Doctor of Philosophy (PhD)
Engineering Science (Interdepartmental Program)
The industrial agriculture complex of the Mississippi River Drainage Basin has the positive effect of feeding more individuals with less land via the use of chemical nutrients, pesticides and drainage. The negative effects of the agricultural nutrient load are carried by the Mississippi River to the Gulf of Mexico. After the flood of 1927 the Flood Control Act of 1928 began changing the Mississippi River into a navigation and flood control project. While successful, the river was turned into a channel where nutrient input was discharged into the Gulf of Mexico. Nitrogen compounds discharged from the Mississippi are claimed to degrade coastal fisheries and create a Gulf of Mexico hypoxia zone where aquatic life dependent on greater than 2 mgL-1 oxygen levels cannot survive. Stratification and nutrients are required for the production of algae blooms. Discussions continue as to whether the causes of the algae bloom are biological or due to physical changes in the river plume, wind currents and amount of river discharge. In this work, the creation of a STELLA® mathematical model correlating the “algae bloom” to the hypoxia zone in the Gulf of Mexico was developed considering numerous inputs and system variables or system data. Analysis of correlative data such as: sediment oxygen content, photosynthesis, turbidity, nutrient content and light penetration aided in defining the limits of hypoxia. Causative data such as urbanization, removal of wetlands, channelization and deforestation was found related to the causes of hypoxia. While data were limited, variables did correlate to the relative size of the hypoxia zone, but revealed no insight into direct causation. Limited data made verification of the model to acceptable standards difficult. The creation or modification of two predator-prey STELLA ® models showed that ecological changes can cause the marine inverted trophic pyramid to invert causing algae to grow out of control. This “bloom” can cause the hypoxia zone by removal of algae filter eaters. Physical factors such as mixing can diminish or eliminate the hypoxia zone. Standardized models were employed individually and in combination to yield insight into ecological variables and those variables’ contributions to causation.
Document Availability at the Time of Submission
Release the entire work immediately for access worldwide.
Brumfield II, Jimmie Arnold, "Dynamic model of ecological factors impacting the Gulf of Mexico dead zone" (2010). LSU Doctoral Dissertations. 2963.
Constant, W. David