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AUTHORS: Nicole M. Dennis, Central Michigan University, Biology Department and Institute for Great Lakes Research; Daelyn A. Woolnough, Central Michigan University, Biology Department and Institute for Great Lakes Research
ABSTRACT: Native freshwater mussels (family: Unionidae) have been used as bioindicators because unionids have been found to be the most sensitive of aquatic fauna, ultimately determining the protective contaminant values for water bodies. We investigated unionid assemblages among seven sites along the North Branch tributary of the Chippewa River (NB) containing known advisory levels of Escherichia coli, and two previously surveyed sites, one upstream (US) and one downstream (DS) of the confluence, on the Main Branch of the Chippewa River (MB), Michigan, USA. We determined which unionid species were present and the variation between unionid assemblages between NB and MB and among NB sites, then correlated these data with surficial geology and standard water quality data to assess these influences on unionid assemblages. Unionid density was positively correlated with aqueous ammonia nitrogen [NH3-N], and negatively correlated with total phosphorus [P] and E. coli most probable number (MPN). Unionid density was higher in the NB than in the MB, however, unionid density decreased US to DS in both the NB and MB with decreasing [NH3-N], and increasing [P] and E. coli MPN from 0.71 m-2 to 0.01 m-2, and from 0.04 m-2 to 0.01 m-2, respectively. Results indicated that upwards of 4.20 mg total ammonia nitrogen (TAN)/L, 103.9 µg P/L, and 1116.8 E. coli MPN count were recorded among the sample sites; well above established EPA water quality criteria levels considered ambient for aquatic environments. Few (