Suspended Sediment Dynamics of Texas Estuaries

A dissertation submitted in partial fulfillment of the requirements for the degree of DOCTOR of PHILOSOPHY in COASTAL AND MARINE SYSTEM SCIENCE from Texas A&M University-Corpus Christi in Corpus Christi, Texas.Suspended sediments are an integral part of estuarine systems in that they impact water quality and form habitats; their flux is driven by the interplay between freshwater inflow, tidal currents, wind-wave resuspension, commercial fishing, and dredging operations. The objective of this dissertation is to investigate the relative importance of the aforementioned drivers of suspended sediment in the three largest Texas estuaries (Galveston, Matagorda, and Corpus Christi Bays) using a variety of analysis methods. Analyses of suspended sediment drivers using a Texas State water quality database of in situ samples (Chapter II), development of an algorithm to transform satellite imagery into suspended sediment concentrations (Chapter III), and analysis of a 12-year time series of satellite-derived suspended sediment concentrations (Chapter IV) were used to accomplish the dissertation objectives. The relative importance of freshwater inflow, tidal currents, and wind-wave resuspension was determined by statistical analyses of in situ point measurements of total suspended solids (TSS) and environmental forcings for the period of 2000-2010. The findings from these analyses show that wind-wave resuspension is the most dominant forcing of TSS in Corpus Christi, Matagorda, and Galveston Bays. The analyses further indicated that freshwater inflow in Galveston Bay and astronomical tides in Matagorda Bay also influence the variability of TSS. An algorithm to transform satellite reflectance data into TSS was created Analyses determined the best model was an exponential fit of a red-green band ratio. The algorithm was then used to create synoptic time series of TSS for the period of 2002-2014 for the estuaries. Analysis of the satellite-derived time series shows how freshwater inflow, tidal currents, wind-wave resuspension, commercial fishing, and dredging operations influence the long-term variability of TSS in Galveston, Matagorda, and Corpus Christi Bays. Median and interquartile range composites of suspended sediments were generated for seasonal wind and inflow regimes in each estuary. TSS patterns show that the Galveston Bay system is dominated by riverine inflow with some influence from frontal passages. Surprisingly, the influence of oyster harvesting causing locally high TSS values in Galveston Bay is the most salient pattern within the estuary. Matagorda Bay’s patterns indicate that the system is mostly controlled by wind-wave resuspension with patterns changing between northern frontal passages and southeasterlies dominated seasons. Corpus Christi Bay is similarly influenced by wind-wave resuspension with different patterns during the predominant northerlies and prevalent southeasterlies seasons. The impact of dredging is also apparent in long-term patterns of Corpus Christi Bay as concentrations of suspended sediments over dredge spoil disposal sites are higher and more variable than surrounding areas, which is most likely due to less consolidated sediments and shallower depths requiring less wave energy for sediment resuspension. For Corpus Christi and Matagorda Bays, this research (Chapters II & IV) showed that wind-wave resuspension is the dominant forcing of TSS. Satellite data allowed the identification of patterns characteristic of different wind regimes. Additionally the point data analysis (Chapter II) showed that tidal forcing has an influence on TSS in Matagorda Bay. Both analyses (Chapters II & IV) show that wind forcing is less influential in Galveston Bay as compared to the other estuaries, and that freshwater inflow are important in Galveston Bay. A major highlight of this research is the advantage provided by long synoptic time series of satellite-derived TSS that elucidated the major drivers of suspended sediments in estuaries as well as their seasonal variability. With usage of satellite data, this research identified oyster harvesting to be a significant source of suspended sediment in Galveston Bay.Physical and Environmental SciencesCollege of Science and Engineerin