RIVER DISCHARGE OF HUMIC SUBSTANCES AND HUMIC-BOUND METALS TO THE GULF OF BOTHNIA

Water from 24 Swedish and Finnish rivers running to the Gulf of Bothni a (comprising the Bothnian Sea and Bothnian Bay) was sampled on five o ccasions in 1991-93, and analysed for concentrations of total organic carbon (TOC), humic substances and metals (Fe, Al, Cu, Zn). in general , TOC is higher in the Finnish rivers, which drain forest and peatland s, than in the Swedish rivers, which drain vast mountainous and forest ed areas. The pH is slightly lower in the Finnish rivers. Humic substa nces comprise approximately 80% of the total amount of organic matter. Calculations of the specific transport of organic matter (i.e. the to tal transport per catchment area) showed that the average release from the Finnish catchments is more than twice the release 14 om the Swedi sh catchments. Fe and Al exhibit the same concentration pattern as TOC . To estimate the humic fraction of some metals (Fe, Cu and Zn), a spe ciation study, utilizing a weak anion-exchange resin, was performed on water from rivers with different hydrochemical properties. The humic fractions of Fe, Cu and Zn were 20-40, 40-60 and <10%, respectively, o f the total metal content. The total load to the Gulf of Bothnia of hu mic substances and Fe, Cu and Zn associated with the humic matter was calculated. It was found that the discharge of humic substances to Bot hnian Bay originates primarily from the Finnish rivers, and the larges t amounts contributed to the Bothnian Sea come from the Swedish rivers . (C) 1997 Academic Press Limited.