Patterns in the aggregate stability of Mancos Shale derived soils

Salt and sediment contributions to the Colorado River and its tributaries pose economic and environmental concerns for the United States and Mexico. Land use decisions promoting the aggregation of Mancos Shale derived soils are one way to reduce the transportation of salts and sediments to water resources. We used a simple field test of soil aggregate stability to determine the site characteristics influencing the soil stability of sedimentary marine shale in the Gunnison Gorge National Conservation Area in Southwestern Colorado. Ninety-six 1 m2 plots were intensively sampled to explore relationships between soil stability and the biological, chemical and physical site characteristics.Analysis of variance showed decreased soil stability when erosion features were present at a sample location suggesting the applicability of stability test results to the erosion potential of Mancos Shale derived soils (p = 0.02). Analysis using generalized linear models with a negative binomial distribution and non-parametric regression tree models determined that the best predictor variable for soil stability was the percent cover of visible biological soil crust. Identifying the importance of biological soil crust in the stabilization of Mancos Shale soils is important for land use planning because biological soil crusts respond to changes in land use. The results of this study lead to improved interpretation of the field soil stability test and may assist in the definition of important ecological or functional thresholds in many arid and semiarid environments.