Water Conveyance-Type Lake Systems Shift toward Carbon Sources under Regulatory Balanced Water Level Metabolic Processes

The water–air interface is the juncture whereby lake carbon (C) emissions are most active. However, the metabolic regulation of lake C exchange rates at the water–air interface remains unclear, especially for water conveyance-type lake systems that undergo dramatic alterations in water regimes. For the first time, underwater regime fluctuations. Findings show that the C exchange status at the water–air interface is regulated by the coupled connective effect of the water regime–water quality–GPP–pCO2 effect. Compared to high- and low-water level periods, C emissions at the water–air interface were highest during the intermediate-water-level period. Moreover, this intermediate period was when this water conveyance-type lake system primarily converted basin-derived C inputs and discharged them into the atmosphere. This study also found that C emissions were most active when net ecosystem production (NEP) was close to 0. If NEP is too high (i.e., >6 g O2 m–2 d–1) or too low (i.e., < −6 g O2 m–2 d–1), the partial pressure of carbon dioxide (pCO2) in water will be constrained either below or close to that of atmospheric pCO2.