Modelling Copper Sources and Fate in Lake Råcksta Träsk, Stockholm : Sediment Copper Content as Indicator of Urban Metal Emissions

Abstract: In Stockholm, Sweden, diffuse emissions of metals have become the dominating source of copper towater. This thesis work made an attempt to link the source of copper emission and the fate of the copper in a lake. These models have been applied in the case study of Lake Råcksta Träsk and its urban drainage area in Stockholm, Sweden. The source analysis model has been adopted and modified from Cui et al (2008) and Sörme and Lagerkvist (2002) and the basic fate model has been taken and modified from Håkanson (2006) and Lindström and Håkanson (2001). For better understanding and improving the modelling, a second type of modelling approach both for source(i.e. StormTac model) and fate analyses (i.e. QWASI model) have been included in this study. The results from the different modelling approaches are compared. Models were presented in an as transparent as possible way and were connected through the urban copper load to the lake. All models were tested against previously published monitoring data. In the source analysis, the traffic and road sections emit the most of copper especially through brake linings of the vehicles. The lakemodel was evaluated using monitoring data from the 15-year period, 1991-2006. Both the water and sediment copper contents respond to a change in the copper load to the lake, but the response is slower for the sediments. Thus it is proposed that the sediment copper contents can be used to follow urban copper emissions.