Network-based perspective on water-air interface GHGs flux on a cascade surface-flow constructed wetland in Qinghai-Tibet Plateau, China

Constructed wetlands (CW), while providing multiple ecosystem services, bring significant changes in greenhouse gas (GHGs) emissions to the atmosphere. To systematically analyze the source-flow-sink of three GHGs (CO2, CH4 and N2O), the Huoshaogou multi-stage free water surface CW in Qinghai Province, China was chosen as the research area. The static chamber-gas chromatography method was utilized to detect GHGs flux of the 6-year old CW. Ecological network analysis (ENA) was utilized to demonstrate the carbon-related source-flow-sink of the CW. By comparing the results of the wetland site with a reference site, we found that: (1) The average GHG emission flux (2018 and 2019) in the wetland area, with an average of 212.27 mg/m2·h (CO2), 8.84 mg/m2·h (CH4), and 197.4 μg/m2·h (N2O), is about 5.8 times the average flux in the reference site; (2) Wetland plants' contribution to GHGs emissions was reduced by 12% when compared with the reference site; (3) The increasing linkages and inter-flow intensity led to more homogeneous emission distribution of GHGs; (4) The pelagic food chain became dominant over the benthic food chain in photoplankton-related carbon flows, resulting in more GHG emission from the bottom of the CW.