Surface pCO 2 and air-water CO 2 fluxes dominated by submerged aquatic vegetation: Implications for carbon flux in shallow lakes.

Inland lakes are crucial for processing, storing, and releasing carbon dioxide (CO ₂ ), and they play a significant role in the global carbon cycle and climate change. Studies have shown that inland lakes are mostly supersaturated in CO ₂ , making them significant sources to the atmosphere. However, estimating CO ₂ fluxes from inland lakes is still challenging due to large variations in surface water CO ₂ partial pressure (pCO ₂ ). Submerged aquatic vegetation (SAV) is widely found in aquatic ecosystems, especially in shallow lakes. However, their role in lake-wide carbonate chemistry has not been thoroughly investigated. Accurately measuring air-water CO ₂ exchange and understanding the environmental factors that control these fluxes in vegetated ecosystems are essential for reducing uncertainties in global CO ₂ emission estimates. In this study, high-resolution (3-h interval) field measurements were made along the nearshore of eastern Lake Taihu during the SAV growing seasons to examine their effects on surface water pCO ₂ and air-water exchange. Our results showed evident daily variations in water chemistry and air-water fluxes. Daytime air-water CO ₂ exchange switched from sinks in summer to sources in autumn. The vegetation sites were observed to be strong CO ₂ sources consistently at night. The density of aquatic vegetation was found to be positively correlated with the daily range of pCO ₂ , highlighting their role in regulating surface water carbonate chemistry. Negative correlations were found between water depth and surface pCO ₂ . These results highlight the importance of aquatic vegetation and daily variations in reducing uncertainties in carbon budgets of shallow aquatic systems.
Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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