, Volume 91, Issue 1, pp 13-35

First online:

Does elevated nitrogen deposition or ecosystem recovery from acidification drive increased dissolved organic carbon loss from upland soil? A review of evidence from field nitrogen addition experiments

  • Chris D. EvansAffiliated withCentre for Ecology and Hydrology, Environment Centre Wales Email author 
  • , Christine L. GoodaleAffiliated withDepartment of Ecology and Evolutionary Biology, Cornell University
  • , Simon J. M. CapornAffiliated withDepartment of Environmental and Geographical Sciences, Manchester Metropolitan University
  • , Nancy B. DiseAffiliated withDepartment of Environmental and Geographical Sciences, Manchester Metropolitan University
  • , Bridget A. EmmettAffiliated withCentre for Ecology and Hydrology, Environment Centre Wales
  • , Ivan J. FernandezAffiliated withDepartment of Ecology and Environmental Sciences, University of Maine
  • , Chris D. FieldAffiliated withDepartment of Environmental and Geographical Sciences, Manchester Metropolitan University
  • , Stuart E. G. FindlayAffiliated withInstitute of Ecosystem Studies
  • , Gary M. LovettAffiliated withInstitute of Ecosystem Studies
    • , Henning MeesenburgAffiliated withForest Research Institute of Lower Saxony
    • , Filip MoldanAffiliated withIVL Swedish Environmental Research Institute
    • , Lucy J. SheppardAffiliated withCentre for Ecology and Hydrology

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Dissolved organic carbon (DOC) concentrations have risen in upland waters across large areas of Europe and North America. Two proposed drivers of these increases are (1) deposition of atmospheric pollutant nitrogen (N) with consequent effects on plant and decomposer carbon dynamics, and (2) soil recovery from acidification associated with decreasing sulphur deposition. Examination of 12 European and North American field N addition experiments showed inconsistent (positive, neutral, and negative) responses of DOC to N addition. However, responses were linked to the form of N added and to resulting changes in soil acidity. Sodium nitrate additions consistently increased DOC, whereas ammonium salts additions usually decreased DOC. Leachate chemistry was used to calculate an index of “ANC forcing” of the effect of fertilization on the acid-base balance, which showed that DOC increased in response to all de-acidifying N additions, and decreased in response to all but three acidifying N additions. Exceptions occurred at two sites where N additions caused tree mortality, and one experiment located on an older, unglaciated soil with high anion adsorption capacity. We conclude that collectively these experiments do not provide clear support for the role of N deposition as the sole driver of rising DOC, but are largely consistent with an acidity-change mechanism. It is however possible that the unintended effect of acidity change on DOC mobility masks genuine effects of experimental N enrichment on DOC production and degradation. We suggest that there is a need, more generally, for interpretation of N manipulation experiments to take account of the effects that experimentally-induced changes in acidity, rather than elevated N per se, may have on ecosystem biogeochemistry.


Nitrogen Acidity ANC Forcing Atmospheric deposition Dissolved organic carbon Manipulation experiments