[Spatiotemporal variations of dissolved CO2 concentration and its water-air flux along a tidal creek of coastal wetland in Minjiang River Estuary].

Tidal creeks are ubiquitous in coastal wetlands and act as key conduits for the transport of nutrients and carbon, making them potential hotspots for greenhouse gas emissions. Nevertheless, the spatiotemporal patterns and controlling factors of greenhouse gas emissions from tidal creeks remains rather limited. To investigate the spatiotemporal patterns of dissolved CO2 concentration (CCO2), water-air CO2 flux (FCO2), and the environmental controls, we conducted multi-seasonal observations along spatial transects in the main tidal creek within the Shanyutan Wetland of the Minjiang River Estuary, southeastern China. Results showed that the CCO2 in the tidal creek water ranged from 13.81 to 82.55 μmol·L-1, with saturations between 105.6% and 548.8%, indicating a supersaturated state. Over the observation period, the tidal creek served as a net carbon source, with CO2 fluxes varying from 0.03 to 2.93 mmol·m-2·h-1. Spatially, the CCO2 and FCO2 reached their maxima at the landward end and exhibited a significant decreasing trend along the land-to-sea direction. Dissolved organic carbon, total dissolved organic nitrogen, salinity, and dissolved oxygen were the dominant factors driving the spatial variations of CCO2 and FCO2. Seasonally, both CCO2 and FCO2 exhibited a distinct seasonal pattern of autumn>winter>summer>spring, which was co-regulated by the seasonal rhythm of external loading, tidal mixing intensity, and the seasonal succession of phytoplankton photosynthesis. This study highlighted the necessity of including tidal creek water carbon emissions in coastal wetland carbon budgets, and underscored the importance of accounting for their spatiotemporal variability to enhance the accuracy and comprehensiveness of regional carbon sink evaluations.