Add chemicals or minerals to sediments to remove or neutralise pollutants
Overall effectiveness category Unknown effectiveness (limited evidence)
Number of studies: 2
Background information and definitions
Marine sediments can accumulate pollutants over time, such as those leaching from aquaculture systems, sewage outfalls, or nearby agriculture fields, and negatively affect subtidal benthic invertebrates. Chemicals or minerals can be added to sediments to reduce or remove pollutants within the sediments (Shin & Kim 2016; Yamamoto et al. 2013). For example, granulated coal ash can be used with the aim of reducing concentrations of phosphates and hydrogen sulphide (Kim et al. 2014). This may reduce pollution levels in the sediment at the treated area and allow subtidal benthic invertebrate communities to recover over time (Kim et al. 2014).
Kim K., Hibino T., Yamamoto T., Hayakawa S., Mito Y., Nakamoto K. & Lee I.C. (2014) Field experiments on remediation of coastal sediments using granulated coal ash. Marine Pollution Bulletin, 83, 132–137.
Shin W. & Kim Y.K. (2016) Stabilization of heavy metal contaminated marine sediments with red mud and apatite composite. Journal of Soils and Sediments, 16, 726–735.
Yamamoto, T., Harada, K., Kim, K.H., Asaoka, S., & Yoshioka, I. (2013) Suppression of phosphate release from coastal sediments using granulated coal ash. Estuarine, Coastal and Shelf Science, 116, 41–49.
Supporting evidence from individual studies
A controlled, before-and-after study in 2008–2010 in one area of soft seabed in Hiroshima Bay, Japan (Kim et al. 2014) found that adding coal ash to sediments to remove phosphate and hydrogen sulphide appeared to result in more species and individual invertebrates compared to before treatment and to adjacent untreated sites, during winter but not summer. However, results were not statistically tested. In winter, species richness increased (post-treatment: 17–22; pre-treatment: 8; untreated: 0–11/sample), and invertebrate abundance increased (post-treatment: 3,345–3,859; pre-treatment: 42; untreated: 0–507/m2). In summer, species richness and invertebrate abundance were similar in post-treatment sites (species: 3–7/sample; abundance: 49–944/m2), pre-treatment sites (species: 2 /sample; abundance: 204/m2), and untreated sites (species: 0–6/sample; abundance: 0–261/m2). Annually between August 2008 and August 2012 (except 2009), two sites were sampled once in winter and once in summer (one sample/site/time point). In May 2010, coal ash was scattered onto the sediment at one site to a depth of 10 cm; the other site was untreated. At the treated site, sediment samples were collected using a 25 x 25 cm quadrat to a depth of 10 cm. At the untreated site, sediment samples were collected using a sediment grab (dimensions unspecified). Invertebrates (> 1 mm) were identified and counted.Study and other actions tested
A controlled study in 2008–2011 in one area of soft seabed in Hiroshima Bay, Japan (Yamamoto et al. 2015) found that adding coal ash to sediments to remove hydrogen sulphide increased combined invertebrate and fish abundance compared to untreated sediments in one of two comparisons, but did not change overall biomass over three years. Abundance at the site treated with Osaki coal ash was greater (41–496 individual/quadrat) than at the untreated site (14–281). The site treated with Onoda coal ash had similar abundance (29–262) to the untreated site. Combined invertebrate and fish biomass at the treated sites were similar (Osaki: 0.3–8.5 unit unspecified; Onoda: 0.3–9) to that of the untreated site (untreated: 0.6–13). In October 2008, two sites (75 x 50 m; 80 m apart) were treated with one of two types of coal ash (Onoda or Osaki; see study for details) to a depth of 20 cm and a third site (50 m away) was not treated. Every three months between February 2009 and November 2011, three sediment samples were collected at each site using a 25 x 25 cm quadrat to a depth of 20 cm. Both invertebrates and fish (>1 mm) were identified, counted, and weighed.Study and other actions tested