The Distribution of Submarine Groundwater Discharge and its Effect on Coastal Water Quality in Mississippi

Description: Submarine groundwater discharge (SGD) is an important, but poorly constrained, hydrologic process that affects coastal water quality by transporting environmental stressors, such as nutrients, contaminants, and pathogens, into the ocean. Although SGD water flux to the coastal ocean is usually lower than that of rivers and streams, it can often represent an equivalent or greater contribution to local nutrient budgets because solutes are highly concentrated in SGD relative to surface waters. Published hydrologic models and preliminary results indicate that SGD occurs in the Mississippi coastal waters and may directly contribute to degradation of water quality including eutrophication, harmful algal blooms, and ultimately hypoxia. However, the spatial and temporal variability of SGD in Mississippi coastal waters, as well as its specific chemical composition, are poorly constrained. Additionally, published results indicate that spatial heterogeneity in subsurface hydraulic conductivity created by infilled paleochannel drainage networks, such as those that underlie the Mississippi Sound (MS) and Mississippi Bight (MB), can control the location of SGD. This project uses geophysical profiling, geochemical tracer surveys, and SGD sampling in the MS and MB to quantify the spatial distribution and temporal variability of SGD as well as its chemical composition. The research evaluates the role of paleochannel features in mediating SGD distribution, the sources of chemically distinct SGD in the study area, and the effect of SGD on water quality with emphasis on nutrient loading and the onset of hypoxia. The results of this research will contribute to an improved understanding of the contribution of SGD to nutrient budgets and water quality degradation in the MS and MB. Additionally, they will constrain the spatial and temporal variability of this poorly understood nutrient transport pathway, which may inform improved management of water quality and the multiple commercial fisheries in coastal Mississippi. Finally, we anticipate that these data will be directly relevant to the multiple productive commercial finfish and shellfish fisheries in the study area, particularly oyster reef sustainability and the optimal siting of future oyster cultch deployments.

Seismic profiles of subsurface stratigraphy in the Mississippi Sound, from 2020-11-10 to 2021-12-07

Chemical tracers in Mississippi Sound water samples collected from 2018-10-28 to 2021-12-07

Chemical composition data of Mississippi Sound surface seawater and groundwater samples collected along the coastline, from 2017-07-28 to 2019-11-13