| Rationale: This work focuses on a relatively new sub-discipline of chemical oceanography, submarine groundwater discharge (SGD), which combines aspects of hydrology and aquatic chemistry. Recent studies indicate that SGD may contribute significant fluxes of dissolved chemical species to the oceans. However, the magnitude of such fluxes is strongly influenced by biogeochemical processes occurring in the subterranean estuary, defined as the mixing zone between groundwater and seawater in a coastal aquifer. | |
One fundamental problem lies in the difficulty of flow measurement and sample collection across the salinity gradient of subterranean estuaries. In order to determine if SGD is important in terms of elemental fluxes to the ocean on a global scale, we must first understand the major geochemical reactions operating on such elements on the scale of subterranean estuaries.
Methodology: Gaining access to a subterranean estuary for sampling purposes is a challenging endeavour. For collecting water samples, permanent monitoring wells or temporary wells (called drive-point piezometers) are the best approach. Sediments are obtained using vibra-core (shallow sediments > 5 m) or motorized auger (deep sediments > 5 m) techniques. Chemical analyses may include natural radionuclides (for determining the rate of SGD) and trace-metals or nutrients (for obtaining SGD-derived chemical fluxes). Samples are analyzed using both modern and traditional techniques such as Inductively Coupled Plasma-Mass Spectrometery (trace metals), Flow Injection Analysis (nutrients), and Alpha/gamma Spectroscopy (radionuclides).
Wider Implications: While the overall importance of SGD on the global cycle of certain elements is uncertain at present, there is little doubt that SGD is important at the local scale both within the United States and throughout the world. Nutrient-rich (phosphate, nitrate, ammonium) groundwater, entering into coastal waters and bays, is not uncommon and represents an environmentally important component of SGD. Hence, studies of subterranean estuaries have important water-quality implications for coastal aquifers and allow insights into fundamental biogeochemical reactions at a major freshwater/seawater interface.
Suitable For: Students with a strong chemistry and/or geology background, and a desire to work in the field. No hydrology background is necessary, though basic and advanced coursework in this area (available at MIT) may be a part of the student's Ph.D. curriculum.
Training: The student will learn a variety of field techniques relating to hydrogeology and aquatic chemistry. In the laboratory, the student will also become proficient in a variety of analytical techniques including trace metal and nutrient analysis. Because of the interdisciplinary nature of this project, the student will obtain a working knowledge of both hydrology and chemical oceanography.
Additional
Relevant Links:
References: