The Regulating Role of Meteorology in the Wetland-Air CO₂ Fluxes at the Largest Shallow Grass-Type Lake on the North China Plain

Lakes are hot spots of carbon cycles in inland aquatic systems. As a vital factor, meteorology, including air temperature, precipitation, wind speed and evapotranspiration, is profoundly affecting or even regulating the wetland-air CO₂ exchanges. Compared with some other similar lakes in China, the largest shallow grass-type Baiyangdian Lake (BYDL) acts as a vital CO₂ sink on the North China Plain. The purpose of this study is to reveal the effects of meteorology on the process of CO₂ flux variation. Based on the method of the eddy covariance, the daily average wetland-air CO₂ flux at the BYDL over the monitoring period from April 2019 to November 2020, reached −0.63 μmol m⁻² s⁻¹, and the annual average reached −0.71 μmol m⁻² s⁻¹ from 12 April 2019 to 12 April 2020. The CO₂ sink fluxes varied with the seasons and reached the maximum in summer. Temperature and evapotranspiration are two major driving factors, whose higher values can positively improve the wetland CO₂ sinks. Precipitation generally coincides with the CO₂ sinks, but the relatively larger summertime precipitation (0.39 m in 2020, compared with that of 0.17 m in 2019) inhibits the CO₂ uptakes on longer timescales. A moderate wind speed in the range of 1.6~3.3 m s⁻¹, promoted the CO₂ sinks for the shallow grass-type lake. Compared with previous studies at the same or similar wetlands, consistent CO₂ sink fluxes are found. Further in this study, the variation trends of CO₂ sinks with the changing meteorological factors are revealed for the first time in this type of wetland. Once meteorology is determined under both the anthropogenic and climatic impacts, the evaluation and prediction of the lacustrine carbon cycling could be more precise. Generally, this study will serve as an important data point into the global understanding of lake carbon fluxes.