B13E-0668
Cycling of Redox-Sensitive Trace Elements in the Lower Mississippi River Delta as a Function of River Stage and Sediment Heterogeneity

Monday, 14 December 2015
Poster Hall (Moscone South)
Katherine Telfeyan1, Alexander Breaux2, Jihyuk Kim3, Karen Haley Johannesson2, Alexander Kolker4 and Jaye Ellen Cable3, (1)Tulane Univ Earth&Environ Sci, New Orleans, LA, United States, (2)Tulane University of Louisiana, New Orleans, LA, United States, (3)University of North Carolina at Chapel Hill, Chapel Hill, NC, United States, (4)Louisiana Universities Marine Consortium, Chauvin, LA, United States
Abstract:
Telfeyan, K.1, Johannesson, K.H.1, Breaux, A.M.2,1, Kim, J.3, Kolker, A.S.2,1, Cable, J.E.3

1 Department of Earth and Environmental Sciences, Tulane University, New Orleans, LA, USA

2 Louisiana Universities Marine Consortium, Cocoderie, LA, USA

3 Department of Marine Sciences, University of North Carolina, Chapel Hill, NC, USA

The Mississippi River drains 40% of the continental United States and discharges 0.1 Pg sediment and an average of 18,400 m3 s-1 water annually to the Gulf of Mexico1. The flow of groundwater through the Mississippi River Delta (MRD) to the Gulf, however, has been largely understudied and is typically overlooked in MRD biogeochemical studies. Previous work demonstrated that sand-rich paleochannels that maintain a hydrologic connection to the Mississippi River could transport riverine water to the MRD2. We present data from biogeochemical surveys at 2 sites in the lower MRD to explore the effects of river-derived submarine groundwater discharge on the biogeochemistry of MRD wetlands. Lac des Allemands is a fresh water lake and Myrtle Grove is a brackish canal with variable salinities. Both are surrounded by extensive wetlands. Over the course of a year, surface water, shallow pore water, and deeper groundwaters were sampled to understand the cycling of redox-sensitive trace elements (Fe, Mn, V, As) and the potential supply from groundwater to surface water bodies. Major ion chemistry suggests that both Lac des Allemands and Myrtle Grove Canal receive river-derived terrestrial water at their heads, the flux of which varies as a function of river stage. However, the lateral flow through adjacent wetlands is altered as a function of sediment heterogeneity. Evidence for sulfate reduction exists in the near-surface sediment and at depth where a continuous vertical organic matter layer exists. In sand-rich layers, iron reduction buffers redox conditions, and V varies inversely with dissolved Fe. Concentrations of V and As are much greater in near-surface pore waters than in deeper groundwaters and in surface waters, suggesting that the subterranean estuary serves as a sink of these redox-sensitive trace elements.

[1] Bianchi and Allison (2009) PNAS 1068085-8092.

[2] Kolker et al. (2013) Journal of Hydrology 498 319-334.

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