SPATIAL AND TEMPORAL ASSESSMENT OF THE COLORADO RIVER BASIN USING GIS TO DETERMINE THE CONTRIBUTION OF CLIMATE, LAND-USE AND LITHOLOGY TO RIVER’S WATER CHEMISTRY

Stream water chemistry is often studied at the individual basin scale which limits the development of geochemical tools and proxies, such as riverine (²³⁴U/²³⁸U) variations, that can help detangle the impacts of changing climatic and land-use conditions from lithology, and thus to project how stream water chemistry will change in the future. This NSF funded project focuses on four Texas river basins as natural intermediate-scale laboratories to investigate factors driving changes in river chemistry and (²³⁴U/²³⁸U) ratios. Here, we focus on the Colorado River basin as a template to expand our research by correlating spatial analysis of lithology, land use, and water availability with hydro-chemical data across the river basin. Specifically, geologic, hydrologic, meteoric, and land-use information was collected from multiple public sources. The watershed was overlayed with vector and raster data including rivers, quaternary faults, lithology, land use, precipitation, and evapotranspiration. Digital elevation models (DEMs) were calculated at a 10-meter resolution for the entire Colorado basin and the contributing sub-basins.

Rock type and land-use percentages were calculated for about twenty-seven long-term water chemistry monitoring sites, providing a quantitative measure of carbonates and sedimentary deposits as well as shrubs and cultivated crops that may influence Colorado River chemistry. The next steps include developing and testing a predictive model for assessing how these variables affect river chemistry by comparing calculated chemistry values to historical stream gauge data and recently collected river samples. These calculations give us direction and provide insight into the various impacts to the water as it flows through different landscapes, climates, and urban settings within the watershed. This model will then be adopted to other rivers basins in Texas.