The evolution of dam induced river fragmentation in the United States

It is established that dams decrease river connectivity; however, previous global scale studies of river fragmentation focused on a small subset of the largest dams. In the United States, mid-sized dams, which are too small for global databases, account for 96% of major anthropogenic structures and 48% of reservoir storage. We conduct a national evaluation of the evolution of anthropogenic river bifurcation over time that includes more than 50,000 nationally inventoried dams. Mid-sized dams account for 73% of anthropogenically created stream fragments nationally. They also contribute disproportionately to short fragments (less than 10 km), which is particularly troubling for aquatic habitats. Here we show that dam construction has essentially reversed natural fragmentation patterns in the United States. Prior to human development, smaller river fragments and less connected networks occurred in arid basins while today we show that humid basins are the most fragmented due to human structures. Dam construction reshaped the river networks of the United States. Arid basins are naturally more fragmented than humid. However, the opposite is true in the US today. Extensive dam building has created highly fragmented basins in the eastern US.

Automated summary

It is well-known that dams reduce river connectivity. However, previous studies on global river fragmentation focused only on a small number of large dams. In the United States, mid-sized dams, which are not included in global databases, account for a significant percentage of anthropogenic structures and reservoir storage. This study evaluates the evolution of anthropogenic river bifurcation in the country, considering over 50,000 inventoried dams. The findings reveal that mid-sized dams contribute to the majority of anthropogenically created stream fragments in the US, especially short fragments, posing a significant threat to aquatic habitats.