Carbon and nutrient export regimes from headwater catchments to downstream reaches Rémi Dupas1, *, Andreas Musolff2, James W. Jawitz3, P. Suresh C. Rao4, Christoph G. Jäger1, Jan H. Fleckenstein2, Michael Rode1, Dietrich Borchardt1 5 1Department of Aquatic Ecosystems Analysis and Management, Helmholtz Centre for Environmental Research UFZ, Magdeburg, Germany 2Department of Hydrogeology, Helmholtz Centre for Environmental Research UFZ, Leipzig, Germany 3Soil and Water Science Department, University of Florida, Gainesville, Florida, USA 4School of Civil Engineering and Department of Agronomy, Purdue University, West Lafayette, Indiana, USA 10 *Now at: INRA, UMR1069 SAS, F-35000 Rennes, France Correspondence to: Rémi Dupas (
[email protected]) Abstract: Excessive amounts of nutrients and dissolved organic matter in freshwater bodies affect aquatic ecosystems. In this study, the spatial and temporal variability in nitrate (NO3), dissolved organic carbon (DOC) and soluble reactive phosphorus (SRP) was analyzed in the Selke (Germany) river continuum from headwaters 15 draining 1 – 3 km² catchments to downstream reaches representing spatially integrated signals from 184 – 456 km² catchments. Three headwater catchments were selected as archetypes of the main landscape units (land use x lithology) present in the Selke catchment. Export regimes in headwater catchments were interpreted in terms of NO3, DOC and SRP land-to-stream transfer processes. Headwater signals were subtracted from downstream signals, with the differences interpreted in terms of in-stream processes and contribution of point-source 20 emissions. The seasonal dynamics for NO3 were opposite those of DOC and SRP in all three headwater catchments, and spatial differences also showed NO3 contrasting with DOC and SRP. These dynamics were interpreted as the result of the interplay of hydrological and biogeochemical processes, for which riparian zones were hypothesized to play a determining role.