Abstract
The research was carried out on Karczemne Lake, a water reservoir located in Kartuzy (northern Poland, Pomeranian Lake District). Monitoring of the water and bottom sediment of Karczemne Lake showed a very high level of contamination of the reservoir by a long-term inflow of untreated municipal sewage. The trophic status index of total phosphorus (TP) was unusually high at 101, and the TP content in the bottom sediments—31 mg g−1 (dry weight)—was the highest value recorded worldwide in a lake. Based on the monitoring results, to achieve constant improvement of the water quality, we recommend a completely new, safe and economically justified method of bottom sediment removal and management. A very important aspect of this method is the prevention of uncontrolled sewage discharge back into the lake basin. Removed sediment with interstitial water will be pumped through a pipeline and transported to a sewage treatment plant. In the sediment mining field in which the sludge will be removed, the first phase of phosphorus inactivation will be carried out to chemically precipitate pollutants distributed in the water column as a result of sediment resuspension. After the deepening of the entire lake basin, the method of phosphorus inactivation will be carried out on the entire surface of the lake as the next stage of restoration. A supporting activity will be biomanipulation. Before the restoration is started, the municipal sewerage system will be modernized.
Highlights
Strong anthropopressure in the catchment areas of lakes, which stimulates an increased supply of nutrients to waters, causes the acceleration of eutrophication [1,2,3]
The analysis revealed that the total phosphorus load introduced from external sources to the lake exceeded the dangerous load and was responsible for accelerated eutrophication
The value of every index calculated from the concentrations of total phosphorus, total nitrogen, Thevalue value ofevery everyindex index calculated from theconcentrations concentrations oftotal totalphosphorus, phosphorus, totalnitrogen, nitrogen, visibility and chlorophyll a exceeded
Summary
Strong anthropopressure in the catchment areas of lakes (urbanization, industrialization, deforestation and intensive livestock), which stimulates an increased supply of nutrients to waters, causes the acceleration of eutrophication [1,2,3]. A sign of excessive eutrophy of the lake is an increase in nutrient concentrations (nitrogen and phosphorus) in the water and an uneven distribution of the amount of oxygen in the water column [7,8,9]. In which the bottom water layers are deoxygenated and accompanied by a reduction in redox potential, the reverse process takes place. The stored substances, such as nutrients, are released into the near-bottom water layers [10,11,12].
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