Simplified Method For The In Situ Collection And Laboratory Analysis Of Cosmogenic Tracers (Sulfur-35 And Sodium-22) To Determine Residence Time Distributions And Water Ages

The use of cosmogenically produced sulfur-35 (T-1/2 = 87 days) and sodium-22 (T-1/2 = 2.6 years) as intrinsic tracers can provide valuable information on catchment hydrology, flow paths, and subsurface storage. A new and straightforward method was created to determine the activities of both S-35 and Na-22 in various water sources by pumping large volumes (up to 1000 L) of water through cation- and anion-exchange resin columns in the field to collect sodium and sulfate ions and simple chemistry in the lab. Samples are counted for S-35 using liquid scintillation counting (LSC) and for Na-22 via gamma spectroscopy. Our novel in situ method provides faster sample throughput as well as better counting statistics and lower detection limits. Both methods were successfully applied at the Southern Sierra Critical Zone Observatory.