Dissolved manganese in the Columbia River estuary: Production in the watercolumn

A chemical sensor was deployed as part of a package of instruments to devel op a highly resolved picture of dissolved Mn and related parameters in the Columbia River estuary. The vertical distribution of dissolved Mn in the ma in channel shows a distinct middepth maximum of 10 to 15 nM. The maximum oc curs at the same depth throughout the estuary, cutting across the salt wedg e. The feature thus does not appear to be advected but produced by an in si tu process. The Mn anomaly occurs at the same depth as the top of the estua ry turbidity maximum where other investigators have found the most intense microbiological activity. These and other observations are consistent with a mechanism of organic carbon oxidation in the suboxic interiors of aggrega tes by microbes that use Mn oxides as electron acceptors. The process turns over 16% of all Mn coming down the river and is pervasive enough to explai n its nonconservative behavior within the estuary. Copyright (C) 2001 Elsev ier Science Ltd.