Impaired benthic macrofauna function 4 years after sediment capping with activated carbon in the Grenland fjords, Norway

Environmental Science and Pollution Research https://doi.org/10.1007/s11356-020-11607-0 RESEARCH ARTICLE Impaired benthic macrofauna function 4 years after sediment capping with activated carbon in the Grenland fjords, Norway Caroline Raymond 1 2 3 4 & Göran S Samuelsson & Stefan Agrenius & Morten T Schaanning & Jonas S Gunnarsson 1 Received: 15 June 2020 / Accepted: 9 November 2020 # The Author(s) 2020 Abstract The sediments in the Grenland fjords in southern Norway are heavily contaminated by large emissions of dioxins and mercury from historic industrial activities. As a possible in situ remediation option, thin-layer sediment surface capping with powdered activated carbon (AC) mixed with clay was applied at two large test sites (10,000 and 40,000 m2) at 30-m and 95-m depths, respectively, in 2009. This paper describes the long-term biological effects of the AC treatment on marine benthic communities up to 4 years after treatment. Our results show that the capping with AC strongly reduced the benthic species diversity, abundance, and biomass by up to 90%. Vital functions in the benthic ecosystem such as particle reworking and bioirrigation of the sediment were also reduced, analyzed by using novel bioturbation and bioirrigation indices (BPc, BIPc, and IPc). Much of the initial effects observed after 1 and 14 months were still present after 49 months, indicating that the effects are long-lasting. These long-lasting negative ecological effects should be carefully considered before decisions are made on sediment remediation with powdered AC, especially in large areas, since important ecosystem functions can be impaired. Keywords Benthic ecology . Macrofauna . Bioturbation . Bioirrigation . Index . Contaminated sediment . Remediation Introduction In coastal marine environments, sediments are often major sinks for contaminants from industrial and municipal activities. Leakage from contaminated sediments may act as new sources to pollution in areas where primary sources have been cleaned or closed down (Larsson 1985). Traditional remediation methods in aquatic environments are dredging or isolation capping. However, dredging is costly and involves moving large amounts of contaminated sediment that need to be deposited elsewhere, and conventional capping use Responsible editor: Vedula VSS Sarma * Caroline Raymond 1 Department of Ecology, Environment and Plant Sciences (DEEP), Stockholm University, 106 91 Stockholm, Sweden 2 Svensk Ekologikonsult, Skiftesvägen 17, 163 43 Stockholm, Sweden 3 Department of Marine Sciences–Kristineberg, University of Gothenburg, 451 78 Fiskebäckskil, Sweden 4 Norwegian Institute for Water Research (NIVA), 0349 Oslo, Norway comprehensive isolation layers, e.g., geotextiles or thick layers of sand, in order to prevent the contaminants from being released to the water column (Reible et al. 2008). An alternative capping method proposes a thin cap containing a strong sorbent such as activated carbon (AC) onto the contaminated sediments (Ghosh et al. 2011). AC can sorb the contaminants and reduce their release to the water column and thereby decrease their bioavailability (Cho et al. 2009, 2007; Millward et al. 2005; Patmont et al. 2014; Zimmerman et al. 2004, 2005). One advantage of the remediation method with AC is that lesser amount of capping material is used compared to conventional capping. Another advantage is that the benthic macrofauna could survive a thin cap and facilitate the mixing of the sorbent into the sediment though their reworking activity (bioturbation) and thus increase the capping efficiency (Ghosh et al. 2011; Sun and Ghosh 2007). In contrast to the positive effects of AC for reducing contaminants’ release and bioavailability, several studies have shown that AC can be harmful to benthic macrofauna (e.g., Janssen and Beckingham 2013; Jonker et al. 2009; Rakowska et al. 2012; Samuelsson et al. 2017). Both AC concentration and particle size seem to be important factors for if, and to what extent, the benthic organisms are affected (Abel and Akkanen 2018, 2019; Kupryianchyk et al. 2013a, 2012; Environ Sci Pollut Res Nybom et al. 2015, 2012). Further, the observed effects of AC seem also to depend on ecosystem conditions such as depth, if it is a limnic or marine system, as well as if it is a laboratory or field study. The reported negative biological effects caused by exposure to AC are sometimes severe, for example reduced survival (Kupryianchyk et al. 2013a, 2011; McLeod et al. 2008), inhibited growth (Janssen et al. 2012; Kupryianchyk et al. 2011; McLeod et al. 2008; Millward et al. 2005; Nybom et al. 2015, 2012), behavioral changes (Jonker et al. 2009; Nybom et al. 2015, 2012), reproduction interferences (Nybom et al. 2015, 2012), and morphological changes (Nybom et al. 2015). Such negative biological consequences are important from an ecological point of view as benthic fauna substantially influence the sediment with their activities, e.g., ingestion, defecation, irrigation, and burrowing. These activities are examples of bioturbation, i.e., the process of organisms’ particle mixing by reworking and exchange of solute and water in burrows (Kristensen et al. 2012). Bioturbation is a vital process in the soft bottom ecosystems, influencing for example geochemical gradients, microbial community structures, and redistribution of food resources within the sediment, as well as regulating the rate of gas exchange and nutrient fluxes with the overlying water (Aller 1994; Meysman et al. 2006; Rhoads 1974). Because different species affect the sediment properties in different ways, the functioning of the sediment ecosystem is dependent on the structure of the benthic community (Dauwe et al. 1998; Gray 1974; Pearson and Rosenberg 1978). From an ecosystem perspective, it is therefore of great importance to find out if a thin layer of AC would have any long-term harmful effects on the benthic fauna, and to quantify potential functional changes in terms of bioturbation activities. In this study, we assessed the long-term effects of thinlayer capping with powdered AC on marine benthic macrofauna communities 49 months (4 years) after capping. The results follow up the initial effects of AC capping on benthic macrofauna that are presented in Samuelsson et al. (2017), which reported negative effects after 1 and 14 months on number of species, total abundance, and biomass. The study was conducted as a large-scale field experiment in the Grenland fjords in southeast Norway, where the sediment is heavily contaminated by dioxins, furans, and mercury from past industrial activities. One unique and novel aspect in this paper is the long-term perspective, where the effects of AC capping on the benthic community are evaluated in situ 4 years after capping. Another novelty is that we assessed the changes on the benthic communities using three recently developed bioturbation indices. In the first index, the potential reworking pr (...truncated)