Title: Submarine groundwater discharge: its role in nutrient fluxes and initiation of hypoxia in estuaries and coastal waters
Speaker: Willard S. Moore (Department of Earth and Ocean Science, University of South Carolina, Columbia, SC, USA)
Venue: Room 3N-01, Kadoorie Biological Sciences Building, HKU
Abstract: Large fluxes of nutrients to estuaries and coastal waters result from biogeochemical processes in coastal aquifers. These processes are initiated by seawater intrusion into these aquifers. Such intrusions are occurring along many coastlines at a quickening pace due to overpumping of freshwater from the aquifer, sea level rise, drainage of coastal wetlands, construction of impermeable surfaces, and dredging of harbors. In addition to the impacts on drinking water, agriculture and industry, seawater intrusion causes profound changes in the biogeochemistry of the affected aquifers, the dynamic systems called subterranean estuaries. Subterranean estuaries receive freshwater from land and saltwater from the ocean. This fluid mixture is subject to intense biogeochemical dynamics that is largely based on the oxidation of organic carbon using sulfate as an electron acceptor. Increased saltwater intrusion supplies sulfate to the aquifer and alters the ensuing reactions that control the chemical composition of water discharging from subterranean estuary into the ocean as submarine groundwater discharge (SGD). These highly altered fluids are enriched in nutrients, carbon, hydrogen sulfide, metals, and radionuclides compared to the source waters. Enhanced nutrient fluxes due to SGD have received the most attention. In this talk I will demonstrate how such fluxes to an estuary may be calculated and discuss this important nutrient source to estuaries and coastal waters. Additionally, I will discuss the effects of anoxic SGD fluxes in causing hypoxia along some coasts.