MONITORING, MASS-BALANCE CALCULATION OF NUTRIENTS AND THE FUTURE OF THE GULF OF BOTHNIA

Based on the intensive hydrochemical measurements of the Gulf of Bothn ia Year 1991, we present descriptions of the regional variations of fr eshwater and nutrient inputs and hydrographic and nutrient conditions in these basins for this particular year. These data are then used to construct nutrient budgets for the Bothnian Sea and Bay, for silicate, inorganic and organic nitrogen and phosphorus. The seasonal variation s of internal sources and sinks and advective transports between the b asins and with the Baltic proper, show the relative importance and mag nitude of biogeochemical and physical processes for the development of nutrient concentrations in these basins. Annual budget estimates show that the Bothnian Sea appears to function as a very efficient sink fo r nitrogen and phosphorus. There is a very small exchange of nitrogen with the Baltic proper, in contrast to the large amounts of phosphorus imported and silica exported. Overall N:P ratios show the high rates typical of the Bothnian Bay, which are drastically reduced in the Both nian Sea, particularly for inorganic nutrients. In spite of the highly variable N:P ratios of the different pools, the calculated net transf ers of inorganic nutrients into organic matter follow classical Redfie ld ratios in both basins.