Influence of Temporal Variations in River Discharge, pH, Alkalinity and Ca on the Speciation and Concentration of Heavy Metals in Some Mining Polluted Rivers

摘要

Dissolved (dialysis in situ) and total concentrations of Cu, Zn, Cd and Al in eight mining polluted rivers in the Roros area, central Norway, were determined by atomic absorption spectrometry (flame and graphite furnace) and compared to pH, Ca concentration and alkalinity through seasonal variations in river discharge. Total concentrations of the metals were highest during early spring flood and during summer and autumn rain episodes. Dissolved concentrations also increased as the spring flood proceeded, but small discharge peaks within this ~2 month period as well as a considerable autumn flood episode appeared to lower rather than to raise the dissolved metal concentrations. Consequently the dissolved fractions of Zn, Cd and Al showed a significant negative correlation with river discharge, and were low at the discharge peaks. Possibly high sediment concentrations occurring at high flood conditions more than counteracted desorption induced by pH decrease, and led to decreased dissolved fractions through adsorption. Cu speciation on the other hand seemed to be more closely linked to pH. Alkalinity and Ca concentration, both assumed to protect aquatic life from metal pollution, were significantly lower during episodes with high Cu and Al total concentrations.