Faunal and Microbial Sediment Community Disturbances Caused by Organic and Inorganic Contamination

Abstract

There are ongoing developments to enable treatment of oil based drill cuttings with subsequent deposition offshore rather than the current practice to transport and treat such material on land. A sample from a step in the development of a microwave based treatment method has been tested in the present study. Microcosm and DGGE experiments were conducted to assess and compare the adverse effects of microwave treated drill cuttings with untreated oil based muds on macrofauna and microbial communities. Sediment sample from Boknafjord at a depth of 134 m were transferred into cores and treated with drill cuttings in an average layer of 11 mm, the adverse effect was measured on macrofauna diversity, biomass, number of species and microbial survival rate. The results showed that the treated cuttings were significantly less affected on the macrofauna number of species than the OBM sample, evidenced by statistical analysis, but less significantly by biomass for the macrofauna, and without significant difference with regards to macrofauna diversity or microbial communities. The cause of the effects for the oil based drill cuttings can be due to the presence of organics while for the microwave treated drill cuttings observations of effects that were different from the control sediment might alternatively have been caused by heavy metals. This latter can be argued for by the fact that the microwave treated drill cuttings was in more fine grained particles than the control sediment which could have made the metals more bioavailable for the macrofauna and microbial communities. This hypothesis needs to be further examined to be conclusive.