Semester of Graduation

Spring 2024

Degree

Master of Environmental Engineering (MEnvE)

Department

Civil Engineering

Document Type

Thesis

Abstract

As sea level rise, subsidence, and abandonment of natural deltaic processes due to a highly engineered Mississippi River continue to threaten Louisiana’s coastal wetlands, the need for a system-wide understanding of natural wetland land-building and preservation processes has never been greater. A key component of any wetland is the ever-changing water environment that periodically floods and dries the marsh platforms. The flooding depth, duration, and frequency, known as the hydroperiod, along with salinity and soil fertility are key determining factors of vegetation and marsh types at a particular location. Different types of vegetation will have different growth characteristics such as root production, which contributes to soil formation. We hypothesize that plant growth response to flooding inundation varies with species in brackish and saline marshes, and that maximum growth response occurs at neither extreme but some mid-inundation range. We further predict that varying hydroperiod and salinity from the brackish to saline zone determines the soil microbial community composition, controlling the cycling of wetland nutrients. This study found that while both dominant brackish and saline species favor high inundation over low inundation, they both also produce the most biomass under a combination of inundated and dry conditions. We also found evidence that the key turning point in soil-surface elevation where inundation becomes too great to support growth can occur on a very small scale, and that identifying salinity transition zones and the response of microorganisms to environmental conditions can be very powerful tools for assessing soil formation properties or predictions. By artificially manipulating soil surface elevation in “marsh organ” mesocosms across a salinity gradient in coastal Louisiana, the relationship between plant growth and inundation can be explored to understand how marsh productivity responds to sea level rise scenarios.

Date

1-14-2024

Committee Chair

Willson, Clint

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