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| Titel |
Effects of decreasing acid deposition and climate change on acid extremes in an upland stream |
| VerfasserIn |
C. D. Evans, B. Reynolds, C. Hinton, S. Hughes, D. Norris, S. Grant, B. Williams |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1027-5606
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| Digitales Dokument |
URL |
| Erschienen |
In: Hydrology and Earth System Sciences ; 12, no. 2 ; Nr. 12, no. 2 (2008-03-05), S.337-351 |
| Datensatznummer |
250010558
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| Publikation (Nr.) |
 copernicus.org/hess-12-337-2008.pdf |
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| Zusammenfassung |
| This study assesses the major chemical processes leading to acid extremes in
a small, moorland stream in mid-Wales, UK, which has been monitored since
1979. Results suggest that base cation (mainly calcium) dilution, the
"sea-salt effect", and elevated nitrate pulses, are the major causes of
seasonal/episodic minima in acid neutralising capacity (ANC), and that the
relative importance of these drivers has remained approximately constant
during 25 years of decreasing acid deposition and associated long-term
chemical recovery. Many of the chemical variations causing short-term
reductions in stream acidity, particularly base cation dilution and organic
acid increases, are closely related to changes in water-flowpath and
therefore to stream discharge. Changes in the observed pH-discharge
relationship over time indicate that high-flow pH has increased more rapidly
than mean-flow pH, and therefore that episodes have decreased in magnitude
since 1980. However a two-box application of the dynamic model MAGIC, whilst
reproducing this trend, suggests that it will not persist in the long term,
with mean ANC continuing to increase until 2100, but the ANC of the upper
soil (the source of relatively acid water during high-flow episodes)
stabilising close to zero beyond 2030. With climate change predicted to lead
to an increase in maximum flows in the latter half of the century, high-flow
related acid episodes may actually become more rather than less severe in
the long term, although the model suggests that this effect may be small.
Two other predicted climatic changes could also detrimentally impact on acid
episodes: increased severity of winter "sea-salt" episodes due to higher
wind speeds during winter storms; and larger sulphate pulses due to
oxidation of reduced sulphur held in organic soils, during more extreme
summer droughts. At the Gwy, the near-coastal location and relatively small
extent of peat soils suggest that sea-salt episodes may have the greatest
influence. |
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