Salinity is one of the most common water quality threats in river basins and irrigated regions worldwide. High salinity in soils and groundwater decreases yield from crops, threatening the longevity of communities worldwide and the livelihood of growers. In many semi-arid river valleys, salt accumulates in the soil due to salty irrigation water, poor drainage in the root zone, and the release of salt from natural mineral deposits in soils. A large quantity of salt, however, can enter the valleys from small streams that drain dry, upland areas. These upland areas often contain vast areas of salt minerals deposits, which can dissolve and flow into streams during large rainstorms. This project will investigate how salt is mobilized during storms and measure the amount of salt leaving the upland area into the river valley. Understanding these processes can assist in managing overall salt movement in large river basins and thereby sustain crop productivity. The field work for this project will take place in the Arkansas River Basin in southeastern Colorado, a region affected by high soil salinity. Due to the similarities between this basin and other irrigated, salinity-affected river valleys worldwide, results from this project can help other regions. This project also includes educational activities for middle schools, high schools, and graduate university classes. Middle school and high school instruction and field trips will introduce students to general and local water issues, teach students about salt and measuring salt in local waters, and seek to instill a desire to pursue careers in sciences. Teachers will be trained so that in-class instruction and field trip experiences can serve students attending the schools in coming years.<br/><br/><br/>Salinity is one of the most common water quality threats in river basins and irrigated regions worldwide. Sustainability of crop production in irrigated areas in semi-arid and arid areas is threatened by over-irrigation, poor quality of irrigation water (high salinity), inadequate drainage, shallow saline groundwater, and salinization of soil and underlying groundwater, all of which can lead to decreased crop yield. Numerous studies have been conducted worldwide to assess salinity build-up, loading, transport, and fate in irrigated regions using a combination of field and modeling methods. However, relatively little attention has been given to upland catchments that mobilize and load salt to the rivers of irrigated regions. These salt loads from upland areas can be significant compared to the salt loads in the main stem of the rivers, thus contributing to decreased crop yield, poor water security, and a decrease in ecological health in downstream regions. This project will enhance understanding of salinity mobilization, movement, and transport in arid upland catchments by quantifying salt mobilization in upland catchment areas during storm events and quantifying the contribution of various transport pathways to total salt export from upland catchments and total salt loading in the river basin. These objectives will be accomplished through laboratory and field rainfall simulator experiments, field data collection, process-based numerical modeling, and educational activities that involve middle school and high school students in knowledge discovery and field methods. Educational activities include STEM kits to guide classroom instruction, field data collection, and analysis. The study sites for data collection and model application are within the Lower Arkansas River Basin in southeastern Colorado, an area with high levels of salinity in groundwater and surface water. For modeling, a salinity transport module for the SWAT watershed model will be developed, which will be included in the main SWAT source code and disseminated for use worldwide to manage salt loadings in watersheds. The module will simulate the reactive transport of major salt ions in soils, groundwater, and surface water, and will account for the effect of soil salinity on crop growth.<br/><br/>This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.