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<p> The search for clean, fresh water is of the utmost importance, especially considering the highly industrialized age in which we live and the rising demand caused by increasing population. Many once-clean groundwater reservoirs have been tainted due to the inadequate storage and handling procedures for hazardous materials. One such site operated as a wood-preservation facility between 1937 and 1999 located in western Louisiana in the town of DeRidder. The contaminants that leached into the soils and groundwater supply at this site included creosote, a coal-tar distillate that is an amalgamate of several toxic constituents. The contamination was first detected in 1981, and within the year monitoring wells were installed to evaluate the extent of the pollution. For this study, 61 monitoring wells, 16 of which consistently record hazardous compounds within the subsurface, were analyzed in order to evaluate the temporal and spatial changes of contamination. The data were further correlated with rising and falling groundwater levels, precipitation data, and lithology in order to better understand the trends of the constituents and how they are affected by their environment. Additionally, an indication as to the efficiency of the current remediation practices put in place is examined by evaluating the diminishing contamination values over time compared to previous studies in the area. Hazardous levels within the soil are at their peak near the contamination sources, and spread outward while following the direction of local groundwater flow. This study shows that the total contamination quantities are slowly declining due to the current remediation practices, however, the total area covered by contamination fluctuates over time, and is currently in a state of expansion towards the southwest. A correlation between rainfall events and contamination spikes was noted in a previous study of the area, however, no such correlation was observed in the more recent data.</p>

<p>The principle of competitive exclusion holds that the strongest competitor for a single resource can exclude other species. Yet in many systems, more similar species appear to stably coexist than the small number of limiting resources. Understanding how and when similar species can stably coexist has taken on new urgency in managing biological invasions and their ecological impacts. Recent theoretical advances emphasize the importance of predators in determining coexistence. The effects of predators, however, can be mediated by behavioral changes induced in their prey as well as by their lethality. In this dissertation, I ask how considering multiple trophic levels changes our understanding of how a grass invasion (Pennisetum ciliare) affects species diversity and dynamics in southeastern Arizona. In considering interactions with plant consumers, and with the predators of those consumers, this research reveals more general ecological processes that determine species diversity across biological communities. I first present evidence from a grass removal experiment in the field that shows increased emergence and short-term survival of native perennial plants without grass. This is consistent with Pennisetum ciliare causing the observed concurrent decline in native plant abundance following invasion. I then present results from greenhouse and field studies consistent with that suppression of native plants being driven primarily through resource competition rather than increased rodent granivory. Granivorous rodents do not solely function as consumers, however, because they cache their harvested seeds in shallow scatter-hoards, from which seeds can germinate. Rodents thus act also as seed dispersers in a context-dependent mutualism. They primary granivores in areas invaded by Pennisetum ciliare are pocket mice (genus Chaetodipus), which have a well-studied tendency to concentrate their activity under plant cover to avoid predation by owls. Because the dense canopy of the grass may provide safer refuge, I hypothesized the pocket mice may be directly dispersing native seeds closer to the base of the invasive grass. Such a behavior could increase the competitive effect of the grass on native plant species, further driving the impacts of the invasion. By offering experimental seeds dusted in fluorescent powder and tracking where the seeds were cached, I show that rodents do preferentially cache experimental seeds under the grass. This dispersal interaction may be more general to plant interactions with seed-caching rodents across semi-arid regions that are experiencing plant invasions. Finally, I ask how the predator avoidance behavior exhibited by these rodents affects their ability to coexist with one another. Not only could their diversity affect that of the plant community, but the effects of plant invasions can cascade through other trophic levels. Theoretical understanding of how similar predator avoidance strategy alters coexistence had not yet been developed, however. Instead of a field study, therefore, I modified a general consumer-resource model with three trophic levels to ask whether avoidance behavior by the middle trophic level alters the ability of those species to coexist. I found that more effective avoidance behavior, or greater safety for less cost, increased the importance of resource partitioning in determining overall niche overlap. Lowering niche overlap between two species promotes their coexistence in the sense that their average fitness can be more different and still permit coexistence. These results provide novel understanding of behavioral modifications to population dynamics in multi-trophic coexistence theory applicable to this invasion and more broadly.

<p> This study of the vegetation of the 100,000-acre Connecticut Tract in western New York examines the presettlement characteristics of the forest, including the tree species composition, tree density, and wetland extent. Presettlement vegetation studies add to what is known about the forests of this region before European settlement in the early 1800s brought widespread changes to these forests. The ecological data in original private land surveys from 1811 were transcribed and then analyzed using ArcGIS and IDRISI GIS software. The surveys contained both witness tree data and line descriptions, which were analyzed for species composition and community type and were compared with Forest Inventory and Analysis (FIA) data about the contemporary forest in the study area. The community type results together with surveyor notes were used to extrapolate wetland coverage, which was compared with the 2006 National Wetlands Inventory Database.</p><p> This study fills in missing historical data between the two largest land purchases in western New York and examines forest composition at a finer-grained scale than surveys of those land purchases. Comparing past and present vegetation clarifies past causes of temporal and spatial variability and provides a reference point for land managers who need to understand the effects of land-use history for ongoing restoration efforts.</p>

<p> Detecting environmental contaminants such as Selective serotonin reuptake inhibitors (SSRIs) and Cr (VI) compounds is essential since they are highly toxic contaminants of many drinking water supplies leading to adverse health effects. Selective serotonin reuptake inhibitors are common antidepressants therapeutics and fluoxetine; Prozac^&reg;, citalopram; Celexa^&reg; and sertraline; Zoloft^&reg; were successfully detected in this study. Ion transfer stripping voltammetry (ITSV) was applied to detect those as cations at nanomolar concentrations using an inexpensive and disposable pencil lead electrode, with a lower detection limit of 30 nM. The pencil lead electrode was modified using the conducting polymer Poly (3, 4-ethylenedioxythiophene) (PEDOT-C14) and PVC (poly-vinyl chloride) membrane. The PVC/PEDOT-C₁₄ -modified electrode demonstrated a linear current response from 100 to 1000 nM for these therapeutics. Ion transfers of Hydrogen chromate as anions were studied using a double-polymer modified glassy carbon electrode using the conducting polymer poly (3-octylthiophene) (POT), and PVC membrane. Lipophilicity of Hydrogen chromate ions were evaluated comparing to other common inorganic contaminants. Exhaustive stripping of Hydrogen chromate ions in cyclic voltammetry and their relative high lipophilicity infer that ITSV can be successfully applied to detect them in future studies. </p>