Browsing by Subject "Barton Springs"
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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 Ecology and conservation of the endangered Barton Springs Salamander (Eurycea sosorum)(2011-05) Gillespie, Jennifer Hayley; Parmesan, Camille, 1961-; Abbott, John; Cummings, Molly; Dries, Laurie; Leibold, Mathew; McClelland, JimAmphibian decline is a major concern worldwide, and a lack of basic ecological and life history information for many species significantly limits our ability to evaluate the degree and possible causes of such declines, and to develop effective conservation strategies for threatened and endangered species. Not only is there a shortage of adequate long-term datasets necessary for robust analyses of population variability, but the elusive nature and obscure microhabitats of many species make it difficult to collect even the most basic natural history data. In a series of observational and experimental studies, I employed both traditional and novel ecological methodologies to examine environmental correlates of temporal population variability, foraging ecology and anti-predator behavior in endangered Barton Springs Salamander (Eurycea sosorum) from Austin (Travis County), Texas. Though headwater springs are typically thought of as habitats with relatively stable environmental conditions, I discovered that E. sosorum population abundance was strongly influenced by periodic extremes of rainfall that affect cycles in spring flow rates, water temperature, and other physico-chemical variables. I also found that population dynamics in E. sosorum are highly consistent with those expected for organisms with a storage effect life-history strategy, in which a few long-lived females capable of high fecundity and prolonged survival in subterranean habitat during adverse environmental conditions may be sufficient for population persistence. In addition, juveniles may use subterranean habitat as a thermal refuge. Using stable isotope analyses and macroinvertebrate prey censuses, I determined that at the population level, adult E. sosorum exhibits high electivity for planarian flatworms (Dugesia sp.). This would not have been detectable using traditional methods of dietary analysis such as stomach or fecal content analysis because Dugesia are soft-bodied animals. Additionally, stable isotope analyses revealed that adult E. sosorum exhibits inter-individual diet variation and is capable of diet switching. Finally, I discovered that anti-predator behavior in E. sosorum is influenced more strongly by visual and bioelectric cues from potential predators, but not olfactory cues. This is the first known demonstration of anti-predatory response mediated only by bioelectric stimuli in an amphibian, and one of very few to observe this phenomenon among aquatic vertebrates.Item Groundwater flow and recharge within the Barton Springs segment of the Edwards Aquifer, southern Travis and northern Hays Counties, Texas(2009-05) Hauwert, Nico Mark; Sharp, John Malcolm, 1944-The Barton Springs Segment, part of the karstic Edwards aquifer in Central Texas, is a Sole Source aquifer, is habitat to rare karst species, and provides water to a well-loved municipal swimming pool, yet its hydrogeologic properties remain insufficiently understood. For this study, the hydrogeologic characteristics of the Barton Springs Segment were investigated using several approaches, including mapping of hydrostratigraphic units and faults, measurement of upland infiltration, groundwater traces, and aquifer tests. The depositional environment, diagenesis, fracturing, down-dropped and dipping faulted blocks, and subsequent dissolution were determined to play important roles in controlling groundwater flow-path development within the Barton Springs Segment. In particular, downdropped fault blocks create groundwater gradients to the southeast that influence flow in the Edwards outcrop area. Upland internal drainage basins were found to be extremely efficient at conveying recharge to the underlying aquifer. The maturity of natural internal drainage sinkholes can be measured by its bowl volume, which grows in proportion to the catchment area it captures. A 19-hectare internal drainage basin, HQ Flat sinkhole, was monitored for rainfall, evapotranspiration, soil moisture, and discrete runoff to the cave drain. During a 505-day period, 5.5% of measured rainfall entered the cave drain as discrete recharge, 26% of measured rainfall infiltrated through soils on the slopes, and the remaining 68% was lost through evapotranspiration. This amount of upland infiltration is consistent with infiltration measurements in other karst areas and is much larger than the 1% upland recharge of rainfall that was previously estimated. A chloride mass balance indicates that at the adjacent Tabor research site, about 50% of rainfall infiltrates to a 6-meter depth. Dye-tracing and pump tests demonstrated that primary and secondary groundwater flow paths are the major influence on transmissivity within the Barton Springs Segment. Groundwater tracing breakthroughs reveal very high advection and relatively low dispersion. Drawdown response to pump tests indicates a very high degree of anisotropy, controlled by location of groundwater flow paths. Overall the Barton Springs Segment is a mature karst aquifer with highly developed rapid, discrete network for both recharge and groundwater-flow.Item New methods for quantifying and modeling estimates of anthropogenic and natural recharge : a case study for the Barton Springs segment of the Edwards Aquifer, Austin, Texas(2011-05) Passarello, Michael Charles; Pierce, Suzanne Alise, 1969-; Sharp, John Malcolm, 1944-; Cardenas, Bayani R.Increased population and recent droughts in 1996 and 2009 for the Barton Springs segment of the Edwards Aquifer have focused attention on groundwater resources and sustainability of spring flow. These springs serve as a local iconic cultural center as well as the natural habitat for the endangered Barton Springs salamander. In response to the potential compromise of these vulnerable groundwater resources, a two-dimensional, numerical groundwater-flow model was developed for the Barton Springs / Edwards Aquifer Conservation District and other governmental entities to aid in aquifer management. The objective of this study is to develop new methods of quantifying and distributing recharge for this model. The motivation for conducting this study includes the following: recent availability of more extensive data sets, new conceptual models of the aquifer system, and the desire to incorporate estimates of urban recharge. Estimates of recharge quantities and distributions for natural and artificial sources were implemented within this model to simulate discharge at Barton Springs and water-level elevations from January, 1999 to December, 2009. Results indicate that the new methods employed generated good agreement amongst simulated and observed discharge and water-level elevations (Root mean square error of 0.5 m3 sec-1 and 10.5 m, respectively). Additionally, these recharge calculations are decoupled from Barton Springs discharge which eliminates the circular logic inherent with the previous methodology. Anthropogenic, or artificial, recharge accounts for 4% of the total recharge between January, 1999 and December, 2009. Using observed data to quantify contributions from leaky utility lines and irrigation return flows, recharge estimates were completed with spatial and temporal resolution. Analyses revealed that on a month by month basis, anthropogenic contributions can vary from <1 to 59% of the total recharge. During peak anthropogenic recharge intervals, irrigation return flow is the most significant contributor. However, leakage from utility lines provides more total recharge during the study period. Recharge contributions from artificial sources are comparable to the mid-size watershed contributions over the ten-year analysis period. Urban recharge can be a critical source for buffering seasonal fluctuations, particularly during low flow periods. Outcomes are relevant for habitat conservation, drought response planning, and urban groundwater management.Item Resurrecting legacy code to revitalize software for groundwater research : reproducibility and robustness for the Barton Springs case, Texas(2016-12) Kwon, Nalbeat; Pierce, Suzanne Alise, 1969-; Kreitler, Charles W; Gil, YolandaAdvanced computing is becoming an indispensable part of geosciences, the interdisciplinary nature of which often requires large-scale and data-intensive numerical modeling. Groundwater in Texas is one such area that can greatly benefit from advanced decision support for understanding aquifer systems, uncertainty analysis, and policy making. However, software developed for research is often used for a relatively short period of time before it is abandoned or lost. The unintentional abandonment of software within the fast changing technological landscape makes model simulation results difficult to replicate, hindering widespread reusability and causing significant effort to be lost on redeveloping new software for researchers pursuing similar or adapted studies. These legacy codes are potentially important assets and may be resurrected and moved to an archive for long-term reuse. This research develops and tests methodologies to inform the design of best practices for documenting and preserving reproducible workflows and scientific software. Methodologies were tested with an existing codebase and assets from the Groundwater Decision Support System (GWDSS), originally developed in 2006 for participatory decision making and groundwater management. The original GWDSS provided a hybrid architecture for integrated assessment models by combining a numerical simulation code for groundwater (MODFLOW) with other systems dynamics and optimization components. Prior attempts to resurrect GWDSS were unsuccessful due to problems commonly experienced with scientific software, such as insufficient documentation and backward compatibility issues. This research experimented with two resurrection strategies: 1) Initially, a virtual machine (VM) approach to handle compatibility issues, which found similar obstacles in addition to the lack of provenance that would yield questionable results, and possibly inherent problems with the codebase due to uncurated changes made in the past. 2) Then efforts were redirected to writing a new application that replicates and improves many of the old functionalities of GWDSS, leveraging high-performance computing for batch processing of data while seeking to integrate new web-based technologies for data visualization. Ultimately, research efforts informed design and preparation of an ideal architecture that uses an open source framework and technology stack that enables users to easily access and use distributed data systems.Item Zilker Park cultural landscape report(2012-08) McGilvray, Julie D.; Holleran, Michael; Steely, James WZilker Park is a large municipal park in Austin, Texas, and while currently an active recreational zone for the city, the parkland is full of historic and natural resources with a period of significance dating back at least 9,000 years. The park is listed on the National Register of Historic Places (NRHP) under two nominations from 1985 and 1997. These nominations document much of the early history of the park, including archaeological sites, historic buildings, objects, and structures. While these reports provide a descriptive history of the parkland, a further study was conducted to understand the park through its cultural and natural systems. This study, known as a cultural landscape report (CLR), examined the park through a defined set of landscape characteristics such as: topography and hydrology, circulation, land use, vegetation, buildings and structures, viewsheds, habitat, archaeological sites, and small scale features. This data was organized to match and compliment the already existing research found within the NRHP nominations, including periods and areas of significance, integrity evaluations, and property types. The CLR was also based on new archival and field research and the report culminated in a set of guiding principles and methodologies for future park management. Thus, the Zilker Park CLR is a site specific planning guide, designed to function as both a descriptive and prescriptive tool for best practices for historic landscape management and stewardship.