This study investigated the spatial distribution, seasonal variation, and drivers of surface seawater alkalinity (Alk) in Zhanjiang Bay (ZJB) using high-frequency seasonal sampling in the summers and winters of 2023. Surface Alk ranged from 525.3 to 2213.3 μmol·L−1, with mean values of 1373.1 ± 420.9 μmol·L−1 (summer, n = 28) and 1612.3 ± 343.7 μmol·L−1 (winter, n = 20). Spatially, Alk increased progressively from the estuary to the inner bay and further to the bay mouth, reflecting a typical dilution gradient. Correlation analyses showed that summer Alk was positively correlated with salinity (ρ = 0.706, p < 0.001), indicating that salinity changes associated with conservative mixing were a dominant control, whereas the weaker winter correlation (ρ = 0.473, p < 0.001) suggested that biological processes may play a more important role. Tidal forcing was significantly associated with diurnal Alk variations, particularly in the estuary and inner bay. In the estuary, high Alk occurred during high tide, consistent with tidal mixing; in the inner bay, elevated Alk was observed during low tide, suggesting a possible tidal pumping effect. These findings provide baseline data on Alk dynamics in a subtropical estuarine bay and contribute to understanding the carbonate system and buffering capacity in similar coastal systems. However, because measurements of dissolved inorganic carbon and pCO2 were unavailable, a quantitative assessment of carbon sink capacity requires further investigation.
Shi L., He Y., Huang X., Yang G., Zhang J. & Zhang P., 2026. Variation and influencing factors of water alkalinity in estuary-bay waters of Zhanjiang Bay, China. Water 18(12): 1453. doi: 10.3390/w18121453. Article.
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