Variations in heavy metal concentrations and speciation in two mining-polluted streams in central Norway

The dissolved (dialysis in situ), colloidal (filtered minus dissolved), and total concentrations of Cu, Zn, Cd, and Al were determined and compared wi th pH, Ca concentrations, and alkalinities through seasonal variations in w ater levels in two streams, Rugla and Naustebekken, in the Roros area of ce ntral Norway. The main objective was to monitor the dissolved fraction of t he metals during the seasons and to establish the extent to which chemical parameters influencing metal toxicity were unfavorable during episodes of h igh total metal concentrations. The average dissolved fractions of Cu, Zn, Cd, and Al were Lower in Rugla (55, 69, 64, and 17%, respectively) compared with Naustebekken (59, 82, 82, and 30%, respectively). This is probably du e to sedimentation of metal particles in a small lake located in the path o f Naustebekken. Alkalinity and Ca concentrations were generally low during the flood episodes, when the highest metal concentrations occurred. This is unfavorable since these parameters are assumed to counteract toxic effects of metals. On the other hand, the results indicate that toxic stress durin g metal concentration peaks was moderated by adsorption of dissolved metal species on colloids and/or particles.