Browsing by Subject "Sediment"
- Results Per Page
- Sort Options
Item Open Access Rethinking Rivers: How Light, Lakes, and Sediment Vary Along the River Continuum(2018) Gardner, JohnThis dissertation focuses on the riverine water column and the lentic (i.e. lake like) nature of rivers in the context of predominant themes in river science: spatial heterogeneity and scale. River science has developed many concepts to describe and understand the hydrologic, geomorphic, and ecological structure and function of rivers. While these core concepts largely grapple with spatial heterogeneity and scale, they have generally not conceptualized the water column as unit of study nor have they integrated lakes and rivers as one hydrologic system. Understanding the spatial heterogeneity and scaling patterns within the water column itself and how lakes fit into river networks will advance our understanding of geomorphic and ecological processes of entire networks.
The study approach includes field campaigns using in-situ sensors, analysis of large data sets, and conceptual modeling. Chapter 2 develops an analytical model implemented with empirical data to find the location along a river where there is more sediment surface area in the water column than the benthic zone. Chapter 3 integrates flowpath and fixed-site measurement approaches to characterize the spatial and temporal scales of variability in water column light regimes. Chapter 4 analyzes large datasets to understand the scaling patterns of lake abundance, lake size, and lake spacing with river size across the conterminous US.
Conclusions from this research have theoretical and practical implications. First, rivers larger than ~5th order had more sediment surface area in the water column than the benthic zone. This suggests material processing may occur largely within the water column in large rivers. Studying large rivers may therefore require different conceptual and methodological approaches, and it may be inappropriate to scale up measurements from small streams. Second, large rivers had an expanding and contracting photic volume over multiple temporal and spatial scales. Photo-reactive processes in the water column are therefore limited by the size of these light and dark zones and turbulent fluctuations along flowpaths through the river. Third, river networks are, in-fact, river-lake networks that have characteristic scaling patterns that describe lake abundance, size, and spacing. This suggests the default conceptual model of river networks should be river-lake networks.
Item Open Access The Effects of Dredging and Trawling on Continential Shelf Sediment Biochemistry(2003) Shively, Eliza BlueThe effects of fishing gear on the seabed are well documented. This study specifically investigates the use of dredges and trawls, which are two of the most commonly towed fishing gears both in the U.S. and abroad. These gears are both "active" bottom-contact fishing gear, which means large bag nets, weighing nearly 1500 pounds empty, are towed by fishing vessels and dragged across the seafloor to catch demersal species such as oyster, crabs, clams, halibut, flounder, cod, and shrimp. The effects of these gears on benthic habitats have been much studied and include fish and invertebrate mortality (target and non-target species), loss of habitat, reduced habitat complexity and community diversity, and a reduction in productivity. Conversely, the impacts of dredging and trawling on sediment biogeochemistry have been seldom considered, but could have far-reaching implications when experimental results are extrapolated to larger scales. This study extensively reviews the current and available research on the effects of mobile fishing gear use on sediment biogeochemistry, processes, and sedimentary rnicroenvironments. Specifically, I wanted to answer the following questions: With the assumption ofa high frequency ofdredging and trawling on the world's continental shelves, does mobile fishing gear resuspend and subsequently oxidize carbon that would otherwise be stored in shelf sediments? If so, could this be an unrecognized and significant source ofcarbon dioxide to the water column and consequently the atmosphere thereby contributing to global warming? An extensive literature review yielded only four scientific studies addressing the biogeochemical implications (for C, N, P, and Si) but none of them tackled the effects to carbon beyond the experimental scale. Consequently, with the assistance of Dr. Richard Barber (Duke University), I created a carbon box model to estimate the carbon contribution (using a 1m^2 study area) induced by dredging and trawling relative to a background sea surface carbon value of 2000mM C/m^3. The goal was to establish an upper bound estimate (or maximum) for the amount of CO2 that dredging and trawling could potentially contribute to the atmosphere and to global warming processes. Calculations were done for 50m, 100m, and 200m water depths using total export production values of lOgC/m^2 and 50gC/m^2 and with values of 10% and 50% of that production reaching the seafloor. Additionally, we assumed that 100% of the C reaching the seafloor was oxidized and trapped in the sediments and 100% of that was resuspended by the fishing gear. The value of lOgC/m^2 represents a representative estimate to how much carbon sinks to substrate, while 50gC/m^2 is wildly high and was used to establish an upper bounds for the estimate. The results yielded an approximately 1.5% addition to the carbon in sea surface waters and subsequently the atmosphere; this illustrates that although there is a net transfer of carbon dioxide from the water column to the atmosphere, dredging and trawling is not a significant and unaccounted for source of CO2 and thus does not influence global warming.Item Open Access Toxicity of Polycyclic Aromatic Hydrocarbons Pre- vs. Post-Bioremediation(2020-04-24) deSouza, BeverlyPolycyclic aromatic hydrocarbons (PAHs) are ubiquitous environmental contaminants implicated in negative human and ecosystem health outcomes, including but not limited to carcinogenicity and teratogenicity. Bioremediation using PAH-degrading bacteria and fungi is a noninvasive, relatively low-cost technology capable of reducing environmental occurrence of PAHs. Employing analytical chemistry methods to detect the extent of degradation of PAHs, while insightful, is insufficient as the sole determinant of efficacy of bioremediation. Metabolites created during bacterial degradation of PAHs can be equally toxic or more toxic than parent compounds. Thus, toxicological assays of samples undergoing bioremediation are a crucial component for monitoring risk. The first objective of this project was to develop methods for toxicological assays that could be employed to determine the efficacy of bioaugmentation strategies currently being developed with microbial strains isolated from the heavily PAH-contaminated sediment at the former Republic Creosoting site in the Elizabeth River, VA, USA. The second objective was to use those methods to test three recently isolated PAH-degrading bacterial strains to determine their suitability for use in bioaugmentation. Experimental design included incubation of PAHs with bacteria; extraction of metabolites; analytical chemistry analysis to determine extent of degradation; then subsequent toxicological assays of extracted metabolites, including Ames assays to determine mutagenic potency and zebrafish morphological assays to determine teratogenicity. Four different PAHs were incubated with three strains of PAH-degrading bacteria in monoculture and co-culture. Significant degradation of only phenanthrene was observed, accompanied by a slight increase in mutagenicity and a significant decrease in teratogenicity. Visual inspection of cultures indicated potential fluoranthene degradation with a concomitant increase in mutagenic potency in monocultures, but not in co-cultures. Results for teratogenicity in fluoranthene cultures were inconclusive. Fluoranthene incubation conditions must be optimized to allow more complete degradation and to achieve more definitive results. Once optimization is attained, these assays can be employed in future studies to test additional strains of bacteria as well as fungi that may have capability of degrading a wider range of PAHs.