Date Awarded

2024

Document Type

Thesis

Degree Name

Master of Science (M.Sc.)

Department

Virginia Institute of Marine Science

Advisor

Marjorie A.M. Friedrichs

Committee Member

Pierre St-Laurent

Committee Member

Mary Fabrizio

Committee Member

Piero Mazzini

Committee Member

Raymond Najjar

Abstract

Climate change is already increasing the volume and duration of coastal hypoxia and threatening living resources, particularly in eutrophic ecosystems. Atmospheric warming exacerbates deoxygenation by decreasing gas solubility and enhancing respiration and remineralization. Changes in terrestrial runoff and sea level influence hypoxia via nutrient availability and altered water temperature, respectively. However, the impacts of other future climate changes, including winds, shortwave and longwave radiation, non-runoff precipitation, and ocean water conditions, are still unknown. In this study, the impacts of such future climate changes on hypoxia in Chesapeake Bay were examined using a 3-D coupled estuarine hydrodynamic–biogeochemical model linked to a regulatory watershed model. A control run simulated 1991-1995; while mid-21st century projections assuming no change in management actions were generated by applying downscaled outputs of three Earth System Models (ESMs), run under a “business as usual” emissions scenario. Mid-21st century hypoxic volume (O2 < 3 mg L-1) integrated over all days of a given year, also called annual hypoxic volume (AHV), is projected to increase by a minimum of 13% up to a maximum of 35%, when using the centroid ESM, with higher freshwater discharge years resulting in smaller percent increases. The use of future climate projections from the other two ESMs resulted in five-year average percent increases in AHV of 5% (relatively cool and dry ESM), 21% (centroid ESM) and 35% (relatively hot and wet ESM). Future changes to hypoxia are projected to vary seasonally, with hypoxic conditions projected to start earlier, but no change or decreased hypoxia in mid-summer. Finally, model runs with subsets of modified climate forcings revealed that air temperature accounted for the majority (72 ± 18%, five-year mean ± standard deviation) of the increase in AHV. Next most impactful to AHV were climate changes to watershed inputs (21 ± 31%) and sea level (-1 ± 24%), with both impacts being highly dependent on freshwater discharge. Finally, changes to winds, radiation, non-runoff precipitation, and ocean water conditions cumulatively accounted for only small future percent increases in AHV (5 ± 3%). To reach regulatory water quality goals despite these competing impacts of climate change, future nutrient management actions will likely need to be more aggressive.

DOI

https://dx.doi.org/10.25773/v5-jf6s-ha77

Rights

© The Author

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