Long-term characteristics of water quality around the Guangdong-Hong Kong-Macau Greater Bay Area: Spatiotemporal variations and meteorological effects

Abstract

Monitoring the coastal water quality (CWQ) and determining the effects of meteorological factors (MF) on the long-term CWQ adjacent to urban agglomerations are key topics in coastal monitoring and management. This study used satellite-derived data to study the long-term CWQ around the Guangdong-Hong Kong-Macau Greater Bay Area (GBA) with indicators of chlorophyll-a concentration (Chla) and diffuse attenuation coefficient for downwelling irradiance at 490 nm (Kd(490)). The sea surface temperature (SST) and total precipitation accumulation (TPA) of the waters around the GBA were also studied from 2003 to 2019. Furthermore, statistical analysis was conducted to identify the impact of the MF on CWQ by quantifying trends and relationships of CWQ & MF. The results showed that (1) An increasing trend of annual Chla, Kd(490), and TPA were observed, whereas a decreasing trend of SST has been recorded from 2003 to 2019. Both CWQ indicators and meteorological variables showed significant differences among seasons, and the values of Chla, Kd(490), and SST were found higher in the coastal area but lower in the open waters area. (2) SST was the crucial factor of the high values of CWQ indicators in summer: the highest values of Chla and Kd(490) in summer are likely to be attributed to the proper SST (r = 0.87; r = 0.83) and higher TPA in spring (r = 0.95; r = 0.93). The precipitation played an uncertain role in driving the CWQ (r > 0.9 and r < −0.9 in spring and winter, respectively). A significant increase in TPA was associated with the decrease of SST in the coming year. (3) Due to the relatively stable change of natural environment and human activities, the trends of Chla, Kd(490), and TPA remained broadly consistent with those of the past 17 years. However, SST indicates a slight downward trend. In summary, the TPA and SST-driven patterns were essential in the management of water quality indicators in the GBA area. This study can improve our comprehensive understanding of the water quality status in the coastal regions of the GBA and provide references to the coastal zone and marine management, as well as the sustainable development of the GBA.