b'7Development in Nitrogen concentrations and loads in Danish streamsWindolf J11Department of Bioscience, Aarhus University, Vejlsvej 25, 8600 Silkeborg, DenmarkThe diffuse loading of nitrogen (N) to the aquatic environment due to farming activities is a well-known fact. During the last three decades, many measures have been taken in order to reduce this loading and to prevent undesired eutrophication of especially coastal waters. In Denmark, a comprehensive monitoring program of the aquatic environment was established in 1989 and has provided information of the success or lack of success in combatting this agricultural driven diffuse N-load. The monitoring programme includes 77 near coastal sampling stations with full times series of concentrations and estimated load of total N and nitrate-N (NO 3 -N)-N. Unfortunately, in some later years the laboratory analysis of total N has been somewhat biased which complicate the interpretation of the trends of N in recent years. However, the time series of NO 3 -N areconsidered to be reliable and a major reduction in the annual flow-weighted concentration of NO 3 -N can be documented during the 30 years of monitoring. The outcome is an overallreduction in the annual flow- weighted NO 3 -N concentrations that amount to 46%.Furthermore, the average annual NO 3 -N concentrations is found to be strongly and significantly related (R2=0.88; P<0.0001) to the estimated national N-surplus (field scale) during the period 1990-2017.A major Danish stream (Odense ) holding measured NO 3 -N for the period sincemid-1970s shows that the annual flow-weighted concentration of NO 3 -N parallels thecalculated national N-surplus (farmgate) for this 40 year time series. The relationship shows a steady increase during the 1970-1980s and a decrease during the 1990s and a more or less constant concentration latest five-eight years. However, such a development in N-concentration is not found in all Danish streams as a few streams show marked delays in responses to reduced Nitrogen surplus. This delay can be explained by a catchment specific low reduction capacity in old oxic ground water. Also, for 46 minor streams some delay in the Nitrogen reductions has been seen. Hence, streams receiving relatively older oxic groundwater showed a lesser reductionthan the remaining of these 46 streams.51'