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| Titel |
The impact of run-off change on physical instream habitats and its response to river morphology |
| VerfasserIn |
Christoph Hauer, Helmut Habersack |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250037650
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| Zusammenfassung |
| Rivers have already been substantially altered by human activity. Channelization, flow
regulation, or changes in land use, especially urbanization, significantly alter the water
discharge, sediment transport, and morphology of rivers. The impacts of these anthropogenic
measures (disturbances) on river morphology and instream habitats were frequently
investigated by the scientific community over the last decades. However, there are forms of
disturbances (often induced by climate change) which cause at the beginning only a slight but
(over the years) a continuous degradation of aquatic habitats (and river morphology). In
the presented study the impact of such disturbances caused by climate change on
summer run-off was investigated within the Gr. Mühl River catchment, Austria. So far,
various studies have documented the impact of run-off change on river morphology
and/or sediment load. Further the impact of run-off change on aquatic ecology
(target fish species) have been documented throughout various scientific papers.
However, there is a lack of knowledge how (climate induced) run-off changes affect
instream aquatic habitats concerning various morphological patterns (e.g. riffle-pool
morphology vs. plane bed river). Thus, the aim of the presented study was to link the
impacts of climate change (e.g. reduced summer run-off) to various morphological
types (riffle-pool, plane bed) using habitat modelling (2-dimensional) as integrative
evaluation method. As target fish species sub-adult/adult grayling was selected due to the
fact, that Thymallus thymallus features especially high sensitivity in water depth
(microhabitat use). Further grayling was one the historically dominant fish species for the
hyporhithral catchment of the Gr. Mühl River. Within the catchment 80% of the total river
length are determined as plane bed river and 20 % as riffle-pool reaches (situated in
former fine material deposits). Six reaches (3 plane-bed, 3 riffle-pool) were selected
and surveyed by total station (Leica805) to derive high quality DTM-models for
modelling. Monitoring data of temperature (period: 1948 – 2006) and gauging data of
three stations (Vorderanger, period: 1966 – 2008; Furthmühle, period: 1951 – 2008;
Teufelmühle, period: 1951 - 2008) along the investigated reach were additionally
provided by the local government agencies. The results of the statistical testing (for
significant breakpoints in temperature trends) exhibited significant changes (p>95%)
for the seasons spring (year 1989) and summer (year 1990) (increase in regional
temperature). Simultaneously, the periods of run-off below statistically determined
low-flow thresholds increased significantly especially for summer periods (e.g. gauging
station Furthmühle: period 1951 – 1990: n = 684 days / 1990 – 2008: n = 760 days).
The impact of those intensified low flow conditions on subadult / adult grayling
were (and are) limiting available physical habitats especially within the plane-bed
sections (n=3). Only riffle-pool reaches exhibited suitable habitats (evaluated by
habitatmodelling) for these dry-periods. However, those riffle-pool reaches are rare
and randomly distributed over the 45 km river length (investigated reach). In the
presented study it could be figured out, that climate change affects instream fish
habitats not only by an increase in water temperatures, but also by limiting physical
habitats (in relation to various morphological types). Thus, the response of fish
(e.g. grayling) could be on the one hand an upstream migration due to the warmer
water temperatures (frequently documented) but on the other hand a downstream
migration caused by unsuitable habitats. This second finding should be seen as
one crucial point especially for the restoration of regulated rivers with respect to
climate change and to fulfil the aims of the European Water Framework Directive. |
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