Scenario analysis of nutrient management at the river basin scale

A new river basin model (TRANS) for studying the transport, removal and acc umulation of nutrients in rivers, lakes and riparian areas has been develop ed and tested on data from a 115 km(2) river basin in Denmark (river Gjern) . The model combines catchment information on soil type and land use with a physical hydrodynamic modelling system and several semi-dynamic empirical models on diffuse nutrient loading and nutrient retention in rivers, lakes and riparian areas. Three main river basin management scenarios were define d for this basin and the environmental effects analysed using the model: 1. Improved sewage treatment at sewage works; 2. 20% set-aside of arable land ; 3. river system rehabilitation. Combining the three scenarios in an overa ll river basin management strategy reduced annual total nitrogen export fro m the river basin by 93 tonnes, corresponding to a 53% reduction in nitroge n export during the hydrological year 1994-95. Similarly, annual total phos phorus export was reduced by 2.6 tonnes corresponding to a 46% reduction in phosphorus export.