Abstract
Measurements of greenhouse gas fluxes over many ecosystems have been made as part of the attempt to quantify global carbon and nitrogen cycles. In particular, annual flux observations are of great value for regional flux assessments, as well as model development and optimization. The chamber method is a popular approach for soil/ecosystem respiration and CH4 flux observations of terrestrial ecosystems. However, in situ flux chamber measurements are usually made with non-continuous sampling. To date, efficient methods for the application of such sporadic data to upscale temporally and obtain annual cumulative fluxes have not yet been determined. To address this issue, we tested the adequacy of non-continuous sampling using multi-source data aggregation. We collected 330 site-years monthly soil/ecosystem respiration and 154 site-years monthly CH4 flux data in China, all obtained using the chamber method. The data were randomly divided into a training group and verification group. Fluxes of all possible sampling months of a year, i.e., 4094 different month combinations were used to obtain the annual cumulative flux. The results showed a good linear relationship between the monthly flux and the annual cumulative flux. The flux obtained during the warm season from May to October generally played a more important role in annual flux estimations, as compared to other months. An independent verification analysis showed that the monthly flux of 1 to 4 months explained up to 67%, 89%, 94%, and 97% of the variability of the annual cumulative soil/ecosystem respiration and 92%, 99%, 99%, and 99% of the variability of the annual cumulative CH4 flux. This study supports the use of chamber-observed sporadic flux data, which remains the most commonly-used method for annual flux estimating. The flux estimation method used in this study can be used as a guide for designing sampling programs with the intention of estimating the annual cumulative flux.
Highlights
CO2 and CH4 fluxes from and to terrestrial ecosystems are important to quantify as they influence the atmospheric greenhouse gas concentrations and climate warming [1,2]
In view of the above-mentioned problems and needs, in this study we focus on multi-source data collection; the objectives are to (1) analyze the relationships between the observed flux in different months and the observed as the cumulative flux (AF) to test the feasibility of using low-frequency flux data to estimate the overall AF; (2) select the optimal months for AF estimation using different observation frequencies and determine the optimal equations for AF estimation
[38], considerably more method than forwhen the eddy covariance method disadvantage of the fluxplots data obtained by the chamber operated manually is the low one disadvantage of the flux data obtained by the chamber method when operated frequency of the data [40]
Summary
CO2 and CH4 fluxes from and to terrestrial ecosystems are important to quantify as they influence the atmospheric greenhouse gas concentrations and climate warming [1,2]. Terrestrial ecosystems have a global annual soil respiration of approximately 90 Pg C yr−1 [3,4]. Methane has a global warming potential 34 times that of CO2 for a period of over 100 years [5], and the terrestrial CH4. Methane emission is currently estimated at 500–600 Tg CH4 yr−1 globally [7]. Ground observations of soil/ecosystem respiration and CH4 fluxes have increased considerably over the past few decades [8], driven by the need to adapt to, and mitigate, climate change. The chamber method is one of the most common methods to observe fluxes and to understand their spatial and temporal variations [9]
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