A longstanding recognition of eutrophication as the most common threat to the entire Baltic Sea has lead to the international agreement on nutrient load reductions within the Baltic Sea Action Plan. The nutrient load reductions were based on quantitative estimates of the “maximum allowed nutrient inputs” evaluated with a help of the decision support system Nest developed within the MARE (Marine Research on Eutrophication) program.
As demonstrated by a comparison to available data derived from observations, the marine biogeochemical model SANBALTS (Simple As Necessary Baltic Long-Term large-Scale) used in this evaluation is capable to realistically simulate both contemporary and preindustrial trophic states of the Baltic Sea. A key to successful performance of SANBALTS lays in accounting for major sources and sinks that determine the size of internal nutrient pools and, thus, govern the large scale Baltic Sea eutrophication.
The next generation marine models in the Baltic Nest system
In order to further revise and elaborate the BSAP, e.g. taking into consideration indicators required by the EU Marine Strategy Framework Directive (MSFD) as well as the need for higher spatial and temporal resolution, the models in Nest needed further development.
In order to meet these needs, as well as building credibility necessary in the national deliberations and international negotiations, the Baltic Nest Institute has worked hard to further develop the model. Our aim is always to ensure that our model scenarios are publicly available through the decision support system Nest, allowing any interested party running hindcast and scenario experiments as well as visualize its results.
For these purposes, we present here the latest developments of the BAltic sea Long-Term large Scale Eutrophication Model (BALTSEM), which captures the main features of the Baltic Sea eutrophication, and now serves as a next generation marine model in the Baltic Nest system. These results as well as hindcast for 1850-2006 and future scenarios can be reproduced and analyzed on-line. Since BALTSEM performance at long-term scales has already been presented by Eilola et al. (2011a) and Gustafsson et al. (2012), this paper is
especially focused on a seasonal scale.