Henrik Scharin

Eutrophication, caused mainly by nitrogen discharge, is one of the major threats to the environmental state of the Baltic Sea. It causes reduction in the cod population, toxic blue green algaes and dead sea bottoms. The Stockholm archipelago is a coastal area of the Baltic Sea suffering from this eutrophication. The major part of the nitrogen load to the Archipelago comes from one of its 30 drainage basins, while the rest is atmospheric deposition from sources in other regions as well as inflows from other coastal areas. Sewage treatment plants, agriculture, and traffic are the main sources of nitrogen in this region. There are three ways of reducing the load, by decreased deposition, by land use changes decreasing the leakage or by increasing the retention. The load from a specific source within a drainage basin finally reaching the recipient is a function of deposited amount, leakage of nitrogen from the root zone, retention of transported nitrogen as well as existing measures. The objective of this study is to determine the most efficient allocation of measures, for a given amount of reduction. All factors influencing the impact a certain measure, in a certain basin, has on the final load is regarded when determining this allocation. The Modeling is done by GAMS-programming. The effect of uncertainty, concerning the actual retention, is also taken into consideration in the study.