Assessing the importance of seepage and springs to nitrate flux in a stream network in the Wisconsin sand plains |
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| Authors: | Robert S Stelzer Eric A Strauss Mamadou Coulibaly |
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| Institution: | 1. Department of Biology, University of Wisconsin Oshkosh, Oshkosh, WI, USA;2. River Studies Center and Department of Biology, University of Wisconsin La Crosse, La Crosse, WI, USA;3. Department of Geography and Urban Planning, University of Wisconsin Oshkosh, Oshkosh, WI, USA |
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| Abstract: | Evaluating the flow paths that contribute to solute flux in stream networks can lead to greater understanding of the linkages between biogeochemistry and hydrology. We compared the contributions of groundwater in spring brooks and in seepage through the streambed to nitrate flux in the Emmons Creek network in the Wisconsin sand plains. We predicted that spring brooks would contribute disproportionately to nitrate flux due to the presumed higher advection rates in springs and less opportunity for nitrate removal relative to seeps. Nitrate flux was measured in 15 spring brooks that entered Emmons Creek. Nitrate flux from seepage was measured at the locations of 30 piezometers, based on Darcy's Law, and by a reach‐scale injection of Rhodamine water tracing (RWT). When seepage discharge was estimated from the RWT release, groundwater inputs from seepage and springs accounted for the discharge gain in the Emmons Creek channel. Springs brooks and seepage (based on the RWT release) contributed 37% and 63%, respectively, to nitrate flux inputs in the study reach. Contrary to our prediction, seeps contributed disproportionately to nitrate flux relative to their discharge. Relatively high rates of seepage discharge and higher than anticipated nitrate concentrations in the shallow pore water at seepage locations contributed to the unanticipated result. |
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| Keywords: | flow path groundwater hydraulic conductivity nitrogen seepage springs |
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