English

Abstract

Saline/sodic waters derived from wells associated with coalbed methane (CBM) gas production are being applied to rangelands and to lands used for production agriculture within the Powder River Basin (PRB) of Wyoming and Montana. Our study areas represent variable vegetation types, soil textures, treatment strategies and water application methods on sites impacted by up to 3 years of land application of saline/sodic CBM water. Vegetation parameters evaluated were forage quality, above ground biomass production, aerial cover, species diversity and infectivity of arbuscular mycorrhizae (AM) fungi. Soil data from six depth intervals to 120 cm were collected early summer, mid/late summer and fall during the 2003 water application season. Samples were analyzed for texture, bulk density, pH, electrical conductivity (EC), and sodium adsorption ratio (SAR). Infiltration and hydraulic conductivity rates were also measured. Waters from CBM gas wells in the PRB vary in quantity and quality, with average flows of around 30 liters per minute, salinity levels of about 2 dS/m and SAR's ranging from low (e.g., 5) to extremely high (e.g., 70) levels. Variable water application methods including center-pivot and side-roll irrigation and mister evaporation systems are utilized for land application. Common CBM water treatment strategies include: 1) varying application rates; 2) chemically treating water to adjust for SAR, salinity, pH and bicarbonate levels; and 3) chemically treating soil surfaces to minimize sodicity and salinity conditions. Potential advantages and disadvantages of various management strategies are discussed based on soil and vegetation data analyses. With about 20,000 CBM gas wells currently permitted or drilled in the PRB and estimates of at least 50,000 future new wells, proper CBM product water utilization is warranted.