Submarine Groundwater Discharge In the Mississippi River Delta A Missing Hydrological Flux

Alexander S. Kolker Louisiana Universities Marine Consortium, Department of Earth and Environmental Sciences, Tulane University; Alex Breaux Louisiana Universities Marine Consortium; Jaye E. Cable Department of Marine Science, University of North Carolina, Chapel Hill; Dan Coleman Department of Earth and Environmental Sciences, Tulane University; Jihyuk Kim Department of Marine Science, University of North Carolina, Chapel Hill; Karen Johannesson Department of Earth and Environmental Sciences, Tulane University; Katheryn Telfeyan Department of Earth and Environmental Sciences, Tulane University, Mead A. Allison The Water Institute of the Gulf, Department of Earth and Environmental Sciences, Tulane University

 

It is well recognized that the Mississippi River (MR) is the dominant driver of hydrological processes in coastal Louisiana. For decades, researchers have examined how surface waters from the Mississippi River (MR) impact the coastal bays that comprise the Mississippi River Delta (MRD). However, other questions remain: how well do surface hydrological and geochemical fluxes in the MRD account for the total fluxes in this system? Are there more diffuse subterranean pathways by which water flows from the MR to the coastal zone? Here we show that there are subterranean pathways that direct water from MR to the MRD. This deltaic submarine groundwater discharge averages about 1,000 m3 s-1, and can reach 5,000 m3 s-1 at high discharge, indicating that groundwater is an important, but overlooked part of the hydrology of coastal Louisiana (Kolker et al., 2013).

 

We hypothesize that groundwater flows from the MR to the MRD through abandoned bayous, buried paleochannels, or other subterranean sand bodies. Further, we posit that groundwater flow is driven by the head differential between the MR and the surrounding wetlands. When river stage is low, there is no head differential between the two, resulting in no SGD flow. When river stage is high, the head differential between the two systems is substantial, resulting in groundwater flow from the river to the coastal bays, and particularly the Barataria and Lake Pontchartrain basins. During extreme low water, groundwater may flow from Louisiana’s coastal embayments to the Mississippi River, resulting in saltwater intrusion.

 

We are actively testing this hypothesis using tools from hydrology, geochemistry geophysics, and sedimentology. Flow appears to be greatest during periods of high discharge and lowest during periods of low discharge. Furthermore, flow appears to be greatest in bayous and other relict distributaries. Our results suggest

that bayous and relict distributaries still carry a substantial amount of flow, despite surface restrictions. These subsurface conduits may further serve as vessels for geochemical reactions. This ongoing research program may improve our understanding of the distribution of habitats, the fate and transport of pollutants, and the distribution of freshwater, all of which are important for modeling future restoration.

 

Reference

 

Kolker, A.S., J.E. Cable, K.H. Johannesson, M.A. Allison, and L.V. Inniss, 2013, Pathways and processes associated with the transport of groundwater. in deltaic systems. Journal of Hydrology. 498: 319-334.

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