A mesocoms experiment on the impacts of water- and olefin-based drill cuttings on benthic communities

Abstract

A three months simulated seabed experiment on water- and olefin-based drill cuttings has been performed at NIVAs Marine Research Station at Solbergstrand. Twelve box-core samples were transferred from 200 m depth in the outer Oslofjord and treated with 2-4 mm layers of cuttings or sediment particles from the fjord location. In treatments with olefin-based cuttings, microelectrode profiles showed reduced penetration of O2 into the cuttings layer, and the consumption of O2 from the overlying water increased after an initial lag phase of 2-3 weeks. The initial (field) structure of the macrobenthic communities was maintained throughout the experimental period, and at community level, no significant difference was observed between treatments at the end of the exposure period. However, three taxa showed reduced abundances in boxes treated with water- and olefin-based cuttings compared with untreated boxes and boxes treated with sediment particles. The effect could not be assigned to olefins or any of the weight materials ilmenite (present in the water-based cuttings) and barite (present in the olefin-based cuttings). Toxic effects of other mud components could not be entirely ruled out, but size or shape of cuttings particles appeared to be a more likely common factor responsible for the observed impact of both types of cuttings.