Master of Science (MS)
Renewable Natural Resources
As one of the most valued and treasured natural resources, today many lakes in the world face degradation of their water quality due to nutrient enrichment, toxic contamination, and hydrological modification from their drainage areas. Among various water quality impairments, dissolved oxygen (DO) depletion is often a leading stressor in lake systems. Despite numerous studies on DO in deep water lakes in temperate regions, the knowledge of DO dynamics in eutrophic shallow lakes in subtropical regions is still limited. This thesis research conducted intensive DO monitoring in an eutrophic shallow lake in south Louisiana to characterize diel cycles of DO to determine trophic state changes, develop a deterministic model that can predict hourly change in DO of a water body with high-time resolution weather parameters, and develop a rapid field method of predicting biochemical oxygen demand (BOD) using chlorophyll-a fluorescence. DO concentrations in the studied lake were recorded at 15-minute intervals during 2012-2014, along with other water quality parameters. Field trips were made to measure lake water fluorescence and collect water samples for BOD and nutrient analysis. Additionally, a comparative study was done to discern trophic state changes over the past 5 years. The research yielded a substantial set of findings and conclusions to the research questions initially proposed. A comparison of diel DO cycles between 2008-2009 and 2013-2014 successfully revealed a clear intensification of eutrophication in the studied lake, indicating that analyzing the change in diel DO ranges can improve the current methods for classifying trophic states and assessing the change of eutrophication status of water bodies. A one-dimensional, deterministic DO model was developed for estimating the hourly change of source and sink components of DO, such as photosynthesis, re-aeration, respiration, BOD and sediment oxygen demand. The modeling yielded successful results of simulating high-time fluctuation of DO in the studied lake overall and showed good predictability for extreme algal bloom events. There was a linear, positive relationship between chlorophyll a fluorescence and BOD, and the relationship appeared to be stronger with the 10-day BOD (r2 = 0.83) than with the 5-day BOD (r2 = 0.76).
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Xu, Zhen, "Dissolved Oxygen Dynamics and Modeling - A Case Study in A Subtropical Shallow Lake" (2014). LSU Master's Theses. 592.