Ecotoxicological assessments of biochar additions to soil employing earthworm species Eisenia fetida and Lumbricus terrestris

Tom Elliston,Ian W Oliver

doi:10.1007/s11356-019-04542-2

Tom Elliston, Ian W Oliver

Open Access

https://doi.org/10.1007/s11356-019-04542-2

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Abstract

Biochar is the degradation-resistant product generated by the pyrolysis of organic materials and is produced for the intended use of land application in order to promote carbon sequestration and soil improvement. However, despite the many potential benefits biochar application offers, it is important to quantify any ecological impacts that may result from soil amendment in order to avoid potentially causing negative effects upon soil biota which are crucial in the many ecosystem services provided by soil. Any impacts on earthworms in particular are important to evaluate because of their pivotal role in organic matter breakdown, nutrient cycling and soil formation. In this study, we conducted a series of ecotoxicological assays to determine lethal and sublethal (avoidance, mass change and moisture content) effects of heavy biochar applications that reflect levels that may be used in soil restoration efforts. Two earthworm species, Eisenia fetida, an epigeic species, and Lumbricus terrestris, an anecic species, were utilised as test organisms. Two types of biochar, produced from wheat straw and rice husk feedstocks, respectively, were applied to OECD artificial soil and to a natural soil (Kettering loam) at rates of up to 20% w/w. The influence of biochar application on soil porewater chloride, fluoride and phosphate concentrations was also assessed. The biochar applications induced only a subtle level of avoidance behaviour while effects on survival over a 4-week exposure period were inconsistent. However, death and physical damage to some individual earthworms at high biochar application rates were observed, the mechanisms and processes leading to which should be investigated further. Earthworm development (mean mass change over time) proved to be a more sensitive measure, revealing negative effects on L. terrestris at 10% and 20% (w/w) wheat biochar applications in OECD soil and at 20% (w/w) applications of both biochars in Kettering loam. The moisture content of E. fetida remained remarkably consistent across all treatments (~ 82%), indicating that this is not a sensitive measure of effects. The high rates of biochar application resulted in increased chloride (2 to 3-fold) and phosphate (100-fold) concentrations in simulated soil porewaters, which has important implications for soil fertility and production but also for environmental management.

Highlights

IntroductionBiochar is the carbonaceous residue created during the pyrolysis, i.e. thermal decomposition, of biomass under low oxygen conditions (Lehmann and Joseph 2009) and is being
Biochar is the carbonaceous residue created during the pyrolysis, i.e. thermal decomposition, of biomass under low oxygen conditions (Lehmann and Joseph 2009) and is beingResponsible editor: Chris Lowe Electronic supplementary material The online version of this article contains supplementary material, which is available to authorized users.increasingly produced and incorporated into soil because of its potential to sequester carbon and mitigate climate change through increasing the long-term storage of carbon in soils (e.g. McHenry 2009)
Biochar applications to land are being promoted by many voices because it can offer a host of other benefits to soils; such benefits may include increasing the recalcitrant organic matter content of soil which decreases bulk density and increases porosity, water holding capacity, hydraulic conductivity and cation exchange capacity (Huang et al 2013)

Summary

Introduction

Biochar is the carbonaceous residue created during the pyrolysis, i.e. thermal decomposition, of biomass under low oxygen conditions (Lehmann and Joseph 2009) and is being. The wider soil ecosystem impacts of biochar addition need to be considered and evaluated, as biochar addition is effectively permanent, lasting for thousands of years, on account of its recalcitrance (Lehmann and Joseph 2009; Lone et al 2015). The effects of biochar applications on earthworms have received very limited attention Earthworms have long been recognised as ecosystem engineers, playing an essential role in organic matter decomposition, nutrient cycling, pore creation and soil formation Lethal and sublethal endpoints were examined in order to identify a range of effects resulting from soil amendment with biochar

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