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Coastal ecosystems are facing critical water quality deterioration, while the most convenient passage to the South China Sea, Beibu Gulf, has been under considerable pressure to its ecological environment due to rapid development and urbanization. In this study, we characterized the spatiotemporal change in the water quality in Beibu Gulf and proposed a machine learning approach to predict the water pollution level in Beibu Gulf on the basis of 5-year (2018–2022) observation data of ten water quality parameters from ten selected sites. Random forest (rf) and linear algorithms were utilized. Results show that a high frequency of exceedance of water quality parameters was observed particularly in summer and autumn, e.g., the exceeding rate of Dissolved Inorganic Nitrogen (DIN) at GX01, GX03, GX06, and GX07 station were 28.2~78.1% (average is 52.0%), 6.0~21.7% (average is 52.0%), 23.0~44.7% (average is 31.9%), and 5.2~33.4% (average is 21.2%), respectively. With regard to the spatial distribution, the pH, Water Salinity (WS), and Dissolved Oxygen (DO) values of stations inside the bay were overall lower than those of corresponding stations at the mouth of the bay and stations outside the bay. The concentrations of Chlorophyll-a concentration (except QZB) and nutrient salts showed a clearly opposite trend compared with the above concerned three parameters. For instance, the average Chl-a value of station GX09 was 22.5% higher than that of GX08 and GX10 between 2018 and 2022. Correlation analysis among water quality factors shows a significant positive correlation (r > 0.85) between Dissolved Inorganic Nitrogen (DIN) and NO3-N, followed by NO2-N and NH4-N, indicating that the main component of DIN is NO3-N. The forecasting results with machine learning also demonstrate the possibility to estimate the water quality parameters, such as chl-a concentration, DIN, and NH4-N in a cost-effective manner with prediction accuracy of approximately 60%, and thereby could provide near-real-time information to monitor the water quality of the Beibu Gulf. Predicting models initiated in this study could be of great interest for local authorities and the tourism and fishing industries. [ABSTRACT FROM AUTHOR]

In recent years, the interaction between aged micro-plastics and heavy metals such as cadmium, chromium and lead, has been one of the hot topics of the researchers, and the interaction mechanism between aged micro-plastics and highly toxic heavy metal Hg(II) was yet unrevealed. In this laboratory experimental study, polystyrene (PS) being aged by ozone was selected as the target micro-plastics, and with the combination of batch adsorption experiment and characterization using instruments including SEM, FT-IR, Zeta potential and contact angles, the adsorption-desorption behavior and mechanism of Hg(II) and the PS (before and after O3 aging) were explored. The findings of the lab experiment indicated that the ozone-aged PS(PS-O3) presented increased surface roughness, decreased contact angles (from 127.2° to 72.8°), and significantly enhanced surface hydro-philicity, in addition, a new carbonyl group appeared. The process of Hg(II) adsorption onto PS- could be well described by the pseudo-second-order kinetics and Langmuir isothermal model, which suggested the single-layer chemical reaction was mainly involved; it was also showed that the maximum adsorption capacity of PS-O3 was estimated to be 15.78 mg/g, seven times greater than that of the original PS (without O3 aging), this fact was mostly attributed to the electrostatic attraction and complexation between the oxygen-containing group and Hg(II). Moreover, PS-O3 desorption rate (c.a 54%) in the environment of gastric fluid (analogous to seawater of 0.04% HCl) was 60 times that in ultra-pure water, 10 times that of the original plastic in gastric fluid: the remarkable desorption capacity could be traced to the high affinity of gastric fluid towards Hg(II), the competitive effect from numerous H+ in the 0.04% HCl, and the abundant cations in seawater. In short, aged microplastics could enrich the aquatic Hg(II), on other hand, Hg(II) would be released in the acidic and hyperhaline environment. So, the aged microplastics could act as the carrier in the migration and transformation of Hg(II). Thus the research provided basic data for understanding the mechanism of interaction between heavy metal and aged microplastics. [ABSTRACT FROM AUTHOR]