<p> This dissertation combines field and laboratory work to examine how delta hydrology and sedimentology affects trace element cycling in marsh porewaters. This work was prompted by our lack of understanding of the hydrogeochemistry in the lower Mississippi Delta and how biogeochemical reactions affect fluxes of groundwater constituents to the ocean. In particular, I measured the concentrations of a suite of redox-sensitive trace elements (Fe, Mn, V, As) to determine the dominant geochemical reactions operating in marsh aquifers. </p><p> Because much more is known about As, I first conducted a study comparing V geochemistry along flow paths in a reducing sand aquifer in Texas and an oxidizing bedrock aquifer in Nevada. In agreement with other studies, V concentrations are much higher under oxidizing alkaline conditions. Under the reducing, circumneutral conditions of the Carrizo Sand aquifer, V concentrations are low but relatively constant, owing to complexation with dissolved organic matter. Similar observations regarding V geochemistry are observed in marsh groundwaters. Specifically, in pore waters of organic-rich sediment experiencing sulfate-reducing conditions, V concentrations are high owing to V complexation with organic matter, whereas in coarser-grained sediments, V may be removed from solution by adsorption. Arsenic geochemistry in pore waters varies as a function of depth. In the shallow subsurface, As concentrations are high and stabilized in solution by formation of thioarsenates. At depth, As appears to be sequestered through coprecipitation with pyrite.</p>

<p> The midcontinent of the U.S. is heavily karstified containing well developed subsurface drainage systems that are covered by beds of coarse-grained, poorly sorted fluvial sediments, resembling those found in upland surface streams. The movement of coarse sediment as bed load within karst streams has been considered negligible in the past as it was assumed that all karst is developed through dissolution rather than mechanical abrasion. The frequency and magnitude of sediment transporting events in karst streams has implications for models of fluviokarst landscape development and the stability of aquatic ecosystems. </p><p> Within Tumbling Creek Cave (TCC) in the Ozark Plateau of south-central Missouri, and Bear Cave Hollow (BCH), one of TCC&#129;es surface drainage streams, bed load entrainment and transport dynamics of coarse-grained (16-180 mm), mainly siliciclastic material, was evaluated using hydrological measurements and 670 painted tracer particles. Tracers are used in this research for the first time in a karst stream. Tracers are well suited for studying the stochastic and spatially variable nature of bed load transport because they reflect the movement of individual particles of known characteristics, and they are also inexpensive and simple to employ.</p><p> Median surficial sediment grain size in the study reaches ranged from 39 to 71 mm in TCC, and from 24 to 37 mm in BCH with bed and/or water slopes ranging from 0.006 to 0.077 in TCC and from 0.002 to 0.009 in BCH. TCC is classified as a pool-riffle channel morphology type and BCH is classified as a plane-bed channel. Preliminary data from surveys of the longitudinal (downstream) movement of tracers over a 10-month period indicate that minor amounts (0-13.2%) of coarse bed material in TCC are mobilized by relatively low flows (5-28% of bankfull) that recur somewhat frequently (less than 3.1 years). BCH transports a higher percentage of material (0-59.1%) during similar flows (2-29% of bankfull) and frequencies (less than 3.59 years). Bed load transport was observed to be in a state of partial transport for any one grain size class in TCC during the study, while the complete mobilization of tracer size classes was observed in BCH at the highest observed flow, indicating &ldquo;phase 2&rdquo; transport and the break-up of the armor layer. The differences are attributed to the wider observed range of grain sizes covering the bed in TCC compared to BCH.</p><p> The use of the Shields (1936) criteria tends to over predict the critical shear stress required for entrainment of the largest mobilized grain size of individual tracers, while the empirical equation of Bagnold (1980) performs much better. Thus, the Shields equation may be better suited as a gage for complete mobilization of a grain size class across a reach, while the Bagnold (1980) equation may be better suited for estimating entrainment of grains from patches of the bed.</p><p>

<p> Magnetic susceptibility is a property that can be used to effectively determine the compositional changes of mineral materials in soil. The objective of this study is to detect the presence of magnetic particles related to the migration of fly ash from a nearby coal-burning power plant over parts of Pointe Coupee Parish, LA. This is based on the idea that the fly ash that is released into the atmosphere during the coal burning process contains heavy metals and magnetic particles in the form of ferrospheres, which can be used to trace back to the source. Maps of the top and sub soil were generated to differentiate the magnetic susceptibility values of the heavy metals potentially attributed to the migration and settling of fly ash onto the surface from any pre-existing or naturally occurring heavy metals in the sub soil. A 60 km² area in Pointe Coupee Parish was investigated in approximately 0.5 km² subsets.</p><p> At each site, a minimum of 20 magnetic susceptibility measurements were obtained using a field probe along with discrete surface and subsurface samples collected for subsequent laboratory analysis. Samples of fly ash obtained directly from the source were also analyzed to verify the field and laboratory analysis. Contour maps representing the spatial distribution of the fly ash along with histograms of magnetic susceptibility values, reflective light microscope, and chemical analysis indicate a correlation between the proximity to the power plant and the predominant wind direction. Acquisition curves of the isothermal remanent magnetization demonstrate the presence of predominantly low coercivity minerals (magnetite) with a small amount of a high-coercivity phase. The microstructure of the magnetic fractions of the fly ash along with select top and sub soil samples were observed using a reflective light microscope for identifying and confirming the presence of ferrospheres associated with fly ash.</p>

<p> Geochemical mixing methods utilizing ²²²Rn and chloride and statistical hydrograph separation techniques were carried out in an attempt to understand baseflow dynamics in a section of the Kern River in the Sierra Nevada of Southern California. ²²²Rn has become a valuable tool for evaluating groundwater inflow to a river, particularly when groundwater and surface water have similar major ion geochemistry. When using geochemical methods it is important to minimize uncertainty through comparison with separate tracers and techniques, though this is complicated in this setting. Snow melt discharge and regulation of natural river flow cause hydrograph-based techniques to suffer from inaccuracies. Geochemical mixing using major ions and stable isotopes are complicated by the chemical similarity between surface water and groundwater. ²²²Rn is a powerful tool to elucidate this relationship in this setting if major uncertainties, like rate of radon degassing and parafluvial and hyporheic radon production can be constrained.</p><p>

<p> The Chico Aquifer System is a sole source aquifer located in the southwest region of Louisiana. A comprehensive study of the groundwater level of the Upper, Massive, and &ldquo;200-foot&rdquo; sands was undertaken to produce potentiometric surfaces for every five years from 1940 to 2015. The historical surfaces were produced for two different periods of the year; peak water-level months (non-irrigation season from January to March) and trough water-level months (irrigation season from May to July). ESRI ArcGIS extensions Arc Hydro Groundwater and Geostatistical Analyst were used to evaluate the spatial variability of the potentiometric surfaces, and ordinary kriging interpolation models were used to produce the surfaces. The cross-validation process indicated that the models were unbiased with satisfactory accuracy. From 1945 to 2015, Acadia Parish had the highest overall groundwater level decline (44.4 feet), followed by Evangeline Parish (32.6 feet), and Jefferson Davis Parish (29.63 feet). After high declines from 1945 to 1980 (33.2 feet), Calcasieu Parish showed signs of recovery since 1980 (+16.3 feet). The rate of change of the potentiometric surface for all parishes in the Chicot Aquifer System was higher from 1945 to 1980 than from 1980 to 2015. The grand average of the change in the potentiometric surface for the Chicot Aquifer System since 1945 was a decline of 23.3 feet. As society continues to improve water resource management, the results and methods presented here demonstrate an improvement in historical hindcasting that could create better plans for water management in the future.</p><p>

No description available.

<p>Southwest Foods in Lafayette, Louisiana has multiple underground storage tanks that leaked petroleum products over a period of time, releasing numerous toxic constituents of concern into the surrounding soil and groundwater. During the assessment phase of risk evaluation, the Synthetic Precipitation Leaching Procedure (SPLP) test was used to measure the leaching potential of possibly contaminated soils and lithologies when exposed to acidic rainfall. However, during the site investigation, SPLP data produced erratic results that apparently are related to the type of geologic material (?soil?) involved. These erratic results could have major implications for assessment, remediation, and the establishment of Risk Evaluation/Corrective Action Program (RECAP) standards in the state of Louisiana. Incorrectly applied RECAP standards could ultimately mean contaminants of concern could reach points of exposure (POEs), and potentially harm nearby residents and the environment. Previously, lithological composition had not been considered when evaluating the environmental impact of the test. At the site, numerous geotechnical soil boring logs were completed, and soil samples were sent to analytical laboratories for analysis of contamination. Soil analytical data compiled by the laboratories along with samples acquired from multiple groundwater monitoring wells at the site provided an in-depth view into the degree of contamination at Southwest Foods and produced the first signs of erratic SPLP test results. Contour maps of contamination and groundwater potentiometric levels were created to show both the level of contaminants in soil and the possible migration paths of affected groundwater. The SPLP sample data were evaluated and categorized into lithological subgroups for further examination. The lithologies, or soil types (with USCS symbols), that produced erratic results (i.e., some ?passed? and some ?failed?) for the SPLP analyses included ?clay, high plasticity? (CH) and ?clayey silt/sandy silt/silt? (ML). The results for ?silty clay/sandy clay? (CL) were more consistent. The inconsistent SPLP data could result in incorrect application of site-specific RECAP standards and the subsequent cleanup at Southwest Foods and conceivably at other contaminated sites as well.

<p>Lake sediments and glacier extents were used to reconstruct late Holocene climate changes from Kurupa Lake (N 68.35&deg;, W 154.61&deg;; 920 m asl) in the north-central Brooks Range, Arctic Alaska. The lake is fed by several tributaries, including meltwater from eight rapidly disappearing cirque glaciers. An age-depth model for the 622-cm-long sediment core was developed using five radiocarbon (¹⁴C) ages and a 239+240Pu profile. Sedimentary chlorin (chlorophyll a and derivatives) content was analyzed at high resolution (0.2 cm = ~2 yr intervals) with visible reflectance spectroscopy for the past 5.7 kyr. Sedimentary bulk density was analyzed with gamma-ray attenuation (1.0 cm = ~10 yr intervals). </p><p> High-resolution measurements of chlorin content from the last 122 yr (top 16 cm of surface sediment) were correlated with a suite of instrumental climate records from Barrow and Bettles, National Center for Environmental Prediction reanalysis data (grid = N&deg;68 to N&deg;70 &times; W&deg;156 to W&deg;154) and with published climate indices for the Arctic (e.g., Arctic Oscillation, North Atlantic Oscillation). Chlorin content correlates most strongly to average June + September temperature (r = 0.68) and a linear inference model was developed using this regression to quantitatively reconstruct summer temperatures for the past 5.7 kyr. The temperature reconstruction (50-year smoothed) shows minimum summer temperature (5.6 &plusmn; 0.9&deg;C) at 650 AD and maximum summer temperature (10.7 &plusmn; 0.9&deg;C) 2.9 ka. </p><p> Fluctuations in bulk density over the past 5.7 kyr were interpreted to reflect changes in up-valley glacier extent. The accumulation-area ratio (AAR) method was used to estimate former equilibrium-line altitudes (ELAs) for the maximum Neoglacial and modern extents of eight cirque glaciers in the study area. Independently dated moraines enable the history of glacier fluctuations to be linked to the lake sediment sequence (r2 = 0.74), and this integrated approach provides a 5.7 kyr quantitative record of centennial-scale ELA variability for Kurupa River valley. The reconstruction supports the previously established onset of Neoglaciation around 4.2 ka, as well as maximum and minimum glacier extents around 700 AD and the present, respectively. The calculated ELA lowering at 700 AD and the LIA, relative to 1982, was 63 and 55 m, respectively. </p>

<p> The hydrogeologic controls, flow velocities and paths, groundwater delineation, and physical characteristics in a joint controlled dendritic conduit-spring system have been characterized. The known conduit branches from C My Shovel (CM) Cave with 4475 meters (m) of measurable passages and tributaries. Surface entrance to CM Cave is located 1360 m upstream from discharge at Magic Springs. </p><p> Four storm events were measured characterizing the dynamics. The maximum discharge of these four events was 1.2 m³/s (41 ft³/s) with 0.08 m³/s (3 ft³/s) baseflow conditions at Magic Springs. The characteristic shape and response of discharge are well defined with a rise time between 5.5 and 6.5 hours (hr). The half flow period time (t_0.5) ranges between 12.9 and 15.7 hr, depending on peak discharge. The rise time and t0.5 occur in less than one day and the conduit volume exceeds 0.5 x 10⁶ m³. The conduit-spring system drains within 3.7 to 7.5 days after the storm event. The thermal effects are event driven, maintaining 85% of the temperature change over 1300 m. The spring discharge has total dissolved solids around 350 mg/L and is chemically stable. </p><p> The field component of this study include a karst density survey, four dye traces, and continuous monitoring of specific conductance, pressure, temperature, water-level stage height, and discharge at Magic Springs and in the conduit below CM Cave. The general karst density survey identifies caves and dolines within given area. There is a sinking stream that transfers flow from Spring Branch Creek into the conduit system and two focused regions in a karst plain having densities of 20 and 44 karst features/0.16 km². </p><p> Hydrographs and chemographs show patterns interpreted as pulses of dilute water recharging through exposed caves, sinkholes, and sinking streams. These pulses have minimal reaction with the rock or matrix during recharge, which is superimposed on baseflow from the joint controlled dendritic conduit-spring system in this karst terrane. </p><p> The groundwater drainage basin has been defined. The dye tracing results identified groundwater piracy across surface water divides and helped define the groundwater drainage basin. Groundwater velocities were measured between 1800 m/d and 3000 m/d under baseflow conditions. The discharge at Magic Springs under these four storm events showed velocities between 8,700 and 15,120 m/d. </p><p> An autosampler and charcoal packets were both employed during dye tracing. Both detected fluorescence from all four injection sites. The measured velocities ranged between 1865 up to 2929 m/d under baseflow conditions. All dye trace tests were conducted under baseflow. Under baseflow conditions, dye was only traced to the Magic Springs locations from the eleven charcoal monitoring locations.</p>

No description available.