WHOI Theses

Permanent URI for this collection

https://hdl.handle.net/1912/1172

WHOI's educational role, at the graduate level, was formalized in 1968 with a change in its charter and the signing of an agreement with the Massachusetts Institute of Technology for a Joint Program leading to doctoral (Ph.D. or Sc.D.) or engineer's degrees. Joint master's degrees are also offered in selected areas of the program. Woods Hole Oceanographic Institution is also authorized to grant doctoral degrees independently.

New theses are added as they are published.

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Browsing WHOI Theses by Author "Charette, Matthew A."
  • Thesis
    Constraining natural and anthropogenic disturbances in the delivery of coastal ecosystem services
    (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 2022-02) Luk, Sheron Y. ; Spivak, Amanda C. ; Charette, Matthew A.
    Coastal ecosystems provide key services that benefit human wellbeing yet are undergoing rapid degradation due to natural and anthropogenic pressures. This thesis seeks to understand how disturbances impact salt marsh and estuarine ecosystem functioning in order to refine their role in coastal ecosystem service delivery and predict future resilience. Salt marsh survival relative to sealevel rise increasingly relies on the accumulation and preservation of soil organic carbon (SOC). Firstly, I characterized SOC development and turnover in a New England salt marsh and found that salt marsh soils typically store marsh grass-derived compounds that are reworked over centuries-to-millennia. Next, I assessed how two common marsh disturbances – natural ponding and anthropogenic mosquito ditching – affect salt marsh carbon cycling and storage. Salt marsh ponds deepen through soil erosion and decomposition of long-buried marsh peat. Further, the SOC lost during pond development is not fully recouped once drained ponds are revegetated and virtually indistinguishable from the surrounding marsh. Mosquito ditches, which were installed in ~ 90% of New England salt marshes during the Great Depression, did not significantly alter marsh carbon storage. In Buzzards Bay, Massachusetts, a US National Estuary, we tested relationships among measures of estuarine water quality, recreational activity, and local socioeconomic conditions to understand how the benefits of cultural ecosystem services are affected by shifts in water quality associated with global change and anthropogenic activity. Over a 24-year period, water quality degradation coinciding with increases in Chlorophyll a is associated with declines in fishery abundance and cultural ecosystem service values ($0.08 – 0.67 million USD). In combination, incorporation of both anthropogenic and natural disturbances to coastal ecosystem functioning and service delivery can produce improved estimates of ecosystem service valuation for effective resource decision-making under future climate scenarios.
  • Thesis
    Distribution and behavior of trace metals in the subterranean estuary of an Arctic coastal lagoon
    (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 2024-02) Schaal, Isabel V. ; Charette, Matthew A.
    Subterranean estuaries (STEs) can be an important location for biogeochemical reactions that may alter concentrations of chemical constituents of groundwater. With warming in the Arctic and the subsequent permafrost thaw, the relative importance of submarine groundwater discharge (SGD) to ocean chemical budgets will grow. In this study, we examined the distribution of select trace metals (Fe, Mn, V, U, Mo and Ba) in the STE, lagoon surface waters, and coastal sediments of Simpson Lagoon along the Beaufort Shelf of Alaska. This location is unique among studies as the STE consists of organic-rich sediments. Samples were collected over two years and throughout seasonal water conditions, including the melting, open-water, and freeze-up periods. Fe, Mn, V, and Ba mainly exhibited non-conservative additions within the estuary, with Fe concentrations being some of the highest among groundwater studies. U exhibited both non-conservative removal and addition in the estuary, and Mo exhibited mainly removal. In the lagoon, non-conservative addition of U allowed for the calculation of an SGD flux. This flux, along with a Ra-derived flux, was used to estimate metal fluxes into the lagoon. Fluxes for all metals were similar to or greater than river flux estimates in all months except for June, when SGD was likely nonexistent. These fluxes can be used to assess SGD impact on the coastal Arctic; however, for reactive metals, processes in the lagoon may continue to alter metal concentrations before mixing with the greater Arctic Ocean. This study provides some of the first estimates of trace metal concentrations and fluxes within Arctic subterranean estuaries and exhibits the importance of considering SGD when assessing metal input to the coastal Arctic.
  • Thesis
    Radium isotopes and radon-222 as tracers of sediment-water interaction in Arctic coastal and lacustrine environments
    (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 2020-09) Dabrowski, Jessica S. ; Charette, Matthew A.
    Arctic marine and lacustrine systems are experiencing rapid warming due to climate change. These changes are especially important at the interface between sediments and surface waters because they are hotspots for biogeochemical transformations such as redox reactions, nutrient consumption and regeneration, organic matter leaching and degradation, and mineral weathering. Radium isotopes (223Ra, 224Ra, 226Ra, 228Ra) and radon-222, naturally occurring radioactive isotopes produced in sediments, are well-suited as tracers of nutrients, trace metals, and organic matter cycling processes at the sediment-water interface. In this thesis, I have applied radon-222 and the quartet of radium isotopes to study fundamental processes in subarctic lakes and on the Arctic continental shelf. First, radon-222 is used to quantify groundwater discharge into a shallow, tundra lake on the Yukon-Kuskokwim Delta in Alaska in summer of 2017. Radon-derived groundwater fluxes were then paired with methane (CH4) measurements to determine delivery rates of methane into the lake via groundwater. Groundwater CH4 fluxes significantly exceeded diffusive air-water fluxes from the lake to the atmosphere, suggesting that groundwater is an important source of CH4 to Arctic lakes and may drive observed CH4 emissions. Higher CH4 emissions were observed compared to those reported previously in high latitude lakes, like due to higher CH4 concentrations in groundwater. These findings indicate that deltaic lakes across warmer permafrost regions may act as important hotspots for methane release across Arctic landscapes. Then, the quartet of radium isotopes is used to study the impacts of storms and sea ice formation as drivers of sediment-water interaction on the Alaskan Beaufort shelf. The timeseries presented in this study is among the first to document the combined physical and chemical signals of winter water formation in the Beaufort Sea, made possible by repeat occupations of the central Beaufort shelf. Radium measurements are combined with inorganic nitrogen and hydrographic measurements to elucidate the episodic behavior of winter water formation and its ability to drive exchange with bottom sediments during freeze-up.