Carbon-based nutrient cycling in the Baltic Sea - Analysis of twelve basins using three-dimensional flow dynamics.

Abstract

Eutrophication is a major problem in the Baltic Sea and is the result mainly of the increase of the anthropogenic nutrient loading. Thus, the links among water quality, sediments, and eutrophication have to be understood in order to predict the consequences of our actions and of the climate change on the Baltic Sea. Therefore, water quality models that take into account the hydrodynamics have to be developed to help policy makers. In that perspective, the Kiirikki model, an ecosystem and sediment model, coupled to a box approach has been used to describe the water quality of the Baltic Sea. The latter has been divided into twelve sub-basins according to the topography, each of them separated into two vertical layers. The Kiirikki model has been implemented on each sub-basin and the hydrodynamics are used to link sub-basins between them. After calibration, it can be seen that the model results are consistent with the monitoring data for the southern part, even if the dissolved inorganic nitrogen levels are too high during the winter and some phase shifts are observed. For the northern part, the primary production is well modelled but there is an offset concerning the dissolved inorganic nutrient. Thus, it can be concluded that the implementation of the Kiirikki model is a realistic tool to describe the water quality and eutrophication of the Baltic Sea. However, the differences indicate that the Baltic Sea model cannot be use for policy making yet and more work is needed to improve the model such as a global sensitivity analysis as well as the use of site specific parameters