Rivers in warm ecoregions

– Water type description –

• Rivers in general

  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.

The pristine status

In the Mediterranean the majority of small rivers are to some degree periodical; in summer, the river is a chain of standing pools while all flowing sections disappear or the river may dry out completely. The species are adapted correspondingly, with many insects having a diapause in the terrestrial adult stage. Mediterranean rivers belong to the most species rich aquatic ecosystems in Europe, with many endemic species which are often restricted to a single mountain range.

Human impact

Besides organic pollution and eutrophication the main human impact is water abstraction, which prolongs the period of low (or no) flow. Particularly water use for irrigation purposes has lead to the almost complete disappearance of small streams from many regions.

Climate change impact

Higher water temperature and transpiration, together with an increased demand for freshwater, are the main expected impacts of Climate Change on Mediterranean streams. This will add to the problem of low flow and disappearing rivers and increase eutrophication.