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. 10.1007/s10533-011-9686-8

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Abstract/Summary

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:	Article
Identification Number/DOI:	10.1007/s10533-011-9686-8
Programmes:	BGS Programmes 2010 > NERC Isotope Geoscience Laboratory CEH Topics & Objectives 2009 onwards > Biogeochemistry
CEH Sections:	Emmett
ISSN:	0168-2563
Additional Keywords:	nitrate leaching, nitrification, 18O, 15N, uplands, lakes, N deposition
Date made live:	25 Jan 2012 14:53
URI:	http://nora.nerc.ac.uk/id/eprint/16506

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