The role of mining and agricultural activity in creating coexisting but divergent soils, San Luis Valley, Colorado, USA

Application of irrigation water, especially through flood or furrow methods can have profound impacts on soil morphological, chemical, and physical properties. Using a variety of field and laboratory techniques, we examined the impact of both acidic and alkaline irrigation water on a host of soil properties in the San Luis Valley of southern Colorado. Impacts on calcium carbonate, clay content, and gypsum to a depth of 1 m are presented for 4 sites; a control, two sites exposed to acidic irrigation water, and one site exposed to alkaline irrigation water. Along with the increased water in this arid ecosystem, water quality and sediment content have likely contributed to the pedologic changes observed in this system. One of the most prominent changes is the removal of carbonate within the upper meter of soil at the site with the greatest exposure to acidic irrigation water. Changes in soil structure and color, differences in clay mineralogy and rock fragment weathering, and the presence of jarosite provide further evidence of accelerated weathering along this management gradient. The sum of these changes has resulted in a shift in the soil classification and has potential implications on buffering capacity and soil productivity.