Nutrient Load Experiments and Oxygen Dynamics

The environmental pressure on the Baltic Sea ecosystem has strongly increased during the last decades. A driving force for changes in the ecosystem, which are described in detail in Chapter 12, is inter alia the man-made increase of nutrient loads to the Baltic Sea. Many abatement strategies with the aim to reduce riverine nutrient loads have been discussed (see e.g., Gren, 2000). However, uncertainties remain concerning the quantitative effect of 

FIGURE 19.9 Isolines of salinity and model current (gray scale) in cm/s across a section at Kriegers Flak at 13 E longitude. The area of inflow after 10 days of model start is marked by dashed contour Unes. 

Oxygen dynamics in the deepwater of the central Baltic Sea is a key issue for the cod reproduction in the Baltic. The recruitment of cod depends on egg survival within the halocline, implying that hypoxia or anoxic condition can significantly decline the number of recruits. The ventilation of the deepwater below the halocline is associated with saltwater inflows, but oxygen consumption is mainly due to mineralization of detritus. 

FIGURE 19.10 Change of phosphorus (dashed line) and nitrogen (black line) due to 50% reduction of riverine nutrient loads. 

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