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| Titel |
The effects of riparian forestry on invertebrate drift and brown trout in upland streams of contrasting acidity |
| VerfasserIn |
S. J. Ormerod, M. E. Jones, M. C. Jones, D. R. Phillips |
| 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 ; 8, no. 3 ; Nr. 8, no. 3, S.578-588 |
| Datensatznummer |
250005625
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| Publikation (Nr.) |
 copernicus.org/hess-8-578-2004.pdf |
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| Zusammenfassung |
| Variations in macroinvertebrate drift and benthic invertebrate abundance were
assessed in 30 upland Welsh streams of varying acidity (pH < 5.7 or pH.> 6.0) and
riparian land-use (conifer, moorland or native broadleaf). The consequences for the diet
and condition of wild brown trout Salmo trutta were also assessed. As expected
from previous studies, there were significant reductions in benthic invertebrate abundance,
aquatic drift density (by >60%), aquatic drift biomass (by >35%), total drift density
(by >35%) and total drift biomass (by >20%) at acid sites by comparison with
circumneutral sites due largely to the scarcity of mayflies. Absolute drift from
terrestrial sources was unrelated to stream pH but formed a significantly greater
proportion of total drift at acid sites (30-65% of density) than at circumneutral sites
(20-40%) as aquatic contributions declined. Most of this apparent land use effect
reflected significantly increased terrestrial drift under broadleaves. There was no
significant reduction in terrestrial or aquatic drift at conifer forest sites
per se after accounting for low pH. Trout diet varied substantially between locations
partly reflecting variations in drift: significantly fewer mayflies and stoneflies were
eaten at acid sites, and significantly more terrestrial prey were eaten under
broadleaves. However, acidity did not reduce trout condition or gut-fullness.
Unexpectedly, trout condition was significantly enhanced at conifer sites, irrespective
of their pH. Hence, acidity has greater effects on the benthic abundance and drift
density of invertebrates in upland streams than does riparian land use. However, trout
forage flexibly enough to offset any possible food deficit, for example by switching to
chironomids and terrestrial invertebrates. Enhanced terrestrial contributions to
invertebrate drift from riparian broadleaf trees may be important in supplementing
foraging opportunities for trout where aquatic prey are scarce. These data illustrate
the value of native tree species in riparian locations in upland Britain and the energy
subsidy they provide might well be disproportionately important for otherwise
impoverished acid streams
Keywords: brown trout, land-use, acidification, drift, forestry, streams |
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