Modified soil respiration model (URESP) extended to sub-zero temperatures for biostimulated petroleum...

It has been increasingly reported that aerobic soil respiration activity (CO₂ production and O₂ consumption) is measurable in frozen cold-climate soils. This study modifies the Generalized Respiration (GRESP) model, a function of soil temperature (T) and unfrozen water content (M), to cover the frozen, partially frozen and unfrozen phases of successfully bioremediated, petroleum hydrocarbon-contaminated, sandy sub-Arctic soils. The Michaelis-Menten equation was modified to express the observable change in unfrozen water content near 0 °C, which is related to soil respiration activity during soil phase changes and at temperatures below the effective endpoint of detectable unfrozen water at -2 °C. The modified Michaelis-Menten equation was further combined with a Q₁₀ temperature term, and was then incorporated into the GRESP equation to produce a new URESP model for the engineered soil bioremediation system at sub-zero temperatures. The URESP model was applied to published input data measured from the biostimulated site soils of a pilot-scale soil tank experiment conducted between -5 and 15 °C. The model fit well with the experimental data for CO₂ production (R² = 0.96) and O₂ consumption (R² = 0.92). A numerical soil thermal model (TEMP/W model) of the thawing biotreated soils in the tank was also used in this study to produce valid alternative (predictive) input T and M data for the URESP model. The URESP-derived respiration quotients (RQ; 0.695 to 0.698), or the ratios of CO₂ production to O₂ consumption, aligned with the experimental RQ values from the soil tank experiment (0.69) and fell within the theoretical RQ range for aerobic hydrocarbon degradation (0.63-0.80). The URESP model combined with the TEMP/W simulation approximated changes in soil respiration during thawing and characterized the computed soil respiration outputs as related to hydrocarbon utilization, based on their RQ values.