Effects of disturbance on soil properties resulting from natural gas production in Wamsutter, WY, and sodic soil reclamation with gypsum, elemental S, langbeinite, and compost

Disturbing soils in arid regions can mix subsurface materials with surface soils salvaged for reclamation. Pre-disturbance assessment of soils can minimize impacts of disturbance, and better understanding of drastic disturbance in arid soils will improve reclamation success. Soil texture and chemical properties were analyzed at 0-15 cm depth in saline and sodic soils from eight paired undisturbed and recently reclaimed sites in the Great Divide Basin of Wyoming. Paired difference analysis across the eight well pads indicated disturbed/reclaimed soils had higher electrical conductivity (EC) than undisturbed soils (12.2 and 3.0 dS/m-1, respectively) and higher sodium adsorption ratios (SAR) (26.1 and 1.3 (mmolc/L-1)0.5, respectively). Soil organic matter and structural properties were analyzed in additional samples from two of the paired sites (one sodic, one saline-sodic). Analysis of variance of soil organic C (SOC), total N, and soil structural properties indicated disturbed soils had nearly one-third less total N and two-thirds less SOC than undisturbed soils in the top 15cm due to dilution, and over 65 times more >9.5 mm dry aggregates by weight, representing predominance of large clods in disturbed soils on both sites. Ultimately disturbed soils exhibited lower organic materials, higher salt contents, altered soil structure, leading to diminished potential for supporting native plant communities. Selected chemical amendments and municipal solid waste (MSW) compost were then evaluated for remediation of a saline-sodic soil under field conditions. Soil was mixed with langbeinite (L), gypsum (G), elemental S (S), and/or compost (C) in eight treatments: L, LC, G, GC, S, SC, C, and control (N), then packed into 0.46 x 0.61 m2 wooden frames with mesh screen on the bottom, and exposed to environmental conditions for one year. Soil samples were taken every three months (January, April, July, and October 2013) at depths of 0-3, 3-8, and 8-15 cm and analyzed for Na concentrations on an ICP-OES. Results indicated that soils treated with L exhibited lower Na concentrations than all other treatments. Depth*time interactions exhibited similar patterns of Na concentration over time in the 0-3 and 3-8 cm depths: the highest Na concentration in January, significantly lower in April, the same or slightly higher in July, and finally the lowest concentration occurred in October. Finally, the same treatments were also evaluated under field conditions for two years, for their ability to reclaim soil properties of the two paired sites previously described: one sodic, one-saline-sodic. Treatments were applied and incorporated in 32 seven by seven m plots on each site in October 2012. Soil samples were taken in June 2013 and 2014 at 0-5 and 5-15cm from treated plots. Soil treatments had no significant effects on Na concentration or exchangeable sodium percentage (ESP) due to insufficient precipitation during the study period. L and LC treatments exhibited increased Mg and K concentrations and EC by 2014, as well as improved soil structure: less clods (>9.5mm, 2-9.5mm) in 2013, more dry microaggregates (53-250microm) in 2013 and 2014, and less <53microm soil, considered dispersed clays, in water-stable aggregate distributions in 2014. GC treatments exhibited increased EC and Ca concentration, lower pH, and more dry microaggregates (53-250microm) in 2014. S and SC treatments behaved similarly to the control (N). Na concentration exhibited a mostly negative relationship with water-stable microaggregates (250microm-2mm and 53-250microm) regardless of treatment. Treatments had no significant effects on root biomass, surface CO2 flux, or vegetation counts. Trade-offs between amendment efficiencies, climatic limitations, and reclamation goals concerning vegetation are critical considerations for reclaiming Na-affected soils in arid regions.