Over 200,000 kilometers of river-fish habitat is lost to impoundments in Europe.

Abstract

We estimate over 200,000 km or 10% of previously free-flowing river habitat length has been lost due to impoundments, an amount equivalent to the entire length of rivers in Italy. This loss strongly depends on the biogeographical location and a type of impounding barrier. European rivers are disconnected by more than one million man-made barriers that physically limit or completely block aquatic species migration and contribute to the loss of freshwater habitats8. One of the pervasive effects of barriers is the one caused by impoundment, which directly modifies lotic (flowing) stretches of river into lentic (lake-like) habitats5. Depending on structure and composition of fish communities expected at the barrier location the biological consequences may vary. EU-wide analysis of fish communities observed at river sections with low human induced alteration resulted in a macrohabitat classification of European rivers into 15 river types with expected fish community structure. This set a baseline for assessing the impacts of six main barrier types (dams, weirs, sluices, culverts, ramps, and fords) on river fish habitats across Europe. The largest habitat losses are caused by dams, weirs and sluices in mountainous areas where fish most sensitive to ponding are expected. Although many impoundments are smaller than in lowlands their individual impacts are the greatest. Hence, regional variation in the magnitude of impoundment impact is not only a function of barrier height and density, but to large extent of biogeographical location and barrier type. Strategies for enhancing European riverine biodiversity should focus on prioritization of most sensitive regions and barrier types causing high degree of habitat fragmentation. This work is based on four novel methodological approaches: fish community grouping into habitat use guilds, continental river reference model for ecological sound river management, landscape scale application of physical habitat models and conceptual model of impoundment impacts on fish habitat.

A paradoxical bias in knowledge about Norwegian freshwater fishes: research efforts during 1980-2020

“…Water is diverted to a wide range of usages, waterways are fragmented by dams and other physical structures (Belletti et al 2020), and terrestrial infrastructures and usages leads to pollution of various kinds. This leads to loss of connectivity and also extensive loss of suitable habitat (Parasiewicz et al 2022). In addition, global climate changes may lead to changes in water temperature, stability and quality (Markovic et al 2017, Pilla et al 2020, Hébert et al 2021, Woolway et al 2021) and ice phenology (Sharma and Magnuson 2014, Sharma et al 2019, L'Abée-Lund et al 2021.…”