La presión sobre los ríos europeos

New study reveals Europe’s rivers under pressure

The largest investigation to date into the extent of human-induced pressure on European rivers concludes that around 80% of rivers are affected by water pollution, water removal for hydropower and irrigation, structural alterations and the impact of dams, with 12% suffering from impacts of all four.

Human-induced alterations to rivers can have serious consequences for ahttp://ec.europa.eu/environment/integration/research/newsalert/latest_alerts.htmquatic life by degrading habitat and affecting the chemical balance of the water. The impact of human pressures on rivers is assessed as part of the Water Framework Directive (WFD)¹, but studies are typically carried out at local or regional scales, which makes it difficult to consistently identify Europe-wide patterns.

In the new study, partly conducted under the EU EFI+ project² and which is the first to be carried out at the European scale, scientists analysed data from a total of 9,330 sites on approximately 3,100 rivers in 14 European countries. The scientists scored each site in terms of the strength of disturbance according to 15 separate criteria, each known to increase mortality in fish and invertebrates through habitat loss, stranding and desiccation (when species become trapped in pools that dry up), sediment disturbance and oxygen depletion, among other effects.

The 15 criteria were grouped into four pressure types: water quality (i.e. acidification, eutrophication, organic pollution), hydrology (i.e. artificial fluctuation in flow speed induced by hydroelectric plants, removal of water for hydropower generation, irrigation and drinking water), morphology (i.e. altered channel form, river bed degradation, dykes for flood protection) and connectivity (interruptions of migratory pathway for fishes by dams).

The scientists then combined the scores for each pressure category into a Global Pressure Index, which ranked each site on a scale of 0-20. This not only identified the dominant pressures in European rivers, but also where multiple pressures exist, i.e. more than one of the four categories. Multiple pressures often interact, sometimes amplifying the effect of individual pressures.

The results suggest that just 21% of rivers remained unaffected by human-induced pressures. Water quality pressures were found in 59% of the sites, hydrological pressures in 41% and morphological pressures in 39%. Connectivity pressures within 10km of each river were found in 35% of the sites. However, over the whole area between the sampling site and the mouth of the river into the sea, connectivity pressures were found in 85% of sites.

In total, 47% of sites suffered multiple impacts; 29% were affected by two pressure types, 28% were affected by three types and 12% were affected by all four pressure types. The distribution of multiple pressures varied with geographical region; the worst affected regions were the Central highlands (which are mainly in Austria and Germany), the Hungarian lowlands, the Western highlands (in France and Switzerland) and the Western plains (which are predominantly in France). The results also revealed that sites near the source of the river were generally less affected than lowland rivers, where multiple impacts were more common.

Human-induced pressures are likely to intensify in the future. The increased number of extreme weather events will result in greater river flow variation, and there will be growing demand for water for agriculture and energy. This study represents a baseline from which future trends can be monitored and evaluated under the requirements of the WFD, say the researchers, and provides information that could help river managers identify the most vulnerable areas and prioritise strategies for recovery.

1. See: http://ec.europa.eu/environment/water/water-framework/index_en.html
2. EFI+ (Improvement and Spatial Extension of the European Fish Index) was supported by the European Commission under the Sixth Framework Programme.
   See: http://efi-plus.boku.ac.at/

Source: Schinegger, R., Trautwein, C., Melcher, A. & Schmutz, S. (2011). Multiple human pressures and their spatial patterns in European running waters. Water and Environment Journal. DOI 10.1111/J.1747-6593.2011.00285.x.
Contact: rafaela.schinegger@boku.ac.at
Theme(s): Water

Fuente: Science for Environment Policy