First Year Soil Impacts of Well-Pad Development and Reclamation On Wyoming's Sagebrush Steppe.

Natural gas extraction activities have disturbed thousands of acres of arid and semiarid regions in Wyoming’s sagebrush steppe ecosystem. Thin, nutrient poor topsoils, combined with subsoils potentially high in salts, limit the resilience of these arid and semiarid soil systems. Stripping, stockpiling, and respreading topsoil stimulates decomposition and loss of soil organic matter (SOM) by breaking apart soil structure and eliminating inputs of plant residues, which can result in reduced SOM content. When the soil structure is disturbed organic matter can rapidly decompose, releasing mineral nutrients that are mobile and can be lost to weeds, leaching, erosion, or volatilization. The purpose of this study is to gain an understanding of how natural gas development and reclamation activities impact soil properties, plant growth re-establishment, and the ability of disturbed sagebrush ecosystems to recover over time. Soil samples were collected from stockpiles, respread topsoil and adjacent undisturbed areas from three natural gas fields located in Western Wyoming. Results suggest that soil organic matter needed for plant growth becomes mineralized or released when the soil is disturbed. The data shows a small increase in plant-available mineral nitrogen (N) concentrations after stripping and stockpiling compared to undisturbed soils, and then a large increase available N following respreading for reclamation. This suggests that easily decomposable organic matter exposed by destruction of soil structure during stripping is conserved in deep stockpiles, but then rapidly decomposed upon re-exposure to air and moisture with respreading. The spike in mineral N likely originates from organic compounds that, in undisturbed conditions, hold and slowly release N and other nutrients. It represents a significant potential loss of this important “time-release” nutrient pool. The spike in mineral nutrients probably stimulates prolific weed production often observed on reclaimed sites. Weeds that stay and decompose on site may conserve and recycle the nutrients, but the data suggest a need for a better way to accomplish this.