Ruth Orlóci-Goodison HBSc thesis abstract

Boreal forest soils represent globally significant stores of carbon, much of which is stabilized in the mineral fraction.  Until recently, carbon stored in the mineral fraction was considered highly stable, cycling on millennial timescales.  Recent research has shown that carbon stored in the mineral fraction is stabilized by a variety of mechanisms with varying strengths.  Despite the frequency of forest disturbance in the Boreal region, relatively few studies have examined  the impacts of wildfire, harvest, and salvage logging on soil organic carbon (SOC) in mineral soils.  Fewer still have focused on the response of stabilization mechanisms therein.  This study examines the effects of wildfire, whole-tree harvest and post-fire salvage logging on mineral-bound SOC and its stabilization mechanisms.  A sequential selective chemical dissolution approach was used to isolate pools of SOC on the basis of stabilization mechanisms.  This study shows the majority of mineral-bound carbon to be stabilized by its interaction with free, polyvalent, metallic cations (the organic non-crystalline colloidal, ONC, pool).  Additionally, a substantial amount of carbon was stabilized in the poorly-understood residual pool. It was found that forest disturbance has a significant effect on SOC stabilized in the ONC pool and the residual pool.  Post-harvest, soils showed a significant increase in both SOC concentration and storage.  Fire appeared to reduce SOC stabilization in the ONC pool at surface, but concentration and storage both recovered with depth. Salvage logging markedly reduced SOC concentration and storage associated with the ONC and residual pools, suggesting that it is highly disruptive to SOC stored in the mineral fraction and may not be in best management practice. SOC concentration associated with secondary crystalline Fe and Al minerals is shown to be constant through the whole profile and across all disturbance types.  This is consistent with the notion of C saturation.  This investigation shows that SOC stabilized in the mineral fraction is not as stable as previously thought and may cycle on much shorter timescales.  Additionally, this research suggests that mineral-stabilized SOC may not be robust to the physiochemical changes in soil wrought by disturbance.  These results demonstrate the need for further research concerning the stabilization mechanisms operating in the mineral fraction and their responses to common disturbances in the Boreal region.