Dynamic Soil Property Change in Response to Reclamation following Northern Appalachian Natural Gas Infrastructure Development

Abstract

Development of historical conventional gas and recent unconventional shale-gas infrastructure in Appalachia has led to extensive landscape disturbance. Construction of >1500 well pads in Pennsylvania thus far has resulted in 2 ha of soil per pad typically being removed, stockpiled, and eventually reclaimed. Based on evidence of infrastructure leading to hydrologic capture and increased erosion and sedimentation risk, we hypothesized that unconventional gas development would cause measurable changes in soil function. To test this hypothesis, we examined dynamic soil property (DSP) change on three types of reclaimed gas infrastructure: 75-yr-old conventional gas pads, 25-yr-old conventional gas pads, and recently developed unconventional gas pads. Disturbed and undisturbed soils within a site were analyzed for bulk density, soil organic C (SOC) pools, soil N pools, and available P pools. Results show that conventional sites do not currently exhibit significant differences in DSPs between disturbed and undisturbed soils, while unconventional sites show significantly higher (potentially root limiting) bulk density and lower SOC and N pools on disturbed soils. We attribute the significant DSP change on unconventional sites to soil compaction during reclamation surface grading and increased soil organic matter decomposition, N mineralization, and soil mixing during soil stockpiling. The 75- and 25-yr-old conventional sites probably exhibit less DSP change currently because more time has passed for these soils to recover.