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This case study presents results from a complex assessment of a biologically impaired urbanized coastal watershed located primarily in South Portland, Maine, U.S.A., the Long Creek watershed. This assessment serves as an example implementation of U.S. Environmental Protection Agency Stressor Identification guidance. Four specific biological effects defining impairment and seven candidate causes of impairment were chosen and evaluated at three impaired sites along long Creek. Decreased dissolved oxygen, altered flow regime, decreased large woody debris, increased temperature, and increased toxicity due to ionic strength were identified as probable causes of impairment. The implications associated with interactions among probable causes are discussed in terms of this case study and causal assessment in general.
U.S. EPA. Causal Analysis of Biological Impairment in Long Creek, a Sandy-Bottomed Stream in Coastal Southern Maine (External Review Draft). U.S. Environmental Protection Agency, Washington, DC, EPA/600/R-06/065A.