@article{DupasMusolffJawitzetal.2017, author = {Dupas, R. and Musolff, A. and Jawitz, J. W. and Rao, P. S. C. and J{\"a}ger, Christoph G. and Fleckenstein, J. H. and Rode, M. and Borchardt, D.}, title = {Carbon and nutrient export regimes from headwater catchments to downstream reaches}, series = {Biogeosciences}, volume = {14}, journal = {Biogeosciences}, number = {18}, pages = {4391 -- 4407}, year = {2017}, 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 three headwaters draining 1-3 km2 catchments to two 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  ×  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 contributions from point sources. 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. In the two downstream reaches, NO3- was transported almost conservatively, whereas DOC was consumed and produced in the upper and lower river sections, respectively. The natural export regime of SRP in the three headwater catchments mimicked a point-source signal (high SRP during summer low flow), which may lead to overestimation of domestic contributions in the downstream reaches. Monitoring the river continuum from headwaters to downstream reaches proved effective to jointly investigate land-to-stream and in-stream transport, and transformation processes.}, language = {en} } @article{YangBuettnerKumaretal.2019, author = {Yang, Soohyun and B{\"u}ttner, Olaf and Kumar, Rohini and J{\"a}ger, Christoph G. and Jawitz, James W. and Rao, P.S.C. and Borchardt, Dietrich}, title = {Spatial patterns of water quality impairments from point source nutrient loads in Germany's largest national River Basin (Weser River)}, series = {Science of The Total Environment}, volume = {697}, journal = {Science of The Total Environment}, year = {2019}, abstract = {We employed the well-established Horton-Strahler, hierarchical, stream-order (ω) scheme to investigate scaling of nutrient loads (P and N) from ~845 wastewater treatment plants (WWTPs) distributed along the river network in urbanized Weser River, the largest national basin in Germany (~46K km2; ~8.4 million population). We estimated hydrologic and water quality impacts at the reach- and basin-scales, at two steady river discharge conditions (median flow, QR50; low-flow, QR90). Of the five WWTPs class-sizes (1 ≤ k ≤ 5), ~68\% discharge to small low-order streams (ω < 3). We found large variations in capacity to dilute WWTP nutrient loads because of variability in (1) treated wastewater discharge (QU) within and among different class-sizes, and (2) river discharge (QR) within low-order streams (ω < 3) resulting from differences in drainage areas. For QR50, reach-scale water quality impairment assessed by nutrient concentration was likely at 136 (~16\%) locations for P and 15 locations (~2\%) for N. About 90\% of these locations were lower-order streams (ω < 3). At QR50 and only with dilution, basin-scale cumulative nutrient loads from multiple upstream WWTPs increase impaired locations to 266 (~32\% of total) for P. Considering in-stream uptake decreased P-impaired streams to 225 (~27\%), suggesting the dominant role of dilution in the Weser River basin. Role of in-stream uptake diminished along the flow paths, while dilution in larger streams (4 ≤ ω ≤ 7) minimizes the impact of WWTP loads. Under QR90 conditions [(QR50/QR90) ~ 2.5], water quality impaired locations will likely double for the basin-scale analyses. Long-term water quality data suggested that diffuse sources are the primary contributors for water quality impairments in large streams. Our data-modeling synthesis approach is transferable to other urbanized river basins and extends understanding of point source impacts on water quality across spatial scales.}, language = {en} }