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| Titel |
The impacts of conifer harvesting on runoff water quality: a regional survey for Wales |
| VerfasserIn |
C. Neal, B. Reynolds, J. Wilkinson, T. Hill, M. Neal, S. Hill, M. Harrow |
| 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 ; 2, no. 2/3 ; Nr. 2, no. 2/3, S.323-344 |
| Datensatznummer |
250000358
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| Publikation (Nr.) |
 copernicus.org/hess-2-323-1998.pdf |
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| Zusammenfassung |
Major, minor and trace element chemistry of
runoff at stormflow and baseflow from 67 catchments (2 to 5 ha in area) has been
determined to investigate the effects of clear felling and replanting of conifers on
stream water quality across Wales. Samples, collected by local forestry workers (Forest
Enterprise staff) on a campaign basis on up to eight occasions, were for 16 mature first
rotation standing forest: the remainder represented areas completely clear felled from
less than one to up to forty years previously. As the waters drain acidic and acid
sensitive soils, acidic runoff is often encountered. However, higher pH values with
associated positive alkalinities and base cation enrichments are observed due to the
influence of weathering reactions within the bedrock. There is little systematic variation
in water quality between baseflow and stormflow for each site indicating a complex and
erratic contribution of waters from the soil and underlying parent material. 80% or more
of the data points show hardly any changes with felling time, but there are a few outlier
points with much higher concentrations that provide important information on the processes
operative. The clearest outlier felling response is for nitrate at five of the more
recently felled sites on brown earth, gley and podzolic soil types. ANC, the prime
indicator of stream acidity, shows a diverse response from both high to low outlier values
(>+400 to -300 μEq/l). In parallel to nitrate, aluminium, potassium and barium
concentrations are higher in waters sampled up to 4 years post felling, but the time
series response is even less clear than that for nitrate. Cadmium, zinc and lead and
lanthanides/actinides show large variations from site to site due to localized vein
ore-mineralization in the underlying bedrock.
The survey provides a strong indication that forest harvesting can have
marked local effects on some chemical components of runoff for the first four years after
felling but that this is confined to a small number of sites where nitrate production and
aluminium leaching are high. In general, deforestation leads to a reversal of
acidification when the nitrate pulse is low. The variability in water quality from
catchment to catchment is too high for generalized conclusions to be made over the extent
of the potential changes from site to site. The value of an organised campaign of
opportunistic sampling using an infrastructure of enthusiastic staff from regionally
dispersed organisations associated with environmental matters (in this case the forestry
industry) is highlighted. |
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