Dominance of biologically produced nitrate in upland waters of Great Britain indicated by stable isotopes

Curtis, Chris J.; Heaton, Timothy H.E.; Simpson, Gavin L.; Evans, Chris D.; Shilland, James; Turner, Simon. 2012 Dominance of biologically produced nitrate in upland waters of Great Britain indicated by stable isotopes. Biogeochemistry, 111 (1-3). 535-554.

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Atmospheric deposition of nitrogen (N) compounds is the major source of anthropogenic N to most upland ecosystems, where leaching of nitrate (NO3−) into surface waters contributes to eutrophication and acidification as well as indicating an excess of N in the terrestrial catchment ecosystems. Natural abundance stable isotopes ratios, 15N/14N and 18O/16O (the “dual isotope” technique) have previously been used in biogeochemical studies of alpine and forested ecosystems to demonstrate that most of the NO3− in upland surface waters has been microbially produced. Here we present an application of the technique to four moorland catchments in the British uplands including a comparison of lakes and their stream inflows at two sites. The NO3− concentrations of bulk deposition and surface waters at three sites are very similar. While noting the constraints imposed by uncertainty in the precise δ18O value for microbial NO3−, however, we estimate that 79–98% of the annual mean NO3− has been microbially produced. Direct leaching of atmospheric NO3− is a minor component of catchment NO3− export, although greater than in many similar studies in forested watersheds. A greater proportion of atmospheric NO3− is seen in the two lake sites relative to their inflow streams, demonstrating the importance of direct NO3− deposition to lake surfaces in catchments where terrestrial ecosystems intercept a large proportion of deposited N. The dominance of microbial sources of NO3− in upland waters suggests that reduced and oxidised N deposition may have similar implications in terms of contributing to NO3− leaching.

Item Type: Publication - Article
Digital Object Identifier (DOI):
Programmes: BGS Programmes 2010 > NERC Isotope Geoscience Laboratory
CEH Topics & Objectives 2009 - 2012 > Biogeochemistry
UKCEH and CEH Sections/Science Areas: Emmett
ISSN: 0168-2563
Additional Information. Not used in RCUK Gateway to Research.: The attached document is the author’s final manuscript version of the journal article, incorporating any revisions agreed during the peer review process. Some differences between this and the publisher’s version remain. You are advised to consult the publisher’s version if you wish to cite from this article. The final publication is available at
Additional Keywords: nitrate leaching, nitrification, 18O, 15N, uplands, lakes, N deposition
Date made live: 25 Jan 2012 14:53 +0 (UTC)

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