EFFECTS OF A CRUDE-OIL SPILL ON THE BENTHIC INVERTEBRATE COMMUNITY INTHE GASCONADE RIVER, MISSOURI

Effects of a 3.3-million-L crude oil spill on the benthic macroinverte brate community of the Gasconade River, a large river in Missouri, wer e evaluated by comparing several macroinvertebrate community indices i n riffle and backwater habitats above and below the spill. Concentrati ons of total petroleum hydrocarbons (TPH) in sediments decreased drama tically in riffle habitats within 6 months of the spill, but elevated hydrocarbon levels (TPH = 80-270 mu g/g) were still present in backwat er habitats at the end of the study. Correspondingly, riffle macroinve rtebrate communities recovered rapidly, but overall benthic diversity continued to be reduced in backwater areas until the end of the study 18 months after the spill. In addition, statistical analysis of benthi c functional feeding groups revealed that both scrapers and shredders were reduced in backwater habitats below the oil spill. Decreased abun dance of shredders and scrapers in these habitats is likely caused by oil contamination of aquatic sediments and associated organic matter r equired by these groups for food and substrate. Results of this study suggest that the persistence of oil in backwater habitats has a negati ve effect on the benthic community in large rivers.