Water and chemical fluxes between aquifers and the ocean are critically important to biological, geological, and geochemical processes at the coast. Groundwater inputs to the sea can cause algal blooms and modify ocean chemistry, and seawater infiltration to land causes aquifer salinization and alters solute and mineral composition of the subsurface. A unique challenge in quantifying aquifer-ocean fluxes is the wide range of spatial and temporal scales over which the mechanisms that drive exchange operate. Forcing occurs on timescales of waves, seasons, and glacial cycles, with corresponding spatial scales from ripples to continental shelves. Integrating the scales of exchange is essential for understanding and predicting the impacts of these fluxes through geologic history and as sea level changes in the future. The long-term vision of this work is to improve understanding of physical processes that connect aquifers and the sea through research and education that link geosciences and mathematics. The research project will explore the influence of geologic heterogeneity (spatial variations in hydrogeologic properties) on continental shelf-scale ocean-aquifer water exchange processes. Geostatistical modeling and variable-density groundwater flow and solute transport simulation will be used to understand the influence of the geometry of heterogeneity on (1) spatial patterns of seafloor water exchange, (2) density-driven saltwater circulation in the subsurface, and (3) seawater intrusion into aquifers, processes important for water resources, coastal ecosystems, and ocean chemistry. Two systems that display very different geometry and connectivity of geologic features will be modeled: the Bengal Delta and the Hawaiian Islands. This research will be linked to an educational program designed to integrate mathematics into geoscience curricula. A groundwater-surface water exchange activity for high school students in Delaware and Hawaii will be developed and implemented through cooperation with the Delaware Nature Society and Kamehmeha Schools, and new and modified undergraduate and graduate courses that incorporate aspects of the research will be offered at the University of Delaware.
This project will create new knowledge of the physical processes that generate water exchange between aquifers and the ocean and the water and chemical fluxes that they produce. The work will fill a gap in understanding of the role of the geologic structure of an aquifer in translating these physical processes into groundwater salinization (flux from sea to land) and groundwater flow to the ocean (flux from land to sea) on the scale of the continental shelf. The work will have impacts on education, water resource management, and ecological preservation. Scientific results will provide water resources managers with a basis for improving management models and risk assessments. Insights gained will improve design of future field studies, enhance efforts to protect fragile coastal ecosystems, and may have implications for offshore drilling activities and siting of wind farms. Improved prediction of land-sea fluxes will also allow us to better anticipate and adapt to potential effects of climate change on coastal water resources and ecosystems.
