Magnitudes and environmental drivers of greenhouse gas emissions from natural wetlands in China based on unbiased data

Abstract

Whether natural wetlands serve as the source or sink of greenhouse gases (GHGs) remains uncertain. Wetlands in China are diverse in type and abundant in quantity and differ greatly in spatial distribution, environmental conditions, and GHG fluxes. However, few studies focused on the differences in GHG emissions from different types of natural wetlands. Here, we adopted strict data collection criteria to create comprehensive and detailed datasets of fluxes of carbon dioxide (CO₂), methane (CH₄), and nitrous oxide (N₂O) from the marsh, coastal, lake, and river wetlands in China, and relevant environmental variables. Our study synthesized 265 field observations on GHGs that lasted at least one year (covering both the growing season and non-growing season) from 109 studies, among which CO₂ measurements using the opaque chamber method were not included for eliminating the influence of absence of photosynthesis on net CO₂ accounting. We found that CH₄ contributed the largest warming effect among the three types of GHGs, and coastal and river wetlands respectively acted as the mitigators and motivators of global warming among the four types of wetlands. Correlation and regression analyses suggested that geographic location, soil moisture and organic carbon, and contents of nitrogen, phosphorus, and dissolved oxygen jointly drove wetland GHG fluxes. The comprehensive global warming potential of Chinese natural wetlands was estimated as 427 Tg CO₂-equivalents year^-1, which might result from increased wetland drainage, reclamation, and external nutrient inputs. This study highlights the incorporation of the full year-round GHG monitoring data without using opaque chambers to measure CO₂ flux when extrapolating net GHG emissions and gives implications for natural wetland management and global warming mitigation strategies.

Keywords: Carbon cycle; Climate change; Global warming; Greenhouse gas emission; Natural wetland; Wetland management.