Long term effects of activated carbon on benthic communities

Thin-layer capping with activated carbon (AC) has a potential as situ remediation method for sediments exposed to hydrophobic organic compounds (HOCs). This treatment was applied at two test fields; one in the Eidangerfjord (95 m) and the other in the Ormerfjord (30 m) in 2009. These two fjords are a part of the Grenland fjord system which have a long history of contaminated sediments. In this study we will address long-term effects of thin-layer capping with AC on the benthic community nine years later. Number of individuals, species and biomass was significantly reduced in both test fields compared to their corresponding reference fields. The differences were particularly notable in the Ormerfjord as the most dominant specie in the reference field, the brittle star Amphiura filiformis, was completely absent in the test field. After 2010 he faunal group Echinoidea was absent in both AC treated field. The indices used to assess the ecological condition in the water framework directive monitoring system for coastal waters in Norway did not reflect negative effects AC treatment had on the benthic communities. The long-term effects of AC on the benthic community should therefore be carefully evaluated before applying this treatment on a larger scale. More research is also needed to improve the understanding of why the AC treatment affects the benthic community