Adverse Impacts of Cooling Water Withdrawals on Populations and Ecosystems: Separating Fact From Conjecture

Impacts of entrainment and impingement (I&E) at cooling water intake structures have been a topic of controversy for nearly 40 years.  It has been argued that cooling water withdrawals at large thermal power plants have contributed to the depletion of valued marine and freshwater fish populations, and that these withdrawals may also disrupt aquatic food webs through indirect impacts on lower trophic levels.  It has also been argued that the mortality caused by I&E is small compared to natural and fishing mortality, and that indirect impacts of cooling water withdrawals are small or non-existent.  What is usually missing in this discussion is an evaluation of historical evidence concerning these impacts from the four decades of fish stock assessment, environmental monitoring, and scientific research that have occurred since I&E first became a significant regulatory issue.  This presentation will address the issue of adverse impacts through a review of published scientific literature relating to the causes of adverse changes in marine and freshwater ecosystems.  The reviewed literature will include (1) peer-reviewed papers and agency stock assessment reports documenting the causes of declines in marine and freshwater fish populations, (2) “blue-ribbon” commission reports and relevant National Academy of Sciences Reports that discuss causes of fish population decline ecosystem degradation, and (3) scientific literature relevant to evaluation of the indirect impacts of I&E on the services provided by freshwater and marine ecosystems.