The Gullmarsfjord on the Swedish west coast has a sill at 40 m and a maximum depth of 118 m. The stagnant bottom water is usually renewed with oxygen-rich water each spring. In 1997 this did not occur, and the fauna was eliminated at depths below about 100 m and severely reduced between 80 and 100 m depth. In spring 1998, the whole fjord was re-oxygenated and the succession of the benthic fauna was studied at 5 stations over a 2 yr period. Simultaneously, the benthic habitat quality (BHQ) was assessed by analysing sediment redox conditions and faunal burrow structures in sediment profile images. Succession of the benthic fauna is described as increases in number of species, abundance and biomass. Conspicuous colonisers below 100 m depth were the polychaete Capitella capitata and the heart urchins Echinocardium cordatum and E. flavescens. Return to preoxygen stressed conditions was slowest at the deepest stations. By using a multivariate technique (multi-dimensional scaling) we show that the benthic communities at all depths more or less returned to the same faunal composition as during pre-disturbed conditions. The pioneering and mature ben-

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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.

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Sediment spiked with 14 C-2, 2', 4, 4'-tetrabrominated diphenyl ether (BDE-47) was added as a single pulse, at a low or a high concentration, to intact soft-bottom sediments in a box-cosm system. The vertical distribution of the pollutant and the bioaccumulation in 39 different taxa of macrofauna were analysed after 10, 20 and 29 wk exposure. Throughout the experimental period, 90% of the recovered BDE-47-derived radioactivity in the sediment was found within the upper 5 cm. The BSAF (biota-sediment accumulation factor) in the different taxa after 29 wk exposure varied between 0.4 and 16.3. The correlation between bioaccumulation and lipid content of all individual specimens in each box-cosm was significantly positive and explained between 11 and 64% of the variation. When the fauna was divided into groups with different feeding strategies, it was found that the mean BSAF was significantly higher for the surface deposit-feeders than for the suspension-feeders, subsurface feeders and the predators. The difference increased with time and was larger after 29 wk exposure than after 10 wk. We also tested whether there was a correlation between 15 N enrichment, i.e. trophic position, in the analysed species and bioaccumulation, but no such correlation was found. Water-soluble metabolites of BDE-47 were detected in 15 of the 39 macrofaunal species. There was no observable correlation between the presence of metabolites in the macrofauna and bioaccumulation of the pollutant.