Impact of earthworms on trace element solubility in contaminated mine soils amended with green waste compost

The common practice of remediating metal contaminated mine soils with compost can reduce metal mobility and promote revegetation, but the effect of introduced or colonising earthworms on metal solubility is largely unknown. We amended soils from an As/Cu (1150 mgAs kg−1 and 362 mgCu kg−1) and Pb/Zn mine (4550 mgPb kg−1 and 908 mgZn kg−1) with 0, 5, 10, 15 and 20% compost and then introduced Lumbricus terrestris. Porewater was sampled and soil extracted with water to determine trace element solubility, pH and soluble organic carbon. Compost reduced Cu, Pb and Zn, but increased As solubility. Earthworms decreased water soluble Cu and As but increased Pb and Zn in porewater. The effect of the earthworms decreased with increasing compost amendment. The impact of the compost and the earthworms on metal solubility is explained by their effect on pH and soluble organic carbon and the environmental chemistry of each element

Do earthworms impact metal mobility and availability in soil? A review

The importance of earthworms to ecosystem functioning has led to many studies on the impacts of metals on earthworms. Far less attention has been paid to the impact that earthworms have on soil metals both in terms of metal mobility and availability. In this review we consider which earthworms have been used in such studies, which soil components have been investigated, which types of soil have been used and what measures of mobility and availability applied. We proceed to review proposed reasons for effects: changes in microbial populations, pH, dissolved organic carbon and metal speciation. The balance of evidence suggests that earthworms increase metal mobility and availability but more studies are required to determine the precise mechanism for this. (C) 2009 Elsevier Ltd. All rights reserved

Impact of the earthworm Lumbricus terrestris (L.) on As, Cu, Pb and Zn mobility and speciation in contaminated soils

To assess the risks that contaminated soils pose to the environment properly a greater understanding of how soil biota influence the mobility of metal(loid)s in soils is required. Lumbricus terrestris L. were incubated in three soils contaminated with As, Cu, Pb and Zn. The concentration and speciation of metal(loid)s in pore waters and the mobility and partitioning in casts were compared with earthworm-free soil. Generally the concentrations of water extractable metal(loid)s in earthworm casts were greater than in earthworm-free soil. The impact of the earthworms on concentration and speciation in pore waters was soil and metal specific and could be explained either by earthworm induced changes in soil pH or soluble organic carbon. The mobilisation of metal(loid)s in the environment by earthworm activity may allow for leaching or uptake into biota

Effects of coastal managed retreat on mercury biogeochemistry

We investigated the impact of managed retreat on mercury (Hg) biogeochemistry at a site subject to diffuse contamination with Hg. We collected sediment cores from an area of land behind a dyke one year before and one year after it was intentionally breached. These sediments were compared to those of an adjacent mudflat and a salt marsh. The concentration of total mercury (THg) in the sediment doubled after the dyke was breached due to the deposition of fresh sediment that had a smaller particle size, and higher pH. The concentration of methylmercury (MeHg) was 27% lower in the sediments after the dyke was breached. We conclude that coastal flooding during managed retreat of coastal flood defences at this site has not increased the risk of Hg methylation or bioavailability during the first year. As the sediment becomes vegetated, increased activity of Hg-methylating bacteria may accelerate Hg-methylation rate

Earthworms accelerate the biogeochemical cycling of potentially toxic elements: results of a meta-analysis

Earthworms are ecosystem engineers, capable of modifying the soil environment they inhabit. Recent evidence indicates that they increase the mobility and availability of potentially toxic elements in soils, but a quantitative synthesis of the evidence required to understand mechanisms and identify soils most susceptible to earthworm-induced potentially toxic element mobilisation is lacking. We undertook a meta-analysis of 42 peer reviewed journal studies, comprising 1185 pairwise comparisons between earthworm-inhabited and earthworm-free soils to quantify the impact of earthworms on potentially toxic element mobility in bulk earthworm-inhabited soil and earthworm casts, and on plant uptake and concentration. We find that endogeic and epigeic earthworms increase the mobility of potentially toxic elements in the bulk soil, and earthworms from all ecological groups mobilise potentially toxic elements during passage of soil through the earthworm gut. We also observe an increase in the concentration and uptake of potentially toxic elements by plants growing on soils inhabited by epigeic (mostly Eisenia fetida) earthworms. Earthworms mobilise potentially toxic elements in geogenic soils to a greater extent than anthropogenically contaminated soils. Soils with very low (<2%) soil organic matter content are most susceptible to earthworm-induced potentially toxic element mobilisation. These findings have important implications for the ability of exotic earthworms to alter soil biogeochemical cycles when introduced to new environments. Mixing amendments with contaminated soils with the intention of reducing the mobility of potentially toxic elements may be aided by the activity of earthworms that accelerate the mixing processes. Furthermore, our findings also highlight a promising phenomenon that, if harnessed, may help to alleviate micronutrient deficiencies in degraded soils

Impacts of epigeic, anecic and endogeic earthworms on metal and metalloid mobility and availability

The introduction of earthworms into soils contaminated with metals and metalloids has been suggested to aid restoration practices. Eisenia veneta (epigeic), Lumbricus terrestris (anecic) and Allolobophora chlorotica (endogeic) earthworms were cultivated in columns containing 900 g soil with 1130, 345, 113 and 131 mg kg1 of As, Cu, Pb and Zn, respectively, for up to 112 days, in parallel with earthworm-free columns. Leachate was produced by pouring water on the soil surface to saturate the soil and generate downflow. Ryegrass was grown on the top of columns to assess metal uptake into biota. Different ecological groups affected metals in the same way by increasing concentrations and free ion activities in leachate, but anecic L. terrestris had the greatest effect by increasing leachate concentrations of As by 267%, Cu by 393%, Pb by 190%, and Zn by 429% compared to earthworm-free columns. Ryegrass grown in earthworm-bearing soil accumulated more metal and the soil microbial community exhibited greater stress. Results are consistent with earthworm enhanced degradation of organic matter leading to release of organically bound elements. The degradation of organic matter also releases organic acids which decrease the soil pH. The earthworms do not appear to carry out a unique process, but increase the rate of a process that is already occurring. The impact of earthworms on metal mobility and availability should therefore be considered when inoculating earthworms into contaminated soils as new pathways to receptors may be created or the flow of metals and metalloids to receptors may be elevated

Importance of Diurnal Temperature Range (DTR) for predicting the temperature sensitivity of soil respiration

During the 21st century, global mean temperature is expected to rise by 1.5°C to 5.7°C (1). Climate change has already resulted in an overall decrease in the number of cold days and nights, and an increase in the number of warm days and hot nights, across most land areas globally (2). Our changing climate will influence soil ecosystems because soils have a complex interaction with the atmosphere through carbon, nitrogen, and hydrological cycles (3). Soil is the largest terrestrial carbon pool (4–6), but it also provides a habitat for diverse and complex communities of organisms (7). Soil represents a huge potential source of volatile carbon and a potential sink for additional carbon. Soil can therefore buffer CO2 losses into the atmosphere, depending on the balance between photosynthesis, autotrophic respiration, and heterotrophic respiration (2, 8). This balance exerts major controls on the biogeochemical interactions between land and atmosphere leading to the exchange of greenhouse gases like CO2, CH4 and N2O (2), the emissions of which could cause positive feedbacks that warm our climate system (9, 10). While the response of autotrophic respiration to changing climates is relatively well understood, predicting changes to the soil carbon sink due to climate change has been a major source of uncertainty in projections. Although it is known that increasing temperature can stimulate microbial degradation of soil organic carbon and increase the atmospheric concentration of CO2 (10–12), the magnitude of this positive feedback is unclear

Biochar modification to enhance sorption of inorganics from water

Biochar can be used as a sorbent to remove inorganic pollutants from water but the efficiency of sorption can be improved by activation or modification. This review evaluates various methods to increase the sorption efficiency of biochar including activation with steam, acids and bases and the production of biochar-based composites with metal oxides, carbonaceous materials, clays, organic compounds, and biofilms. We describe the approaches, and explain how each modification alters the sorption capacity. Physical and chemical activation enhances the surface area or functionality of biochar, whereas modification to produce biochar-based composites uses the biochar as a scaffold to embed new materials to create surfaces with novel surface properties upon which inorganic pollutants can sorb. Many of these approaches enhanced the retention of a wide range of inorganic pollutants in waters, but here we provide a comparative assessment for Cd2+, Cu2+, Hg2+, Pb2+, Zn2+, NH4+, NO3-, PO43-, CrO42- and AsO43-