Role of Aquatic Plants in Carbon Dioxide Exchange Between the Littoral Zone of a Eutrophic MidLatitude Lake and the Atmosphere

Inland water is a crucial component of the land-atmosphere carbon exchange. The role of aquatic plants in carbon dioxide (CO₂) exchange has been understudied, and few studies have considered their influence on diel variation. This study analyzed 2 years of eddy covariance CO₂ flux data obtained in the littoral zone of a eutrophic midlatitude lake with differing aquatic plant cover. In the summer of 2022, when floating-leaved plants were abundant, marked CO₂ uptake was observed during the day, whereas in the summer of 2020, with minimal floating-leaved plant cover, daytime uptake was less pronounced. When averaged, the maximum CO₂ uptake occurred in the afternoon in the summer of 2020, when CO₂ exchange at the air-water interface likely dominated the total exchange, and uptake was enhanced due to a high gas transfer velocity and presumably low dissolved CO₂ concentrations in the afternoon. By contrast, CO₂ uptake reached a maximum around noon in the summer of 2022, in phase with solar radiation. The leaves of plants protruded into the air, and direct uptake, due to the leaf photosynthesis, likely caused the cooccurrence of the peak CO₂ uptake and solar radiation. The estimated annual CO₂ exchange was 14 ± 7 gC m⁻² in 2020 and −170 ± 4 gC m⁻² in 2022. This study found that the abundance of aquatic plants determined the diel environmental dependence of the summer CO₂ exchange in the littoral zone of a midlatitude lake, as well as the magnitude and direction of the annual CO₂ exchange.