Extrapolation and Uncertainty Evaluation of Carbon Dioxide and Methane Emissions in the Qinghai-Tibetan Plateau Wetlands Since the 1960s

Jiang Zhang,Xinwei Liu,Lin Jiang,Minshu Yuan,Meng Wang,Qiuan Zhu,Zhenan Yang,Pengxiang Zhao,Changhui Peng,Huai Chen

doi:10.3389/feart.2020.00361

Abstract

Wetlands are important modulators of atmospheric greenhouse gas (GHGs) concentrations. However, little is known about the magnitudes and spatiotemporal patterns of GHGs fluxes in wetlands on the Qinghai-Tibetan Plateau (QTP), the world’s largest and highest plateau. In this study, we measured soil temperature and the fluxes of carbon dioxide (CO2) and methane (CH4) in an alpine wetland on the QTP from April 2017 to April 2019 by the static chamber method, and from January 2017 to December 2017 by the eddy covariance (EC) method. The CO2 and CH4 emission measurements from both methods showed different relationships to soil temperature at different timescales (annual and seasonal). Based on such relationship patterns and soil temperature data (1960–2017), we extrapolated the CO2 and CH4 emissions of study site for the past 57 years: the mean CO2 emission rate was 91.38 mg C m–2 h–1 on different measurement methods and timescales, with the range of the mean emission rate from 35.10 to 146.25 mg C m–2 h–1, while the mean CH4 emission rate was 2.75 mg C m–2 h–1, with the ranges of the mean emission rate from 1.41 to 3.85 mg C m–2 h–1. The estimated regional CO2 and CH4 emissions from permanent wetlands on the QTP were 94.29 and 2.37 Tg C year–1, respectively. These results indicate that uncertainties caused by measuring method and timescale should be fully considered when extrapolating wetland GHGs fluxes from local sites to the regional level. Moreover, the results of global warming potential showed that CO2 dominates the GHG balance of wetlands on the QTP.

Highlights

Since the beginning of the Industrial Era, large amounts of greenhouse gases (GHGs) have been released into the atmosphere (Boden et al, 2011)
Peak CO2 fluxes were registered in August 2017 by both methods (EC:395.74 mg C m−2 h−1; chamber: 106.94 ± 9.29 mg C m−2 h−1)
During the non-growing season on the Qinghai-Tibetan Plateau (QTP) wetlands, the soil temperature was below freezing, which may inhibit the transport of oxygen from the soil to the rhizosphere zone, resulting in low CO2 flux

Summary

Introduction

Since the beginning of the Industrial Era, large amounts of greenhouse gases (GHGs) have been released into the atmosphere (Boden et al, 2011). The increasing concentration of GHGs in the atmosphere is due mainly to human activities, about one third derives from natural resources, such as wetland soils (MarinMuniz et al, 2015). Wetlands are unique in that they are formed by the interaction of terrestrial and aquatic ecosystems (Lewis and Ebrary, 1995). This allows them to serve many important functions, including improving water quality and micro-climate, sequestering carbon, and protecting biodiversity (Costanza et al, 1997; Engelhardt and Ritchie, 2001; Lamers et al, 2014). Quantifying and modeling the emission of GHGs from wetlands is very important for understanding the impacts of climate change on terrestrial ecosystem processes (Liu et al, 2017)

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Conclusion