Abstract
Abstract. The objective of this study was the detection and assessment of nutrient entry pathways in a complex mesoscale lowland catchment. The central aim was the development of a transferable method for an efficient estimation of instream water quality in rural environments. The investigated Kielstau catchment with a size of approximately 50 km2 is located in the North German lowlands. Land use is dominated by agriculture as well as pasture and is characterised by extensive artificial drainage systems. Additionally wastewater treatment plants influence the river water quality. Six measuring campaigns were carried out over the period of one year. Each time, water quality was assessed at 16 locations along a 12 km longitudinal transect of the stream to consider the influence of each tributary or inflow. The results showed that the applied measuring method was useful to assess nutrient entry pathways into surface waters from diffuse and point sources. Some tributaries increased the main stream NO3-N concentrations especially in autumn. Using a German classification system (LAWA, 1998), the NO3-N results can mostly be assigned to water quality class III (heavily contaminated). Water balance and nitrate loads were modelled with the river basin scale model SWAT (Soil and Water Assessment Tool, Arnold et al., 1998). The measured and modelled discharges showed a good correlation. While nitrate load range and dynamics are well represented during the summer periods, they show a poor correlation during the winter period.
Highlights
Since December 2000, the integrated protection of all water bodies has been legally regulated for all European Union member states by the European Water Framework Directive (EC, 2000)
The results showed that the applied measuring method was useful to assess nutrient entry pathways into surface waters from diffuse and point sources
Nutrient entry pathways into surface waters from diffuse and point sources were assessed by measurements and an ecohydrological modelling
Summary
Since December 2000, the integrated protection of all water bodies has been legally regulated for all European Union member states by the European Water Framework Directive (EC, 2000). Tributaries can have a substantial influence on the nutrient balance of surface water bodies. David et al (1997) detected high NO3-N concentrations within the range of 5 to 49 mg/l in drainage tiles in an agricultural catchment area in Illinois. Drainage systems like tile drainage and open ditches change the natural water balance and influence the instream water quality due to a faster nutrient transport. In addition they found that during high flow events and intense precipitation the drainage systems have a substantial contribution to the NO3-N loss from agricultural fields
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