Quantifying in-stream retention of nitrate at catchment scales using a practical mass balance approach
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As field data on in-stream nitrate retention is scarce at catchment scales, this study aimed at quantifying net retention of nitrate within the entire river network of a fourth-order stream. For this purpose, a practical mass balance approach combined with a Lagrangian sampling scheme was applied and seasonally repeated to estimate daily in-stream net retention of nitrate for a 17.4 km long, agriculturally influenced, segment of the Steinlach River in southwestern Germany. This river segment represents approximately 70 % of the length of the main stem and about 32 % of the streambed area of the entire river network. Sampling days in spring and summer were biogeochemically more active than in autumn and winter. Results obtained for the main stem of Steinlach River were subsequently extrapolated to the stream network in the catchment. It was demonstrated that, for baseflow conditions in spring and summer, in-stream nitrate retention could sum up to a relevant term of the catchment’s nitrogen balance if the entire stream network was considered.
KeywordsNitrate retention In-stream processes Mass balance approach Stream network Catchment scale
The authors thank J. H. Fleckenstein for helpful comments on earlier versions of the manuscript. This work was supported by a grant from the Ministry of Science, Research and Arts of Baden-Württemberg (AZ Zu 33–721.3-2) and the Helmholtz Center for Environmental Research, Leipzig (UFZ). The study was also supported by the EU FP7 Collaborative Project GLOBAQUA (Grant Agreement no 603629).
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