Small artificial impoundments have big implications for hydrology and freshwater biodiversity

Headwater streams are critical for freshwater ecosystems. Global and continental studies consistently show major dams as dominant sources of hydrological stress threatening biodiversity in the world's major rivers, but cumulative impacts from small artificial impoundments (SAIs) concentrated in headwater streams have rarely been acknowledged. Using the Murray Darling River basin (Australia) and the Arkansas River basin (US) as case studies, we examined the hydrological impacts of SAIs. The extent of their influence is considerable, altering hydrology in 280-380% more waterways as compared to major dams. Hydrological impacts are concentrated in smaller streams (catchment area <100 km(2)), raising concerns that the often diverse and highly endemic biota found in these systems may be under threat. Adjusting existing biodiversity planning and management approaches to address the cumulative effects of many small and widely distributed artificial impoundments presents a rapidly emerging challenge for ecologically sustainable water management.

Automated summary

Headwater streams are crucial for freshwater ecosystems, but the hydrological impacts of small artificial impoundments (SAIs) in these streams have been largely ignored. Using case studies in Australia and the US, it was found that SAIs alter hydrology in a significantly larger number of waterways compared to major dams. This poses a threat to the diverse and endemic biota found in smaller streams.