Carbon budgets of wetland ecosystems in China

Abstract

Wetlands contain a large proportion of carbon (C) in the biosphere and partly affect climate by regulating C cycles of terrestrial ecosystems. China contains Asia's largest wetlands, accounting for about 10% of the global wetland area. Although previous studies attempted to estimate C budget in China's wetlands, uncertainties remain. We conducted a synthesis to estimate C uptake and emission of wetland ecosystems in China using a dataset compiled from published literature. The dataset comprised 193 studies, including 370 sites representing coastal, river, lake and marsh wetlands across China. In addition, C stocks of different wetlands in China were estimated using unbiased data from the China Second Wetlands Survey. The results showed that China's wetlands sequestered 16.87 Pg C (315.76 Mg C/ha), accounting for about 3.8% of C stocks in global wetlands. Net ecosystem productivity, jointly determined by gross primary productivity and ecosystem respiration, exhibited annual C sequestration of 120.23 Tg C. China's wetlands had a total gaseous C loss of 173.20 Tg C per year from soils, including 154.26 Tg CO2‐C and 18.94 Tg CH4‐C emissions. Moreover, C stocks, uptakes and gaseous losses varied with wetland types, and were affected by geographic location and climatic factors (precipitation and temperature). Our results provide better estimation of the C budget in China's wetlands and improve understanding of their contribution to the global C cycle in the context of global climate change.

Soil GHG fluxes are altered by N deposition: New data indicate lower N stimulation of the N2O flux and greater stimulation of the calculated C pools

“…On the one hand, high‐dose anthropogenic N fertilizer inputs are an important cause of the higher GHG emissions from the soil in agricultural ecosystems; moreover, agricultural ecosystems usually experience more anthropogenic activity, such as tillage (Zhong, Wang, et al, ; Zhong, Yan, et al, ). In contrast, wetlands are different from other ecosystems because their soil is water‐logged, anaerobic and acidic (Xiao, Deng, Kim, Huang, & Tian, ); thus, the enrichment of wetlands with N led to a significant stimulation of GHG emissions (Tao, Song, & Guo, ). Furthermore, this study estimated that N deposition increased the global terrestrial soil C sink by 6.34 Pg CO 2 ‐Geq (CO 2 equivalents)/year (Table ), but the net changes to GWPs in units of CO 2 ‐Geq were estimated to be 10.20 Pg CO 2 /year (Table ).…”

Anthropogenic disturbances caused declines in the wetland area and carbon pool in China during the last four decades

“…Previous studies tend to estimate carbon pools in different wetland types globally, such as tidal wetlands and freshwater wetlands (Bernal & Mitsch, 2012; Chmura et al, 2003). Estimates of wetland carbon stocks based on published data in China are highly variable, ranging from 5.39 to 16.56 Pg (Xiao et al, 2019; Zheng et al, 2013). Also, carbon pools in China's wetlands change from 4.51 ± 1.63 Pg in the 1980s to 3.75 ± 0.89 Pg in the 2010s for the top‐100 cm wetland soil (Xu et al, 2019).…”

Hydrologic Export Is a Major Component of Coastal Wetland Carbon Budgets

“…Coastal habitats are also among the most threatened ecosystem types, and although these services are collectively valued at ~$10,000 USD ha −1 year −1 , human‐driven sea level rise (SLR), eutrophication, and land conversion have resulted in the loss and degradation of up to 50% of global coastal wetland extent (Barbier et al, 2011; Worm et al, 2006). For these reasons, the protection and restoration of coastal vegetated habitats have been widely regarded as an efficient and cost‐effective tool to combat human‐driven CO 2 release and climatic change (Duarte et al, 2013; McLeod et al, 2011; Nellemann et al, 2009; Xiao et al, 2019).…”

“…Given that few tidal wetland NECBs exist (Feijtel et al, 1985; Forbrich et al, 2018; Troxler, 2013; Webb et al, 2018), and none include direct, high‐resolution measurements of lateral C flux, these findings provide important ecological and biogeochemical insights into coastal wetland processes. They also provide a comprehensive and scalable evaluation of coastal wetland C cycling that will help to constrain C budgets at coastal margins (Bauer et al, 2013; Cai, 2011; Jassby et al, 1993; Maher et al, 2018; Najjar et al, 2018; Wang et al, 2016; Windham‐Myers et al, 2018; Xiao et al, 2019).…”