Combining summertime freshwater inputs and oxygen consumption impacts on coastal low aragonite saturation state: Case of the Pearl River Estuary, South China

Wenting Shi; Weidong Zhai

doi:10.1016/j.marpolbul.2025.118293

Combining summertime freshwater inputs and oxygen consumption impacts on coastal low aragonite saturation state: Case of the Pearl River Estuary, South China

Mar Pollut Bull. 2025 Jun 17:219:118293. doi: 10.1016/j.marpolbul.2025.118293. Online ahead of print.

Authors

Wenting Shi¹, Weidong Zhai²

Affiliations

¹ Institute of Marine Science and Technology, Shandong University, Qingdao 266237, China.
² Frontier Research Center, Southern Marine Science and Engineering Guangdong Laboratory (Zhuhai), Zhuhai 519082, China. Electronic address: zhaiweidong@sml-zhuhai.cn.

PMID: 40532584
DOI: 10.1016/j.marpolbul.2025.118293

Abstract

Seawater aragonite saturation state (Ω_arag) is crucial for growth of calcifying organisms. Water with an Ω_arag below 1.5 restricts marine shellfish growth and threatens the aquaculture industry's health. Based on data of three summertime cruises along the Pearl River Estuary (PRE), China, we found that both low salinity (S_P) and high apparent oxygen deficit (AOD) decreased Ω_arag. Semi-quantitative results showed that either low S_P of <15 (inducing calcium concentration decline) or high AOD of >100 μmol/kg (revealing organic-matter remineralization and a consequent CO₂ rise) led to critical Ω_arag values of <1.5. Moreover, the combination of moderate S_P and a moderate AOD also led to critically low Ω_arag values, potentially threatening the coastal aquaculture industry of shellfish. Taking a relatively dry year in 2023 as the case, the freshwater-endmember alkalinity exhibited a relatively low value of 1326 μmol/kg before the Pearl River flood, and Ω_arag^Pre-flood = 0.0101 × (8.26 × S_P - 123/138 × AOD) + 0.02 in the PRE mixing zone. After the Pearl River flood, the freshwater-endmembe alkalinity was added to a relatively high value of 1510 μmol/kg, while Ω_arag^Post-flood = 0.0102 × (5.59 × S_P - 123/138 × AOD) + 1.20. These formulae performed pretty well in warning the ecological risk of the PRE carbonate chemistry below and/or around the critical Ω_arag value of 1.5, providing idea for publics to easily assess potential ecological risk of the coastal Ω_arag decline.

Keywords: Aragonite saturation state; Coastal acidification; Ecological risk assessment; Pearl River Estuary.