Fate and effects of oil and dispersed oil on mangrove ecosystems in Australia


In the field experiment, we applied oil and dispersed oil treatments on replicated mature plots of R. stylosa under strictly controlled conditions.

Field sites were monitored for approximately two years Field sites were monitored for approximately two years. Approvals were granted to conduct field experiments in mangroves at Fishermans Landing, Port Curtis, near Gladstone in Queensland. Treatments included Gippsland Light crude oil on its own and as dispersed oil using Corexit 9527 in a 1:20 mixture. Both treatments were pre-weathered in a shallow pond of seawater for 24 hours prior to application in field plots. Weathered oil treatments, totalling ~1,277 L, were successfully applied to, and contained in, field plots of mature mangrove stands.
Successful simulation of a large oil spill was based on concentrations of hydrocarbons in surface sediments averaging ~30,000 ug.g-1, and extensive mortality of trees 2-7 months after oiling. Oil adhered to above-ground roots and sediments mostly on the first settling and deposition from tidal waters. Enclosures were removed within two weeks without loss of oil from plots into adjacent mangroves.
Plate 5a, b, c, d, e, f.Field trials were used to further investigate short term effects of spills of Gippsland crude oil and dispersed oil.
Study sites A.Study sites were established in and near to mangrove stands, soon to be filled in with reclamation works associated with the Gladstone Port development, fringing Port Curtis, Queensland.
Enclosures B.Enclosures, around 35 m2each, were installed around replicate plots of matureRhizophoratrees, approximately 5-8 m tall. Enclosures were tested prior to application of oil treatments to confirm that oil would remain inside while tidal waters could flow in and out.
Oil and dispersed oil treatments C.Oil and dispersed oil treatments were prepared in a shallow pond prior to application, and weathered for 24 hours with periodic mixing using a small pump.
Approximately 200 litres of oil mixtures D.Approximately 200 litres of oil mixtures were to be applied to each plot. Difficulties in moving throughRhizophoramangrove forests meant that the drums full of oil had to be deployed by helicopter.
The final preparations E.The final preparations for applying oil included surrounding each plot with absorbent booms and having bags of absorbent material in readiness next to each plot should there be any leakage outside the enclosures.
adding oil treatments F.Once our preparations were complete, we awaited the arrival of tidal waters within the plots before adding oil treatments.

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April 7, 2010