Abstract
We investigated the response of the dominant bacterial taxa in gravelly sand to the addition of biochar and/or mixtures of volatile petroleum hydrocarbons (VPHs) using denaturing gradient gel electrophoresis (DGGE) and sequencing of cut bands. Biochar addition alone had only weak effects on the soil bacterial community composition in batch study samples, while VPH addition had strong effects. Indirect effects of biochar on soil bacterial communities were apparent in column study samples, where biochar-enhanced sorption affected VPH spreading. Following VPH addition, cell abundance increased by no more than a factor of 2 and several Pseudomonas spp. became dominant in soil with and without biochar. We present a VPH fate model that considers soil bacterial biomass dynamics and a nutrient limited soil biomass carrying capacity. The model simulates an apparent lag phase before the onset of a brief period of intensive VPH biodegradation and biomass growth, which is followed by substantially slower VPH biodegradation, when nitrogen needs to be recycled between decaying and newly formed biomass. If biomass growth is limited by a factor other than the organic pollutant bioavailability, biochar amendment may enhance VPH attenuation in between a VPH source below ground and the atmosphere by reducing the risk of overloading the soil's biodegradation capacity.
Highlights
Biomass-derived charred materials, so-called biochars, have attracted significant research interest due to their carbon storage and climate change mitigation potential (Lehmann, 2007)
Cells numbers significantly increased from the cell counts of the initial soil samples (IS and ISB) in both treatments (t-test, p < 0.01 for IS/ ISB vs average of all ports in soil/biochar column), which lends support to our presumption that biomass growth needs to be considered for modelling the volatile petroleum hydrocarbons (VPHs) fate in the columns
Biochar-enhanced sorption of VPHs affected the local solidewatereair partitioning of, in particular, monoaromatic hydrocarbons, and their vapour-phase migration and thereby spatial distribution within the columns. These results suggest that the main biochar effect on soil bacteria is indirect e through its sorption of VPHs, which are much better growth substrates than biochar, and implications for VPH spreading and availability for biodegradation
Summary
Biomass-derived charred materials, so-called biochars, have attracted significant research interest due to their carbon storage and climate change mitigation potential (Lehmann, 2007). The use of biochar as an amendment for the remediation of contaminated soil (Beesley et al, 2010) offers benefits in addition to those of storing CO2 captured from the atmosphere. The application of biochars as sorbents for soil remediation is motivated by the successful use of coal-derived activated charcoals for the in-situ sequestration of hydrophobic organic compounds (HOCs) (Ghosh et al, 2011). Hydrophobic organic compounds (HOCs) are strongly bound in microporous domains of charred materials and become unavailable for uptake by soil organisms and plants (Ehlers and Luthy, 2003). This occlusion reduces HOC ecotoxicity, and hinders HOC accessibility for intracellular biodegradation by soil microorganisms
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