Water Quality Modeling System for Coastal Archipelagos

Laura Tuomi1, Elina Miettunen2, Kaarina Lukkari2, Irma Puttonen3, Janne Ropponen4, Kimmo Tikka1, Jonna Piiparinen2 and Risto Lignell2, (1)Finnish Meteorological Institute, Marine Research Unit, Helsinki, Finland, (2)Finnish Environment Institute, Marine Research Centre, Finland, (3)Åbo Akademi University, Environmental and Marine Biology, Finland, (4)Finnish Environment Institute, Freshwater Centre, Finland
Abstract:
Coastal seas are encountering pressures from eutrophication, fishing, ship emissions and coastal construction. Sustainable development and use of these areas require science-based guidance with high quality data and efficient tools.

Our study area, the Archipelago Sea, is located in the northern part of the semi-enclosed and brackish water Baltic Sea. It is a shallow, topographically heterogeneous and eutrophic sub-basin, covered with thousands of small islands and islets. The catchment area is 8950 km2and has ca. 500 000 inhabitants.

We are developing a modeling system that can be used by local authorities and in ministry level decision making to evaluate the environmental impacts that may result from decisions and changes made both in the watershed and in the coastal areas. The modeling system consists of 3D hydrodynamic model COHERENS and water quality model FICOS, both applied to the area with high spatial resolution. Models use river discharge and nutrient loading data supplied by watershed model VEMALA and include loading from multiple point sources located in the Archipelago Sea. An easy-to-use interface made specifically to answer the end-user needs, includes possibility to modify the nutrient loadings and perform model simulations to selected areas and time periods.

To ensure the quality and performance of the modeling system, comprehensive measurement dataset including hydrographic, nutrient, chlorophyll-a and bottom sediment data, was gathered based on monitoring and research campaigns previously carried out in the Archipelago Sea. Verification showed that hydrodynamic model was able to simulate surface temperature and salinity fields and their seasonal variation with good accuracy in this complex area. However, the dynamics of the deeper layers need to be improved, especially in areas that have sharp bathymetric gradients. The preliminary analysis of the water quality model results showed that the model was able to reproduce the basic characteristics of the surface layer dynamics. The further research will aim at implementing more advanced approach for internal loading of phosphorus based on classification of sea floor types and chemical analysis of the sediment data.

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