Advances in Geosciences www.adv-geosci.net 1680-7340 1680-7359 18 Advances and visions in large-scale hydrological modelling 2008 10.5194/adgeo-18-37-2008 http://www.adv-geosci.net/18/37/2008/ http://www.adv-geosci.net/18/37/2008/adgeo-18-37-2008.html http://www.adv-geosci.net/18/37/2008/adgeo-18-37-2008.pdf 37 41 2008-06-20 A method to assess instream water quality – the role of nitrogen entries in a North German rural lowland catchment B. Schmalz bschmalz@hydrology.uni-kiel.de K. Bieger N. Fohrer Dept. Hydrology and Water Resources Management, Ecology Centre, Kiel Univ., Olshausenstr. 40, D-24098 Kiel, Germany 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. <br><br> 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. Arnold, J.-G., Srinivasan, R., Muttiah, R. S., and Williams, J. R.: Large area hydrologic modelling and assessment, Part I: Model development. Journal of the American Water Resources Association 34(l), 73–89, 1998. BGR (Bundesanstalt für Geowissenschaften und Rohstoffe (Ed.)): Bodenübersichtskarte im Maßstab 1:200 000, Verbreitung der Bodengesellschaften, Hannover, 1999. Bieger, K.: Integrierte Analyse der Wasserqualität eines Fließgewässers im ländlich geprägten Raum des Norddeutschen Tieflands. Diplomarbeit im Fach Geographie, Ökologie-Zentrum Christian-Albrechts-Universität zu Kiel. p. 142, http://www.hydrology.uni-kiel.de/lehre/abschlussarbeiten/2008_kbieger_kielstauqualitaet.pdf, 2007. David, M. B., Gentry, L. E., Kovacic, D. A., and Smith, K. M.: Nitrogen balance in and export from an agricultural watershed, J. Environ. Qual., 26(4), 1038–1048, 1997. DLR (Deutsches Zentrum für Luft- und Raumfahrt): Landsat TM5-Scene of 1995, upper left corner: RW: 3503180 HW: 6084975, spatial resolution 25 m$\times$25 m, Köln, 1995. DWD (Deutscher Wetterdienst): Climate data 1957–2006, 2007. DWD (Deutscher Wetterdienst): Means of precipitation and air temperature of the period 1961–1990, http://www.dwd.de/de/FundE/Klima/KLIS/daten/online/nat/index_mittelwerte.htm, last access 3~Januar~2008, 2008. EC: Directive 2000/60/EC of the European Parliament and of the Council of 23 October 2000 establishing a framework for the Community action in the field of water policy. Official Journal of the European Communities L 327/1. 2000. Fohrer, N., Schmalz, B., Tavares, F., and Golon, J.: Ansätze zur Integration von landwirtschaftlichen Drainagen in die \mboxModellierung des Landschaftswasserhaushalts von mesoskaligen Tieflandeinzugsgebieten. Hydrologie & Wasserbewirtschaftung, 51(4), 164–169, 2007. Hooda, P. S., Moynagh, M., Svoboda, I. F., Thurlow, M., Stewart, M., Thomson, M., and Anderson, H. A.: Streamwater nitrate concentrations in six agricultural catchments in Scotland. Science of the Total Environment, 201, 63–78, 1997. Johnes, P. J. and Burt, T. P.: Nitrate in Surface Waters. In: Nitrate: Processes, Patterns and Management, edited by: Burt, T. P., Heathwaite, A. L., and Trudgill, S. T., John Wiley & Sons Ltd., Chichester. 269–317, 1993. Kreis Schleswig-Flensburg: Kläranlagen-Einleiterdaten, FD Wasserwirtschaft, Schleswig, 2006. LAWA (Länderarbeitsgemeinschaft Wasser): Beurteilung der Wasserbeschaffenheit von Fließgewässern in der \mboxBundesrepublik Deutschland – Chemische Gewässergüteklassifikation, Kulturbuchverlag Berlin, 1998. LVermA (Landesvermessungsamt Schleswig-Holstein): Digitales Geländemodell für Schleswig-Holstein. Quelle: TK 25. Gitterweite 25 m$\times$25 m und TK 50 Gitterweite 50 m$\times$50 m, Kiel, 1995. Nash, J. E. and Sutcliffe, J. V.: River flow forecasting through conceptual models part I - A discussion of principles, J. Hydrol., 10(3), 282–290, 1970. Royer, T. V., David, M. B., and Gentry, L. E.: Timing of riverine export of nitrate and phosphorus from agricultural watersheds in Illinois: Implications for reducing nutrient loading to the Mississippi River, Environ. Sci. Technol. 40, 4126–4131, 2006. Schmalz, B., Tavares, F., and Fohrer, N.: Assessment of nutrient entry pathways and dominating hydrological processes in lowland catchments, Adv. Geosci., 11, 107–112, 2007. StUa Schleswig (Staatliches Umweltamt Schleswig): Hourly discharge data 1984–2006, 2007. Tavares, F.: Continuous, spatially distributed, stream flow and quality assessment of a lowland catchment in Northern Germany. Master thesis in "Environmental Management", Ecology Centre Kiel University, p. 134, http://www.hydrology.uni-kiel.de/lehre/abschlussarbeiten/msc_tavares.pdf, 2006.