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From the land to the sea: Impacts of submarine groundwater discharge on the coastal ocean of California and Alaska

  • Lecher, Alanna Louise
Publication Date
Jan 01, 2015
eScholarship - University of California
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Submarine groundwater discharge to oceans is an ever-increasing topic of study in theearth sciences due to the dynamic geochemical and biological effects it imposes onaquatic systems both by the chemical reactions it induces and the constituents ittransports. Studies indicate groundwater discharge can represent a major source ofnutrients, fecal indicator bacteria, caffeine, trace metals, and mercury to aquaticsystems. In some systems, groundwater discharge can rival rivers and upwelling, as asource of nutrients. The implications of groundwater discharge include harmful algalblooms caused by nutrient loading and poor water quality caused by pollutantstransported through groundwater discharge. Much research has been directed atquantifying the flux of groundwater and associated constituents through groundwaterdischarge using radium isotopes as geochemical tracers. Radium isotopes representsome of the most common geochemical proxies used to calculate groundwaterdischarge rates to lakes, oceans, and other water bodies. However well-establishedthese tracers are in the scientific community, they are often used as a single proxy forgroundwater discharge resulting in large errors due to natural variability anddependence on residence time, and these errors compound through the calculations.Large errors in the estimates of the volume flux of groundwater discharge lead to large errors in constituent fluxes through groundwater discharge, which diminishesthe usefulness of such efforts. Additionally most SGD-focused studies stop atcalculating the SGD and associated constituent fluxes, and pondering the impacts ofthe constituents on the marine ecosystem, with out directly measuring the impact onthe system through other methods. The focus of my thesis is to integrate methods ofcalculating SGD fluxes based on multi-radium isotope measurements with mixingmodels, bioassay incubation experiments, and water isotopes to better understand theimpacts of SGD on marine systems. First (Chapter 1) I will integrate a multi-radiumisotope method to calculate SGD fluxes with water isotopes to better understand thehydrology of the systems to understand the governing processes and importance ofSGD as a conduit of methane to the North Pacific and Artic Oceans. Then (Chapter2) I will combine a single radium isotope SGD flux model with a bioassay incubationexperiment to determine the ability of SGD to impact phytoplankton ecology inMonterey Bay, California. Last (Chapter 3) I will combine a multi-radium isotopeand nutrient flux mixing model with a multi-radium isotope SGD flux model todetermine the importance of SGD as a nutrient source compared to sub-thermoclinewater and river water in Monterey Bay, California.

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