Large-scale field study on thin-layer capping of dioxin contaminated sediments in the Grenland fjords, Norway : Effects on marine benthic fauna

• The Grenland fjords on the South East Coast of Norway are heavily contaminated with dioxins and furans after emissions from past industrial activities. Thin layer capping with a 1.1 to 3.7 cm cap was tested as a remediation option in a large-scale in situ study in two different parts of the fjord system, in the Ormefjord at 25-30 meters depth and in the Eidangerfjord at 80-100 meters depth. Three different capping materials: Limestone gravel, Clay, and powdered activated carbon (AC) mixed into clay (AC+clay) was compared to untreated reference fields in order to evaluate their effects on contaminant sequestering and possible effects on the benthic communities. Sediment to water fluxes of contaminants were significantly reduced by the capping materials, especially with AC-clay and is reported in a companion study.This study discusses the ecological effects of the remediation 1 and 14 months post treatment. Capping with Clay and Lime had minor and short-lasting effects on benthic fauna. Capping with AC+clay, however, had led to profound and more long-lasting perturbations of the macrofauna. An initial massive decline in filter feeders and suspension feeders was observed after 1 month in the shallower Ormefjord. The negative effects got worse after 14 months and resulted in dramatic reductions of all feeding guilds. The number of species, organism abundances and biomass in the AC+clay field were ca 80-90 % lower compared to the reference fields after 14 months.The negative effects were less pronounced at the deeper (80-100 meters) location in the Eidangerfjord and were also stable with time, suggesting that the benthic community the deeper habitat was more resilient to the capping compared to the shallower community in Ormefjord.The differences in response of the two communities are hypothesized to be due to the higher macrofaunal diversity in the deeper location, as well as to differences in abiotic factors such as available food and temperature. Results from this study show that amendment with powdered AC can lead to serious perturbations of the benthic community, at least initially, i.e. one year post capping in this study. These results stresses that further long-term monitoring of these benthic communities is necessary before capping with AC+clay could be advocated as a potential remediation option.

Ämnesord

NATURVETENSKAP  -- Biologi (hsv//swe)

NATURAL SCIENCES  -- Biological Sciences (hsv//eng)

NATURVETENSKAP  -- Kemi (hsv//swe)

NATURAL SCIENCES  -- Chemical Sciences (hsv//eng)

NATURVETENSKAP  -- Geovetenskap och miljövetenskap (hsv//swe)

NATURAL SCIENCES  -- Earth and Related Environmental Sciences (hsv//eng)

Nyckelord

Contaminated Sediment Remediation

Benthic Community

Activated Carbon

Stress

Resilience

marin ekotoxikologi

Marine Ecotoxicology

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