Abstract

Submarine groundwater discharge (SGD) is recognized to supply nutrient elements nitrogen and phosphorous to coastal waters. In some cases, these nutrients are essential for biological productivity; in other cases, the nutrients are in excess or are in the wrong proportions and lead to algal blooms and eutrophication. Often overlooked is the role of reducing substances in salty SGD such as H₂S, NH₄⁺, CH₄, DON and DOM, which create a direct demand for dissolved oxygen (DO) and lower its concentration in estuarine and coastal waters. We call this SGD-Oxygen Demand or SGD-OD. These reduced substances primarily result from the oxidation of carbon in aquifers and aquicludes by seawater sulfate. Thus, coastal aquifers transitioning from freshwater to seawater due to seawater intrusion are most vulnerable. When saturated, seawater DO concentrations are on the order of 200 µM. Reducing DO in coastal waters to <150 µM induces biological stress on many organisms; reducing it to <60 µM (hypoxic conditions) can be deadly. There are studies directly correlating the depletion of DO with increased SGD fluxes off the coast of South Carolina and Mississippi, USA, and in the Yangtze delta, China. These depletions initially affect near-bottom dwelling organisms and may be recognized by sudden fish kills. In this talk I will review a data base of reducing substances in coastal groundwaters and illustrate how the discharge of this water could impact estuaries and coastal waters. I will show additional examples which we think are related to SGD-OD in hopes others will have the resources to investigate these areas.

Biography

Willard S. Moore received his doctorate degree in earth and space sciences from State University of NY. He has served on the National Advisory Council/National Research Council, the international commission on Marine science (SCOR), and the Groundwater Discharge Working Group. Professor emeritus Willard Moore was elected as a Fellow of American Geophysical Union in 2006 and Fellow of the American Association for the Advancement of Science in 2014.

The primary research of his laboratory is based on the use of natural radioisotopes as tracers of geological and oceanographic processes. By measuring precisely radioisotopes that result from the decay of uranium and thorium in the environment, his group investigates such diverse topics as interactions of river water and sediments with sea water; flow of ground water through salt marshes; the mixing rate of the ocean; hydrothermal processes at ocean spreading centers; the internal structure of minerals; the ages, rates, and processes of formation of manganese nodules; the rate of growth of corals; and sea level changes.