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Large-scale field study on thin-layer capping of dioxin contaminated sediments in the Grenland fjords, Norway: Effects on marine benthic fauna
Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
Department of Biological and Environmental Sciences, Göteborg University, 405 30 Göteborg, Sweden.
Norwegian Institute for water research (NIVA), 0349 Oslo, Norway.
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

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.

Keyword [en]
Contaminated Sediment Remediation; Benthic Community; Activated Carbon; Stress; Resilience
National Category
Biological Sciences Chemical Sciences Earth and Related Environmental Sciences
Research subject
Marine Ecotoxicology
Identifiers
URN: urn:nbn:se:su:diva-94840OAI: oai:DiVA.org:su-94840DiVA: diva2:656551
Projects
CarbocapOpticapThinc
Funder
Swedish Research Council, 210-2007-282Formas, 210-2007-282Vinnova, 210-2007-282
Available from: 2013-10-16 Created: 2013-10-16 Last updated: 2013-10-16
In thesis
1. In situ remediation of contaminated sediments using thin-layer capping: efficiency in contaminant retention and ecological implications
Open this publication in new window or tab >>In situ remediation of contaminated sediments using thin-layer capping: efficiency in contaminant retention and ecological implications
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Hydrophobic organic contaminants (HOCs) often reside in sediments sorbed to particles, most tightly to particles with high content of organic carbon. If persistent, such pollutants can accumulate in the sediment for many years and constitute a contamination risk for sediment-living organisms and organisms at higher trophic levels, including humans.

Since traditional remediation techniques are associated with complications (e.g. release of contaminants during dredging operations, disturbance of benthic faunal communities), or constraints (handling of large amounts of contaminated sediment and water, limitations due to depth and size of the area, high costs), there is a need for new alternative methods.

In situ remediation through thin-layer capping (a few centimeter cover) with a sorbing material such as activated carbon (AC) has been proposed as an alternative remediation method. Compared to traditional remediation techniques, AC amendment in a thin layer means less material handling and lower costs and is assumed to be less disruptive to benthic communities. The objectives of this thesis were to investigate the ecological effects from thin layer capping as well as the efficiency in contaminant retention.

Thin layer capping amended with AC proved to reduce availability of HOCs to the tested organisms, the gastropod Nassarius nitidus (Paper II), the clam Abra nitida (Paper III) and to polychaete worms  (Paper II and III). The remediation technique also decreased the sediment-to-water fluxes of the contaminants (Paper II and III).

However, AC amended thin-layer capping was also found to cause negative biological effects. In laboratory studies with only a few species the negative effects were minor, or difficult to discern with the endpoints used (Paper II and III). In a larger multi-species mesocosm (boxcore) study, on the other hand, the negative effects were more prominent (Paper I) and in a large scale field study the benthic community was found to be profoundly disturbed by the AC amendment, with the effects persisting or even worsening ca one year (14 months) post amendment (Paper IV).

Place, publisher, year, edition, pages
Stockholm: Department of Ecology, Environment and Plant Sciences, Stockholm University, 2013. 34 p.
Keyword
Contaminated Sediment Remediation, Activated Carbon, Benthic Community, Ecological Effects, Stress, Resilience, Contaminant Sequestration, Capping Efficiency, Bioavailability, Bioaccumulation, Sediment-to-water fluxes
National Category
Biological Sciences Environmental Sciences Oceanography, Hydrology, Water Resources
Research subject
Marine Ecotoxicology
Identifiers
urn:nbn:se:su:diva-94845 (URN)978-91-7447-795-5 (ISBN)
Public defence
2013-11-15, Nordenskiöldsalen, Geovetenskapens hus, Svante Arrhenius väg 12, Stockholm, 09:00 (English)
Opponent
Supervisors
Projects
CarbocapOpticapThinc
Funder
Swedish Research Council, 210-2007-282Formas, 210-2007-282Vinnova, 210-2007-282
Note

At the time of the doctoral defence the following papers were unpublished and had a status as follows: Paper 3: Manuscript; Paper 4: Manuscript.

Available from: 2013-10-24 Created: 2013-10-16 Last updated: 2014-06-27Bibliographically approved

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