-lake TP concentrations are within the limits that facilitate successful restoration. As phytoplankton biomass was significantly limited by phosphorus in Lake Ulemiste, its water quality improvement will be driven primarily by reduced nutrient concentrations, and then by zooplankton grazing. Internal TP loading and a new phytoplankton species community were assessed as major challenges for successful implementation of biomanipulation as a means of improving the water quality of Lake Ulemiste.