STABLE ISOTOPES FROM SPRINGS USED TO DELINEATE LOCAL VS. REGIONAL GROUNDWATER FLOW IN WESTERN NORTH AMERICA

The largest dataset of springs stable isotopes from across Western North America in Arizona, Nevada, and Alberta were analyzed to test a local vs. regional flow derived hypothesis. The combination of location-specific precipitation data with stable isotopic groundwater data provides a simple and cost-effective method for flow path determination at springs. The recharge location for many springs is unknown because they can be sourced from proximal, shallow, atmospheric sources or long-traveled, deep, regional aquifers. Very few aquifers in the West have data to accurately delineate the source of springs. The stable isotope (18O and 2H) geochemistry of springs water can provide indications of relative flow path distance without the expense of drilling boreholes, conducting geophysical studies, or building groundwater flow models. Locally sourced springs generally have an isotopic signature similar to local precipitation for that region and elevation. Springs with a very different isotopic composition than local meteoric inputs likely have non-local recharge, representing a regional source. We found springs in Arizona issue from a mix of regional and local recharge sources. These springs have a weak elevation trend across 1588m of elevation where higher elevation springs are only slightly more depleted than low elevation springs with a δ18O variation of 5.9‰. Data from the high elevation, local, Clover and Hoxworth Springs are contrasted with the regional, Fossil Springs and Cottonwood Springs. Springs sampled in Nevada showed a strong elevation-isotope relationship with high-elevation sites discharging depleted waters and lower elevation springs issuing enriched waters; only a 2.6‰ difference exists in 18O values over an elevation range of more than 1500 m. Alberta’s springs are mostly sourced from local flow systems and show a moderate elevation trend of 1200 m, but the largest range in δ18O, 7.1‰.