| dc.description.abstract | The Western United States (WUS), also known as the American West and the Far West, is the largest region in the country, taking up almost half of the contiguous United States’ total land area. The vast region has various physical features, such as glaciers, mountain ranges, deserts, and temperate rainforests. The complex interplay of temperature, disturbance, and varying vegetation across spatial landscape patterns influence ecosystem dynamics.
The region’s entire area is approximately 1200 million acres. In 2012, the primary land uses were grassland pasture and range lands with an area of 655 million acres (29 percent of the US total), forest land use with an area of 632 million acres (28 percent), and cropland with an area of 392 million acres (15 percent); totaling slightly more than 35 percent of the US land area or 798 million acres (Bigelow et al., 2006).
The Missouri River, a tributary of the Mississippi River, and the Colorado River (CR) are the only significant rivers in the area. The CR originates in the Rocky Mountains and empties into the Gulf of California after passing through parts of seven Western US and Mexico (Christensen et al., 2004). Between seven Western States (Arizona, California, Colorado, New Mexico, Nevada, Utah, and Wyoming) and northern Mexico, the Colorado River Basin (CRB) spans an area of around 640,000 km^2.
Salinity in the CR has increased two-fold due to anthropogenic activity in the basin. CR transports estimated salt loads of 7 to 9 million tons annually. Irrigation consumes 70% of the river’s flow and contributes to salinity. However, most salts run naturally off soils and rocks (Mancos Shale).
The overall goal of this study is to use an integrated and enhanced APEX modeling tool to understand processes governing the transport of sediment and salt from upland areas to streams in the CRB, identify critical source areas, and assess the efficiency of suggested management scenarios. Plant functional groups (FGs) parameters, a crucial input data set for modeling the various CRB vegetation types, must be developed before the APEX model can be used. Plant FGs parameters were developed by adapting the minimum basic plant parameters to fit a given FG representative plant species using three approaches: i) modifying parameters of plant species out of three models: Agricultural Land Management Alternatives with Numerical Assessment Criteria (ALMANAC), Environmental Policy Integrated Climate (EPIC)/APEX, and Soil & Water Assessment Tool (SWAT); ii) data from the literature, United States Department of Agriculture (USDA) Natural Resources Conservation Services (NRCS) Plants Database; and iii) expert judgments. Remotely sensed satellite data for ET and LAI were collected for 19 sites across CRB. In addition, plant height data was collected from the Landscape Monitoring Framework (LMF) dataset using the NRCS-NRI methodology. APEX models were built for chosen locations. Developed FGs parameters were used to simulate and test the integrated APEX model and Bureau of Land Management (BLM) field and remote sensing data to evaluate ET, LAI, and plant height outputs. A total of 18,876 distinct plant species were assigned to 55 FGs throughout the WUS. Sensitivity analysis was conducted for each output to determine the parameters most sensitive to outputs. Soil water limit (PARM 15), DLAI, and HMX were observed to be the most sensitive parameters for ET, LAI, and plant height. Results demonstrated the viability of using FG to parameterize, simulate, and perform sensitivity analyses on biophysical models to simulate alternative land management strategies. This technique can address various eco-hydrological issues, including water quality and quantity, salinity, sediment transport, pesticide and fertilizer fate, movement, soil carbon sequestration, N and P nutrient cycles and losses, and land management practices across the CRB. | |
