Increasing intrusion of high salinity water alters the mariculture activities in Zhanjiang Bay during the past two decades identified by dual water isotopes

Qibin Lao; Junhui Wu; Fajin Chen; Xin Zhou; Zhiyang Li; Chunqing Chen; Qingmei Zhu; Ziyun Deng; Jiacheng Li

doi:10.1016/j.jenvman.2022.115815

Increasing intrusion of high salinity water alters the mariculture activities in Zhanjiang Bay during the past two decades identified by dual water isotopes

J Environ Manage. 2022 Oct 15:320:115815. doi: 10.1016/j.jenvman.2022.115815. Epub 2022 Aug 1.

Authors

Qibin Lao¹, Junhui Wu¹, Fajin Chen², Xin Zhou¹, Zhiyang Li³, Chunqing Chen¹, Qingmei Zhu⁴, Ziyun Deng¹, Jiacheng Li¹

Affiliations

¹ College of Ocean and Meteorology, Guangdong Ocean University, Zhanjiang, 524088, China; Guangdong Province Key Laboratory for Coastal Ocean Variation and Disaster Prediction, Guangdong Ocean University, Zhanjiang, 524088, China.
² College of Ocean and Meteorology, Guangdong Ocean University, Zhanjiang, 524088, China; Guangdong Province Key Laboratory for Coastal Ocean Variation and Disaster Prediction, Guangdong Ocean University, Zhanjiang, 524088, China; Key Laboratory of Climate, Resources and Environment in Continental Shelf Sea and Deep Sea of Department of Education of Guangdong Province, Guangdong Ocean University, Zhanjiang, 524088, China. Electronic address: fjchen@gdou.edu.cn.
³ Guangdong AIB Polytechnic College, Guangzhou, 551507, China.
⁴ College of Ocean and Meteorology, Guangdong Ocean University, Zhanjiang, 524088, China; Guangdong Province Key Laboratory for Coastal Ocean Variation and Disaster Prediction, Guangdong Ocean University, Zhanjiang, 524088, China; Key Laboratory of Climate, Resources and Environment in Continental Shelf Sea and Deep Sea of Department of Education of Guangdong Province, Guangdong Ocean University, Zhanjiang, 524088, China.

PMID: 35926386
DOI: 10.1016/j.jenvman.2022.115815

Abstract

The decrease of river runoff caused by the intensified human activities (e.g. artificial dams) and increasing intrusion of high salinity water in the coastal bays have become a worldwide environmental problem. However, the mixing can hardly be identified by traditional method with temperature and salinity due to the complicated water sources in the coastal area. Thus, it is difficult to quantify the impact of intrusion of high salinity water on coastal ecological environment. Here, seasonal dual water isotopes (δD and δ¹⁸O), hydrographic parameters, and nutrients were investigated in a typical semi-enclosed mariculture bay in South China Sea (SCS), to quantify the intrusion of high salinity water and its impact on the water environment. The results showed that salinity in the bay has increased significantly (18%) over the past two decades due to the decrease of runoff and dredging activity. Zhanjiang Bay is mainly affected by the seawater from the SCS in outer bay, and the seawater from the outer bay (89%) was significantly higher than that of freshwater (7%) in summer, despite the increase in freshwater input from the river during this period. In winter, the intrusion of high salinity water increased (accounting for 94%) due to the decrease of runoff input. However, the contribution of groundwater was similar in summer (4%) and winter (5%). The estimation results from the relationship of δ¹⁸O-salinity and δD-salinity showed that the intrusion of high salinity water has increased significantly for the past two decades (increased by 23%). This resulted in the area suitable for oyster breeding is decreasing, and the oyster breeding activities have been gradually moving to the inner bay. Moreover, the nutrients in Zhanjiang Bay were mainly originated from freshwater input in summer (54%-90%), while it changed to the SCS input from the outer bay in winter (40%-97%). This study suggests that the intrusion of high salinity water significantly increases the salinity, and seriously retains the pollutants of freshwater in the bay, which poses a great threat to the oyster breeding activities in the semi-enclosed bay.

Keywords: Intrusion of high salinity water; Mariculture area; Nutrients; Zhanjiang bay; δ(18)O; δD.

MeSH terms

Animals
Bays
China
Environmental Monitoring
Groundwater*
Humans
Isotopes
Ostreidae*
Salinity
Seawater
Water

Substances

Isotopes
Water