APPLICATION OF MULTIPLE GEOCHEMICAL TRACERS TO UNDERSTANDING ANTHROPOGENIC INFLUENCES ON GROUNDWATER FLOW TO GRAND CANYON SPRINGS, GRAND CANYON NATIONAL PARK

Springs and associated riparian environments provide critical habitats for both aquatic and terrestrial wildlife in the Grand Canyon region. Springs from the north rim also provide drinking water for Grand Canyon National Park. Grand Canyon springs are fed by world-class karst aquifer systems (both shallow and deep) on the Colorado Plateau, but increasing pressure on groundwater resources from climate change, mining and other development activities pose major challenges to resource managers. Developing a robust monitoring and geochemical sampling program is important in providing data for preserving these rare and ecologically diverse habitats, as well as for understanding the sustainability of spring-fed water supplies for anthropogenic use. General hydrologic models for the Colorado Plateau aquifers highlight the importance of recharge areas for water supply. Our geochemical studies of spring waters (including stable isotopes, solutes and dissolved gases) throughout the Colorado Plateau and western U.S. have also identified the importance of tectonic activity in contributing CO₂ and dissolved salts to the regional aquifer systems with fluid input from deep levels along faults providing important controls on water quality. Quantitative forecasting of the effects of climate change (diminishing surface flows affecting recharge rates) on water quality depends on our understanding of these deep inputs, as well as aquifer recharge flowpaths and quantities. Previous studies in Grand Canyon National Park have revealed the importance of rapid, conduit-dominated (fault and fracture-controlled) flow paths as well as longer residence-time base flow through the system. Examining a suite of springs along the canyon corridor highlights how two integrated datasets are useful in understanding hydrologic flow paths and modeling potential impacts of groundwater development on Grand Canyon springs. We show that stable isotopes clearly delineate north rim and south rim recharge. We quantify the recharge of north rim-derived (pipeline) water to south rim springs using multiple tracers. Combined, these results indicate the need for a wider application of environmental sensors in hydrologic systems to inform water management decisions.