Experimental investigation of the effect of vegetation on soil, sediment erosion, and salt transport processes in the Upper Colorado River Basin Mancos Shale formation, Price, Utah, USA

- Soils under vegetation have greater concentrations of ions than interspace soil.
- Soil salinity increases with depth and also decreases proportional to infiltration.
- Mat-forming saltbush may have a protective effect on soils from rainfall.
- Dissolution of detached sediment particles may drive salinity transport.
- RHEM sediment output was successfully used to predict salinity on the Mancos Shale.

Because of concerns about salinity in the Colorado River, this study focused on saline and sodic soils associated with the Mancos Shale formation with the objective of investigating mechanisms driving sediment yield and salinity loads and the role of vegetation in altering soil chemistry in the Price-San Rafael River Basin. Rainfall simulations using a Walnut Gulch rainfall simulator were performed at two study sites (Ferron and Price, Utah) across a range of slope angles and rainfall intensities to evaluate the relationship between sediment yield, salinity transport processes, and rainfall-induced changes in soil chemistry. Soil at Ferron had substantially greater salinity than Price as expressed in evaluated sodium absorption ratio, cation exchange capacity in soil, sediment, and total dissolved solids (TDS) in runoff. Principal component analysis and t-tests revealed that the two sites have different runoff and soil chemistry ions. Greater concentrations of K+, NO3−, and Cl− were present in soil-under-vegetation microsites compared to interspace soil areas. Soil soluble phase ions generally increased with depth and underwent vertical fluxes at rates proportional to rainfall intensity. Vegetation appears to have a protective effect on the soils from increasing rainfall intensity. Mat-forming saltbush found at Ferron was related most strongly to soil protection. The dissolution of sediment particles in runoff may be a key component of salinity transport processes on the Mancos Shale. Plot-averaged sediment and TDS had a positive linear relationship. The Rangeland Hydrology and Erosion Model successfully predicted TDS in runoff derived from these upland rangelands in central Utah.