Natural recovery of soil organic matter in 30-90-year-old abandoned oil and gas wells in sagebrush steppe

We addressed the rarely studied issue of how different soil organic matter pools respond to disturbances from historical oil and gas well development in semi-arid Intermountain sagebrush steppe. We selected twenty-nine study well sites in south-central Wyoming that were plugged and abandoned 3390 years ago. We designed our study to understand the long term impact of oil and gas development for soil organic matter pools on non-reclaimed sites, and evaluate the importance of this disturbance type relative to other major influences on soil organic matter and the fine-scale, shrub-induced heterogeneity of soil organic matter. We compared total, labile, and recalcitrant pools of soil C and N in disturbed sites to adjacent, un-disturbed sites. We found that that natural site-specific conditions such as soil texture and fine-scale heterogeneity associated with shrubs are the most important controls over soil C and N, particulate organic matter C and N, and potential C and N mineralization, and that these older well-pad disturbances did not have a significant effect on any soil organic matter pools. Fine-scale, shrub-induced heterogeneity was higher for those pools that have a fast turnover rate than those with a slow turnover rate. Moreover, fine-scale heterogeneity of total soil C was higher for well sites that were located in loamy sand soils compared to well sites on sandy soils. In addition, heterogeneity of total soil C recovered through time on the finer textured soils. Overall our study suggests that soil organic matter pools were not affected by old oil well development, and that recovery of shrub cover is a key component of soil organic matter recovery in these semi-arid shrublands. A comparison of our work to other work on recent and reclaimed sites suggests that some reclamation procedures may decrease soil organic matter more than the absence of reclamation.