Highlights
- Seawater pH was regulated by a combination of temperature and biological effects.
- Changes in seawater Ωarag were primarily driven by biological processes.
- CO2 flux and water mixing exerted little influence on seawater pH and Ωarag.
- Seawater Ωarag serves as a more suitable indicator for assessing acidification.
Abstract
Coastal seasonal acidification has severely impacted marine aquaculture, particularly shellfish farming. However, factors controlling seawater acidification vary in different aquaculture conditions. This study conducted summer cruises of a typical shellfish farming in China, from June to July 2022 to analyze the spatiotemporal distributions of seawater pH and aragonite saturation state (Ωarag), and their response to temperature, sea-air CO2 exchange, mixing, CaCO3 formation/dissolution, and biological effects. The pH and Ωarag of bottom seawater were both lower than surface seawater, with the pH of surface and bottom seawater ranging from 8.02 to 8.09 and 7.87 to 8.02, while the Ωarag ranging from 2.80 to 3.80 and 2.21 to 2.43, respectively. The bottom seawater pH and Ωarag both show a decreasing trend, with Ωarag at certain stations close to or below 2. Biological (surface seawater: 51 % ± 4 %; bottom seawater: −39 % ± 8 %) and temperature (surface seawater: −28 % ± 6 %; bottom seawater: −41 % ± 8 %) effects were crucial on regulation of seawater pH. Biological effects were the dominant factor in the variation of Ωarag in both the surface (64 % ± 7 %) and bottom (−48 % ± 9 %) seawater. Additionally, the dissolution of calcium carbonate in bottom seawater contributed to an increase in Ωarag to some extent (15 % ± 27 %). Ωarag better reflects the influence of non-temperature processes (e.g., CaCO3 formation/dissolution and biological effects). This study advocates for Ωarag as a more suitable indicator of seawater acidification in coastal aquaculture areas.
Wang H., Zhang Z., Bian H., Ren H., Xue L. & Hu Y., 2025. Deciphering seawater acidification in the Muping Marine Ranch in summer: pH vs. aragonite saturation state. Marine Environmental Research 209: 107196. doi: 10.1016/j.marenvres.2025.107196. Article (subscription required).
