Thesis (Ph. D.)--University of Washington, 2002. / Vita. Includes bibliographical references (leaves 105-115).

Thesis (Ph. D.)--West Virginia University, 2003. / Title from document title page. Document formatted into pages; contains xxi, 298 p. : ill. (some col.), maps (some col.). Vita. Includes abstract. Includes bibliographical references (p. 149-157).

The presence of agrochemical residues in both urban and agricultural water bodies has become ubiquitous, often producing deleterious effects in the impacted watershed including reductions in biodiversity, alterations in species interactions, and toxicity to non-target organisms. While these effects have been studied on metazoan consumers, the consequences of agrochemical contamination on microorganisms, such as bacteria, protozoa, and viruses, are poorly understood. Agrochemicals could act directly on microorganisms, including pathogens, by either facilitating their survival or decreasing their abundance. Further, a multitude of indirect effects of agrochemicals on microorganisms are possible, whereby agrochemicals alter predation, competition, or parasitism on or available nutrient to microbes. The primary method by which agrochemicals enter water bodies is through stormwater and agricultural runoff, which can also introduce agriculturally-associated zoonotic pathogens. Presently, regulatory standards utilize fecal indicator bacteria (FIB) to predict the presence of pathogens in contaminated watersheds. However, if agrochemicals have different effects on FIB and bacterial pathogens, then these regulatory standards might be confounded by the presence of pesticide residues in impacted water bodies. Additionally, if agrochemicals promote the survival of zoonotic pathogens, then the presence of pesticide residues could potentially increase risks to human health. The studies in this dissertation investigated both the direct and indirect effects of agrochemicals on the growth and survival of FIBs ( Escherichia coli and Enterococcus faecalis), zoonotic bacterial pathogens (E. coli O157:H7, and Salmonella enterica), and two virus groups (human polyomaviruses and adenoviruses). The agrochemicals utilized in these experiments are among the most prominently used in their respective pesticide classes and included the herbicide atrazine, the insecticide malathion, the fungicide chlorothalonil and inorganic fertilizer containing phosphate and fixed nitrogen. Initially, complex mesocosms containing zooplankton, phytoplankton, leaf litter, and vertebrate and invertebrate species were used to examine net (direct and indirect) effects of agrochemicals on FIB in sediments. Subsequent studies utilized experiments in simplified microcosms to detect direct or indirect effects (i.e., predation, competition or effects on nutrient resources) on FIBs and pathogens. In complex mesocosms, atrazine and fertilizer significantly increased FIB densities in the sediment; however, because of the complexity of the mesocosms, it was not possible to determine whether these results were the product of direct or indirect agrochemical effects. Simplified microcosms, limited to predominantly direct effects, as well as in vitro growth curves, revealed no direct effects of any agrochemical treatment on either growth or survival of FIB or bacterial pathogens. When algal communities were allowed to establish, however, atrazine significantly reduced both phytoplankton and E. coli densities in the water column, but increased E. coli densities within the sediments. These effects on E. coli were indirect because they required the presence of algal species. To investigate indirect effects of predation on FIBs and E. coli O157:H7, we manipulated the presence and absence of an obligate heterotroph, Tetrahymena pyriformis, a facultative heterotroph, Ochromonas danica, and natural protozoan populations. In both laboratory and greenhouse microcosm experiments, the fungicide chlorothalonil significantly reduced all protozoan populations, which resulted in increased densities of FIBs and E. coli O157:H7 because of reduced predation. Atrazine was not found to have any significant direct effect on the densities of T. pyriformis or natural protozoans; however, atrazine did significantly reduce O. danica densities in greenhouse experiments. In laboratory experiments with O. danica, atrazine treatments resulted in decreased densities of E. coli O157:H7. Presumably, atrazine prevented or reduced photosynthesis forcing O. danica to increase its predation on E. coli thus shifting its trophic level. These studies reveal that agrochemicals can have a significant effect on microbial communities, but that these effects are often indirect and mediated through alterations of nutrient resources and predation. Atrazine application reduced FIB and pathogen densities in the water column via reduction of phytoplankton and increased predation by O. danica. These data suggest that the net effects of atrazine is deleterious to FIB survival in the water column and that application of this herbicide could result in an ecosystem service, reducing the abundance of zoonotic pathogens and lessening the risk to human health. However, elevation of FIB densities was observed in the sediments when atrazine was applied. The potential resuspension of increased sediment bacteria may negate or out-weigh the deleterious effects of atrazine on bacteria in the water column. Chlorothalonil application decreased protozoan densities, lessening the stress of predation on the bacterial targets and increasing FIB and E. coli O157:H7 densities. The use of chlorothalonil may therefore have negative implications for human health risks, as the reduction in predation seems to facilitate the survival of zoonotic waterborne pathogens. Understanding the net effects of agrochemicals is important for public health, as pesticide applications can act to either maintain or diminish potential bacterial and protozoan pathogens of humans. These studies show that indirect effects of agrochemicals on non-target microbes tend to be more prominent than direct effects and can significantly impact the fate of bacterial pathogens in aquatic environments.

Fecal indicator bacteria (FIB) such as Escherichia coli and enterococci are used to assess microbiological water quality in recreational waters worldwide. FIB are used with the assumption that their presence correlates with that of fecal-associated pathogens in recreational waters. In aquatic habitats, several factors can interfere with the predictive relationship between FIB and pathogens including extended survival of FIB in secondary habitats such as sediment, vegetation and sand. Furthermore, many biotic (e.g. predation from bacterivorous protozoa and competition from indigenous bacteria) and abiotic factors (e.g. temperature, salinity, ultraviolet (UV) light irradiation, and nutrient availability) can influence the fate of FIB and pathogens associated with gastrointestinal tracts of animals (enteric pathogens) in secondary habitats. The relative importance of these factors is not well characterized, thus limiting our knowledge on the efficacy of FIB as indicators of fecal contamination and microbial pathogens in water. The studies presented in this dissertation investigated the influence of biotic (predation from bacterivorous protozoa and competition from indigenous bacteria) and abiotic factors (e.g. nutrient availability) on the survival of FIB (E. coli and Enterococcus faecalis) and pathogens (E. coli O157 and Salmonella enterica) in aquatic habitats. Water and sediment samples were collected from a fresh water river source (Hillsborough River, Tampa, FL) and used to prepare a series of outdoor mesocosm experiments. In each experiment, biota treatments were varied to include various combinations of predation and competition, both or neither. Manipulation of biota treatments involved disinfection of water and baking of sediments to remove indigenous microbiota, or addition of cycloheximide or kanamycin to diminish the effect of predation from natural protozoa or competition from indigenous bacteria respectively. Bacterial levels in all experiments were monitored over a five day period. In the mesocosms investigating the effect of predation and competition on FIB (E. coli and Ent. faecalis) and a pathogen (E. coli O157:H7), predation had a detrimental effect on the survival of the FIB and pathogen in the water column but only influenced the survival of the FIB in the sediment. Unlike predation, competition from indigenous bacteria influenced the survival of E. coli but not Ent. faecalis in both water and sediment. The second set of mesocosms investigated the effect of predation on two motile and non-motile enteric bacteria types (E. coli O157 and S. enterica), each with a motile and non-motile counterpart. An allochthonous predation source (Tetrahymena pyriformis) was added into the mesocosms to supply a consistent level of predation. Motility had a significant positive effect on the survival of S. enterica in the water and sediment but had negative significant effect for E. coli O157 in sediment only. Motility also played a more important role in the sediment compared to predation while predation played a more important role in the water column for both bacteria types. The third study compared the relative effects of predation, competition and nutrients on the survival of E. coli. Natural waters (not amended with nutrients) served as a baseline condition to which organic nutrients were added in two increments. Significant interactions among predation, nutrients and competition (all possible combinations) were observed. Interactions between predation and nutrients as well as competition and predation also accounted for the greatest effects (10% and 8% respectively). The interaction between predation and competition was particularly pronounced at the highest nutrient level. These studies reveal that predation, competition and nutrients are all important factors in the survival of FIB and enteric bacteria in water and sediment, and provide new observations on the relative magnitude of these effects. I show that survival characteristics of FIB and enteric bacteria in secondary habitats can vary depending on bacteria type (FIB or pathogen), location (water or sediment), prey characteristics (motile or non-motile) and specific environmental stressor present (predation, competition or nutrients). The findings of this dissertation provide new insights on the ecology of FIB and enteric bacteria in secondary habitats and underscore the importance of biotic and abiotic factors as determinants of the fate of FIB and enteric bacteria in secondary habitats.

Mercury -contaminated sediments often act as a sink of mercury and produce methyl-mercury, an acute neurotoxin which readily bio accumulates, due to the presence of bacterial communities hosted by the sediment. One common remediation approach to manage methyl-mercury is to amend the sediment by capping or directly mixing with a sorbent. This thesis aims to assess the capabilities of some calcium-based sorbent to act in that capacity. Laboratory experiments were implemented to simulate mercury fate and behavior in geochemical conditions that capping would likely create. Well-mixed slurries showed that gypsum materials were disparate and their behavior was similar from sand to organocaly. Mercury sorption capacities of these gypsums were poor with a sorption coefficient approximately equal to 300 L/kg. Reduction of methylmercury was minimal and even increased in two of the three materials. Therefore, the three gypsums, which tend to be more cohesive when wetted, doesn’t constitute a viable material for sediment capping. / 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

published_or_final_version / Environmental Management / Master / Master of Science in Environmental Management

published_or_final_version / Environmental Management / Master / Master of Science in Environmental Management

published_or_final_version / Architecture / Master / Master of Landscape Architecture

A prototype raster geographic information system (GIS) for agricultural water quality analysis was developed considering the farm as an aggregation of spatial units with homogeneous physical and management characteristics. A crop model that simulates the farm and environment response to different management scenarios was integrated with the GIS. The integrated GIS-model is then run on each homogeneous area. The results of crop yield and chemical leaching are geographically referenced for further display and analysis, and to serve as an input to the decision model. A decision model based on maximization of expected utility (MEU) was also integrated to help assess and evaluate the impacts of fertilizer application on the faun system and the environment. By using utilities for both crop yield and chemical leaching the model circumvents the issue of assigning a monetary value to the environment. Accommodating both the farmers' goals, in terms of higher yield and the well being of the environment, in terms of lower chemical leaching, the model computes the expected utility of each management scenario. The management practice with the maximum expected utility is then recommended. The integrated model was tested with an example of lettuce production in Arizona. Results were compared to published field reports, the model recommendation matched well with the field results. The prototype model was simple to use, and very well integrated, which makes it an alternative to the more complex and expensive coupling of commercial GIS and simulation models.