Long-term water and sediment quality of the Elbe River’s oxbow lake near the town of Poděbrady, the Czech Republic

Abstract

The studied oxbow lake near the town of Poděbrady (the Czech Republic) belongs to unique, less influenced old meanders of the Elbe River that are still completely surrounded by floodplain forests. The research works (2004–2015) included bathymetry, hydrological regime, water and sediment quality, and hydrobiological analyses. Due to the connection with the river, the hydrological regime was significantly determined by the Elbe River. Spatial electrical conductivity differences were found. Values of pH fluctuated (lower ANC4.5) during the year rising with phytoplankton development. Associated parameter of organic matter content (mean CODMn = 5.5 mg L−1) was similar to that in the river. The Elbe represented a source of nitrogen (max. N-NO3 = 5.9 mg L−1) and phosphorus for the lake, where the phosphorus concentrations reached maximum levels in summer (max. TP = 0.220 mg L−1) under low oxygen saturation. The concentrations of Cd, As, Hg, and Pb in sediments exceeded the upper limit values set in the new assessment system developed by the International Commission for the Protection of the Elbe River, and together with a high index of geoaccumulation in the case of Ag, the concentrations of these elements indicate significant contamination. Although the lake was not extremely polluted, high concentrations of nutrients and sediment load could represent a risk for aquatic ecosystems. The comparison of the results with other studies on oxbow lakes situated in different river basins provided new and complex conclusions in a broader context.