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UBC Theses and Dissertations

The effects of biochar application on carbon dioxide and methane soil surface fluxes Webster, Cameron


Soils contain the largest terrestrial organic carbon (C) stock, representing two-thirds or more of terrestrial C. Soils can act as a source or sink for carbon dioxide (CO₂) and methane (CH₄). One common technique for studying soil surface effluxes of CO₂ (FCO₂) and of CH₄ (FCH₄) is the soil chamber. This involves placing an enclosure over the soil surface and measuring the change in headspace concentration of the gas of interest over time. Due to the air-filled pore spaces within the near-surface soil, and adsorption of gases of interest onto chamber walls, the effective volume (Veff) of the chamber which contributes to FCO₂ and FCH₄ measurements is generally higher than the geometric volume (Vg) of the chamber. It is necessary that Veff be known in order to estimate fluxes accurately. This study coupled a flow-through non-steady-state automated chamber system to a laser-based cavity ring-down spectrometer (CRDS) to estimate Veff of the chamber system using separate standard additions of CO₂ and CH₄ calibration gases. The system was then mounted onto soil cylinders which had been filled with a forest soil from Vancouver Island, British Columbia, Canada. There has been recent interest in the ability of biochar to provide multiple environmental benefits upon application to soil, including the long-term sequestration of C. There are conflicting studies as to the effect of biochar on FCO₂ and FCH₄ and overall greenhouse gas (GHG) emissions. After making background measurements of FCO₂ and FCH₄ in soil columns, biochar was applied to one of the columns and the resulting FCO₂ and FCH₄ were measured. The results from this study showed that the coupling of the CRDS to the automated chamber system proved to be successful. The estimated Veff during CO₂ and CH₄ calibration gas injections agreed with past studies as the Veff was 5 to 10% larger than the geometric volume of the chamber. Following biochar application, the amended soil produced 36.9% more CO₂ and consumed 20.4% less CH₄ than the control over the four month experiment. The results showed that soil water content was an important factor in controlling FCO₂ and FCH₄ following biochar amendment.

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Attribution-NonCommercial-NoDerivs 2.5 Canada