Ecosystem Modeling of Direct and Indirect Effects of Impingement Mortality and Entrainment

The 2014 Existing Facilities Rule for  CWA Section 316b compliance emphasizes the evaluation of indirect effects (changes in food webs, nutrient cycling, and ecosystem resilience) resulting from changes in impingement and entrainment as well as chemical loading, thermal loading, and flows associated with alternative cooling water intake technologies.  USEPA specifies that if possible, these indirect effects be quantified and monetized as part of the benefits report. One tool available to quantify these indirect changes and provide a foundation for monetization of nonuse values is the Comprehensive Aquatic Ecosystem Model (CASM).  This model has been implemented to quantify combined direct and indirect effects of impingement and entrainment mortalities, nutrient enrichment, and thermal loading for a hypothetical facility located on the shore of western Lake Erie. The CASM simulations characterized the direct and indirect food web effects of hypothetical, but data based, scenarios using individual and combined stressors. The relative sensitivities of modeled species (plankton, invertebrates, planktivores, piscivores) to individual stressors, and the modeled food web interactions determined the nature and magnitude of western Lake Erie food web alterations. The model also described associated effects on nutrient (N, P) dynamics and ecosystem resilience for the alternative stressor scenarios.