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  • 1
    Language: English
    In: Hydrology Research, 11/2013, Vol.44(6), p.995
    Description: This study uses a high-frequency discharge and nitrate concentration dataset from the Weida catchment in Germany for the catchment scale hydrologic response analysis. Nitrate transport in the catchment is mostly conservative as indicated by the nitrate stable isotope ( delta 15N and delta 18O) analysis. Discharge-nitrate concentration data from the catchment show distinctive patterns, suggesting flushing and dilution response. A self-organizing feature map-based methodology was employed to identify such patterns or cluster in the datasets. Based on knowledge of the catchment conditions and prevailing understanding of discharge-nitrate concentration relationship, the clusters were characterized into five qualitative flow responses: (1) baseflow; (2) subsurface flow increase; (3) surface runoff increase; (4) surface runoff recession; and (5) subsurface flow decrease. Such qualitative flowpaths were used as soft data for a multi-objective calibration of a hydrological model (WaSiM-ETH). The calibration led to a reasonable simulation of overall discharge (Nash-Sutcliffe coefficient: 0.84) and qualitative flowpaths (76% agreement). A prerequisite for using such methodology is limited biogeochemical transformation of nitrate (such as denitrification).
    Keywords: Catchment Area ; Biogeochemistry ; Denitrification ; River Discharge ; Hydrology ; Nitrogen Isotopes ; Oxygen Isotope Ratio ; Runoff ; Response Analysis ; Oxygen Isotopes ; Hydrologic Analysis ; Nitrate Transport ; Numerical Simulations ; Catchment Basins ; Base Flow ; Surface Runoff ; Nitrogen Isotopes ; Subsurface Flow ; Isotopes ; Nitrates ; Biogeochemistry ; Denitrification ; Catchments ; Simulation ; Hydrology ; Hydrologic Models ; Assessments ; Surface Runoff ; Calibrations ; Nitrates ; Denitrification ; Catchment Areas ; Storm Seepage ; Hydrologic Data ; Hydrologic Models ; Assessments ; Surface Runoff ; Calibrations ; Nitrates ; Denitrification ; Catchment Areas ; Storm Seepage ; Hydrologic Data ; Germany ; Freshwater ; Identification of Pollutants ; Sewage ; General (556) ; General ; General ; Cluster Analysis ; Discharge-Nitrate Concentration Relationship ; Hydrological Flowpaths ; Model Calibration ; Nitrate Stable Isotopes ; Self-Organizing Feature Maps;
    ISSN: 0029-1277
    ISSN: 19989563
    E-ISSN: 22247955
    Source: CrossRef
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  • 2
    Language: English
    In: Environmental Earth Sciences, 2013, Vol.69(2), pp.381-393
    Description: In this study near-continuous time series of nitrate, electrical conductivity, and discharge were used to identify the dominating hydrological mechanisms that control nitrate export dynamics in two agricultural catchments. The main goal was to assess relationships between contrasting event based as well as long-term nitrate transport behaviour and catchment hydrology. Data records were obtained from online probes that allow field based high-frequency analyses over long time periods. The catchments of the Ammer River (southwestern Germany) and the Weida River (eastern Germany) are similar with respect to size (~100 km²), morphology, and climate and are dominated by agricultural use. Main differences are the stronger urbanization and the occurrence of karstic rocks in the Ammer catchment. Nitrate concentrations are high in water of both streams and range mostly between 20 and 50 mg l −1 . Nitrate export in the Ammer catchment is dominated by baseflow and a minor second, diluting runoff component generated in urbanized areas. In contrast, nitrate dynamics of the Weida catchment is governed by the interplay of at least three runoff components, while the largest amount of nitrate is mobilized intermittently by a delayed fast component generated in the catchment’s soils during wet conditions. These interpretations, derived with one online probe at the outlet of each catchment, are well in line with the former modeling results. This study shows that high-resolution data obtained by online techniques offers a large potential to improve the conceptualization of dominating flow and transport processes at catchment scales at relatively low costs and effort.
    Keywords: Nitrate export ; Catchment ; Hydrology ; High-frequency monitoring ; Online probe
    ISSN: 1866-6280
    E-ISSN: 1866-6299
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  • 3
    Language: English
    In: Environmental Earth Sciences, 2013, Vol.69(2), pp.317-333
    Description: Sustainable water quality management requires a profound understanding of water fluxes (precipitation, run-off, recharge, etc.) and solute turnover such as retention, reaction, transformation, etc. at the catchment or landscape scale. The Water and Earth System Science competence cluster (WESS, http://www.wess.info/ ) aims at a holistic analysis of the water cycle coupled to reactive solute transport, including soil–plant–atmosphere and groundwater–surface water interactions. To facilitate exploring the impact of land-use and climate changes on water cycling and water quality, special emphasis is placed on feedbacks between the atmosphere, the land surface, and the subsurface. A major challenge lies in bridging the scales in monitoring and modeling of surface/subsurface versus atmospheric processes. The field work follows the approach of contrasting catchments, i.e. neighboring watersheds with different land use or similar watersheds with different climate. This paper introduces the featured catchments and explains methodologies of WESS by selected examples.
    Keywords: Water and solute fluxes ; Water quality ; Catchments ; Land-surface atmosphere exchange ; Processes and feedbacks ; Modeling ; Monitoring
    ISSN: 1866-6280
    E-ISSN: 1866-6299
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  • 4
    In: Water Resources Research, December 2006, Vol.42(12), pp.n/a-n/a
    Description: Nitrate pollution from agricultural activities often persistently affects groundwater quality due to long residence times in the vadose and saturated zone. In this study we used a lumped parameter approach to estimate the residence time of groundwater and nitrate from the agriculturally used Jahna‐Aue drinking water catchment in Saxonia, Germany. Inverse modeling of measured concentrations of tritium and tritiogenic He revealed consistent mean residence times between 25 and 50 years for the young, nitrate‐rich groundwater component, and high contributions (〉75%) of an old, tracer‐free, and nitrate‐poor groundwater. The obtained age distributions are in accordance with the complex hydrogeological situation of the investigated catchment, suggesting that the shallow and therefore most vulnerable part of the aquifer is not connected to the production wells. High residence times are supported by low concentrations of CFCs and by radiogenic He as an independent age indicator. CFC concentrations only yield lower age limits due to identified problems with CFC contamination. Using the tracer‐calibrated age distributions, future nitrate concentrations in the production wells most probably will remain below the drinking water limit because of the high dilution with old, nitrate‐poor groundwater. Deterioration of the groundwater quality with respect to nitrate may occur if the groundwater pumping regime is changed so that the fraction of the younger, nitrate‐bearing water is increased.
    Keywords: Groundwater Age Distribution ; Lumped Parameter Model ; Nitrate Pollution ; Nitrate Stable Isotopes ; Tritium/He
    ISSN: 0043-1397
    E-ISSN: 1944-7973
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