Variability of pCO2 in surface waters and development of prediction model

pCO2 Dynamics of Stratified Reservoir in Temperate Zone and CO2 Pulse Emissions During Turnover Events

This study explores the dynamic changes in the partial pressure of CO2 (pCO2) with depth, and the temporal variations of CO2 net atmospheric flux (NAF) in a stratified reservoir. A total of 16 field campaigns were conducted from the summer stratification to fall turnover period in 2017. A random forest (RF) model was developed to estimate the pCO2 using concurrently measured water quality variables. The results showed that the vertical distribution of pCO2 and associated temporal variations of the NAF are closely related to the stratification strength of the reservoir. The reservoir surface pCO2 was supersaturated (1542 µatm) in summer (July 11), but this decreased to undersaturation as algae grew. Meanwhile, dissolved CO2 continuously accumulated below the reservoir mixed-layer due to the thermal stratification barrier and organic-rich floodwater intrusion. Vertical mixing began instantly as the stratification strength began to weaken in mid-October, and the surface pCO2 increased sharply up to 1934 µatm. Consequently, the NAF drastically increased to 3235 mg−CO2 m−2·day−1, which implies that the NAF changes seasonally and large CO2 pulsing occurs during the turnover events. The results provide valuable information about pCO2 variability and physical mixing processes, as well as carbon budget estimation in stratified reservoirs, and offer an improved understanding of these phenomena.