Degree

Doctor of Philosophy (PhD)

Department

Civil and Environmental Engineering

Document Type

Dissertation

Abstract

Mesocosms were constructed to allow scientists to isolate variables in a microtidal marsh environment, mimicking the natural conditions found in Terrebonne Bay. The control offered by these mesocosms is given by a process control system that takes user inputs and automates water movement. Twelve mesocosms were constructed, each holding 4.02 m3 (142 ft3) of marsh soil and 3.88 m3 (137 ft3) of water to give 3 experimental levels and a control, all in triplicate.

Each mesocosms that was constructed contained marsh plants in soil plugs 9 feet in diameter and 3 feet deep. These marsh plugs are held in fiberglass tanks that allow for tides to vary up to 11 inches above and below the marsh surface, with the low tide dropping along an exposed side of the marsh. The backbone of the mesocosms’ design is the airlift, which allows for centralized air blowers to move water to mimic tides, keeping each system isolated and mechanical parts shielded from corrosion. The system exchanges experimental water with water from the nearby bayou using a system of ball valves and pumps and returns used water to the bayou after going through a treatment system.

The operator of the system uses a GUI (graphical user interface) to input commands to a computer program that then operates the various components of the system. The central program was coded using the Processing© program with control over various valves and sensors in the field controlled with the Arduino Uno. The two programs communicate wirelessly using the XBee software and hardware. The results of the process control system show that the system closely matches what was input by the user, giving the operators of the system the ability to control the system without needing a deep understanding of computer code.

Date

1-15-2019

Committee Chair

Malone, Ronald

DOI

10.31390/gradschool_dissertations.4797

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