Hydropower Effluent as a Marine Pollutant; Impacts of River Regulation on Estuarine and Coastal Ecology

ABSTRACT The confluence of rivers with the ocean creates biological hotspots where temperature, salinity, and nutrients mix to provide excellent conditions for rearing, growth, and refuge to a multitude of organisms. Worldwide, estuaries are highly productive and biodiverse. However, estuaries are also highly degraded by development and pollution due to human settlement and exploitation of waterways. As global energy systems transition to renewable energy sources, rivers are increasingly stressed by regulation to produce power. Effluent water flowing from rivers is channeled through the river and eventually reaches the ocean, meaning that power production can dramatically alter the dynamics of freshwater input at estuaries, including marked changes in the annual cycle of discharge. Despite much research focusing on understanding and mitigating the impacts of hydropower production on river ecosystems, less research has been conducted to understand how alterations to the flow regime affect marine ecosystems where the water is discharged. We address the status of knowledge at the interface of freshwater and marine ecosystems and highlight research priorities to better understand how sensitive estuarine and coastal habitats are affected by thermal, osmotic, and physical changes caused by hydropower production in rivers.