Manganese Biogeochemistry in Toolik Lake, Alaska

Toolik Lake, Alaska is an arctic lake characterized by a short open water period, low rates of primary production, and diagenetically-formed Mn and Fe oxide horizons in slowly accumulating sediments. The cycling of Mn in Toolik Lake was determined using stream mass balances of dissolved and particulate Mn, water column Mn concentrations, sediment trap-determined Mn sedimentation, sediment Mn recycling rates, and 210Pb geochronology-based Mn burial. Most Mn inputs were observed at the outset of stream flow after spring thaw, with about half of the Mn retained in the lake. Higher concentrations of Mn appeared in the outlet rapidly after initial streamflow, with incoming water traversing the lake immediately under the ice. Sediment trap-based Mn deposition was consistent with the stream mass balance and estimates of burial in the sediments. While ongoing sediment diagenesis of Mn represented the largest biogeochemical flux of Mn in Toolik Lake, Mn was not an important terminal electron acceptor relevant to the oxidation of organic matter.