Influence of bioturbation by Hediste diversicolor on mercury fluxes from estuarine sediments: A mesocosms laboratory experiment

Abstract

Mercury, with its reactive forms being the most deleterious for the trophic chains, has been identified as a major pollutant in a few confined bodies of the coastal zone. Due to feeding, burrowing, and bioirrigation activities, infauna are known to play a crucial role in the biogeochemical processes of contaminants. The main goal of the present study is to evaluate the effects of Hediste diversicolor bioturbation on mercury fluxes from estuarine sediments in a mesocosms laboratory experiment. Additionally, an attempt was made to establish a relationship between the amount of remobilised mercury to the water column and the degree of contamination of the sediments using a mercury contamination gradient.The present experiment demonstrated that the bioturbation activity caused by the gallery-diffuser H. diversicolor did not influence the remobilisation of mercury (in dissolved reactive forms) from the sediment to the water column. The concentration of dissolved reactive mercury in the water column also did not reflect the degree of contamination in the sediments. The results obtained were in accordance with the sediment characteristics of the Mondego Estuary and Ria de Aveiro (Portugal), since they are very rich in organic matter content, iron/manganese total and hydrous oxides. These physicochemical characteristics of the sediments may partially justify the retention of mercury by these systems, even when they are subjected to bioturbation.In conclusion, sediments with high organic matter content and a high concentration of iron/manganese hydrous oxides allowed for efficient retention of mercury, and the bioturbation process did not seem to affect the system. Another conclusion from this study is that the remobilisation of mercury by bioturbation to the water column is not a fast process, requiring more than 24 h. This study constitutes an important work in the area of the effects of bioturbation on mercury remobilisation. Considering the toxicity of mercury for the biota, it is essential to evaluate the real magnitude of mercury processes occurring in estuarine systems in order to obtain essential information on metal behaviour.

Distribuição de mercúrio total em sedimentos da plataforma continental Amazônica: Brasil

“…Além disso, o processo de transporte e deposição/sedimentação do material particulado em suspensão dependerá também de um conjunto de fatores físico-químicos, que incluem além da salinidade, o tempo de residência das águas, a baixa velocidade de fluxo de corrente, potencial redox, pH, teor de matéria orgânica, tamanho das partículas, concentração de sulfetos e presença de bactéria sulfatoredutoras (Machado 2004;Cardoso et al 2008;Reboreda et al 2008). Segundo os autores ainda, ambientes aquáticos com maior tempo de residência ou que não apresentam competência de transporte possibilitam a deposição do material particulado em suspensão no sedimento, ficando a biodisponibilidade dos metais associados controlada aos fatores físico-químicos supracitados.…”

Bioturbation/bioirrigation effect on thallium released from reservoir sediment by different organism types

“…Metals coprecipitated with or absorbed to FeS and MnS are rapidly oxidized following sediment resuspension, due to their relative solubility in oxic conditions (Allen et al, 1993;Caetano et al, 2003). Also, organic matter has a relevant role since its structural features allow its interaction with substances like metals, modifying its mobility and availability to organisms (Cardoso et al, 2008). Thallium may also exist in the sediments precipitated as sulfides or associated with Fe and Mn sulfides.…”

“…Jiang et al (2010) compared bioturbation efficiency in Chironomus plumosus and Tanypus chinensis both of arthropoda; the authors demonstrated that the two organism types differ greatly in their feeding and burrowing activities, and certain Chironomid species may play important roles in driving nutrient cycling. Other researchers (Cardoso et al, 2008;Michaud et al, 2006) found that the gallery-diffusers (e.g., Hediste diversicolor) have greater effects than biodiffusers (e.g., bivalves) on the biochemical processes in marine sediment. Gallery-diffuser animals produce diffusion in the layer with very dense gallery systems and a bio-transport at the end of the burrows.…”

Bioturbation effects on heavy metals fluxes from sediment treated with activated carbon

“…However, most earlier studies addressed the effectiveness of AC on remediation of HOCs contaminated sediment (Cho et al 2009;Kupryianchyk et al 2013), whereas the effectiveness on heavy metals has been studied less frequently. Bioturbation can influence the fate, transport, and bioavailability of sediment-bound heavy metals (Ciutat and Boudou 2003;Schaller 2014), it may be responsible for a major fraction of the pollutants released from sediments to the water column (Cardoso et al 2008;Josefsson et al 2010;Thibodeaux and Bierman 2003). In addition, bioturbation may affect sediment remediation processes because it is a main process controlling mobilization of elements including dissolved organic carbon (DOC) from sediments (Schaller 2014).…”