AN 26 - Real-Time, Field-Based Water Vapor Isotope Measurements with a Picarro Analyzer

While stable isotope techniques have been previously applied to partition evapotranspiration fluxes in crops1, it has only recently become possible to take in situ, long-term, continuous (every 10 seconds) measurements of stable water vapor isotopologues. A Picarro water vapor isotope analyzer based on CRDS was recently deployed at China’s National Experimental Station for Precision Agriculture during the FAO/IAEA 2nd Research Coordination Meeting on “Managing Irrigation Water to Enhance Crop Productivity under Water-Limiting Conditions using Nuclear Techniques.” Measurements were conducted continuously over several days, sampling from five different heights within and above the canopy of a corn (Zea mays) ecosystem.

The isotope analyses can allow the partitioning of evapotranspiration into its components: soil evaporation and leaf transpiration. Once daily, during the vapor measurements, liquid water isotope standards were measured by the Picarro analyzer using its included autosampler and subsequently used to calibrate the vapor-phase data.