Reclamation potential of experimental oak mat and conventional natural gas drill pad construction techniques in a sagebrush steppe community

Abstract

Conventional cut-and-fill drill pad construction associated with natural gas production displaces existing plant communities and results in surface disturbances requiring extensive soil remediation and revegetation. At the Jonah natural gas field, Wyoming, use of an oak mat drilling platform placed atop the intact landscape was evaluated to facilitate drilling while minimizing disturbances to soil and plant resources. Concerns inherent to both techniques include adverse, long-term impacts to vegetation communities, soil compaction and soil physical and chemical characteristics. The percent change (%Δ) in grass density at oak mat removal areas (OMRA) (+37 %) was significantly greater than at cut-and-fill locations reclaimed pre-2005 (RCAF<05) (+16 %). Forb density %Δ at OMRA (+24 %) was significantly higher than at RCAF<05 locations (-86 %). At RCAF<05 locations 99 % of forb density was contributed by weedy forb species. This indicates that OMRA were more successful in promoting high grass density, maintaining forb populations and minimizing weedy forb components than RCAF<05 locations. RCAF<05 locations indicate an -84 %Δ in shrub density whereas OMRA indicate a -33 %Δ. Wyoming big sagebrush seedling density was highest at OMRA indicating that shrub density had a greater potential to recover there relative to RCAF<05 locations. Mean soil bulk density (ρb) at OMRA had -3.0, +1.8 and +3.9 %Δ in depth increments between 0-30.5 cm. The mean ρb at cut-and-fill locations reclaimed in 2005 or later (RCAF > or equal to 05) had +7.0, +10.9 and +11.7 %Δ in different depth increments between 0-45.7 cm. Using a ρb range of 1.45-1.70 g/cm 3 as an indicator of potential plant growth problems, ρb exceeding 1.45 g/cm 3 occured infrequently at OMRA compared to RCAF > or equal to 05 locations. RCAF > or equal to 05 locations had significant increases in %Δ soil saturated-paste extract ECe (+209 %), CaCO 3 percentage (+48 %) and sand percentage (+16 %) compared to OMRA, presumably due to mixing of soil horizons. It is counterintuitive to expect that oak mats should alter physicochemical soil properties. Although limited to construction on slopes < or equal to 3 %, measured vegetation and soil characteristics indicated that the reclamation success of oak mat drill pads was greater than that obtained at reclaimed cut-and-fill locations.