Examining the role of SGD on the nitrogen budget of the fourth largest estuary in the USA, Mobile Bay, Alabama

The present study aims to help understand further the importance of submarine groundwater discharge (SGD) to Mobile Bay, Alabama with respect to associated nitrogen (N-) fluxes. Based on a three-year long study we found that on a large scale, when comparing Mobile River discharge to SGD, during the dry season, the SGD flux is only 2.5% of Mobile River discharge, whereas, during the wet season, this contribution is less than 1%. However, when examining the nitrogen budget of MB, we found that during the dry season, SGD delivers about half of the fluxes to the Bay. Furthermore, we found that the distribution of these SGD-derived inputs along the MB shoreline is very heterogeneous. Shallow geophysical electrical resistivity imaging and multiple sediment cores recovered in the examined areas reveal a rich organic sediment layer (up to 80 cm thick at some locations) which is perhaps responsible for the observed enhanced N-fluxes. Ongoing microbial, DOM and stable isotope sediment examination aim to explain the geochemical processes responsible for the disproportionally large SGD-delivered nitrogen fluxes in the identified impacted coastal areas.