Arsenic, vanadium, iron, and manganese biogeochemistry in a deltaic wetland, southern Louisiana, USA

Journal Article · Wed Apr 05 00:00:00 EDT 2017 · Marine Chemistry

DOI:https://doi.org/10.1016/j.marchem.2017.03.010· OSTI ID:1352446

Telfeyan, Katherine ^[1]; Breaux, Alexander ^[2]; Kim, Jihyuk ^[3]; Cable, Jaye E. ^[3]; Kolker, Alexander S. ^[2]; Grimm, Deborah A. ^[1]; Johannesson, Karen H. ^[1]

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1. Tulane Univ., New Orleans, LA (United States)
2. Tulane Univ., New Orleans, LA (United States); Louisiana Univ., Marine Consortium, Cocodrie, LA (United States)
3. Univ. of North Carolina, Chapel Hill, NC (United States)

Geochemical cycling of the redox-sensitive trace elements arsenic (As) and vanadium (V) was examined in shallow pore waters from a marsh in an interdistributary embayment of the lower Mississippi River Delta. In particular, we explore how redox changes with depth and distance from the Mississippi River affect As and V cycling in the marsh pore waters. Previous geophysical surveys and radon mass balance calculations suggested that Myrtle Grove Canal and bordering marsh receive fresh groundwater, derived in large part from seepage of the Mississippi River, which subsequently mixes with brackish waters of Barataria Bay. In addition, the redox geochemistry of pore waters in the wetlands is affected by Fe and S cycling in the shallow subsurface (0-20 cm). Sediments with high organic matter content undergo SO₄^2- reduction, a process ubiquitous in the shallow subsurface but largely absent at greater depths (~3 m). Instead, at depth, in the absence of organic-rich sediments, Fe concentrations are elevated, suggesting that reduction of Fe(III) oxides/oxyhydroxides buffers redox conditions. Arsenic and V cycling in the shallow subsurface are decoupled from their behavior at depth, where both V and As appear to be removed from solution by either diffusion or adsorption onto, or co-precipitation with, authigenic minerals within the deeper aquifer sediments. Pore water As concentrations are greatest in the shallow subsurface (e.g., up to 315 nmol kg^-1 in the top ~20 cm of the sediment) but decrease with depth, reaching values <30 nmol kg^-1 at depths between 3 and 4 m. Vanadium concentrations appear to be tightly coupled to Fe cycling in the shallow subsurface, but at depth, V may be adsorbed to clay or sedimentary organic matter (SOM). Diffusive fluxes are calculated to examine the export of trace elements from the shallow marsh pore waters to the overlying canal water that floods the marsh. The computed fluxes suggest that the shallow sediment serves as a source of Fe, Mn, and As to the surface waters, whereas the sediments act as a sink for V. Iron and Mn fluxes are substantial, ranging from 50 to 30,000 and 770 to 4,300 nmol cm^-2 day^-1, respectively, whereas As fluxes are much less, ranging from 2.1 to 17 nmol cm^-2 day^-1. Vanadium fluxes range from 3.0 nmol cm^-2 day^-1 directed into the sediment to 1.7 nmol cm^-2 day^-1 directed out of the sediment

• Research Organization: Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
• Sponsoring Organization: National Science Foundation (NSF); USDOE
• Grant/Contract Number: AC52-06NA25396; EAR-1141692; EAR-1141685; EAR-1141716
• OSTI ID: 1352446
• Report Number(s): LA-UR-16-25809
• Journal Information: Marine Chemistry, Vol. 192, Issue C; ISSN 0304-4203
• Publisher: Elsevier
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
earth sciences
vanadium
arsenic
subterranean estuary
Myrtle Grove
wetland biogeochemistry
redox-sensitive trace elements
diffusive fluxes