Submarine groundwater discharge (SGD) is a significant mechanism for contaminant transport from terrestrial to marine and estuarine environments. Nutrient and contaminant loads carried by groundwater contribute to the eutrophication and contamination of marine and nearshore waters and, unlike contributions from surface water flows, are often unrecognized and rarely quantified. SGD is also a target for groundwater explorationist trying to identify as yet untapped sources of freshwater to supply ever growing coastal populations. Even where it will not be developed explicitly, the identification and quantification of SGD is needed to develop reliable models of groundwater flow and impacts to groundwater resources in coastal basins. In that regard, understanding the spatial distribution of SGD is as important as quantifying the total discharge.
In the summer of 2021, we used an automated underwater vehicle (AUV) equipped with water chemistry sensors (CTD, pH, DO, and turbidity) and high-resolution side scan and multibeam scanners to identify discrete locations of SGD in the Adriatic Sea off the coast of Croatia. We identified multiple submarine springs on the basis of water chemistry signatures. The AUV allowed us to survey areas as large as 100,000 m2 along transects spaced between 10 and 20 meters apart and at less than three meters from the bottom. The onboard multibeam and side-scan sensors allowed us to identify and characterize the locations of the spring vents, which we subsequently confirmed and photographed using SCUBA. Vent depths ranged from approximately 10 to 30 meters below mean sea level. Runs at shallower depths over the same area produced data from which we’ve developed 3D models of parameter distributions within the water column above and around the spring vents. In 2022, we plan to conduct similarly detailed surveys in the Black Sea at locations in Romania and Georgia that we have been studying since 2019.
Todd is a hydrogeologist, underwater explorer, and advocate for science-based conservation of water resources and aquatic environments. He holds BS, MS, and Ph.D. degrees in geology and hydrogeology, and is the founder of GeoHydros, a consulting firm specializing in the development of computer models that simulate groundwater flow through complex hydrogeologic environments. He has more than 30 years of experience in the characterization and modeling of groundwater flow through karst and fractured rock aquifers. His work has focused on submarine springs in the Gulf of Mexico and the Black Sea since 2008.