Deltaic Submarine Groundwater Discharge: An issue of global importance?

Abstract:

The topic of submarine groundwater discharge (SGD) has garnered extensive interest over the past few decades. Many initial studies of SGD focused on karstic aquifers or small sandy systems. SGD associated with large river deltas has often been overlooked; though the limited number of studies that exist suggest it is important. This oversight is important, as large rivers are one of the primary pathways by which water and dissolved materials flow from the continents to the oceans. Deltas are also important loci for nutrient regeneration, carbon sequestration and authigenic mineral formation; and exchanges between salt and freshwater in these systems could be of geochemical importance globally. This talk will examine the topic of deltaic SGD, its regional and global implications, and use case studies from ongoing work in the Mississippi River Delta (MRD). Recent results indicate that SGD in the MRD averages 1,000 m³ s^-1, and can reach 5,000 m³ s^-1; making this system one the 25 largest pathways for water transport in North America. Flow appears to be driven by the stage differential between the Mississippi River and its surrounding wetlands, and likely passes through paleochannels and other buried semi-permeable bodies. This process may be amplified by a network of levees that inflate river stages, particularly during floods. Given the increases in flood control structures that may be built to cope with changing climates, deltaic SGD may become more important during the Anthropocene.