Rainfall stimulates large carbon dioxide emission during growing season in a forest wetland catchment

Forest wetland catchments are widely distributed in middle-high latitude and their hydrological and biogeochemical processes are sensitive to climate change. The net ecosystem exchange (NEE), meteorological forcing, and hydrological data in the Shuidong forest wetland catchment (SFWC) were continuously measured by eddy covariance (EC) tower and water monitoring instruments from 2019 to 2020. During rainy season, large carbon dioxide emission was detected with mean NEE value of 1.85 g C m(-2) d(-1) from local footprint area. Significant positive correlation was observed between daily NEE and air temperature (T-air), relative humidity (RH). We further found that the NEE was mainly controlled by ecosystem respiration (RE) instead of gross primary production (GPP), which might be caused by local high Q(10) value. In addition, dissolved organic carbon (DOC) and dissolved organic (DON) concentrations near the stream outlet also had significant positive relationship with NEE, indicating the hydrological transport from upland forests may trigger the soil priming effect and result in higher CO2 emission within the local footprint area. Soil CO2 flux measurements from different land uses suggested that wetland may be the primary CO2 emission source during rainy season. Under the Representative Concentration Pathway (RCP) 8.5 scenario, the CO2 emission hotspot was expected to occur in this forest wetland catchment due to more frequent rainfall events predicted in this region.

Automated summary

The study revealed that carbon dioxide emissions in the Shuidong forest wetland catchment were mainly controlled by ecosystem respiration instead of gross primary production, and were significantly correlated with air temperature and relative humidity. Additionally, hydrological transport from upland forests may trigger the soil priming effect, leading to higher CO2 emissions within the local footprint area.