User:Darcycarlson/Riffle

Anthropogenic Threats

Riffles provide important habitat and food production for various aquatic organisms, but humans have altered aquatic ecosystems worldwide through infrastructure and land use changes. Human interference of stream or river flow decreases sediment sizes, resulting in less riffles.

Specifically, weirs and other dams have reduced existing riffles by flattening the channel with smaller substrate, resulting in habitat fragmentation. Dam removal has increased in recent times and its effects on riffles vary and are complex, but generally, riffles may redevelop. As these riffles develop, however, they often have a lower biodiversity than the pre-dam ecosystem but benefit aquatic biodiversity in the long term. Following weir removal, riffle fish populations have increased in diversity and density, and these fish have moved upstream to inhabit new riffles that redevelop after dam removal. The importance of riffles in supporting diverse assemblages of aquatic biota within streams and rivers may contribute to the increasing trend of dam removal.

Human land use change, specifically development of land, can indirectly affect riffles and riffle quality. Terrestrial vegetation, such as tree branches and leaf litter, contribute to the formation of riffles and stabilization of the ecosystem's channel, and as development reduces this vegetation, riffles may be diminished. Species richness and diversity within riffles are susceptible to anthropogenic land use changes, and management options for restoring these riffles to increase aquatic biodiversity include removing sand and sedimentation and enhancing water flow, to offset impacts from land use change.