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| Titel |
Isotopic investigation of the discharge driven nitrogen dynamics in a mesoscale river catchment |
| VerfasserIn |
Christin Mueller, Matthias Zink, Ronald Krieg, Michael Rode, Ralf Merz, Kay Knöller |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250131860
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| Publikation (Nr.) |
 EGU/EGU2016-12308.pdf |
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| Zusammenfassung |
| Nitrate in surface and groundwater has increased in the last decades due to landuse change,
the application of different fertilizer for agricultural landuse and industrial dust in the
atmospheric deposition. Increasing nitrate concentrations have a major impact on
eutrophication, especially for coastal ecosystems. Therefore it is important to quantify
potential nitrate sources and determine nitrate process dynamics with its drivers. The Bode
River catchment (total size of 3200 m2) in the Harz Mountains in Germany was intensively
investigated by a monitoring approach with 133 sampling points representing the same
number of sub-catchments for a period of two years. The area is characterized by a strong
anthropogenic gradient, with forest conservation areas in the mountain region, grassland, and
intensively mixed farming in the lowlands. Consecutive discharge simulations by a mesoscale
hydrological model (mhM) allow a quantitative analysis of nitrate fluxes for all
observed tributaries. The investigation of nitrate isotopic signatures for characteristic
landscape types allows the delineation of dominant NO3− sources: coniferous forests
are characterized by recycled nitrified soil nitrogen; grassland is mainly impacted
by organic fertilizer (manure) and nitrified soil-N; in agricultural land use areas
nitrate predominantly derives from synthetic fertilizer application. Besides source
delineation, the relationship between runoff and nitrate dynamics was analyzed
for the entire Bode river catchment and, more detailed, for one major tributary
with minor artificial reservoirs (Selke River). Thereby, it becomes apparent that
nitrate isotopic variations increase with decreasing discharge. This effect might be
due to a local, more intense impact of bacterial denitrification under low discharge
conditions (higher residence time) in the anoxic soil zone, in the groundwater that
discharges into the river and in the hyporheic zone. Generally, δ15N and δ18Oof nitrate
decrease with increasing runoff, which can be caused by a preferential wash-out
of more easily mobilizable, isotopically lighter fractions of the soil nitrate pool. |
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