Stratification and hypoxic conditions in the hypolimnion of reservoirs leads to the reductive dissolution and release of manganese (Mn) and iron (Fe) into reservoir waters.  High concentrations of redox-active Mn and Fe interfere with oxidation unit processes in water treatment facilities.  This project is in collaboration with the City of Ithaca Water Treatment Plant and seeks to better understand the timing of Mn mobilization in the Ithaca Reservoir and the speciation of Mn released to reservoir waters.  We use wet chemical analysis of water chemistry, sensing of dissolved oxygen, and spectrophotometric analysis of Mn speciation to evaluate physio-chemical controls on Mn mobilization and guide the development of predictive models to be used by utility staff.  This project also addresses the role of groundwater inputs as a source of Mn, and uses stable isotope mixing models to determine seasonal variations in groundwater vs. surface water inputs to the reservoir.