Graduate Thesis Or Dissertation

 

Response to ultraviolet (UV-B) radiation by attached assemblages of estuarine diatoms Public Deposited

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  • Global atmospheric pollution from chlorofluorocarbons has the potential of causing significant reductions in the concentrations of stratospheric ozone. If the production of chlorofluorocarbons were to continue into the future at the rate prevalent in 1977, the steady state reduction in total global ozone could be between five percent to ten percent. This predicted ozone loss would result in an increase in the daily transmission of biologically harmful solar ultraviolet (UV-B, 290-320 nm) radiation. However, there have been relatively few studies concerned with the biological significance of increased UV-B radiation at the earth's surface. Two different estuarine benthic diatiom assemblages were exposed to solar visible radiation and three levels of simulated solar UV-B radiation. A sun!amp/filter system was used to simulate a natural UV-B spectrum. Artificial substrates colonized by diatoms recruited from Yaquina Estuary and sediment-associated diatoms removed from intertidal sandflats in Yaquina Estuary were the two diatom assemblages examined for UV-B sensitivity. Experiments were conducted in flow-through microcosms located in a greenhouse at the Oregon State University Marine Science Center in Newport, Oregon. All three experimental UV-B radiation treatments (high, low, control) were present in each microcosm. The artificial substrate assemblages were sampled during the winter and several spring/summer experiments. Sediment community experiments were conducted in the summer. Chlorophyll a concentration, biomass (ash-free dry weight) and primary productivity (radiocarbon uptake) were the parameters measured at each sampling date for the sediment and artificial substrate studies; community composition was determined for diatom assemblages attached to artificial substrates. A consistent response of the diatom assemblages attached to artificial substrates was an alteration of community structure following four weeks of exposure to UV-B radiation. Analysis of variance of biomass, chlorophyll a and radiocarbon uptake data indicated no significant depression in these parameters by UV-B radiation during each experiment. In fact, in some experiments UV-B radiation appeared to have a beneficial effect. The response of sediment-associated estuarine diatom assemblages to UV-B radiation was different than that observed with the artificial substrate diatom assemblages. There was a significant depression in biomass accumulation following one week of exposure to UV-B radiation and a significant depression in primary productivity following three weeks of exposure to high levels of UV-B radiation.
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