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A cross-site comparison of ecosystem- and plot-scale methane fluxes across multiple timescales
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DOI：10.5194/bg-23-4379-2026.png)
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Abstract
En 中文
Abstract. Wetland and upland ecosystems play significant but opposing roles in the global methane (CH4) budget; acting as natural sources and sinks; respectively. Two of the most common approaches for measuring CH4 fluxes (FCH4) are chambers; which measure fluxes at fine spatial scales (ca. 1 m2); and eddy covariance (EC) towers; which integrate fluxes across larger footprints (ca. 100–10 000 m2). Although chamber and EC observations have been combined in various syntheses and databases to estimate CH4 budgets; a unified cross-site evaluation of FCH4 estimates at plot and ecosystem scales is lacking. As a first step toward a systematic spatiotemporal scaling of EC tower and chamber footprints; we quantified differences in site-level aggregate FCH4 between EC and chamber measurements (ΔFCH4) across ten wetland and upland sites at half-hourly; hourly; daily; weekly; monthly; and annual timescales. We found that ecosystem-scale median FCH4 was consistently higher than plot-scale FCH4 at all temporal scales; with the smallest difference at the daily timescale (multi-site median ΔFCH4: 1.36 nmol m−2 s−1; median ecosystem-scale FCH4 = 1.56 nmol m−2 s−1; median plot-scale FCH4 = 0.06 nmol m−2 s−1) and the largest at annual scales (2.58 nmol m−2 s−1; median ecosystem-scale FCH4 = 25.91 nmol m−2 s−1; median plot-scale FCH4 = 6.55 nmol m−2 s−1). In general; the agreement between ecosystem- and plot-scale FCH4 decreased with finer temporal resolution (from Spearman ρ = 0.95 at the annual scale to ρ = 0.65 at the half-hourly scale); while ΔFCH4 variation was greatest at daily-to-annual scales. Key environmental predictors of ΔFCH4 across the ten sites included plot-scale spatial heterogeneity; dominant vegetation type; vapor pressure deficit; atmospheric pressure; and friction velocity at the daily and monthly scales. Wind direction was a significant predictor only at the monthly scale; suggesting EC footprint effects at these sites. These findings suggest that accounting for variability in EC footprint extent; chamber measurement placement; and measurement artifacts is key to reconciling multi-scale FCH4 observations across diverse ecosystems and refining CH4 budgets.
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