Plant and soil samples not re-dried prior to carbon/nitrogen analyses, impacts to data quality
January 19, 2021
Due to a miscommunication, samples analyzed for carbon (C) and nitrogen (N) concentrations and stable isotopes were not previously re-dried prior to weighing and analysis at the external laboratory.
While all NEON plant and soil samples are dried at 65C in the domain labs soon after collection, they are sometimes then stored in intermediate containers for weeks or even months before staff have time to conduct final sample processing and transfer them to closed vials for shipment to external labs. During this time they may accumulate moisture, especially in humid areas. Subsequent testing revealed that because samples were not re-dried, previous %C data from vegetation and organic soil horizons may be underestimated by 1.5-2.5%.
As vegetation and organic horizon soil samples tend to have high %C (20% - 55%), this bias may have only minor impacts on many analyses, but is something for end users to keep in mind. For the other parameters (%N, C:N, d15N, d13C) as well as all parameters in mineral soils, testing suggests there were no detectable differences between re-dried samples and originals.
Affected data have been flagged with dataQF = dryingProtocolError in the product-specific table containing C and N data. As soon as this issue was discovered, a new protocol was implemented such that all samples are re-dried at 65C prior to analysis in the external lab. Samples collected in 2020 may have been analyzed before or after the change; check the data product specific Issue Logs and dataQF values to determine which individual samples are affected. Please use the contact form for further inquiries; enter any of the data products from the list above into the Data Product dropdown list and refer to INC0042192 in your request.
