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| Titel |
Untangling hydrological pathways and nitrate sources by chemical appraisal in a stream network of a reservoir catchment |
| VerfasserIn |
M. A. Yevenes, C. M. Mannaerts |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1027-5606
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| Digitales Dokument |
URL |
| Erschienen |
In: Hydrology and Earth System Sciences ; 16, no. 3 ; Nr. 16, no. 3 (2012-03-08), S.787-799 |
| Datensatznummer |
250013211
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| Publikation (Nr.) |
 copernicus.org/hess-16-787-2012.pdf |
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| Zusammenfassung |
| The knowledge of water source contributions to streamflow is important for
understanding chemical contamination origins and the status of
biogeochemical cycling in stream networks of catchments. In this study, we
evaluated whether a limited number of spatially distributed geochemical
tracer data sampled during different hydrological seasons were sufficient to
quantify water flow pathways and nitrate sources in a catchment. Six
geochemical water constituents (δ2H, δ18O,
Cl−, SO2−4, Na+, NO−3 and K+) of precipitation, stream water, alluvial sediment pore water and shallow
groundwater of a 352 km2 agricultural catchment in the Alentejo region
of Portugal were analysed. Exploratory data analysis and end-member mixing
analysis (EMMA) were performed to estimate the water source mixing
proportions. Residual analysis of principal components was used to identify
the appropriate geochemical tracers and the number of end-members (water
sources and flow paths), and their proportional contributions to streamflow
were quantified. Spearman's rank correlation analysis was further used to
identify nitrate origins in the streamflow. Results showed that, when using
data from both wet and dry seasons, streamflow chemistry was strongly
influenced by shallow groundwater. When only wet season data were modelled,
streamflow chemistry was controlled and generated by three end-members:
shallow groundwater, alluvial sediment pore water and precipitation. Isotope
signatures of stream water were located mostly below the local meteoric
water line (LMWL) and plotted along a local evaporation line (LEL),
reflecting the permanence in the streamflow of shallow groundwater subjected
to prior evaporation. Interpretation of isotope signatures during summer
showed an isotopic enrichment in both streamflow and shallow groundwater.
Measured and historical stream nitrate concentrations appeared to be
strongly related to shallow groundwater. In addition, two hydrochemical data
outliers for almost every solute from two sample points were identified by
the analysis and could be related to local waste water outfalls. The results
of this study have improved our understanding of water source contributions
to streamflow in the catchment, and also yielded indications of nitrate
consumption related to biogeochemical processes in the streamflow network.
Moreover, we could conclude that the relatively limited geochemical spatial
sample database used in this study was an adequate input for the end-member
mixing analysis and diagnostic tools to quantify water sources and nitrate
origins in the streamflow of the catchment. |
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