Streamflow life cycles spanning the USA

Tuesday, 16 December 2014: 9:15 AM
Scott Jasechko, University of New Mexico Main Campus, Albuquerque, NM, United States, Jeffrey McDonnell, University of Saskatchewan, Saskatoon, SK, Canada and Jeffrey M Welker, University of Alaska Anchorage, Department of Biological Sciences, Anchorage, AK, United States
Rivers are replenished by precipitation that works its way through watersheds and into stream networks. The time that precipitation requires to travel into a stream regulates contaminant transports, nutrient mobility and bedrock weathering, but has not yet been evaluated at a continental scale. Here we synthesize a pan-U.S.A. dataset of rain, snow and streamflow 18O/16O and 2H/1H ratios and analyze the data to show that the lion’s share of USA streamflow is generated by precipitation that takes ~2 months to ~2.5 years to flush through watersheds and into networks of streams (i.e., rivers replenished by “infant-to-toddler aged” precipitation). These streamflow ages are considerably shorter than the average amount of time that water spends within streams themselves (~1 month, globally), and much shorter than the global groundwater residence time of more than ~1000 years. We also estimate the depth of “dynamic” groundwater storage that actively generates the majority of streamflow and discover that less than ~1% of watershed flowpaths generate the bulk of continental runoff. Our finding showcases that the most hydrologically-active zone within Earth’s hydrosphere is located nearest to the surface where atmosphere-biosphere-lithosphere interactions are at a maximum. This research emphasizes the importance of critical zone research for developing accurate forecasts of how human modifications to the land and climate will impact downstream water, nutrient and contaminant fluxes.