Many tributaries of the Pearl River carry large amounts of terrestrial pollutants into estuarine areas. Heavy metals accumulate in estuarine sedimentary environments, and coupled and changing biogeochemical processes occur in estuarine areas. The results of this study showed that the heavy metal contents in the sediment were the highest near the confluence of the Humen and Jiaomen outlets in 2005 and 2019; they were the second-highest near the remaining outlets, and gradually decreased toward the lower reaches, with high contents on the western shore and low contents on the eastern shore. The heavy metal pollution mainly originated from the Pearl River runoff. The historical evolution of heavy metals in the Pearl River Estuary (PRE) effectively reflected the impacts of pollutant inputs from the river basin as well as industrial and agricultural production and anthropogenic activities in the Guangdong–Hong Kong–Macao Greater Bay Area (GBA). In 2019, the surface sediments were not contaminated with Hg, and the Pb and Zn contents decreased significantly, indicating significant advances in environmental management; however, the Cu and Cd levels still indicated heavy pollution level in the upper reaches.

A gulf is a typical ecological zone where carbon cycle is jointly affected by complex environmental factors and strong human activities, and the Beibu Gulf has complex water masses and circulation structures. In this study, we used underway, continuous observational data of the surface water partial pressure of carbon dioxide (pCO₂), temperature (SST), salinity (SSS), dissolved oxygen (DO), and chlorophyll α along with vertical profile observations of temperature, salinity, carbonate system parameters and nutrients to determine the spatiotemporal variations and research effects of water masses and circulation on summer pCO₂ in the eastern part of Beibu Gulf. In the summers of 2011 and 2014, the mean pCO₂ in the eastern part of Beibu Gulf was 417 μatm and 405 μatm, respectively, and the mean sea–air CO₂ flux was 3.3 mmol m⁻² d⁻¹ and 1.6 mmol m⁻² d⁻¹, respectively. In the summer of 2011, the northern part of the Beibu Gulf was controlled by a cyclonic circulation, and pCO₂ at the center of the cyclonic circulation increased by more than 15 μatm to a mean value of more than 10 μatm above that of the surrounding waters. The southern part of the Beibu Gulf was affected by an anticyclonic circulation and western coastal water masses, with a high temperature, low salinity, low pCO₂, and downwelling surface waters. In the summer of 2011, the mean pCO₂ was approximately 17 μatm lower than that in the surrounding waters, and no clear downwelling was observed in summer 2014. The eastern part of Beibu Gulf was a source of atmospheric CO₂ in the summer, only the region affected by the northern coastal water in the eastern part of Beibu Gulf was a sink of atmospheric CO₂, and pCO₂ had distinctly different spatiotemporal distributions under the influence of complex water masses and circulation structures.