1.2M BARRIERS HINDER WATER FLOW IN EUROPEAN RIVERS

Free-flowing rivers are crucial harbingers and guardians of life. They not only provide humans with clean water for drinking, agriculture, and other economic activities, they also house around 40% of the world’s species of fish.

However, Europe’s rivers have become increasingly constricted due to dams, as well as many smaller, less visible barriers that, nevertheless, have a great impact due to their numbers, Tibi Puiu reported for ZME Science.

A new study that surveyed more than 2,700 kilometers of rivers in Europe said there are 1.2 million in-stream barriers across 36 European countries — 60% more than previously believed.

“People think about the impact of large dams but these are relatively uncommon. Most of the 1.2 million barriers that fragment Europe’s rivers are not large dams, but small structures that go unnoticed because they are hard to detect unless you go into the field and walk the rivers,” Carlos Garcia de Leaniz, a professor at the Department of Biosciences at Swansea University in the UK, told ZME Science.

Too small to be detected by satellites or Google maps, these seemingly harmless barriers — most of which were ramps and bed sills, weirs, and culverts — can be highly disruptive. Barriers as small as 20 cm in height can obstruct many species from crossing up and down the stream. Such barriers also disrupt the transport of sediment.

Initially, Garcia de Leaniz and colleagues were interested in how river barriers were affecting salmon and other migratory fish. However, during their fieldwork, it soon became clear that river barriers represented a much bigger problem than authorities had estimated or cared to admit.

The team surveyed 147 rivers in 26 countries using barrier inventories from local authorities, as well their own data collected in the field, all of which took two years — a long time but given the sheer volume of work and the difficult challenges they faced, the researchers moved extremely fast.

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