Chemistry of N and Mn Cox Hollow Lake, Wis., Following Destratification

Concentrations and forms of nitrogen and manganese species were determined in Cox Hollow Lake, Wisconsin, after the lake was destratified by artificial aeration. Destratification of this impoundment was accomplished within one month of aeration, and dissolved oxygen appeared throughout the water column at the same time. Nitrogen (mainly Kjeldahl N) decreased in the Lake during destratification, apparently as a result of sedimentation. Nitrate and nitrite appeared in the water column soon after the initial appearance of oxygen in the bottom water, but rates of nitrification were estimated to be low, 3 mg per 1-hr to 40 mg per 1-hr. Inorganic nitrogen remained low following destratification. Destratification was also effective in removing manganese from the hypolimnion; bottom concentrations decreased from about 2 mg Mn per 1 to about 0.3 mg Mn per 1 after one month of aeration. About 50% of the total Mn was particulate (as defined by a 0.45 u filter). After reoxygenation some of the particulate Mn was found to be oxidized Mn, but most particulate Mn was Mn (II), presumably sorbed onto inorganic or organic particles.