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Hydrology and Earth System Sciences An interactive open-access journal of the European Geosciences Union
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Volume 12, issue 2
Hydrol. Earth Syst. Sci., 12, 393–403, 2008
https://doi.org/10.5194/hess-12-393-2008
© Author(s) 2008. This work is licensed under
the Creative Commons Attribution-NonCommercial-ShareAlike 2.5 License.

Special issue: Role of climate change in recovery of acidified surface waters...

Hydrol. Earth Syst. Sci., 12, 393–403, 2008
https://doi.org/10.5194/hess-12-393-2008
© Author(s) 2008. This work is licensed under
the Creative Commons Attribution-NonCommercial-ShareAlike 2.5 License.

  05 Mar 2008

05 Mar 2008

Winter climate affects long-term trends in stream water nitrate in acid-sensitive catchments in southern Norway

H. A. de Wit1, A. Hindar1, and L. Hole2 H. A. de Wit et al.
  • 1Norwegian Institute for Water Research (NIVA), Gaustadalléen 21, 0349 Oslo, Norway
  • 2Norwegian Institute for Air Research (NILU), P.O. Box 100, 2027 Kjeller, Norway

Abstract. Controls of stream water NO3 in mountainous and forested catchments are not thoroughly understood. Long-term trends in stream water NO3 are positive, neutral and negative, often apparently independent of trends in N deposition. Here, time series of NO3 in four small acid-sensitive catchments in southern Norway were analysed in order to identify likely drivers of long-term changes in NO3. In two sites, stream water NO3 export declined ca 50% over a period of 25 years while in the other sites NO3 export increased with roughly 20%. Discharge and N deposition alone were poor predictors of these trends. The most distinct trends in NO3 were found in winter and spring. Empirical models explained between 45% and 61% of the variation in weekly concentrations of NO3, and described both upward and downward seasonal trends tolerably well. Key explaining variables were snow depth, discharge, temperature and N deposition. All catchments showed reductions in snow depth and increases in winter discharge. In two inland catchments, located in moderate N deposition areas, these climatic changes appeared to drive the distinct decreases in winter and spring concentrations and fluxes of NO3. In a coast-near mountainous catchment in a low N deposition area, these climatic changes appeared to have the opposite effect, i.e. lead to increases in especially winter NO3. This suggests that the effect of a reduced snow pack may result in both decreased and increased catchment N leaching depending on interactions with N deposition, soil temperature regime and winter discharge.

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