ABSTRACT
Field experiments were conducted to test the suitability of different types and amounts of cuttings as substrate for a benthic community. Trays with defaunated sea-bed sediment and overlaid with test layers of water-based, low aromatic and diesel-based cuttings, were exposed on the sea floor at 11 m depth for 4 and 5.3 years. During this time a significant loss of oil hydrocarbons, 65-99%, was measured from the surface of the oil-based trays. Significant biodegradation of oil was observed in all trays within 2 years, with lag time positively correlated to dose. The oil contaminated sediments rapidly developed reduced conditions, but the redox values
gradually increased, and the redox potential discontinuity layer shifted downwards as animal recolonization and bioturbation increased. Macrofauna recolonization during the first year indicated no recovery from the oil contamination, but the fauna structure after 4 years showed that slight contamination stimulated colonization by opportunistic species, presumably as an effect of organic enrichment overrode any toxic effect. The heavily loaded sediments ( 10 mm layer of cuttings) prevented macrofauna recolonization for 5.3 years, and since the layer of cuttings still formed a physical barrier to burrowing, an extremely slow recovery can be expected. A 10 mm layer of water-based cuttings gave no apparent negative effect on recolonization, but redox conditions were subnormal. Low aromatic cuttings showed only slight improvement above diesel cuttings with respect to redox conditions and recolonization.
