Modeling point and non-point nutrient fluxes in river systems of lake Peipsi drainage basi

Abstract

N and P compounds work as key elements causing bioproduction and eutrophication inwater bodies of the Baltic Sea region, A large-scale dynamic GIS-embedded PolFlowmodel considers all point and diffuse emission sources in a river basin simulating alsotransport and retention of nutrients in time steps of five years, This modeling approachwas originally developed for simulating past and present nutrient loads for the Rhine andElbe rivers. In addition, a statistical model MESAW was employed for nutrient sourceapportionment and emission estimations. This paper analysis the modeling results in LakePeipsi basin, shared by Estonia, Russia and Latvia, for long-term trends since 1985 till1999. Results of modeling, as well as monitoring data indicate quite stable long-term Pload while agricultural N load has decreased significantly in connection with dramaticchanges in agricultural structures. That, in turn, has lead to sharp decrease ofN/P ratio inriverine runoff while in lakes (L Peipsi, L Vortsjii.rv) and coastal seas, NIP ratio hasdropped below 10. These changes, enhancing cyanobacterial blooms, have significantlyworsened the ecological state of these water bodies, in the conditions of decreasedemissions. The paper concludes that wastewater treatment should focus on better removalofphosphorus.