Estuarine Oil Spill Effects in the Context of Dispersant use Changes

Abstract

ABSTRACT Surveys of rock, cobble, gravel, and salt marsh shores, intertidal macrobenthos, hydrocarbons, and estuarine bird populations were carried out over twelve months following the El Omar spill of 3 December 1988, when 100 metric tons (t) of Iranian light crude oil were spilled in Milford Haven, United Kingdom. Although small, this incident resulted in more widespread shoreline oiling than any previous spill in 30 years of operations at Milford Haven. About 20 t of chemical dispersant were used in the lower estuary. Dispersants were not used where there was a danger of oil and dispersant mixtures impinging on fish farms. Rock/cobble shores have been studied since the arrival of the oil industry in 1960 and spill impacts were, therefore, discernible at some sites against the baseline data. Serious impacts occurred locally due to excessive oiled algae and substrate removal. On gravel and salt marsh study sites, natural removal of oil was an efficient cleanup option. Some evidence was detected, however, that oil deposited on seed heads of Spartina was later transferred to the sediment surface as part of the litter fall. The marsh vegetation recovered by the end of the 1989 growing season, confirming the resilience of this community to single oil spills, provided intrusive cleanup is not attempted. The increase in aromatic hydrocarbon concentrations found in the surface sediments of the salt marsh was found also in mudflats adjacent to heavily-oiled areas, although no biological effects on the infauna of the inner estuary were detected (compared to a macrobenthic and hydrocarbon survey of 1984). No significant impacts were recorded on the population of 20,000 waders, wildfowl, and gulls present at the time of the spill. This is believed to be partly fortuitous due to the mild 1988/89 winter. The arrival in Milford Haven of intensive fish farming means that the previously routine use of chemical dispersants in the oil port will now be increasingly challenged. From the El Omar, it may be predicted that, in future spills, more oil will become stranded in marshes and rock and cobble shorelines. Not only are guidelines and scientific advice during shoreline cleanup essential, but also it is recommended that scientific monitoring, which lapsed in the early 1980s, be reinstated. These data would help make the important tradeoff between commercial and conservation interests in future spills.