High‐density sampling reveals biologically and tidally driven spatiotemporal variation in carbon dioxide fluxes in a tropical lagoon

Abstract Lagoons are recognized as significant CO 2 sources in the global carbon cycle. However, the lack of comprehensive measurements capturing simultaneous spatiotemporal variations in partial pressure of CO 2 ( p CO 2 ) limits our understanding of mechanisms driving CO 2 dynamics in lagoons. In this study, autonomous buoys were deployed at five stations across Chiku Lagoon (Taiwan) during the wet season, continuously measuring temperature, salinity, and p CO 2 for over 24 h. Discrete water samples of total alkalinity and dissolved inorganic carbon were collected to establish a freshwater‐to‐seawater mixing model. Our analysis revealed that biological activity accounted for most of the p CO 2 variability (59%), followed by mixing processes (36%) and the temperature variations effect (5%). These effects contributed to spatial heterogeneity, with the upper lagoon exhibiting stronger emissions (4.8 ± 2.5 mmol m −2 h −1 ; mean ± standard deviation) than the middle and lower lagoon (0.6 ± 0.8 to 1.4 ± 1.3 mmol m −2 h −1 ). Meanwhile, tidal influences on CO 2 fluxes were evident, with emissions at low tide (1.4 ± 0.5 mmol m −2 h −1 ) nearly double those at high tide (0.6 ± 0.3 mmol m −2 h −1 ). On average, all stations acted as net sources of atmospheric CO 2 over the sampling period (1.2 ± 1.2 mmol m −2 h −1 ). A resampling sensitivity test of the high‐resolution buoy data suggests a 3‐h interval is optimal in biologically and tidally driven lagoons such as Chiku. These results provide a framework for understanding spatiotemporal CO 2 dynamics and serve as a guide for future monitoring and carbon management strategies in coastal environments.