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Long-term declines in stream and river inorganic nitrogen (N) export correspond to forest change
Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
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2016 (English)In: Ecological Applications, ISSN 1051-0761, E-ISSN 1939-5582, Vol. 26, no 2, 545-556 p.Article in journal (Refereed) PublishedText
Abstract [en]

Human activities have exerted a powerful influence on the biogeochemical cycles of nitrogen (N) and carbon (C) and drive changes that can be a challenge to predict given the influence of multiple environmental stressors. This study focused on understanding how land management and climate change have together influenced terrestrial N storage and watershed inorganic N export across boreal and sub-arctic landscapes in northern Sweden. Using long-term discharge and nutrient concentration data that have been collected continuously for over three decades, we calculated the hydrologic inorganic N export from nine watersheds in this region. We found a consistent decline in inorganic N export from 1985 to 2011 over the entire region from both small and large watersheds, despite the absence of any long-term trend in river discharge during this period. The steepest declines in inorganic N export were observed during the growing season, consistent with the hypothesis that observed changes are biologically mediated and are not the result of changes in long-term hydrology. Concurrent with the decrease in inorganic N export, we report sustained increases in terrestrial N accumulation in forest biomass and soils across northern Sweden. Given the close communication of nutrient and energy stores between plants, soils, and waters, our results indicate a regional tightening of the N cycle in an already N-limited environment as a result of changes in forest management and climate-mediated growth increases. Our results are consistent with declining inorganic N efflux previously reported from small headwater streams in other ecosystems and shed new light on the mechanisms controlling these patterns by identifying corresponding shifts in the terrestrial N balance, which have been altered by a combination of management activities and climate change.

Place, publisher, year, edition, pages
2016. Vol. 26, no 2, 545-556 p.
Keyword [en]
boreal forest, climate-mediated growth increases, forest management, soil N storage, Sweden, rrestrial biogeochemistry, terrestrial N retention
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URN: urn:nbn:se:umu:diva-120366DOI: 10.1890/14-2413.1ISI: 000374118700018OAI: diva2:928676
Available from: 2016-05-16 Created: 2016-05-16 Last updated: 2016-05-16Bibliographically approved

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