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| Titel |
Upland streamwater nitrate dynamics across decadal to sub-daily timescales: a case study of Plynlimon, Wales |
| VerfasserIn |
S. J. Halliday, R. A. Skeffington, A. J. Wade, C. Neal, B. Reynolds, D. Norris, J. W. Kirchner |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1726-4170
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| Digitales Dokument |
URL |
| Erschienen |
In: Biogeosciences ; 10, no. 12 ; Nr. 10, no. 12 (2013-12-09), S.8013-8038 |
| Datensatznummer |
250085464
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| Publikation (Nr.) |
 copernicus.org/bg-10-8013-2013.pdf |
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| Zusammenfassung |
| Streamwater nitrate dynamics in the River Hafren, Plynlimon, mid-Wales were
investigated over decadal to sub-daily timescales using a range of
statistical techniques. Long-term data were derived from weekly grab samples
(1984–2010) and high-frequency data from 7-hourly samples (2007–2009) both
measured at two sites: a headwater stream draining moorland and a downstream
site below plantation forest. This study is one of the first to analyse
upland streamwater nitrate dynamics across such a wide range of timescales
and report on the principal mechanisms identified. The data analysis provided
no clear evidence that the long-term decline in streamwater nitrate
concentrations was related to a decline in atmospheric deposition alone,
because nitrogen deposition first increased and then decreased during the
study period. Increased streamwater temperature and denitrification may also
have contributed to the decline in stream nitrate concentrations, the former
through increased N uptake rates and the latter resultant from increased
dissolved organic carbon concentrations. Strong seasonal cycles, with
concentration minimums in the summer, were driven by seasonal flow minimums
and seasonal biological activity enhancing nitrate uptake. Complex diurnal
dynamics were observed, with seasonal changes in phase and amplitude of the
cycling, and the diurnal dynamics were variable along the river. At the
moorland site, a regular daily cycle, with minimum concentrations in the
early afternoon, corresponding with peak air temperatures, indicated the
importance of instream biological processing. At the downstream site, the
diurnal dynamics were a composite signal, resultant from advection,
dispersion and nitrate processing in the soils of the lower catchment. The
diurnal streamwater nitrate dynamics were also affected by drought
conditions. Enhanced diurnal cycling in Spring 2007 was attributed to
increased nitrate availability in the post-drought period as well as low flow
rates and high temperatures over this period. The combination of
high-frequency short-term measurements and long-term monitoring provides a
powerful tool for increasing understanding of the controls of element fluxes
and concentrations in surface waters. |
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