Date Thesis Awarded

4-2020

Access Type

Honors Thesis -- Access Restricted On-Campus Only

Degree Name

Bachelors of Science (BS)

Department

Geology

Advisor

Matthew Kirwan

Committee Members

Christopher Bailey

Gregory Hancock

Shannon White

Abstract

Tidal marshes are coastal landforms that provide invaluable ecosystem services but are vulnerable to sea-level rise and saltwater intrusion. Processes at the marsh seaward and landward boundaries control their size and survival. At the seaward boundary, a primary cause of marsh loss is erosion. However, it is currently unknown how increased saltwater intrusion will affect erosion rates. At the landward boundary, marshes migrate into adjacent terrestrial uplands which undergo stresses from rising sea-level, expanding wetland lateral extent. This thesis assesses marsh vulnerability to saltwater intrusion by quantifying marsh erodibility and migration potential along a salinity gradient in the York River in southeastern Virginia.

Because processes at the seaward and landward boundary control marsh vulnerability, this study examines interactions at both locations in the marsh to assess resiliency against sea-level rise. For the first chapter of this thesis, I measure soil shear strength as a proxy for marsh erodibility at five sites and find that freshwater marshes are weaker than salt marshes. Results show marsh interior erodibility decreases with an increase in belowground biomass. Furthermore, there is a correlation between soil shear strength and soil properties at the marsh edge, but this relationship varies between salinity regimes. For the second chapter of this thesis, I calculate the elevation of the marsh-forest boundary using remotely-sensed LiDAR data to determine marsh migration potential. Threshold elevation data exhibit narrow distributions, with only a 3cm difference between all five sites. I then generate maps depicting future wetland-upland conversion under different sea-level rise scenarios using the marsh-forest boundary elevations. Marsh migration varies visually between all sites predominantly depending on the slope of the adjacent upland coastal forest. Sea-level rise and saltwater intrusion in the York River will strengthen and expand marshes through decreasing erodibility and increasing migration potential—augmenting marsh resiliency against sea-level rise.

Recommended Citation

Gillen, Megan, "Vulnerability and Resilience of Tidal Marshes along an Estuarine Salinity Gradient" (2020). Undergraduate Honors Theses. William & Mary. Paper 1552.
https://scholarworks.wm.edu/honorstheses/1552