The entire thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file; a non-technical public abstract appears in the public.pdf file. Title from PDF of title page (University of Missouri--Columbia, viewed on January 19, 2010). Thesis advisor: Dr. Charles F. Rabeni. Includes bibliographical references.

Bottom sediment from a 750-square-mile area offshore from the mouth of the Brazos River, Texas, has been analyzed statistically to determine the pattern and processes of sedimentation of the neritic environment and of a modern delta. The Brazos delta is characterized by topset beds of poorly sorted laminated sand, silt, and clay, foreset beds dipping at approximately 1° composed of fine sand grading downward (seaward) into clay, and poorly developed bottomset beds representing slow deposition of clay from the Brazos combined with reworking of material from a submerged Pleistocene deltaic plain. Interpretation of the sediment on the basis of its modal characteristics indicates that effective sorting by waves develops a unique uniform distribution of sediment types from the beach to a depth of 60 feet. Farther offshore from this depth exotic agents such as hurricanes and uncharted bottom currents are predominant and act to bring "obstacles" (topographic irregularities) into a marine profile of equilibrium. Maps of sediment types, mean size, inclusive standard deviation, inclusive skewness, and kurtosis precisely describe the geologic history of the surface sediments. Individual and bivariant plots of the statistical parameters are shown to be useful in determining direction to the shoreline as well as completely defining the modality of the sediment, which in effect defines the environment of deposition. Fluctuations in source area are reflected by the relation of mean size and depth. Heavy mineral distribution shows that the suite of durable minerals carried by the present Brazos River is diluting an existing widespread suite of less durable minerals characteristic of the Colorado River drainage area. Variation in clay mineral composition results from differential sedimentation and reflects source area, providing no evidence of alteration of the clay minerals during deposition by diagenesis. / text

The Mississippi River is considered the ultimate single channel meandering river. Five hundred km upstream from its mouth, about 25% of the river’s discharge is diverted into the Atchafalaya River. This diversion is controlled by the Old River Control structure, built by the US Army Corps of Engineers in stages since 1963, to stop the avulsion of the Mississippi River into the Atchafalaya. The study area is a 119 km sandy bedded reach near Old River Control that is highly impacted by engineering measures. Channel dimensions average 1,000 m wide with average thalweg depths of 23 m. The mean annual discharge is 15,000 m3s-1 with a water surface slope of 0.06 m per river mile. In a sandy bedded river, the effective discharge is the discharge which cumulatively transports the most sand. This study evaluates how the Old River Control structure has influenced an adjusting effective discharge between 1978 and 2011. The bed load component of sand transport is included by employing a novel, automated, cross-correlation technique. It was found that the upper limit for discharges that cumulatively transport 85% of the total sand load has decreased from 34,000 m3s-1 to 28,000 m3s-1 between 1978 and 2011. Sand transport from 1982 to 2011 occurred during progressively greater ratios of water discharge to the Atchafalaya River and corresponded to an aggradational trend in the nearby Mississippi River at Red River Landing stream gage. The combination of this sand transport trend and nearby channel aggradation is some indication that the diversion may not be stable and that the avulsion of the lower Mississippi River is ongoing. However, sand was transported at similar discharge ratios in the 1978 to 1982 and 2002 to 2011 periods. Future trends will reveal definitively if these findings indicate that the lower Mississippi River avulsion is continuing. Two aims are pursued by placing the effective discharge approach into the geomorphologic context of the study area. Ten zones are categorized by four distinct geomorphologic classes: meander, no islands; meander, geologic control; meander, islands and divided flow; and straight zones. One, these classes have merit for future research and are shown to be geomorphologically distinct in several ways: natural levee height and channel planform adjustment relationships, sinuosity and width to depth ratios, and bedform depth to height scaling. Two, this approach allows the comparison of the effective discharge to the study area’s geomorphology. Process-form linkages can be made between sediment transporting events and the three levels in a fluvial hierarchy: fluvial bedforms and channels, bars, and levees. Median grain size and channel position of sediment samples from these three levels were plotted on combined LiDAR and bathymetric derived cross- sections from specific geomorphologic zones. This analysis indicates that the fluvial hierarchy coincides with the stages of effective discharge but seems to scale to the elevation of natural levees. This study interjects a geomorphologic approach into the lower Mississippi River discourse and raises a number of interesting questions for further research. / text

published_or_final_version / Earth Sciences / Doctoral / Doctor of Philosophy

Groundwater is now being considered as an alternative water supply in the Pearl River Delta (PRD) because of the increasing demand for fresh water coupled with deterioration in river water quality as a result of rapid urbanization and industrialization. There are thick aquitards in the PRD as a result of several times transgression and regression in the Holocene. This study considers this aquitards as a research object because it has a significant impact on the underneath confined aquifer. It is necessary to analyze the hydraulic properties of the aquitards. A slug-test is a reasonable method to determine the hydraulic conductivity and specific storage of the low-permeability aquitards of silt and clay in the PRD. In this study, several slug-test methods were used to determine the hydraulic parameters of aquitards in several piezometers at the key site MZ04in the PRD. The results from these methods were compared to obtain the most reasonable group of hydraulic parameters. A reasonable equivalent numerical method is applied at the key site MZ04 site after the calibration with the C-B-P solution and the KGS model. The natural groundwater regime is obtained, which is helpful for the further research. A three-dimensional numerical model using MODFLOW is carried out under some assumptions and the simplification for the sediments structure. The characteristics of regional groundwater flow and the influence of hydraulic properties of the aquifer-aquitard system on groundwater flow were analyzed. The simulated groundwater level both in the unconfined aquifer and confined aquifer agree reasonably well with the observed data. Study on the water budget of the groundwater showed that the quantity of ground water discharged from participation to participate the water exchange is very small. In the groundwater participated water exchange, 97% of them flow into rivers, while only 3% of them flow into the sea. Moreover, the vertical flow is more important than the horizontal flow to the regional ground water balance in aquitards according to the water budget obtained from the model. The research of the PRD needs numerous data due to the complicated deposition and evolution process of the sediments and the intensive river network. The modeling results are preliminary because of the complexity of the geological and hydrogeological conditions in the PRD and the limitation of the observed water level data. The hydraulic parameters calculated for this study and the model results can provide a basis for further research on groundwater in the PRD. / published_or_final_version / Earth Sciences / Master / Master of Philosophy

An aquitard is not only a confining layer in the aquifer-aquitard system, but also a functional complex for nutrient reservation and microorganism inhabitation. Geochemical characteristics and geomicrobial processes in aquitards play an important role in groundwater quality, and should be well studied. The Pearl River Delta is dominated by clay-rich aquitards and was intensively influenced by Holocene transgression. In this thesis, the aquifer-aquitard system in the PRD was studied from various perspectives including geophysics, geochemistry and geomicrobiology. Sediment and groundwater samples were taken from representative locations in the PRD at different lithological units. Particle size distribution, computed axial tomography, optically stimulated luminescence dating and scanning electron microscopy were analyzed to understand the geophysical properties. Concentrations of major ions and abundances of environmental isotopes were measured for geochemical analysis. Bacterial 16S rRNA gene clone libraries were constructed to analyze microbial identifications and community structures in different strata. Gene abundances of anammox 16S and bacteria amoA in both sediment and groundwater samples were quantitatively analyzed with 15N isotope at the same depth. The mixing process of seawater and river water was the dominant factor controlling the isotopic and chemical characterizes of groundwater in the system. Isotopic fractionation in the aquitards was majorly controlled by chemical and biological reactions other than diffusion. Chemical pattern in this system was mainly controlled by topography and sea level in the Holocene. Independent sedimentary centers of strong reducing environment were located in the depressions controlled by fault zones, and generated massive amount of pyrite minerals in the sediment and NH4+ in the groundwater. The sea level and depositional environment in the Holocene determined the physical structures of the sediment and seawater/river-water ratio in the estuary. Isotopic research also demonstrated that South Asia Monsoon was the major source of atmospheric precipitation in the PRD. Bacterial species in the PRD sediment were identified. Canonical correspondence analysis between bacterial linages and environment factors showed that community structures were significantly modified by geological conditions. High bacterial diversity was observed in samples from the Holocene aquitard M1 and aquifer T1, while in the older aquitard M2 and basal aquifer T2, the bacterial diversity was much lower. Chloroflexi, γ-proteobacteria and δ-proteobacteria were the dominant phyla in the aquitard sediment. β-proteobacteria was the dominant phylum in sediment which was strongly influenced by fresh water. Anammox was the controlling biochemical process in microbial-derived ammonium loss, as demonstrated by gene abundance coupling with 15N isotope and ammonium concentration. The 16S gene abundance of anammox bacteria ranged from approximately 105 to 106 copies/g in the aquitard sediment, and ranged from 104 to 105 copies/g in aquifers. amoA gene abundance was 1-2 orders lower than anammox bacteria 16S in aquitard sediment, but in aquifers, the gene abundances of amoA and anammox 16S were similar. Interface between aquifer and aquitard was demonstrated as biochemically enhanced zone. The results of this study significantly benefited the understanding of geochemistry and microbiology in the aquifer-aquitard system, and showed directions for future work on geomicrobiology in aquitards. / published_or_final_version / Earth Sciences / Doctoral / Doctor of Philosophy

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No description available.

No description available.

River ice is an important component of the traditional way of life for the communities along the Slave River both culturally and economically. During the winter, a stable ice cover provides local residents with safe access to their traditional hunting, trapping, and fishing grounds along the river. Periodic spring ice breakup flooding is required to maintain the ecological balance along the Slave River Delta. Recently, however, local observations have indicated changes in ice cover characteristics (e.g. air pocket formation, double layer ice, ice cover flooding) during the winter, which increase the risks of travelling on the ice. Also prolongs dry periods during the spring are leading to rapid growth of invasive vegetation that reduces the lake and channel areas of the Delta. Although some attempts have been made to understand the patterns of spring flood frequency in the Delta, very little is known about the Slave River’s ice cover characteristics and behaviour. Remote sensing techniques and field surveys were used in this study to understand the ice cover progression and to examine ice cover characteristics along the river during the winters of 2013-2014 and 2014-2015. RADARSAT-2 satellite imagery captured the changes in the ice cover and identified different types of ice during the winter seasons at two primary study sites – downstream of Fort Smith and the Slave River Delta. The mechanism of ice cover growth, with the formation of air pockets and layers underneath the ice cover was investigated. Steeper channels and several open water sections appear to be contributing to significant amounts of air entrainment into the water in winter. Changes in the hydraulic characteristics due to flow regulation and ice cover progression can also change the quantity and distribution of air pockets along the river ice cover. Additionally, the impact of flow fluctuations on the ice cover (e.g. ice cover flooding) was also observed. Increases in discharge cause the ice cover to crack or dislodge from the river banks, leading to water seeping onto the ice and flooding it, which has implications for the muskrat and beaver populations. A geospatial model was developed to determine the spatial patterns of ice cover breakup along the river from Fort Fitzgerald to the delta. This model successfully identified the areas of breakup initiation and persistence of ice until the end of the breakup. MODIS satellite imagery was used to describe the temporal patterns and evolution of breakup events between the years 2008 and 2011. In addition to geomorphological influences, air temperature and flow conditions also have strong impacts on the spatial and temporal patterns of the ice cover breakup.