A conceptual model about nutrients flow in Haapsalu bay

Abstract: Haapsalu Bay is a very shallow area consisting of semiclosed regions partly separated by peninsulas in the coastal zone of West Estonia. The main inflow of fresh water, 33.875.436 m3/year, from some small rivers (Ungru, Taebla, Vönnu, Asukula) falls into the eastern part of Haapsalu Bay, with the Nitrogen load 72.331 Kg/year and Phosphorus load 2.327,88 Kg/year. The central part of the Bay receives municipal and industrial sewage waters from the town of Haapsalu with a discharge of nutrients 28.591,6 Kg N/year and 4.34,17 Kg P/year . In addition, atmospheric deposition constitutes an important part of the nutrients load with 40.936 Kg N/year and 183 Kg P/year. As a consequence, intensive production of organic matter and accumulation of nutrients lead to a constant eutrophication process. In order to understand biochemical processes occurring in the marine ecosystem where the turnover of both phosphorus and nitrogen is included a conceptual model has been built up. Haapsalu Model, implemented in Stella Software, illustrates the phosphorus and nitrogen cycles and the concentration of nutrients in their different stages in Haapsalu Bay. Moreover, how various reduction strategies will affect the environment in the bay and in the Baltic proper may be simulated. The model tests nowadays the bay acts a giant waste stabilization pond resulting in the fact that the amount of nutrients carried by flowing water out to Baltic Sea should be small.