| Summary: | In this paper, preliminary results of a study investigating the impact of stormwater discharges on the bottom sediment of stormwater recipients in Luleå, northern Sweden are presented. The aim was to evaluate sediment metal concentrations taken in front of stormwater sewer discharge points from two ditches/recipients, their seasonal variation and the influence of geomorphology and vegetation on the metal distribution. Compared with northern Sweden background values, the Cd, Cu, Pb and Zn concentrations in the sediment samples were elevated. However, besides stormwater discharges, local sulphide soils in the catchment areas can affect the metal concentrations. Partly, seasonal variations in the metal concentrations were noticed; higher metal concentrations were observed in spring associated with a high LOI content and large fractions of fine grain size particles (<0.125 mm). Low/no runoff in winter and metal accumulation in snow followed by continuous snow melt runoff transports mostly fine grain sizes and therewith associated metals, which then settle and accumulate in the ditches/recipients. Dense reed vegetation can retain coarse grain sizes and supplies the sediment with decomposing organic material. Decomposition processes affect the redox conditions in the sediment through oxygen consumption. In the reduced sediment metals can be trapped in combination with sulphide formation. Godkänd; 2011; 20111209 (ysko)
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