Response of marine benthic fauna to thin-layer capping with activated carbon in a large-scale field experiment in the Grenland fjords, Norway

Abstract

A field experiment with thin-layer capping was conducted in the Grenland fjords, Norway, for remediation in situ of mercury and dioxin-contaminated sediments. Experimental fields at 30 and 95 m depth were capped with (i) powdered activated carbon (AC) mixed with clay (AC+cla`y), (ii) clay, and (iii) crushed limestone. Ecological effects on the benthic community and species-feeding guilds were studied 1 and 14 months after capping, and a total of 158 species were included in the analyses. The results show that clay and limestone had only minor effects on the benthic community, while AC+clay caused severe perturbations. AC+clay reduced the abundance, biomass, and number of species by up to 90% at both 30 and 95 m depth, and few indications of recovery were found during the period of this investigation. The negative effects of AC+clay were observed on a wide range of species with different feeding strategies, although the suspension feeding brittle star Amphiura filiformis was particularly affected. Even though activated carbon is effective in reducing sediment-to-water fluxes of dioxins and other organic pollutants, this study shows that capping with powdered AC can lead to substantial disturbances to the benthic community.Electronic supplementary materialThe online version of this article (doi:10.1007/s11356-017-8851-6) contains supplementary material, which is available to authorized users.

Contaminated Sediments

“…The effect of capping increased with layer thickness and in particular with addition of active materials (Josefsson, Schaanning et al 2012, Schaanning, Beylich et al 2014, Cornelissen, Schaanning et al 2016. The Opticap project has also revealed some long-time persistent negative effects of active carbon on bottom fauna (Samuelsson et al 2017), which is potentially important when considering remediation of large areas with viable benthic communities. Modelling of the transport of contaminants has been suggested to be a good tool for assessing the suitable thickness of the capping (Josefsson, Schaanning et al 2012.…”

“…At two occasions in the following years, the long-term effect of capping on benthic habitat quality and biodiversity has been monitored with SPI-images and macrofauna investigations, and the effect on bioavailability of dioxins/furans has been investigated from chemical analyses of sediment and flux measurements in situ and in mesocosms. Reduced leakage of dioxins/furans to the overlying water was observed on fields capped with clay and activated carbon (Schaanning and Allan 2012, Eek et al 2014, Schaanning, Beylich et al 2014, Cornelissen, Schaanning et al 2016, Samuelsson, Raymond et al 2017. Reduced bioaccumulation in Hinia reticulata and Nereis diversicolor was found in sediments capped with clay and activated carbon Allan 2012, Schaanning, Beylich et al 2014).…”

“…In the Norwegian Opticap project (Eek 2014, Schaanning, Beylich et al 2014, Cornelissen, Schaanning et al 2016, Samuelsson, Raymond et al 2017) the effect of capping with different thicknesses and materials on the leaching and bioaccumulation from dioxin contaminated sediment were tested in large scale field and laboratory experiments. The effect of capping increased with layer thickness and in particular with addition of active materials (Josefsson, Schaanning et al 2012, Schaanning, Beylich et al 2014, Cornelissen, Schaanning et al 2016.…”

“…Reduced bioaccumulation in Hinia reticulata and Nereis diversicolor was found in sediments capped with clay and activated carbon Allan 2012, Schaanning, Beylich et al 2014). However, monitoring has shown loss of individuals, species and diversity compared to the reference fields (Schaanning, Beylich et al 2011), with up to 90% reduction in abundance, biomass, and number of species (Samuelsson, Raymond et al 2017). A nine-year follow-up study of capefficiency and recolonization has been funded by The Norwegian Environment Agency in 2018-19.…”

“…Following dredging operations there are several challenges related to water treatment and deposition of dredged material, which may give adverse effects to the environment. The pilot study in the Grenlandfjords area considered the adverse effects of thin-layer capping including AC amendment and found negative effects on benthos (Schaanning, Beylich et al 2014, Samuelsson, Raymond et al 2017. There are indications that the potential effects of AC amendment depend on the quality as well as the particle size of AC, in addition to depend on the various feeding strategies of benthic organisms.…”