Foliar chlorophyll data quality issues: sample storage temperature deviation and invalid quality assurance metrics
December 4, 2023
NEON recently discovered two issues with external laboratory analysis of foliar pigments (chlorophyll A, chlorophyll B, carotenoids), which are reported as part of DP1.10026.001 Plant Foliar Traits. The first issue involves inappropriate sample storage temperatures. Foliar tissue subsamples are flash-frozen in the field using dry ice, then are supposed to be analyzed within two weeks of collection and held either on dry ice or in ultra-low temp (-80C) freezers in the meantime. Unfortunately, for samples collected between 2022-05-10 and 2023-06-09, the analytical lab instead stored subsamples in a standard -20C freezer for the period between sample receipt and sample analysis, generally one to seven days. As soon as NEON discovered this during an audit, the laboratory switched to storing samples at ultracold temperature. All affected records are flagged with handlingQF = 'sample held at -20 C instead of ultracold' in the cfc_chlorophyll table. It is unclear how much of an impact this has on pigment data quality. If more information becomes available about data quality impacts, a new notification will be posted.
The second issue involves reporting on quality assurance (QA) for sample runs. NEON's standard procedure is to request a QA sample with known chlorophyll concentration be run alongside samples to assess precision and accuracy of the run. However, during a recent audit it was revealed that the external laboratory analyzing foliar pigments was unable to procure an appropriate QA material for the 2021, 2022, and 2023 sampling seasons. As a result, the 'relativeAccuracyScale' values in the cfc_chlorophyll table for those sampling years were not based on a valid assessment of the accuracy of the run. Once this was discovered, entries in the field 'relativeAccuracyScale' were edited to be 'not available' for all records created between 2021-04-23 to 2023-07-25. This change appears in provisional data and will appear in data collected in 2021 starting with RELEASE-2024.
Note that as of the 2024 field season, NEON will be working with a different external laboratory for foliar pigment analyses.
Please use the Contact Us form for further inquiries; please select DP1.10026.001 in the Data Product dropdown list and include the term "PRB0041082" in the body of your request
