NITROGEN AND PHOSPHORUS FLUXES FROM FINNISH AGRICULTURAL AREAS TO THEBALTIC SEA

Nutrient losses from small drainage basins were compared to the nutrie nt fluxes in small coastal rivers in order to study the representative ness of the Finnish monitoring network of small basins, especially as regards agricultural loading to the Baltic Sea. Additionally flux esti mates from the period 1986-1990 were compared to those of the period 1 981-1985 in order detect possible trends. The results suggest that in coastal regions with high proportions of agricultural land and with lo w lake percentage, the nutrient losses from agricultural areas mostly enter coastal waters with negligible retention in river channels. The net effect of the various processes in the rivers is small because mos t of the nutrient losses occur in spring, fall or early winter in conn ection with high water flows and current velocities, short residence t imes of water and low intensities of biogeochemical processes. Nitroge n losses from agriculture has probably increased during the 1980s due to increased winter flows and increased use of nitrogen fertilizers. T he results indicate that nitrogen loading of the southern and south-we stern coastal waters of Finland has increased as well.