We studied temporal and spatial variations of trace metal (TM) concentrations (As, Cd, Co, Cr, Cu, Ge, La, Ni, Pb, Rb, Sc, and Y) in stream water and their correlation with catchment properties (i.e. coverage of wetland and forest), but also with Fe and Mn. During 2004 and 2005 water samples were collected from 10 streams (0.13 km2 to 67 km2) in the Krycklan Catchment Study, a boreal stream network in northern Sweden. Since spring snowmelt is the most important hydrological event, the monthly sampling was intensified during spring flood (April-May) when samples were collected every second day. Total and dissolved (<0.4µm) concentrations of Fe and Mn were determined by ICP-OES. Dissolved concentrations of TM were determined by ICP-MS.
Preliminary results show a seasonal variation for all TM, in particular during spring flood. In forested catchments most TM concentrations increased at spring flood, but for Rb and Sc a decrease was observed. Conversely, in wetland influenced catchments the opposite seasonal variation was observed, i.e. concentrations of all TM decreased by a factor of 2 to 3. The seasonal variation of Fe shows a similar pattern to many TM, due to the association of TM to Fe oxyhydroxides. In particular, Fe correlates significantly with Cr and Pb in a forested headwater stream (r2=0.77 and r2=0.71, respectively, p<0.05). In the wetland headwater stream similar correlations between Fe and TM are found, but DOC also correlates significantly with As, Cd, Ni, and Pb (r2=0.92, p<0.05).
A significant negative correlation (p<0.05) was observed between coverage of wetlands and average concentrations of Cr, Cu, Ge, Ni, Sc and Y. The results indicate that wetlands act as sinks for these elements. Alternatively, there is a source limitation in wetlands and that increased concentrations during base flow are due to mineral groundwater influence. Positive correlation with wetland coverage was only observed for Pb (r2=0.79, p<0.05), indicating that wetlands acts as a source for this element. Sulfate concentrations correlated negatively (r2=0.97, p<0.05) with increasing coverage of wetlands, which highlights the importance of sulfate reduction within wetland areas.
This study emphasizes the importance of considering stream water chemistry from a landscape perspective.
2007. A95- p.