![Hier klicken, um den Treffer aus der Auswahl zu entfernen](images/unchecked.gif) |
Titel |
Using the N2/Ar-Method to check modelled diffuse NO3¯ emissions from soils into the groundwater of Lower Saxony (Germany) |
VerfasserIn |
Lisa Krienen, Heinrich Höper, Wolfram Eschenbach, Reinhard Well, Jörg Elbracht |
Konferenz |
EGU General Assembly 2013
|
Medientyp |
Artikel
|
Sprache |
Englisch
|
Digitales Dokument |
PDF |
Erschienen |
In: GRA - Volume 15 (2013) |
Datensatznummer |
250080683
|
|
|
|
Zusammenfassung |
Diffuse NO3ˉ emissions derived from agricultural N surpluses are the main cause of NO3ˉ pollution of aquifers and open water bodies. Denitrification is the key process for the attenuation of these anthropogenic NO3ˉ concentrations in soils and groundwater. Since the greenhouse gas N2O is an obligate intermediate of denitrification this process is also a major regulator of N2O emissions from soils and indirect N2O fluxes from aquifers and open water bodies which result from NO3ˉ-leaching. Up to now the denitrification potential of soils and the potential NO3ˉ concentration in the groundwater recharge are modelled from agricultural N-surpluses, water balances (GROWA) and soil properties (DENUZ) (Wendland et al. 2009) (LBEG 2008).
In this study we compare modelled NO3ˉ emissions (pot-NO3ˉ) (DENUZ) to the groundwater recharge with the calculated initial NO3ˉ concentrations in the groundwater at time of groundwater recharge (NO3ˉt0) (N2/Ar-method (Weymann et al. 2008)). NO3ˉt0 can be calculated from the measurement of dissolved gases N2, N2O, Ar and NO3ˉ concentrations in groundwater samples.
We analysed groundwater samples from 534 groundwater monitoring wells throughout Lower-Saxony (Germany). Median NO3ˉ and NO3ˉt0 concentrations were 0,4 and 29 mg NO3ˉ lˉ1 respectively, showing that considerable proportions of the anthropogenic N-surplus is denitrified within the saturated zone.
First results showed a good agreement between measure and modelled NO3ˉ emissions for areas of coastal marshes in the North of Lower-Saxony (predominantly Fluvisols). Medians of measured and modelled NO3ˉ emissions are 12,5 mg NO3ˉt0 lˉ1 and 0,3 mg pot-NO3ˉ lˉ1 (mean values 20 mg lˉ1 NO3ˉ pot and 9,3 mg lˉ1 NO3ˉt0), respectively. Compared to the coastal marshes and in accordance with modelled pot-NO3ˉ concentrations our measurements show small-scale spatial heterogeneities of NO3ˉt0 concentrations in soil regions where the dominant parent material of soils are glacio fluviatile and moraine deposits (predominantly Podzols, Cambisols and Gleysols) in Lower-Saxony. In these regions the median of measured NO3ˉt0 concentrations was between 29 and 38 mg NO3ˉ lˉ1 and on average 25 to 30 mg NO3ˉ lˉ1 below the modelled NO3ˉ lˉ1 concentrations. To further compare the modelled NO3ˉ emissions (pot-NO3ˉ) with results of the N2/Ar-method (NO3ˉt0 values) we select groundwater monitoring wells with more homogenous soil properties, soil water residence times in their catchment areas.
We expect that further analysis will help to validate existing denitrification models. NO3ˉt0 values might then be used as a lower boundary condition if denitrification in soils is modelled.
References:
Wendland, F., Behrendt, H., Gömann, H., Hirt, U., Kreins, P., Kuhn, U., Kunkel, R., and Tetzlaff, B. (2009): Determination of nitrogen reduction levels necessary to reach groundwater quality targets in large river basins: the Weser basin case study, Germany, Nutr. Cycl. Agroecosyst., 85, 63-78, 10.1007/s10705-009-9248-9.
Weymann, D., Well, R., Flessa, H., von der Heide, C., Deurer, M., Meyer, K., Konrad, C., and Walther, W.(2008): Groundwater N2O emission factors of nitrate-contaminated aquifers as derived from denitrification progress and N2O accumulation, Biogeosciences, 5, 1215-1226.
LBEG (Landesamt für Bergbau, Energie und Geologie (2008): Nutzung bodenkundlich-hydrogeologischer Informationen zur Ausweisung von Zielgebieten für den Grundwasserschutz, Geoberichte 9. |
|
|
|
|
|