HOW CAN GERMAN RIVER BASINS CONTRIBUTE TO REACH THE NUTRIENT EMISSION TARGETS OF THE BALTIC SEA ACTION PLAN?

摘要

Since the 1900s, the Baltic Sea has changed from an oligotrophic clear-water sea into an eutrophic marine environment. The currently high nutrient emissions into the Baltic sea lead to intense algal growth, oxygen depletion and lifeless sea bottoms. To reduce the high nutrient emissions, the Baltic Sea Action Plan demands a reduction of nutrient loads. For the German catchments the reduction target is about 5,6201 for nitrogen and 240 t for phosphorus. Measures have to be taken to reduce the high nutrient emissions into rivers and seas. To identify the most effective measures, the sources and pathways of nutrient emissions into rivers have to be quantified. Furthermore, the reduction potential of different measures has to be assessed and measure packages have to be composed. The MONERIS model is applied, a semi-empirical, conceptual model, which has gained international acceptance as a robust meso- to macro scale model for nutrient emissions. MONERIS quantifies nitrogen and phosphorus emissions into river basins, via various point and diffuse pathways, as well as the retention and the nutrient load in rivers. For 172 subcatchments of the german Baltic Sea river basins nutrient emissions were calculated and the pathways and sources were defined. The effect of measures can be quantified with the 'management alternative tool' in MONERIS. Therefore, on one hand the effect of agricultural measures and on the other hand measures concerning urban sources and waste water treatment plants can be assessed. Furthermore, the cost efficiency of those measures will be evaluated with a newly developed tool 'CEA' (cost-effectiveness-analysis) in MONERIS. Currently, most nitrogen emissions come from tile drainages (63%), groundwater flow (19%), and point sources (5%), whereas most phosphorous emissions come from point sources (29%), groundwater flow (23%) and tile drainages (16%). Due to the high impact of tile drained areas, measures to reduce diffuse nitrogen emissions from tile drainages will be in the focus of our study. For phosphorous measures focus especially point sources. Results presented at the Conference will show the most cost effective measure packages for this region to reach the reduction targets of the Baltic Sea Action Plan.