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Sampling and interpolation strategies derived from the analysis of continuous soil CO 2 flux
Author(s) -
Gana Cécilia,
Nouvellon Yann,
Marron Nicolas,
Stape Jose Luiz,
Epron Daniel
Publication year - 2018
Publication title -
journal of plant nutrition and soil science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.644
H-Index - 87
eISSN - 1522-2624
pISSN - 1436-8730
DOI - 10.1002/jpln.201600133
Subject(s) - interpolation (computer graphics) , flux (metallurgy) , sampling (signal processing) , environmental science , statistics , multivariate interpolation , temperate climate , mathematics , soil science , remote sensing , atmospheric sciences , geology , computer science , ecology , bilinear interpolation , animation , computer graphics (images) , filter (signal processing) , computer vision , biology , materials science , metallurgy
Soil CO 2 flux ( F s ) can be measured either manually or automatically. While manual measurements are well suited to capture the spatial variability of F s , automated measurements are able to capture its temporal variability at fine time scales. The manual method is the most commonly used method to estimate annual carbon budgets. However, such estimates can be biased depending on the measurement frequency, the time at which measurements are made, and the method used to interpolate F s between two measurements. In this study, we investigated the effects of within‐day measurement frequency and of the time of measurement on the estimation of daily F s . We also investigated the effects on cumulative F s estimates of weekly and fortnightly sampling frequencies over several months and of the interpolation method used to cumulate F s . We based our analyses on two complete datasets of automated measurements (one 12‐month and one 4‐month) recorded in two contrasting ecosystems (a tropical eucalypt plantation and a temperate poplar plantation). Low‐frequency time step within a day (every 360 min for the eucalypt and every 180 min for the poplar plantations) was sufficient to capture mean daily F s accurately. Furthermore, in the tropical site, measurements averaged over any 6h period provided good estimates of the daily flux. By contrast, biases were observed in the temperate site. With one measurement per week, linear interpolation methods provided accurate cumulative fluxes at both sites. However, all interpolation methods failed to produce robust estimates of cumulative F s in the temperate plantation with one measurement every two weeks. Automated measurements will help to select the best time slot for manual measurements or to correct manual measurements from the apparent deviation between measurements collected during the sampling period and the 24 h‐mean CO 2 flux. It will also be useful to elaborate empirical equations used to cumulate F s obtained manually. Combining manual and automated methods will enhance the accuracy of annual soil carbon budgets in forest plantations.