Barton Springs Pool (BSP) is an important ecological and recreational resource to the City of Austin (CoA). Due to sediment accumulation, excessive algal growth, and concern for water velocities through salamander habitat, improving the flow regime of BSP was identified as an important focus for future infrastructure development in Barton Springs Pool. The CoA commissioned this project to develop and test a hydrodynamic model to provide a basis for understanding the flow dynamics of BSP, and to aid in future infrastructure developments in BSP. This phase of the project included the collection of bathymetric and velocity data, creating a hydrodynamic model of BSP that dynamically represents space-time varying 3D velocities, and testing the model using the default settings and an adjustment of the outlet coefficients. The model was run with three targeted inflow scenarios to determine both how the model responds with varying inflows, and to provide a general idea of how flow in BSP is affected by the magnitude of the inflow. The model used was the Fine Resolution Environmental Hydrodynamic Model that solves the 3D non-hydrostatic Navier-Stokes equations in a split hydrostatic/non-hydrostatic approach. The model was run using the default settings and the outputs were compared to available data. Results from these initial runs showed that further calibration is necessary. Model runs under the targeted inflow scenarios showed that as inflow increases, velocities in the upstream portion of BSP increase correspondingly, but this is not reflected in the downstream portion of BSP. / text

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. / text

Amphibian 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. / text

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. / text

The Barton Springs salamander (Eurycea sosorum) is a federally endangered species that is endemic to Barton Springs in Austin, Texas. Development within the Barton Springs watershed threatens the continued existence of E. sosorum. A factor that may be contributing to its decline is contamination from polycyclic aromatic hydrocarbons (PAHs). Nearby asphalt parking lots paved with coal-tar and asphalt sealants can be sources of PAHs. Unaltered parent compounds of PAHs can have toxic effects, but oxidation and ultraviolet radiation can create degradation products 100 times more toxic than the parent compounds. The objective of this project was to determine if PAHs are potentially harmful to E. sosorum using two surrogate species. Adult eastern newts (Notophthalmus viridescens) and larval spotted salamanders (Ambystoma maculatum) were exposed to sediments with nominal concentrations of total PAHs that ranged from 0 to 1500 mg/kg under UV (290 - 400 nm) and visible (400 - 700 nm) light to determine concentration/response relationships. No statistically significant mortality occurred under any treatment. Exposure to both coal-tar sealant and UV light resulted in sublethal effects such as decreased righting ability and swimming speed. Difficulty in performing such movements would make it difficult to catch prey and increase susceptibility to predation. Exposure to UV light also resulted in elevated numbers of micronucleated erythrocytes and white blood cells. This study shows that simultaneous exposure to PAHs and UV light result in sublethal effects that could make the population of E. sosorum vulnerable to further decline.

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. / text

Modern cities are often perceived as the antithesis of nature; the built environment is understood as the transformation of raw and untamed nature into a rationalized human landscape. However, a variety of scholars since the nineteenth century have noted the persistence of nature in cities, not only in providing essential services but also resisting human control. Most recently, urban geographers and environmental historians have argued that processes of urbanization do not entail the replacement of natural with artificial environments, but are more accurately understood as a reconfiguration of human/nature relations. In this dissertation, I employ this relational perspective to study a specific form of urban nature: stormwater flows. Urban drainage or stormwater management activities in US cities are a vivid example of the tensions between nature, society, and technology. In this study, I present a comparative case study of two US cities--Austin, Texas and Seattle, Washington--where stormwater issues have been a central focus of public debate over the last four decades. Using textual analysis, in-depth interviews, and experiential research methods, I argue that stormwater management practices involve not only the rational management of technological networks but also implicate a wide range of seemingly unrelated issues, such as local governance, environmental protection, land use decisionmaking, community development, aesthetics, and social equity. To describe the relational implications of urban nature, I present a framework of ecological politics to characterize drainage activities as rational, populist, or civic. I argue that the latter form of politics has the greatest potential to relieve the tensions between urban residents and their material surroundings by embracing a systems perspective of human/nonhuman relations and engaging local residents in the hands-on management of environmental flows. It is through the development of deliberative and grounded forms of civic politics that urban residents can forge new relationships between technology and nature, and in the process, understand their place in the world. / text