Browsing by Subject "groundwater"
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Item Adsorption of As(V), As(III) and methyl arsenic by calcite and the impact of some groundwater species(2009-05-15) Jones, Robert GarretThe objective of this research was to investigate the retention of arsenate (iAsV), arsenite (iAsIII), monomethyl arsenate (MMAsV) and dimethyl arsenate (DMAsV) by calcite and assess the impact of dissolved Ca2+, Mg2+, phosphate and sulfate on arsenic solubility, adsorption and precipitation phenomena. Adsorption kinetics of iAsV, evaluated at a low and high concentration, was a relatively rapid process, with a fast initial reaction rate within the first few minutes and a subsequent slower reaction rate as equilibrium was approached. The relative adsorption of arsenicals decreased in the following order: iAsV > iAsIII > DMAV > MMAV. In no case was a clear adsorption maximum observed with increasing dissolved arsenic concentration. Dissolved 0.01 M Ca2+ resulted in an increase in iAsV adsorption; however, in the presence of 0.1 M Ca2+ adsorption of iAsV was decreased. The presence of Mg2+ as 0.01 M Mg(NO3)2 resulted in decreased iAsV adsorption probably the result of a lower iAsV affinity for adsorbed Mg2+ as compared to Ca2+. Phosphate and sulfate were highly competitive with iAsV in adsorption to calcite and both resulted in decreased iAsV adsorption. The total prevention of iAsV adsorption at initial equimolar arsenic/phosphate concentrations > 88 ?M each could be from the consumption of available calcite surface sites by the specific adsorption of phosphate. Equilibrium modeling, using the geochemical and mineral speciation of equilibrium model (MINTEQA2), indicated that at low concentrations of arsenate or phosphate solid-phase precipitation was not likely and adsorption processes likely controlled solubility. At high concentrations of arsenate Ca3(AsO4)2 ? 3 2/3 H2O and Ca3(AsO4)2 ? 4 1/4 H2O solid phases could be controlling arsenate solubility. This study indicates that arsenic adsorption response by calcite was different than that of phosphate suggesting that arsenic may not be specifically adsorbed to calcium at the calcite surface. Reduction and biomethylation of arsenic decreased adsorption, suggesting that processes which could affect the speciation of arsenic in the environment, could increase arsenic mobility in environmental systems where calcite and dissolved aqueous calcium play a predominant role in controlling arsenic solubility. Dissolved aqueous concentrations of magnesium, phosphate and sulfate generally reduced the ability of arsenic to be adsorbed to calcite.Item Delineating controls on hydrologic variability and water geochemistry in central Texas(2013-08) Wong, Corinne I; Banner, Jay L.There is a strong concern about how water resources will be affected by future climate change. Investigation of how a hydrologic system might respond to climate change, however, requires a detailed understanding of the controls on and factors that might affect that system. The research presented in this dissertation focuses on improving the understanding of the Barton Springs segment of the Edwards aquifer in central Texas. The first three chapters of this dissertation present research investigating spatial and temporal controls on groundwater geochemistry. The fourth chapter focuses on characterizing and understanding the controls on long-term hydrologic variability by reconstructing past climate from a speleothem (cave mineral deposit) collected from a central Texas cave. On spatial scales, Edwards aquifer groundwater geochemistry is influenced by water-rock interaction (calcite and dolomite recrystallization, gypsum dissolution, and calcite precipitation) and mixing between fresh groundwater and saline groundwater. On temporal scales, variation in groundwater geochemistry is dictated by the extent to which fresh groundwater mixes with recharging stream water. The degree of mixing is sensitive to changes in climate conditions (i.e., more mixing under wetter conditions) and type of flow path (i.e., conduit or diffuse) that dominantly supplies a given site. The geochemistry of stream water, which provides the majority of recharge to the aquifer, is degrading over time and indirectly controlled by anthropogenic sources under both wet and dry conditions. Climate reconstructed from a speleothem suggests that central Texas moisture conditions were relatively constant from the mid to late Holocene (0 to 7 ka), except for an extended dry interval from 0.5 to 1.5 ka. Speleothem δ18O values spike during this dry interval, suggesting that decreases in Pacific-derived moisture or decreased tropical storm activity might have been coincident with the prolonged dry interval. This research has improved understanding of the natural variability of and controls on physical and geochemical components of hydrologic system in central Texas.Item Hillslope Hydrological Processes in a Costa Rican Rainforest: Water Supply Partitioning Using Isotope Tracers(2014-04-24) DuMont, Andrea LynCosta Rican tropical premontane rainforests are among the world's most valuable ecosystems in terms of diversity of animals, plants, and natural resources. These environments are dependent on water resources which fluctuate in quantity during the dry and wet seasons and which are significantly influenced by vegetation feedbacks. Currently, tropical premontane forest watersheds are insufficiently characterized in terms of groundwater and stream water interactions due to their limited accessibility and complex geological conditions. However, water produced from these watersheds is a critical renewable resource in Costa Rica. It plays a significant role in the production of downstream hydropower and acts as a supply for water distribution systems in many rural areas. In this study, stable isotope tracing of ?^(18)O and ?D was used to determine the source of water in a stream, and the relative contributions of water budget components (e.g., groundwater, soil water). Samples were collected beginning in the dry season and continuing through the wet season from 2013-2014 as the soil became progressively wetter. The ?^(18)O and ?D samples represent precipitation in the tropical forest, as well as groundwater, soil water, and stream water at several locations. This data is important to understanding the influence of vegetation and hydrogeological properties on groundwater and stream water in tropical headwater catchments. Streamflow averaged 0.06 m^(3)/min in baseflow and greater than 0.10 m^(3)/min during storms. Groundwater was seen to contribute to 80% of streamflow and was the main stream component even during storm events. A small proportion of the total amount of streamflow came from interflow and soil water (1%). Additional findings indicated that precipitation, about 4200 mm/yr, in the rainforest can be recycled source water. Storm tracks alternate from distribution starting in the Pacific Ocean to the Caribbean Sea over the course of the wet season. Overall precipitation was seen to be dominated by deep convection and enhanced during the wet season due to the North American Monsoon and the Intertropical Convergence Zone.Item Landowners' perceptions on coordinated wildlife and groundwater management in the Edwards Plateau(Texas A&M University, 2006-10-30) Limesand, Craig MiltonSince Texas contains less than 5% public land, private landowners are critical to the success of environmental management initiatives in the state. This has implications for resources that traverse property boundaries, such as wildlife and groundwater. Texas landowners are increasingly capitalizing on the income potential of fee-based hunting, and many have banded together to form Wildlife Management Associations (WMAs). Not only can such landowner associations enhance the coordination of resource management decisions, they also have the potential to increase social capital, which is reflected by interpersonal trust, reciprocity and civic participation. To improve the management of common-pool resources it is important to understand the relationship between social capital and coordinated resource management because long-term community stability and resource sustainability appear to be highly correlated. A 600-landowner mail survey (with 48.1% response) was conducted in the Edwards Plateau region of Texas to compare the land management characteristics and social capital of landowners who are members of WMAs with non-member landowners. The goal of this research was to determine how WMA membership, property size, and location affect levels of social capital and interest in cooperative resource management. It was hypothesized that members, large landowners, and northern landowners would be more interested in cooperative management and exhibit higher social capital. While WMA members and large-property owners were more involved in wildlife management than non-members and small-property owners, this interest in resource management did not carry over to groundwater. These groups were not more involved in groundwater management activities, and all survey groups were disinterested in joining private cooperatives for groundwater marketing. Social capital differences were more evident between large- and small-property owners than between WMA members and non-members. Members scored higher only on community involvement, while large owners scored higher on community involvement as well as trust. These results suggest that WMA membership per se does not significantly increase social capital among Edwards Plateau landowners, but do not necessarily refute the importance of social capital within WMAs. Differences in trust between members were positively correlated with increased communication and meeting frequency, suggesting ways WMAs can improve intra-association social capital.Item Measuring The Effectiveness of Groundwater Management Policies for the Carrizo-Wilcox Aquifer of Texas(2014-11-03) Gamache, Kevin RobertIn the United States, more than 80% of the population now lives in urban areas. By 2050, a significant portion of that population will live in megaregions consisting of two or more metropolitan areas linked with interdependent environmental systems, a multimodal transportation infrastructure, and complementary economies. The Texas Triangle Megaregion, one of 8 to 10 such regions in the United States, is spatially delineated by the metropolitan areas of Dallas/Fort Worth, Austin, San Antonio, and Houston, with a total land size of nearly 35,435 square kilometers. Supporting the modern industrial infrastructure of a major metropolitan megaregion has required extensive water-related modifications to the critical zone. These modifications come in the form of an extensive network of dams and reservoirs; a high-density matrix of wells for extracting water, oil, and gas from the critical zone; significant alterations of land cover; and interbasin transfer of ground and surface water. Progressive depletion of critical zone reserves threatens sustainable development in the heavily groundwater-dependent Texas Triangle and requires robust and effective water resource policy for the megaregion to remain economically viable. Facing growth that is expected to double the population of the state to more than 46 million by 2060, Texas has increased its efforts to implement comprehensive water resources planning during the past decade. State policy in Texas dictates that groundwater management is best accomplished through locally elected, locally controlled groundwater conservation districts (GCD). This study examined the effectiveness of GCDs as a water resource management tool in Texas. This research demonstrated no measurable difference in the annual rate of decline in groundwater levels in the Carrizo-Wilcox Aquifer in Texas after establishment of a GCD. The data did not show a correlation between the water allocation method used and the impact on average annual drawdown of the aquifer. The study was not able to demonstrate a relationship between the length of time a GCD has been in existence and the average annual drawdown rates in the aquifer.Item Restoration of resaca wetlands and associated wet prairie habitats at Palo Alto Battlefield National Historic Site(Texas A&M University, 2006-08-16) Margo, Michael RayCultivation and drainage projects associated with livestock production have substantially disturbed resaca wetlands and wet prairie habitats in southern Texas. As a consequence of the anthropogenic disturbances, the area of these wetlands has been reduced and the ecological integrity of the remaining wetlands has been compromised. The goal of this study was to explore effective strategies for ecological restoration of coastal prairie and resaca ecosystems in south Texas and provide restoration recommendations to the National Park Service at Palo Alto Battlefield National Historic Site (NHS). Field experiments were conducted to evaluate the effectiveness of different approaches for restoring Spartina spartinae on disturbed saline flats. A resaca hydrologic study was initiated to evaluate the groundwater hydrology in disturbed versus undisturbed resaca wetlands and explore potential restoration strategies. Transplanting S. spartinae in the fall season was more successful (80% survivability) than seeding (0% initial establishment), spring transplanting (0% survival), spring and fall mechanical transplanting (0% and 6% survivability, respectively). Soil disturbance significantly affected (p < 0.05) survival of transplanted tillers and basal diameter of both the bare root and container-grown transplants in the fall manual treatments. The initial hydrologic study of the resaca wetlands found that vegetation rooting zone hydrology was likely dependent on surface water rather than groundwater. These findings suggest that strategies that restore surface hydrologic regimes will likely restore the ecosystem structure and function of disturbed resacas. Manually transplanting bare-root stock of S. spartinae in the late fall season without soil disturbance will increase the likelihood of successful saline flat restoration.Item Spatial and temporal controls on biogeochemical indicators at the small-scale interface between a contaminated aquifer and wetland surface water(2009-05-15) Baez-Cazull, Susan EnidThis high-resolution biogeochemical study investigated spatial and temporal variability in the mixing interface zones within a wetland-aquifer system near a municipal landfill in the city of Norman, Oklahoma. Steep biogeochemical gradients indicating zones of enhanced microbial activity (e.g. iron/sulfate reduction and fermentation) were found at centimeter-scale hydrological and lithological interfaces. The small resolution study was achieved by combining passive diffusion samplers with capillary electrophoresis for chemical analysis. The spatial and temporal variability of biogeochemical processes found at the interfaces was evaluated in a depth profile over a period of three years. Correlations between geochemical parameters were determined using Principal Component Analysis (PCA) and the principal factors obtained were interpreted as a dominant biogeochemical process. Factors scores were mapped by date and depth to determine the spatial-temporal associations of the dominant processes. Fermentation was the process controlling the greatest variability in the dataset followed by iron/sulfate reduction, and methanogenesis. The effect of seasonal and hydrologic changes on biogeochemistry was evaluated from samples collected in a wet/dry period from three locations exhibiting upward, downward, and negligent hydrologic flow between aquifer and wetland. PCA was used to identify the principal biogeochemical processes and to obtain factor scores for evaluating significant seasonal and hydrological differences via analysis of variance. Iron and sulfate reduction were dominated by changes in water table levels and water flow paths, whereas methanogenesis and bacterial barite utilization were dominated by season and associated with a site with negligible flow. A preliminary study on microbial response to changes in geochemical nutrients (e.g. electron acceptors and electron donors) was conducted using in situ microcosms with the purpose of quantifying iron and sulfate reduction rates. Problems encountered in the experiment such as leaks in the microcosms did not allow the determination of respiration rates, therefore the experiments will be repeated in the future. The results suggest that iron and sulfate reduction were stimulated with the addition of sulfate and ferrihydrite (electron acceptors) and acetate and lactate (electron donors). This research demonstrates the importance of assessing biogeochemical processes at interface zones at appropriate scales and reveals the seasonal and hydrological controls on system processes.