Manganese redox buffering limits arsenic release from contaminated sediments, Union Lake, New Jersey

The sediments of Union Lake in Southern New Jersey are contaminated with arsenic released from the Vineland Chemical Company Superfund site 11 km upstream. Seasonal anoxia has been shown to release arsenic from sediments to similar lakes; this process was hypothesized as a major arsenic source to Union Lake. Data indicate, however, that releases of arsenic to bottom waters from the sediments or from pore waters within the sediments are relatively minor: bottom water arsenic concentrations reached-30 ppb (similar to 12 mu M) at most, representing < 13% of the dissolved arsenic content of the lake. Manganese concentrations increase more quickly and to higher levels than arsenic and iron concentrations; maximum [Mn] = similar to 13 ppm (similar to 250 mu M), maximum [Fe] = similar to 6 ppm (similar to 120 mu M). Incubation experiments support the hypothesis that manganese acts as a redox buffer and prevents large arsenic releases. Under the observed conditions, little of the arsenic in the water column is from contaminated bottom sediments. This study also suggests that arsenic release from sediment to lake water may be more important in lakes that remain anoxic more continuously. (C) 2016 Elsevier Ltd. All rights reserved.