HYDROGEN AND OXYGEN ISOTOPE RATIOS OF WATER FROM THE WEBER RIVER HEADWATERS TO THE GREAT SALT LAKE

Changes in the isotopic composition of water within the water cycle can provide information regarding the magnitude of various hydrologic processes through space and time, and a recognizable signature that can be traced through large watersheds. The 6475 km2 Weber River drainage system is located in northern Utah, USA, and is characterized by a variety of landcover types, large elevation and urbanization gradients, multiple storage reservoirs, numerous diversions for municipal and agricultural purposes, and represents one of the major freshwater inputs into the Great Salt Lake. In order to better understand the dynamics of this important drainage system, the stable hydrogen and oxygen isotopic composition of surface waters was characterized from early spring runoff through the summer and fall drought time periods. The hydrogen and oxygen isotope ratios of surface waters in the Weber River drainage to the Great Salt Lake varied from -131‰ to -45‰ and -17.2‰ to -0.9‰, respectively on the SMOW scale, between spring runoff and summer drought periods. These large gradients in isotope ratios reflect a combination of differential precipitation inputs along elevational gradients (approximately 3657 to 1280 m), and evaporative opportunities within the drainage system associated with reservoirs. Moisture inputs as snow and/or precipitation followed a relationship similar to the global meteoric water line. Isotopic evaporative enrichment of catchment waters occurred throughout the year, consistent with Craig-Gordon patterns. These data provide a tool for quantifying the various inputs and outputs in the Weber River drainage system, and provide the framework for identifying complex hydrologic processes that makeup the Great Salt Lake.