The project's objective is to test sediment remediation in situ through thin-layer capping with two new types of sorbents: activated carbon (AC) and marl (CaCO3) in order to decrease the release of contaminants from historically pollutant sediments (eg. dioxins) and to increase the sequestration of phosphate in sediment and counteract eutrophication.

The project focuses on advancing knowledge in new environmental mitigation strategies, a relatively new research field that is in high demand due to increased anthropogenic pollution in coastal areas. Pilot studies on eventual negative effects of these new thin-layer capping techniques on benthic communities and essential ecosystem functions they mediate (nutrient cycling) demanded by environmental agencies, technical experts and consultants before these techniques can be suggested for larger field trials in Sweden.

Previous studies show that sediment remediation in situ by adding a thin layer of clay mixed with AC is a highly efficient method that decreases the sediment-to-water release fluxes of organic contaminants (e.g. PCBs, PAHs, dioxins) and their biovailability to aquatic organisms, including fish by 80 % or more. This technique seems promising, yet some studies have also shown that AC can cause negative effects on benthic fauna, such as a decreased abundance of filter and deposit feeders, decrease in species diversity, decreased lipid content and growth and physiological alterations e.g. decrease in gut microvilli. The majority of studies, however, have reported no or only mild transitory effects of AC on benthic organisms. No studies have been done in the Baltic Sea yet.

Another promising remediation technique in situ is the use of calcareous materials to increase the sequestration of phosphate in the sediment and counteract eutrophication. Calcareous matter is known to efficiently bind phosphorus. In previous experimental studies, fine-crushed marl (lutite) has been used as a test absorbent. The marl is a by-product of quarries on Gotland. As a first order estimate, a single addition of prepared marl to a certain sediment area might be sufficient for a permanent, large improvement of the water quality in the Baltic Sea. Before proposing this technique more research is needed on eventual secondary negative ecological effects of adding marl. In the proposed project, various types of granular AC and marl will be tested.

Researchers and departments:
Jonas Gunnarsson, Department of Ecology, Environment and Plant Sciences
Anna Sobek, Department of Environmental Science and Analytical Chemistry