Urban land use influences on heavy metal fluxes and surface sediment concentrations of small lakes

To study urban land use influences on heavy metal (Cd, Cr, Cu, Hg, Ni, Pb and Zn) lake fluxes and sediment concentrations, ten headwater lakes and catchment areas in Stockholm, Sweden, were investigated. The catchment land use consisted of a gradient of urbanisation and was described on a detailed level, including all parts of the catchments, natural and urban. Covariation between catchment variables made interpretations difficult, however, and no detailed conclusions regarding metal sources could be drawn. Regression models for lake metal fluxes were calibrated using an urban status variable and a lake size variable (representing regional background sources). Hg showed no significant correlation with urban status, indicating a distribution pattern unaffected by local sources, mainly controlled by regional background sources. Cd showed a weak influence from urban land use. For Cu (and to some extent Cr) the urban status influences dominated. Pb, Ni and Zn were in between these two groups and showed relations to both urban land use and regional background.