Variability of Environmental Conditions in Postglacial Temperate Lake and Possibilities for Slowing Down Its Eutrophication Process

Assessing the water quality of lakes with complex morphometry requires the assumption that hydrochemical differences may exist between distinct parts of the lake. Understanding the mechanisms behind these differences may be useful in planning protection and restoration efforts. The subject of the two-year study was Lake Studzieniczno-Kłączno-Ryńskie (215.5 ha, 17.1 m) (Pomeranian Lake District, northern Poland), with a maximum length of 5.6 km and an elongation index of 7.9. The studies revealed significant variation in the hydrochemical parameters of individual parts of the lake. The worst environmental conditions were found in the northern part of the lake (water transparency at approximately 1 m, chlorophyll a concentration up to 35 µg/L, BOD5 of 35 mg O2/L, TP concentrations up to 1.82 mg P/L, and TN concentrations up to 7.50 mg N/L in the bottom layer of the water due to deoxygenation and internal loading). This was due to the lake’s orientation in the direction of winds, the blowing of various materials towards the northern end of the lake, and the inflow of a stream draining the marshland areas. To restore recreational use in the northern part of the SKRL, a simple and inexpensive solution (costing approximately EUR 300,000) was proposed: installing a curtain to reduce suspended solids emissions into this part of the reservoir and installing a pipeline to introduce inflow water to the bottom of this bay, which should slow down eutrophication.