Coarse woody debris effects on greenhouse gas emission rates depend on cover soil type in oil sands reclamation

Abstract

Peat mineral soil mix (PMM) and forest floor mineral soil mix (FMM) are cover soils commonly used for land reclamation, while coarse woody debris (CWD) can be added to create structural diversity and provide an additional source of organic matter. However, the effect of cover soil type and CWD on emission rates of greenhouse gases, such as carbon dioxide (CO2) methane (CH4) and nitrous oxide (N2O) in reclaimed oil sands soils has not been studied. Soil respiration, CH4 uptake and N2O emission rates were studied in a factorial experiment consisting of 2 cover soils (FMM vs PMM)×2 sampling distances from the CWD (near vs away from CWD). Greenhouse gas emission rates were measured in July, August, and September 2012 and 2013 using static chambers. Soil respiration rates were greater in FMM than in PMM regardless of the distance from CWD at each sampling time (p<0.05). Rates ranged from 461 to 1148 and 293 to 677mg CO2 m−2h−1 for FMM and PMM, respectively, in 2012, and from 355 to 1318 and 235 to 700mg CO2 m−2h−1, respectively, in 2013. The CWD increased soil respiration by 22–33% in FMM but not in PMM. Soil respiration rates were positively related to microbial biomass carbon (p=0.004) and nitrogen (p<0.001). Soil respiration rates decreased from July to September in 2012 and 2013, and were positively related to soil temperature (p<0.01) but not with soil water content measured at 5cm depth. Methane uptake rates were greater in FMM (0.026–0.037) than in PMM (0.015–0.028mg CH4 m−2h−1). The CWD increased CH4 uptake rates only in July and August 2012 in FMM, and were negatively related to soil water content (p<0.001) but not to soil temperature. Nitrous oxide emission rates (0.001–0.016mgN2Om−2h−1) were not affected by either cover soil type or CWD. Global warming potential of CO2, CH4 and N2O effluxes was greater in FMM than in PMM and near CWD than away from CWD, especially in FMM. Our study demonstrates that applying CWD for oil sands reclamation increases organic matter decomposition (increased CO2 evolution), driven by the effect on microbial populations. Results from this study provide support to findings in earlier studies that CWD application benefits vegetation establishment through enhancing soil processes in reclaimed oil sands lands.