Combined sewer overflows, sediment accumulation and element patterns of river bed sediments: a quantitative study based on mixing models of composite fingerprints

Stormwater runoff from urban areas and subsequent stormwater-induced effluents from sewer systems may deteriorate the quality of the receiving water sediments by emitting particulate matter and associated pollutants. However, the relevance of stormwater and combined sewer effluents for the pollution of bed sediments was not yet quantified. Therefore, we applied a multivariate mixing model of composite fingerprints to investigate how much stormwater effluent may contribute to the accumulation of fines and associated pollutants in the bed sediment of the Bode River, Germany. In our study, stormwater and combined sewer effluents contribute about 10 % of the fines accumulated in the bed sediment. As stormwater overflow fines are a major carrier of C, N, P, Cu and Zn, up to 40 % of these pollutants in the bed sediment originate from stormwater effluents. Especially N and Zn have to be seen critically because high nutrient concentrations trigger excessive macrophyte growth within the studied river stretch and Zn contents exceed German sediment quality standards (LAWA 1998) in the bed sediment.