Recovery of Soil Organic Matter on Reclaimed and Unreclaimed Oil and Gas Wellpads in the Sagebrush Steppe of the Western U.S.

Worldwide, dryland soils store 10-15% of all the soil organic matter (SOM) to 1m. Drylands are increasingly threatened by agriculture, overgrazing, mining, and energy development. To prevent loss of carbon from these soils, it is important to understand, first, how disturbances impact SOM and second, how SOM recovers after disturbance. In this study, we address current gaps in our understanding of the impacts of oil and gas development and reclamation on SOM in sagebrush steppe of the western U.S. Most studies in this region have found that reclamation and the associated soil-handling are damaging to SOM pools; however, research on old, unreclaimed oil and gas wellpads found that there was no difference in SOM between wellpads and undisturbed sites. Using a chronosequence approach and 19 paired wellpad-undisturbed sites in southwest Wyoming, we directly compare reclaimed wellpads to unreclaimed wellpads to better elucidate the effect of reclamation on SOM in this system.

Most of the variance in soil C and N pools across wellpads was explained by location relative to plants, time, and disturbance from oil and gas development. We found no overall significant effect of reclamation on recovery of SOM. Our results suggest that the most important factors in recovery of SOM after disturbance are spatial heterogeneity of soils associated with individual plants and time, and that these factors do not affect all aspects of SOM equally. The lack of effect of reclamation may indicate that current reclamation practices do not result in an increase or decrease of SOM recovery, and that some components of the soil may be easier to successfully reclaim than others. Further study into the effectiveness of different reclamation techniques is warranted if our goal is to aid SOM recovery and prevent continued C loss from these systems.