Alternative strategies for reducing nitrogen loading

Two alternative strategies for reduction in nitrogen loading are analysed: (1) changes in agricultural production structure and (2) lake creation/restoration. The former includes spatial redistribution of the agricultural production, setting aside areas and changes in agricultural practice. The latter includes five scenarios with different lake location and size. A 342 km2 agricultural watershed is used as study area. Two GIS-based models are applied: (1) a distributed riverine nitrogen loading model for analysis of agricultural changes and (2) a linked-lumped model for lake creation analysis. The analysis shows that each of the agricultural measures would result in a 11-13% reduction. In combination they would amount to 30% reduction. The five lake scenarios were giving area specific reductions varying from 46 to 2375 kg N ha-I year-I. The best lake creation strategy seems to be a high number of smaller lakes distributed in all parts of the watershed. Results indicate that comprehensive lake creation would result in a 20-30% reduction. The results emphasise the need for integrated watershed management.