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- Title
A Physical Perspective of Recurrent Water Quality Degradation: A Case Study in the Jiangsu Coastal Waters, China.
- Authors
Chen, Shufen; Jiang, Long; Cheng, Xuhua; Liao, Guanghong; Gerkema, Theo
- Abstract
Estuarine‐coastal systems receive pollutants from various sources at an alarming rate. Some systems are extremely susceptible to terrestrial input, as a relatively small amount of pollutant loading induces lasting water quality degradation. The Jiangsu coastal waters (JCWs), located in the southwestern Yellow Sea, are such areas that lack large river discharge but suffer from recurrent eutrophication recently. We hypothesize that the low flushing efficiency in the JCWs largely accounted for the susceptibility to coastal pollution. To test it, transit time (TT) and pollutant flushing rates in the JCWs were estimated under various scenarios using a validated three‐dimensional hydrodynamic model. Results show that TT in many inshore waters of the JCWs and the northern radial sand ridges is >240 days, which are consistent with the observed frequently eutrophic areas. The JCWs are better flushed and thus less eutrophic in summer, as a consequence of the stronger tidal residual coastal circulation. The baroclinic pressure gradient, modulated by the formation and destruction of thermal stratification in offshore waters, poses a dominant control on the seasonal variations of the coastal circulation and flushing rates, while wind effects are secondary. River‐borne pollutants from the Yangtze and Jiangsu local rivers are shown to primarily affect regions south and north of 32.5°N, respectively. Our study interprets the vulnerability of the JCWs to pollutant enrichment from a physical perspective and finds the flushing efficiency to be a good indicator of eutrophication, providing references for environmental managers of local and global estuarine‐coastal systems with recurrent pollution. Plain Language Summary: Some estuarine‐coastal systems are vulnerable to pollution, as a relatively small amount of pollutant loading induces lasting water quality degradation. The Jiangsu coastal waters (JCWs), located in the southwestern Yellow Sea, lack large river discharge but suffer from poor water quality in recent years. In order to understand the reason, this study simulated the tracer dispersal processes in a hydrodynamic model. The model is verified with observational water elevation, tidal currents, temperature, and salinity. It is found that the distribution and duration of pollution can largely be attributed to how fast the pollutants are flushed. Regions with a low flushing rate tend to accumulate nutrients in the JCWs and are observed to be frequently eutrophic. The JCWs are better flushed and thus less eutrophic in summer, as a consequence of the stronger coastal circulation. The summer circulation is primarily controlled by the density‐driven processes. Seasonal warming and cooling of surface offshore waters change seawater density and coastal circulation. Model results also show that the river‐borne pollutants from the Yangtze and Jiangsu local rivers mainly affect regions south and north of 32.5°N, respectively. The study provides pollutant‐control references for environmental managers of local and global coastal systems suffering from recurrent pollution. Key Points: The low flushing efficiency largely accounts for recurrent water quality degradation in the Jiangsu coastal waters (JCWs)The JCWs are better flushed and thus less eutrophic in summer due to the stronger tidal residual coastal circulationThe baroclinic pressure gradient poses a dominant control on the seasonal variations of coastal circulation and pollutant flushing rates
- Subjects
JIANGSU Sheng (China); CHINA; WATER quality; SAND waves; TIDAL currents; TERRITORIAL waters; POLLUTANTS
- Publication
Journal of Geophysical Research. Oceans, 2023, Vol 128, Issue 8, p1
- ISSN
2169-9275
- Publication type
Article
- DOI
10.1029/2022JC019607