Heavy metals in rivers of Latvia.

Total heavy metal concentrations in waters and sediments (HNO3 digestible Pb, Cu, Co, Ni, Mn, Zn) and their speciation forms in sediments (exchangeable, carbonate bound, iron-manganese oxide bound, organic matter bound and residual) in major and common small watercourses (31 sampling stations) along their flow in Latvia were determined. The metal loads entering the Baltic Sea from Latvia were calculated. Increased metal concentrations were found only in lower reaches of the largest rivers and locally around known industrial pollution sources. Differences in metal concentrations and loads in rivers from different regions of Latvia were related to natural geochemical processes. Metal speciation analysis showed that the dominant metal species are residual metals and those bound to organic matter. Residual and carbonate-bound metal dominated only in rhitral regions of rivers. The concentrations of exchangeable metals increased below pollution sources.