The effects of oil and dispersed oil on three temperate Australian seagrass : scaling of pollution impacts
- Publication Type:
- Thesis
- Issue Date:
- 2011
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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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