Dynamics and Biogeochemistry of River Corridors and Wetlands (Proceedings of symposium S4 held during the Seventh IAHS Scientific Assembly at Foz do Iguaçu, Brazil, April 2005). IAHS Publ. 294, 2005, 46-54

1 UFZ Environmental Research Centre Leipzig-Halle, Brueckstrasse 3a, D-39114 Magdeburg, Germany

2 UFZ Environmental Research Centre Leipzig-Halle, Theodor-Lieser-Straße 4, D-06120 Halle, Germany

Abstract Biogeochemical transformations and hydraulic processes in soil and groundwater can moderate nitrate loads in surface waters compared to nitrogen inputs to soil. A modelling approach was developed based on the loose coupling of a soil nitrogen model with a groundwater flow and a multi-species reactive groundwater-transport model. This approach combines transport time with availability of reaction partners and nitrate turnover. A case study was conducted in a small lowland catchment (Schaugraben, ~20 km²) close to Osterburg in the north of Saxony-Anhalt, Germany, and demonstrated the spatial heterogeneity of nitrate loads and concentrations resulting from the spatial distribution of nitrate inputs, the arrangement of input areas to the channel network, and the consumption of reactive substances in the aquifer. An extension of this approach aims to describe turnover processes at the groundwater–surface water interface in order to close the gap between groundwater exfiltration and catchment outlet.

Key words groundwater; lowland catchment; modelling; nitrate; nitrogen; reactive transport; soil