Rivers in cold 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

The main common character of rivers in cold ecoregions is cool water temperature throughout the year, which supports high oxygen concentrations. Woody riparian vegetation is often naturally lacking, and the river bed may be covered by ice and snow for several months. Consequently macrophytes and benthic algae are poorly developed or completely lacking in winter. Fish and invertebrates are adapted to cold temperatures, their life cycles being synchronised with the ice-free period.

Nevertheless, most species are widely distributed in Northern Europe, since time since the Pleistocene was not sufficient for the development of endemic species.

Human impact

Rivers in cold ecoregions belong to the least impacted aquatic ecosystems in Europe. Main human impacts are due to atmospheric pollution (particularly acidification) and intense forestry. Organic pollution and eutrophication are more local problems.

Climate change impact

The impact of Climate Change, however, will be severe. Extension of the ice-free period and increased water temperature will lead to enhance primary production and eutrophication, desynchronise life cycles and cause physiological problems for cold-adapted species.