Lookup NU author(s): Robert Spencer,
Dr Guenther Uher,
Professor Robert Upstill-Goddard
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Nitrogen isotope ratios (δ15N) were used to help elucidate the sources and fate of ammonium (NH4+) and nitrate (NO3-) in two northeastern English estuaries. The dominant feature of NH4+ in the heavily urbanised Tyne estuary was a plume arising from a single point source; a large sewage works. Although NH4+ concentrations (ranging from 30-150 μM) near the sewage outfall varied considerably between surveys, the sewage-derived δ15N-NH4+ signature was remarkably constant (+ 10.6 ± 0.5‰) and could be tracked across the estuary. As indirectly supported by 15N-depleted δ15N-NO3- values observed close to the mouth of the Tyne, this sewage-derived NH4+ was thought to initiate lower estuarine and coastal zone nitrification. In the more rural Tweed, NH4+ concentrations were low (< 7 μM) compared to those in the Tyne and δ15N-NH4+ values were consistent with mixing between riverine and marine sources. The dominant form of dissolved inorganic nitrogen (DIN) in the Tweed was agricultural soil-derived NO3-. A decrease in riverine NO3- flux during the summer coinciding with an increase in δ15N-NO3- values was mainly attributed to enhanced watershed nutrient processing. In the Tyne, where agricultural inputs are less important compared to the Tweed, light δ15N-NO3- (ca. 0‰) detected in the estuary during one winter survey pointed to a larger contribution from precipitation-derived NO3- during high river discharge. Regardless of the dominant sources, in both estuaries most of the variability in DIN concentrations and δ15N values was explained by simple end-member mixing models, implying very little estuarine processing. © 2006 Elsevier B.V. All rights reserved.
Author(s): Ahad JME, Ganeshram RS, Spencer RGM, Uher G, Upstill-Goddard RC, Cowie GL
Publication type: Article
Publication status: Published
Journal: Science of the Total Environment
ISSN (print): 0048-9697
ISSN (electronic): 1879-1026
PubMed id: 17097720
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