Temperature and Oxygen Profiles of Restored Water Bodies

Abstract

The study covered three lakes: Nowe Wloki (with two pools – Main Basin and Northern Bay), Setalskie Duze and Setalskie Male – connected by the Setal Stream (Struga Setal) to form a riverine-lacustrine system. Due to their specific location (slope), the investigated water bodies form a cascade system. They are situated 25 km from the city of Olsztyn, in the Dywity municipality (Olsztyn Lakeland), in an agricultural catchment. Due to their low average depth (1 to 2 m), the analyzed water bodies can be classified as polymictic. The aim of this study was to analyze the temperature and oxygen profiles of water bodies restored approximately 30 years ago. The profiles were determined during winter stagnation (2005 and 2006) and summer stagnation (2007). An analysis of temperature and oxygen conditions performed in the summer confirmed close correlations between the studied parameters. All lakes were characterized by incomplete thermal and oxygen stratification, typical of shallow water bodies. The oxygen profiles determined in the winter showed a temperature distribution pattern characteristic of reverse thermal stratification. In all investigated water bodies, surface water temperature was close to 0 C, and it increased gradually from a depth of 30–50 cm. During winter stagnation, the highest dissolved oxygen content was noted in the top layer of water under the ice, and oxygen concentrations varied widely between years. The lowest oxygen content was observed at the bottom, and critically low values (from 0.16 mgO2 dm –3 to 0.29 mgO2 dm ), were recorded during the severe winter of 2006, when ice cover thickness reached 40 cm and organic matter decomposition and aerobic respiration processes led to almost complete oxygen depletion.