A study of an estuarine benthic community subjected to petrochemical effluents

This study has assessed the impact of a petrochemical complex, which discharges its effluents onto an intertidal mudflat. The Grangemouth petrochemical complex on the Forth Estuary, Scotland discharges two effluents on to the Kinneil intertidal area. The results of a 24-year monitoring programme of the Kiimeil intertidal area, carried out between 1976 to 1999, are analysed. The relative impact of the effluents on the macrobenthic community is considered along with other potential pollution sources and climatic factors. During the study period a clear increase in the diversity, evenness and species richness was observed over the whole area. This is attributed to the increased quality of the refinery effluent, the chemical effluent and the River Avon, which also crosses the area. The group analysis showed that although all areas have shown an increase in diversity there are still three areas that can be considered impacted (Groups 1, 2 and 4). Two major changes in the species composition were seen in 1979 when Manayunkia aestuarina was first found and in 1994 when Streblospio shrubsolii was first recorded. \n \nThe impact of the recent movement of the chemical outfall from a hightide position to a lower shore site is also considered. A detailed survey of the areas around the new lower shore and old upper shore outfalls indicated that there was a spatial difference in the species distribution, which can be explained by the distance from the refinery outfall, the hydrocarbon concentration of the sediments and/or the station height. No change in the community composition was detected after the movement of the chemical outfall in January 1998, although seasonal changes were seen.