COS 252-1 - Modeling and validation of a half-hourly soil carbon flux product at six terrestrial core NEON sites

Abstract: This project describes efforts to model and validate half-hourly soil carbon fluxes at a subset of sites from the National Ecological Observatory Network (NEON). Our aim is to apply the flux gradient method at half-hourly intervals using publicly accessible soil measurements at six NEON sites (SJER in California, SRER in Arizona, WREF in Washington, KONZ in Kansas, UNDE in Michigan, and WOOD in North Dakota). Field measurements for the first three sites were completed during summer 2022. In addition to these field measurements, we used the R statistical software program to develop an R package (NEONSoils, https://github.com/jmzobitz/NEONSoils) and an interactive web-applet software (https://jmzobitz.shinyapps.io/NEON-soil-fluxes/) to acquire, tidy, and compute soil carbon flux estimates across all NEON sites. Across 2020-2022, our data processing method retrieved fluxes for an average of 63% of the half-hourly periods at the initial three focal sites (spanning 92% to 7% for the replicate sensor setups at each site). The remaining fluxes were not calculable due to missing data. During the summers of 2022 and 2023, we measured in situ soil carbon fluxes using a LI-6800 and temporary soil collar plots across the previously mentioned six NEON sites in order to validate and adjust the soil respiration modeling product and determine any site-specific modeling calibrations. We found agreement between soil flux measurements at collars proximate to a particular soil sensor array. Future work will include refinement of the soil flux model and associated software products with ongoing validation using data from the latter three NEON sites.