pCO(2) 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 (pCO(2)) 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 pCO(2) using concurrently measured water quality variables. The results showed that the vertical distribution of pCO(2) and associated temporal variations of the NAF are closely related to the stratification strength of the reservoir. The reservoir surface pCO(2) was supersaturated (1542 mu atm) 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 pCO(2) increased sharply up to 1934 mu atm. 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 pCO(2) variability and physical mixing processes, as well as carbon budget estimation in stratified reservoirs, and offer an improved understanding of these phenomena.