Identifier

etd-03272017-113450

Degree

Master of Science in Civil Engineering (MSCE)

Department

Civil and Environmental Engineering

Document Type

Thesis

Abstract

Coastal deltaic floodplains provide an important ecosystem service by removing or retaining nitrate from enriched riverine water. Wetland plants, soils, and microbes within these floodplains use nitrate through uptake, burial, and denitrification, thereby reducing the impact of nitrate on algal blooms and hypoxia in the Gulf of Mexico. However, these processes depend on the physical, biological, and chemical conditions within the floodplain. Understanding and characterizing the hydrodynamics of these systems and the relative impact of river, tide, and wind forcings are the first steps in understanding the biogeochemical processes controlling nitrate removal. Motivated by the desire to identify biogeochemical hotspots within coastal deltaic floodplains, this project focuses on modeling the hydrodynamics of these complex wetland ecosystems. Biogeochemical hotspots occur where anaerobic soils, sufficient organic carbon supply, longer residence times, and warmer water temperatures create optimal conditions for processes such as denitrification. The latter two conditions are strongly controlled by the hydrodynamics of the system. A Delft3D-FLOW model is developed for Wax Lake Delta, an actively prograding delta in southeastern Louisiana, in order to simulate daily and seasonal changes in water temperature and residence time within different hydrogeomoprhic zones of coastal deltaic floodplains. From January to March 2015, intertidal floodplains have warmer temperatures and longer residence times (up to 2.5 days) than subtidal floodplains (up to 1.5 days). However, when river discharge increases during spring floods, connectivity between channels and floodplains increases and residence times within all zones decreases as water is flushed more quickly to the Gulf of Mexico. Correctly simulating residence time of water within floodplains is essential to future efforts to model the transformation of nitrate in these systems.

Date

2016

Document Availability at the Time of Submission

Release the entire work immediately for access worldwide.

Committee Chair

Willson, Clinton S

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