Semester of Graduation

Spring, 2024

Degree

Master of Oceanography and Coastal Sciences (SOCS)

Department

Oceanography and Coastal Science

Document Type

Thesis

Abstract

Coastal marshes provide many valuable ecosystem services. However, these wetlands are threatened worldwide, being subject to sea level rise, sediment starvation, subsidence, coastal edge erosion, etc. Many efforts are being made to counteract this wetland loss and preserve the ecosystem services. Two such methods are sediment diversion and the thin layer placement (TLP) of dredged sediment.

Sediment diversion involves reconnecting the main channel of a river body to disconnected wetlands, supplying much needed soil-building materials. However, this method affects the salinity of the waters, introducing large amounts of freshwater into the system. Salinity changes can affect marsh biogeochemistry. Most ecological impact predictions make use of surface water salinity data, but this study argues that porewater salinity is more biogeochemically relevant, as most plants in marsh ecosystems access porewater rather than surface water. This study took soil cores from a salt marsh in Barataria Bay, Louisiana, the site of the upcoming Mid-Barataria Sediment Diversion. In the lab, these cores underwent an experiment in which they were inundated with deionized water for 28 days to mimic the freshwater input into the marsh over the course of the planned 4-week period of diversion activity. This study found that the soil cores experienced some degree of freshening throughout the entire 0-10 cm soil depth range.

Thin layer placement involves the deliberate application of sediment, often dredged sediment, onto a wetland in order to achieve a target thickness. This method, like sediment diversion, is used to nourish the marsh with sediment. Thin layer placement is a relatively modern technique, and thus there is little known about the long-term effects of the practice, particularly regarding microbial community responses. This study took soil samples from a coastal marsh in Avalon, New Jersey about 7 years after the completion of the TLP project at the site. The TLP sediment, buried soil, and a control marsh were sampled. After a water quality denitrification experiment and soil characterization, it was found that these TLP soils had denitrification ability equal to that of a natural marsh, and that many of the soil properties (bulk density, N-cycling properties, etc) had begun approaching the values of the control after 7 years.

Date

3-26-2024

Committee Chair

White, John

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Available for download on Saturday, March 22, 2025

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