Characterisation of the water and nutrient balance in the small rural lowland catchment of the Kielstau

Kielstau is a small rural catchment in the north of Schleswig-Holstein with a size of about 50 km². Hydrological data are available since 1985. Additionally, water quality and field campaign measurements have been taking place since 2005 by the Department of Hydrology and Water Resources Management of the University of Kiel. Since 2010 the Kielstau catchment is recognized as a UNESCO demonstration site for ecohydrology. The aim of this study is the characterisation of the water and nutrient balance in the lowland catchment Kielstau as well as the detection of seasonal and long-term trends. To this end, water quality measurements with high temporal resolution are analysed over a period of ten years (2007 to 2016). In addition to descriptive statistics, the statistical analysis covers trend analysis as well as auto-and cross-correlation tests. Our results indicate the great effect of groundwater and vegetation on runoff processes in the catchment. In the study period, a significantdecrease of 0.12 mg/l NO3-N and 0.006 mg/l NH4-N per year was detected. For PO4-P no significant trend was found. This is a result of great social relevance, especially in light of the overall nitrate pollution of water bodies in Germany and Schleswig-Holstein. Moreover, the results underline the importance of long-term measurements for process understanding and sustainable river basin management.