River ecosystems
A river forms a continuum, along which many parameters change: discharge, current, sediment and temperature, food sources as well as species composition. Small mountain rivers mainly have single channels, more downstream the channel changes to braided and meandering patterns. Floodplain and river are closely interlinked, for the main energy source for the macroinvertebrate and ultimately the fish community are leaves and wood.
Like all other aquatic ecosystems in Europe river systems have been changed by a multitude of impacts. Small streams in mountain areas remained nevertheless relatively undisturbed; many small streams have never been severely polluted as almost all large rivers. Physical alterations in their catchments affect most European rivers, disrupt their continuum and the interactions between the stream and its terrestrial surroundings.
Obviously, Climate Change will worsen this situation by increasing water temperatures and associated parameters. It will contribute to a general upstream movement of river zones, particularly affecting species bound to small streams and springs, which can not move further upstream. Most fish of small rivers, especially the salmonids, are cold-adapted and will be particularly affected by rising temperatures.
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