The effects of oil and dispersed oil on three temperate Australian seagrass : scaling of pollution impacts
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The thesis is a comprehensive assessment of the effects of oil and dispersed oil on subtidal seagrass using a range of in situ and laboratory experiments on whole plants and seagrass leafblade sections. Apart from assessing the effects of oil and dispersed oil on seagrass between seasons, locations, and morphologically different species, the study determines whether laboratory results are indicative of those obtained in situ as an initial step in developing a rapid laboratory testing protocol for seagrass assessment. Petrochemical treatments, consisting of a range of concentrations of the water accommodated fraction (WAF) of oil alone (Tapis crude, IFO-380), dispersant alone (Corexit 9527, Ardox, Slickgone, Corexit 9500) and dispersed oil were exposed to whole plants, in both the laboratory and in situ, for ten hours followed by a four day recovery period, and for five hours in the leafblade experiments. Photosynthetic health was monitored by assessing the effective quantum yield of photosystem II (ΔF/Fm') and chlorophyll a pigment concentrations, whilst semi-quantitative methods of total petroleum hydrocarbon (TPH) concentration were used to determine the percent TPH remaining in the water column following the exposure period. In most cases, the non-dispersed oils, Tapis crude oil and IF0-380, had less of an impact to both Zostera capricorni and Halophila ovalis than the dispersed oil treatments, whilst Zostera muelleri did not show any negative impact from either dispersed or non-dispersed Tapis crude oil. Winter in situ experiments found slightly greater reductions of ΔF/Fm' in Z. capricorni in most treatments compared with summer in situ, but generally there was minimal impact whilst Z. muelleri exhibited a stimulatory response to both non-dispersed and dispersed Tapis crude oil in Corio Bay, Victoria (summer in situ only). Laboratory whole plant experiments found Z. capricorni was for the most part less resilient to Tapis crude oil (non-dispersed and dispersed) treatments than Halophila ovalis whereas, with exposure to IF0-380 (non-dispersed and dispersed) H. ovalis was less resilient than Z. capricorni. Quite severe, and, or prolonged, photosynthetic stress was evident in both Z. capricorni and H. ovalis when exposed to most of the dispersant alone treatments (Corexit 9527, Ardrox and Corexit 9500), however the Slickgone alone treatment caused only a very short-lived stress response in H. ovalis only. The results of the laboratory whole plant experiments, conducted under Sydney summer water temperature conditions, were generally more similar to those observed in the summer in situ experiments than those observed in winter in situ. The effects to the leafblades of Z. capricorni were commonly greater than those observed in the whole plant experiments, even within the short exposure period. ΔF/Fm' appeared a more reliable indicator than that achieved with the chlorophyll a pigment analyses. Large differences in the percent TPH recovered between in situ and laboratory experiments suggests microbrial activity and sediments play a substantial role in the partitioning of oils m these experiments. This research suggests that assessments of seagrass health in laboratory experiments can in some cases be representative of that observed in situ when similar experimental conditions are maintained. The increased sensitivity of leafblade sections is considered beneficial when rapid comparisons of different petrochemical impacts to seagrass are required, i.e. once an oil spill has occurred.
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