BIOGEOCHEMICAL CYCLING OF MANGANESE IN ONEIDA LAKE, NEW-YORK - WHOLE LAKE STUDIES OF MANGANESE

Oneida Lake, New York is a eutrophic freshwater lake known for its abu ndant manganese nodules and a dynamic manganese cycle. Temporal and sp atial distribution of soluble and particulate manganese in the water c olumn of the lake were analyzed over a S-year period and correlated wi th other variables such as oxygen, pH, and temperature. Only data from 1988 are shown. Manganese is removed from the water column in the spr ing via conversion to particulate form and deposited in the bottom sed iments. This removal is due to biological factors, as the lake Eh/pH c onditions alone can not account for the oxidation of the soluble manga nese Mn(II). During the summer months the manganese from microbial red uction moves from the sediments to the water column. In periods of str atification the soluble Mn(II) builds rep to concentrations of 20 mu M or more in the bottom waters. When mixing occurs, the soluble Mn(II) is rapidly removed via oxidation. This cycle occurs more than once dur ing the summer, with each manganese atom probably being used several t imes for the oxidation of organic carbon. At the end of the fall, whol e lake concentrations of manganese stabilize, and remain at about 1 mu M until the following summer when the cycle begins again. Inputs and outflows from the lake indicate that the active Mn cycle is primarily internal, with a small accumulation each year into ferromanganese nodu les located in the oxic zones of the lake.