Semester of Graduation

Fall 2025

Degree

Master of Science (MS)

Department

Oceanography and Coastal Sciences

Document Type

Thesis

Abstract

Estuarine mud is composed of clay and silt particles, which are transported in different ways but are often lumped together into a single class. Here we monitor silt and clay dynamics in a salt marsh in South Carolina (USA) using a novel approach, previously tested in the laboratory, in which optical backscatter (turbidity) is a proxy for suspended clay and acoustic backscatter is a proxy for suspended silt. . Using these measurements, we found that clay is about 55-75% of the total suspended mud, in accordance with previous independent estimates. Using the water clearing rate and eddy covariance methods we found a settling velocity of ~0.02 mm/s for clay and ~1 mm/s for silt, in accordance with previous laboratory estimates. We also found that silt and clay are transported differently: the former is in near equilibrium with local resuspension (akin expected for sand), whereas the latter is not. This non-equilibrium is most evident on the marsh platform, where clay concentration only drops by 20-30% over four hours around slack tide and it remains nearly constant over 20 m across the marsh interior, indicating a low retention rate for clay. More effort should be put into understanding how the mud type (clay vs silt) affects the overall mud transport and deposition on the marsh platform. For the same amount of sediment, marshes with a high clay content might have less deposition on the marsh platform and presumably a lower accretion rate.

Date

11-3-2025

Committee Chair

Mariotti, Giulio

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