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| Titel |
Spatial variability of nitrate concentration in lakes in Snowdonia, North Wales, UK |
| VerfasserIn |
M. R. Kernan, T. E. H. Allott |
| 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 ; 3, no. 3 ; Nr. 3, no. 3, S.395-408 |
| Datensatznummer |
250001090
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| Publikation (Nr.) |
 copernicus.org/hess-3-395-1999.pdf |
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| Zusammenfassung |
| At a regional scale, high nitrate (NO3‾)
concentrations in upland surface
waters generally occur in tandem with high nitrogen (N) deposition levels.
However, significant differences in the patterns of surface water NO3‾
concentration have been observed within areas of similar N deposition yet
relatively few studies have been undertaken which examine within-region
variation of NO3‾ concentrations. A study of
76 lakes in Snowdonia, north Wales,
an area of high deposition and sensitive catchments, was undertaken to assess
variation in surface water NO3‾ concentration across
a 20 x 20 km grid square
and to identify catchments vulnerable to NO3‾ leaching.
Nitrate concentrations
vary considerably, particularly during winter when values range from 0.7 to
70 μeq l-1. Although retention by vegetation and soil microbes in summer reduces
the amount of NO3‾ reaching the lakes, 37 % of sites are
characterised by NO3‾
concentrations greater then 4 μeq l-1. The elevated concentrations occurring in
summer suggests that N breakthrough has occurred. By examining the ratio of NO3‾
to total strong acid anions, it is shown that NO3‾ contributes significantly to
freshwater acidity, particularly during the winter. Redundancy analysis shows
that NO3‾ leaching is greatest, both in winter and summer, in catchments with
high proportions of bare rock where soil and vegetation cover is limited.
Nitrogen cycling in these catchments, generally at higher altitudes, may no
longer be governed by seasonal biological controls. They are likely to be
saturated with respect to nitrogen (i.e. incapable of further N retention)
as a result of the elevated deposition levels in the area. The contribution of
NO3‾ to acidity is also greatest at these sites. In winter, significant positive
relationships are also evident between NO3‾ concentration and soil pH and
coniferous woodland. The study demonstrates the importance of catchment factors
in modifying the relationship between N deposition and N leaching in upland
catchments. |
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