Submarine discharge in South and Central San Francisco Bay
Creators: name: University Of California Office Of The President
Publisher: name: University of California Office of the President
publisherIdentifier: https://ror.org/00dmfq477
publisherIdentifierScheme: ROR
Year: 2024

description: This project will examine groundwater-surface water exchange in San Francisco Bay (SFB) to understand how exchange across this interface will impact constituent loadings available to coastal ecosystems. San Francisco Bay is one of the most urbanized coastal systems in the world and is the largest in the western US. Coastal submarine groundwater discharge (SGD) presents a mechanism for transformations of the redox-sensitive nutrients, trace elements, and greenhouse gases, and may be a significant source of groundwater-borne contaminants to the coastal ecosystem. To our knowledge, a comprehensive estimate of nutrient and trace metal loading resulting from groundwater input and exchange does not exist for SFB, and is necessary to accurately assess human-induced and natural changes to (1) the water balance of the bay, (2) factors controlling harmful algal blooms, (3) the role of phosphorus, and (4) associated bacterial transport. We propose a joint 2-year project between LLNL and two UC campuses to quantify the temporal and spatial patterns and rates of SGD, calculate associated constituent loadings, and discuss the potential ecological impacts to San Francisco Bay. More broadly, the work proposed here would represent one of the most complete and multi-disciplinary SGD studies to date, and would contribute significantly to the scientific community outside of San Francisco Bay. This proposal builds on the existing knowledge base of San Francisco Bay and on close collaboration between staff and faculty at Lawrence Livermore National Laboratory, UC Santa Cruz, UC Berkeley and the USGS to determine the ecosystem implications of groundwater-surface water interactions throughout the bay. The strength of this proposal is in the combined geophysical, geochemical and modeling studies of near-shore exchange processes as a vector for constituent loading to San Francisco Bay. We have all worked on various aspects of groundwater-surface water interactions and we bring different perspectives and experiences. LLNL will develop new methods using naturally occurring non-radiogenic noble gas tracers and methane to provide additional constraints on SGD; nitrate isotopics and excess nitrogen to quantify nutrient dynamics; and modeling of aquifer heterogeneity and metal/nutrient transport. UC-Berkeley researchers will focus on the on the interaction of the sediment bed with the overlying water column using hydrodynamic measurements of pressure, velocity and scalar concentrations; UC-Santa Cruz researchers will focus on utilizing naturally occurring radium, trace metals and nutrients; our USGS collaboration will add the geophysical component (resistivity) and radon measurements. Two post-docs and/or graduate students will be jointly mentored. Our primary focus in the proposed research will be on assessment of submarine groundwater discharge (SGD) and associated constituent loading to San Francisco Bay to test the following hypothesis: Seasonal and inter-annual variations in bay hydrographs and increased urbanization combine to make submarine groundwater discharge an important, though poorly constrained, source of dissolved nutrients, trace elements, and bacteria to San Francisco Bay. To address this hypothesis, this project aims to (1) assess the relative importance of the terrestrial, marine, and geologic factors that influence fluid exchange across the seabed at two contrasting sites within the Bay; (2) evaluate the fluxes of nutrients and trace m