English

Abstract

Changes in soil physical and chemical properties due to land application of coalbed methane (CBM) waters were investigated in study sites located in northwest Powder River Basin (PRB) of Wyoming. Samples of CBM water used for land application and analyzed for pH, electrical conductivity (EC), and sodium adsorption ratio (SAR) values. Water quality data indicated that EC and SAR values of CBM water samples were greater than the recommended values for irrigation use (0.75 dS m -1 and <10 SAR). Impacts of these poor- quality CBM waters on soil physical and chemical properties were evaluated by collecting soil samples during the 2003 irrigation season from 6 depths (0-5, 5-15, 15-30, 30-60, 60-90 and 90-120 cm) from 6 sites that received CBM water applications for up to 3 years, which were compared to control sites. Changes in soil physical (e.g., infiltration rates, bulk density) and soil chemical (pH, EC, and SAR of saturation paste extracts) properties were determined. Our study indicates that the pH values are significantly (p = 0.05) greater in irrigated plots than control plots at depths of 0-5 and 30-60 cm in site 1 and 0-60 cm in site 4. The EC values were significantly greater in irrigated sites than control plots at 0-60 cm depth in sites 1, 4 and 6, 5-30 cm in site 3, and 0-15 cm in site 5. SAR values were significantly greater in irrigated sites than control plots in the upper 60 cm in sites 1 and 5, 0-5 cm site 4, and 5-30 cm in site 6. Irrigated sites 1, 3, and 4 had significantly lower %clay. Hydraulic conductivity in sites 1 and 5 were significantly lower than control plots. Thus, irrigation with poor-quality CBM water had significant impacts on soil chemical and physical properties. It has been estimated that over the next 15 years CBM water production in the PRB will exceed 366,000 ha-m. The results of this study will be useful to understand the potential changes in soil properties due to land application of CBM waters and to develop possible mitigating criteria for preserving impacted PRB ecosystems.