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Erik Nygaard, Geological Survey of Denmark and Greenland (Denmark)
Klaus Hinsby, Geological Survey of Denmark and Greenland (Denmark)
Mette Dahl, Geological Survey of Denmark and Greenland (Denmark)
Jette Vindum, Kolding Municipality (Denmark)
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The water quality in European surface water bodies, i.e. lakes, streams and fjords, is regulated via the EU Water Framework and Groundwater Directives. Regulation of the anthropogenic input of nutrients is an essential means to ensure a good status with low nutrient loads to surface waters. To facilitate prioritation of managemental steps a typology of groundwater-surface water interaction (GSI typology) is provided as a framework for evaluating nitrate loads to surface water systems. The typology has been applied and tested in the Aakaer riparian stream catchment in a moraine landscape in Denmark. As a first step the groundwater recharge area, and its potential for supplying nitrate from the upland via groundwater bodies into the riparian area aquifer, is classified. In the second step the distribution of flow paths through, and the relative nitrate reduction capacity of, the riparian area aquifer is characterised. Finally the leaching into the stream and the nutrient loads via different flow paths is evaluated against measured nitrate concentrations in riparian aquifers, drains, ditches, and streams.
The evaluations indicate that the likelihood of nitrate discharging into riparian area aquifers may be grouped based on hydrogeological setting and land use of the upland areas. Within the riparian area the nitrate concentration is high springs, ditches and drains coming directly form agricultural areas. The nitrate content is the lower the longer and better contact the water appears to have had with anaerobic, organic C containing sediments during passage of the riparian area. The investigation shows that the utilisation of the nitrate reduction capacity of the riparian area would likely be optimised by cutting drains at the marginal hill slope of the valley and distributing water from agricultural areas within wetland areas in the valley.
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