Only one third of the world’s longest rivers (over 1,000 kilometres in length) remain free-flowing, and these are restricted to remote regions in the Arctic and the Amazon and Congo basins, according to a paper published in Nature. The findings demonstrate how human activity disrupts river connectivity, which threatens the ecosystems and services provided by free-flowing rivers.
Rivers are important ecosystems and also support human societies by providing food and water, economic resources and agricultural opportunities. In recent years human demands have led to the natural courses of rivers being altered and managed with infrastructural development, including dams and levees. The importance of river connectivity has been recognized, but a lack of global information has made it hard to assess their current state.
Gunther Grill and colleagues develop a new method to comprehensively evaluate river connectivity, assessing 12 million kilometres of rivers around the world. They consider the well known influence of dams, but add key factors representing broader human influences on river connectivity, including barriers to lateral flow and infiltration, water use and regulations, and sediment trapping. They find that around half of all rivers worldwide show diminished connectivity and 63% of the world’s longest rivers (over 1,000 kilometres in length) are no longer free-flowing, representing nearly 41% of global river volume. The authors indicate that dams and reservoirs are key contributors to the loss of river connectivity, as they regulate and interrupt the flow of rivers.