Successful reduction of diffuse nitrogen emissions at catchment scale: example from the pilot River Odense, Denmark.

Land-based total nitrogen (N) loadings to Danish coastal waters have been markedly reduced since 2000. This has been achieved by general measures reducing discharges from all point sources and N leaching from farmed land supplemented with more local and targeted mitigation measures such as restoration of wetlands to increase the catchment-specific N retention. In the catchment of River Odense, restoration of wetlands has been extensive. Thus, in the major gauged catchment (485 km(2)) eleven wetlands (860 ha) have been restored since 2000. A comparison of data on N concentrations and loss from a gauging station in the River Odense with data from a control catchment (772 km(2)), in which a significantly less intensive wetland restoration programme has been undertaken, showed an excess downward trend in N, amounting to 124 t N yr(-1), which can be ascribed to the intensive wetland restoration programme carried out in the River Odense catchment. In total, the N load in the River Odense has been reduced by 377 t N yr(-1) (39%) since 2000. The observed downward trend is supported by monitoring data from two wetlands restored in 2001 and 2004 in the River Odense catchment.

Danish policy measures to reduce diffuse nitrogen emissions from agriculture to the aquatic environment.

In Denmark, the first Action Plan for the Aquatic Environment (I) was introduced in 1987. The target was a 50% reduction in nitrogen emissions to the aquatic environment by 1993. Measures were directed towards the individual farmer and included the establishment of slurry tanks with 9 month storage capacity and obligations to grow winter crops on 65% of the area. In the early 1990s, it was obvious that agricultural practice had not changed towards a more efficient use of manure and fertilisers. Therefore, the Action Plan for Sustainable Agriculture was adopted in 1991, the reduction target being postponed until 2000. The plan set out restrictions on the actual utilisation of fertilisers and manure, obligations for the farmers to submit nitrogen accounts to the Ministry of Agriculture, and a levy system. However, the implemented measures were still insufficient to reach the reduction target. A second Action Plan for the Aquatic Environment (II) was adopted in 1998 and the reduction target was again postponed until 2003. This plan contained a range of measures, including reduced nitrogen standards for crops. The results from the Danish action plans confirm the need for an effective control body, and a continuous monitoring and evaluation programme.