Dissolved vanadium on the Louisiana Shelf: effect of oxygen depletion

New measurements of dissolved vanadium in waters of the Louisiana Shelf affected by outflow from the Mississippi/Atchafalaya River system are presented here. These measurements complement previously published estuarine vanadium data and allow a reexamination of prior conclusions. In estuarine and coastal regions it appears that the most significant vanadium depletions occur in association with reducing conditions. These reducing conditions are frequently driven by anthropogenic eutrophication. Sedimentary inputs also appear to be a factor in affecting the flux of vanadium to the ocean in certain environments. In contrast to previous results we find no compelling evidence of biological removal of vanadium from estuarine surface waters. Given the uncertainties, it is difficult to accurately estimate the natural flux of dissolved vanadium from the land to the open ocean. Nonetheless, increasing coastal anthropogenic eutrophication could substantially alter the natural fluvial vanadium input as well as possibly shift the primary locus of oceanic vanadium removal.