Historical Associations of Molecular Measurements of Escherichia coli and Enterococci to Anthropogenic Activities and Climate Variables in Freshwater Sediment Cores

This study investigated the long-term associations of anthropogenic (sedimentary P, C, and N concentrations, and human population in the watershed), and climatic variables (air temperature, and river discharge) with Escherichia coli uidA and enterococci 23S rRNA concentrations in sediment cores from Anchor Bay (AB) in Lake St. Clair, and near the mouth of the Clinton River (CR), Michigan. Calendar year was estimated from vertical abundances of 137Cs. The AB and CR cores spanned c.1760–2012 and c.1895–2012, respectively. There were steady state concentrations of enterococci in AB during c.1760–c.1860 and c.1910–c.2003 at ∼0.1 × 105 and ∼2.0 × 105 cell equivalents (CE) per g-dry wt, respectively. Enterococci concentrations in CR increased toward present day, and ranged from ∼0.03 × 105 to 9.9 × 105 CE/g-dry wt. The E. coli concentrations in CR and AB increased toward present day, and ranged from 0.14 × 107 to 1.7 × 107 CE/g-dry wt, and 1.8 × 106 to 8.5 × 106 CE/g-dry wt, respectively. Enterococci was associated with population and river discharge, while E. coli was associated with population, air temperature, and N and C concentrations (p < 0.05). Sediments retain records of the abundance of fecal indicator bacteria, and offer a way to evaluate responses to increased population, nutrient loading, and environmental policies.