Response of natural microbial populations to ultraviolet irradiation in a simulated estuarine microcosm Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/2z10wt81r

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  • Ozone, present in the earth's atmosphere, filters incident solar ultraviolet radiation such that only a portion of the total ultraviolet spectrum emitted by the sun reaches the planet's surface. Violation of the integrity of this filter could mean an alteration in the solar ultraviolet radiation penetrating the atmosphere. Atmospheric increases in oxides of nitrogen and chlorofluoromethanes-- represent a threat to this shield. Among the known sources of these substances are the emissions from the engines currently used in the supersonic transport aircraft, fuels which are to be used for the space shuttle aircraft, propellants in aerosol spray cans, refrigerants, and the heat generated by nuclear explosions. It is not known how much perturbation can be tolerated by the ozone system. Nor is it well established how alterations of the incident solar radiation will be tolerated by the organisms residing at or near the earth's surface. The purpose of this investigation was to detect possible effects of increased solar ultraviolet irradiation on a particular portion of the biosphere. Samples of estuarine water were cultured in the laboratory in five liter rectangular containers which provided a surface area to volume ratio of 0.1. Autotrophic growth was encouraged by enrichment with inorganic nutrients and exposure to cool-white fluorescent lamps for 14 hours a day. Community photosynthesis and respiration were monitored over a six-week period and demonstrated oscillations suggesting that succession was occurring and that the microcosms were able to maintain themselves. Replicate microcosms were exposed to increased ultraviolet radiation (above 290 nm) for ten of the fourteen hours of exposure to cool-white radiation (310-750 nm) during the second through the fifth week of the experimental period. The algal blooms which resulted supported the growth of the heterotrophic portion of the community. Changes in the natural bacterial populations were followed through enumeration studies and through an examination of a number of selected heterotrophic metabolic activities. Dilution plate counts, three-tube most probable number (MPN) determinations, and the utilization of a uniformly 14C labelled organic compound were the three methods used to characterize the heterotrophic populations. The differences observed in the bacterial populations of the two groups of microcosms indicate that increased ultraviolet irradiation does have a measurable effect. Among the effects of exposure to UV radiation were: a selection against non-pigmented cells; a selection against certain specific metabolic types of organisms, such as cellulose degrading heterotrophs, and an increase in heterotrophic respiration.
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