Grant Award Year:
Winter drawdowns are a common lake management strategy in Massachusetts that lower lake elevation during the winter to kill nuisance aquatic vegetation, among other purposes. Reservoir water elevations are altered by managing water releases from dams, resulting in increased downstream discharges during the fall and decreased discharges during the spring, relative to systems not managed for winter drawdowns. These changes in water quantity likely translate to altered habitat (e.g., bed mobilization) and water quality (e.g., temperature), with potential consequences on productivity, biotic integrity, and ecosystem health. Current state-issued guidelines for planning and permitting for winter drawdowns focus primarily on in-lake impacts and claim that “properly conducted” drawdowns should not alter flows beyond normal variation or downstream ecosystems, despite a lack of information on downstream impacts. We propose to collect continuous, high-resolution discharge and temperature data below drawdown dams and dams managed without altered discharges. These data will be used to describe variation in hydrologic and thermal regimes downstream of drawdown reservoirs and develop mechanistic hypotheses on the effects of altered flows on downstream ecosystems. Results will help managers and policy makers consider previously overlooked downstream impacts when updating management guidelines.