Uranium in rivers and estuaries of globally diverse, smaller watersheds

Abstract

Data for uranium concentrations in 29 rivers and eight estuaries are presented. The river data expands the existing database on riverine uranium transport to include more smaller watersheds which collectively account for a large portion of material transport from the continent to the oceans. Riverine concentrations for these smaller watershed range from less than 50 to 660 pM. The results for these systems, when combined with previously published data on mostly larger rivers, do not change significantly the calculated global riverine flux and thus earlier estimates by Palmer and Edmond wPalmer, M.R., Edmond, J.M., 1993. Uranium in river water. Geochim. Cosmochim. Acta, 57, pp. 4947–4955x are substantiated. Uranium transport through eight diverse estuaries was studied to assess the importance of estuarine removal in the global marine uranium budget. Results indicate that uranium is conservatively transported in most systems studied. Results reported here for the Savannah estuary, however, indicate significant uranium removal. Our results suggest that uranium is removed in salt marsh estuaries at a rate of ca. 70 mmolrm2. This compares to a rate of 15 mmolrm2 for Delaware salt marshes wChurch, T.M., Sarin, M.M., Fleisher, M.Q., Ferchlman, T.G., 1996. Salt marshes: an important sink for dissolved uranium. Geochim. Cosmochim. Acta, 60, pp. 3879–3887x. We suggest that uranium removal to salt marsh sediments is due to anaerobic microbially mediated processes. We use these results to estimate the global significance of the salt marsh sink in the oceanic budget of uranium. We estimate that 2.7=107 mol of uranium are removed to salt marshes annually as compared to an annual global riverine input of 3–6=107 mol estimated by Palmer and Edmond wPalmer, M.R., Edmond, J.M., 1993. Uranium in river water. Geochim. Cosmochim. Acta, 57, pp. 4947–4955x. q2000 Elsevier Science B.V. All rights reserved.