Diatoms are useful indicators of ecological conditions but the mechanisms driving assemblage distribution are not clearly defined. Understanding the mechanisms underlying assemblage distribution is necessary to make accurate predictions about the effects of environmental change, such as hydrologic management, restoration, and climate change. The examination of diatom distribution and key drivers across a large wetland over several years can provide a resolved spatio-temporal framework for determining the relative importance of environmental and spatial factors influencing assemblage patterns. I examined a 6-year record of diatom distribution across the Everglades, a large hydrologically-managed subtropical wetland. Successful restoration of this ecosystem depends on using reliable ecological targets and bioassessment strategies based on a comprehensive understanding of the biotic responses to the variables being manipulated, especially hydrology. The components of my research are: 1) characterizing the relationship between diatom distribution and environmental factors; 2) investigating the taxonomy of species presumably with little or no limitation to dispersal by spatial factors; and 3) examining the relative importance of environmental and spatial factors on diatom distribution patterns within a hydrologically-managed environment. Building upon the well-documented utility of Everglades diatom transfer functions for phosphorus based on species optima and tolerance ranges, I developed transfer functions for hydroperiod and biovolume of periphyton (consortium of algae, bacteria, and fungi) and evaluated the utility of resultant diatom-based inference models for bioassessment. Considering the importance of environmental factors, diatoms in the Everglades and Caribbean wetlands may have restricted distributions. My taxonomic investigation of two species with presumed continental distributions and the consequent description of two new species suggest spatial factors can restrict diatom dispersal. The importance of both environmental and spatial controls on Everglades diatom distribution may be related to the availability of calcareous (high mineral content) periphyton that diatoms inhabit because periphyton mineral content is correlated with environmental factors, which differ among compartments within the ecosystem because of hydrologic management. I found environmental factors were more important controls on the distribution of persistent inhabitants of calcareous periphyton, suggesting spatial factors are relatively less important when species are well-suited to the habitats made available by environmental conditions influenced by hydrologic management.

Magister Scientiae (Biodiversity and Conservation Biology) / Kelp forests are dynamic and productive ecosystems which host large biodiversity of sessile fauna and flora, including diatoms. These microalgae occur at the base of coastal marine food webs and contribute substantially to the productivity of marine ecosystems. Diatoms constitute one of the most common and species-rich groups of both phytoplankton and phytobenthos. Possessing a unique silica cell wall, diatoms play a key role in the global carbon and silicon cycles. As the changes in species composition of diatom communities are a direct reaction to the combination of environmental factors prevailing in their ecosystems, diatom analysis is widely and successfully used in biomonitoring of various environmental conditions and paleoecological reconstructions.

abstract: The hierarchical silica structure of the Coscinodiscus wailesii diatom was studied due to its intriguing optical properties. To bring the diatom into light harvesting applications, three crucial factors were investigated, including closely-packed diatom monolayer formation, bonding of the diatoms on a substrate, and conversion of silica diatom shells into silicon. The closely-packed monolayer formation of diatom valves on silicon substrates was accomplished using their hydrodynamic properties and the surface tension of water. Valves dispersed on a hydrophobic surface were able to float-up with a preferential orientation (convex side facing the water surface) when water was added. The floating diatom monolayer was subsequently transferred to a silicon substrate. A closely-packed diatom monolayer on the silicon substrate was obtained after the water evaporated at room temperature. The diatom monolayer was then directly bonded onto the substrate via a sintering process at high temperature in air. The percentage of bonded valves increased as the temperature increased. The valves started to sinter into the substrate at 1100°C. The sintering process caused shrinkage of the nanopores at temperatures above 1100°C. The more delicate structure was more sensitive to the elevated temperature. The cribellum, the most intricate nanostructure of the diatom (~50 nm), disappeared at 1125°C. The cribrum, consisting of approximated 100-300 nm diameter pores, disappeared at 1150°C. The areola, the micro-chamber-liked structure, can survive up to 1150°C. At 1200°C, the complete nanostructure was destroyed. In addition, cross-section images revealed that the valves fused into the thermally-grown oxide layer that was generated on the substrate at high temperatures. The silica-sintered diatom close-packed monolayer, processed at 1125°C, was magnesiothermically converted into porous silicon using magnesium silicide. X-ray diffraction, infrared absorption, energy dispersive X-say spectra and secondary electron images confirmed the formation of a Si layer with preserved diatom nano-microstructure. The conversion process and subsequent application of a PEDOT:PSS coating both decreased the light reflection from the sample. The photocurrent and reflectance spectra revealed that the Si-diatom dominantly enhanced light absorption between 414 to 586 nm and 730 to 800 nm. Though some of the structural features disappeared during the sintering process, the diatom is still able to improve light absorption. Therefore, the sintering process can be used for diatom direct bonding in light harvesting applications. / Dissertation/Thesis / Masters Thesis Materials Science and Engineering 2018

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The study was concerned with the horizontal and vertical distributional patterns and the possible summer periodicity of diatoms epiphytic on eelgrass, Zostera marina L., in the vicinity of Gloucester Point, Virginia. Samples were collected in August 1963 and June and July 1964. Horizontal and vertical distributional patterns were demonstrated with respect to the change of total numbers of organisms present. The distributional pattern was, however, more pronounced in the vertical direction. The vertical comparisons generally indicated more pronounced growth of epiphytic diatoms at the blade tip than blade base. Horizontal comparisons generally show more growth in deep than shallow water, but there are exceptions. Two trends were present which suggested periodicity and a shift in generic dominance. Cocconeia and Navicula appeared to reach peak densities on or shortly before June, Whereas, Dimerogramma, Epithemia, and Nitzochia appeared to have reached a peak considerably before the June sampling date. The former two organisms maintained relatively high densities throughout the sampling period, whereas, the latter three did not reach a comparable average density until August. Of the eighteen genera identified, four were chosen for detailed graphical illustration in 1963 and 1964 because of their predominance throughout the sampling period. Cocconeis, Dimerogramma, Epithemia 2 and Navicula were predominant genera in 1963; Epithemia was replaced in abundance by Nitzschia in 1964. / Master of Science

Great (Mw >8.5) earthquakes occur over long temporal intervals that extend beyond current historical (written and oral) records along most subduction zone coastlines often leading to the underestimation of magnitude, recurrence, and spatial extent of these events. Paleoseismic studies target low energy depositional environments that record primary and secondary evidence of earthquake occurrence within the coastal stratigraphy over much longer temporal scale, thus improving our understanding of the behavior of subduction zone earthquakes. Diatoms preserved within coastal stratigraphic records are sensitive to earthquake-induced environmental change and are useful bioindicators in paloesiesmology studies. The two studies in this dissertation employ diatoms to create novel approaches to investigate behavior and recurrence of earthquakes along two subductions zones: Alaska-Aleutian subduction zone and the Cascadia subduction zone. In these chapters we use diatoms to explore 1) the potential for combined slip along the Patton Bay splay fault system and the eastern Alaska-Aleutian subduction zone within Prince William Sound, Alaska, and 2) lacustrine turbidite source mechanisms in Ozette Lake, Washington to potentially improve the spatial and temporal earthquake record for the northern Cascadia subduction zone. This work has implications for improving our earthquake chronologies along subduction zone coastlines and making important contributions to coastal hazards assessments. / Doctor of Philosophy / Subduction zones are capable of producing great (>Mw 8.5) earthquakes with accompanying tsunamis that can impact nearby coastlines with devastating force. Great earthquakes occur over long timescales (thousands of years) and are often not captured in short historical records, leaving questions about the recurrence, behavior, and range of potential future earthquakes along these boundaries. Paleoseismology, the study of earthquake history, employs methods that use the earthquake-induced environmental changes along subduction zone coastlines to provide long-term records of earthquake occurrence. Diatoms, a type of siliceous microalgae entrained in coastal sediments, react to changes in pH, salinity, water depth, and sediment type, and are important indicators of environmental change that can be used to expand our understanding of earthquake behavior. This dissertation uses diatoms in two projects that explore the earthquake history along the Alaska-Aleutian subduction zone and the Cascadia subduction zone. First, we determine that secondary faults, called splay faults, in Prince William Sound are likely triggered only by slip along the Alaska-Aleutian subduction zone, suggesting that combined slip has occurred during four of the eight total megathrust earthquakes in the last ~4,200 years. Second, we investigate the sediment origins of the youngest six deposits (turbidites) in Ozette Lake, linking them to diatoms located on the subaqueous delta and shallow lake surfaces, leading us to infer the source is likely earthquake-induced slope failure. Both projects help to expand our understanding of subduction zone earthquake behavior, and will help inform future hazards assessments for coastal communities.

published_or_final_version / Ecology and Biodiversity / Doctoral / Doctor of Philosophy