ECOSUPPORT: A Pilot Study on Decision Support for Baltic Sea Environmental Management

Abstract

The Baltic Sea is a semi-enclosed sea with limited water exchange with the world ocean and with a freshwater surplus resulting in a brackish water body with strong vertical and horizontal stratifications (e.g., Lepparanta and Myrberg 2009). The discharge of large rivers causes a wide range of sea surface salinities between 2 g kg in the north (Bothnian Bay) or east (Gulf of Finland) and 20 g kg in the south (Kattegat) (Fig. 1). Also, the vertical gradients of salinity are large. For instance, the vertical salinity gradient in the eastern Gotland Basin amounts to about 4 g kg. This specific hydrography prevents a sufficient ventilation of the deep water with the consequence of oxygen depletion. In addition to this natural factor, the anthropogenic impact of 85 million people, living in the catchment area of the Baltic Sea, is significant. Inter alia, intensive agriculture and inadequately treated sewage water result in eutrophication, reinforcing oxygen depletion. The latter effect is today so pronounced that large areas of the sea bottom are covered by hypoxia or even anoxia, i.e. by bottom water with a dissolved oxygen concentration below *2 ml O2 l , or completely depleted, respectively (Hansson et al. 2011). To counteract the consequences of eutrophication, the Baltic Sea Action Plan (BSAP) by the Helsinki Commission (HELCOM) was designed to improve the environmental conditions of the Baltic Sea (Backer et al. 2010). Nutrient load reductions at country level were calculated to fulfil scientifically based environmental targets (Wulff et al. 2007). However, the original figures of the BSAP were estimated without taking climate change into account. To overcome this shortcoming, the ECOSUPPORT project (Advanced modelling tool for scenarios of the Baltic ECOsystem to SUPPORT decision making) was initiated to investigate the combined impacts of changing climate and changing human activity (anthropogenic nutrient load changes, coastal management, fisheries) on the marine ecosystem.