Journal
ENVIRONMENTAL POLLUTION
Volume 156, Issue 3, Pages 636-643Publisher
ELSEVIER SCI LTD
DOI: 10.1016/j.envpol.2008.06.019
Keywords
Nitrate; Atmospheric deposition; Nitrogen saturation; N-15 tracer; Immobilisation
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Funding
- UK Department of the Environment, Food and Rural Affairs [CPEA 17]
- NERC Stable Isotope Facility of the Centre for Ecology and Hydrology, Lancaster
- Natural Environment Research Council [ceh010023, lsmsf010003] Funding Source: researchfish
- NERC [lsmsf010003] Funding Source: UKRI
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Nitrate (NO3-) is often observed in surface waters draining terrestrial ecosystems that remain strongly nitrogen (N) limited. It has been suggested that this occurs due to hydrological bypassing of soil or vegetation N retention, particularly during high flows. To test this hypothesis, artificial rain events were applied to 12 replicate soil blocks on a Welsh podzolic acid grassland hillslope, labelled with N-15-enriched NO3- and a conservative bromide (Br-) tracer. On average, 31% of tracer-labelled water was recovered within 4 h, mostly as mineral horizon lateral flow, indicating rapid vertical water transfer through the organic horizon via preferential flowpaths. However, on average only 6% of N-15-labelled NO3- was recovered. Around 80% of added NO3- was thus rapidly immobilised, probably by microbial communities present on the surfaces of preferential flowpaths. Transitory exceedance of microbial N-uptake capacity during periods of high water and N flux may therefore provide a mechanism for NO3- leaching. (C) 2008 Elsevier Ltd. All rights reserved.
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