A coastal zone represents the intersection of ocean and land, and is characterized by high primary productivity, biodiversity, and rich resources but with strong sensitivity and vulnerability of the natural environment. In this study, 29 indicators reflecting the status of ecological security were selected to construct an ecological security evaluation index system using the Driving force Pressure State Impact Response (DPSIR) model. The comprehensive index method was used to evaluate the ecological security of Qinzhou coastal zone from 2011 to 2020 and to explore the driving factors of its evolution. The results showed that (1) In the past 10 years, the ecological security of Qinzhou coastal zone fluctuated and developed, and the security level changed from early warning – safer – more dangerous – early warning to safer; and the security level was the lowest (0.361) in 2014. The main reason was the impact of ecological marine disasters, such as three red tides with the eutrophication index of seawater as high as 4.170. (2) Since 2015, the ecological security of the coastal zone has shown an upward trend, which was mainly due to the implementation of the newly revised environmental protection law in the same year, the comprehensive promotion of “The 13^th Five-Year Plan for environmental protection”, and a series of measures related to the construction of ecological civilization and environmental protection, which provided a strong guarantee for the ecological security of the coastal zone. This study proposes measures to promote the better development of the ecological environment of Qinzhou coastal zone.

Nutrients function as essential biological substrates for coastal phytoplankton growth and serve as pivotal indicators in marine environmental monitoring. The intensification of land-based nutrient sources inputs has exacerbated eutrophication in Chinese coastal water, while mechanistic understanding of differential self-purification processes among distinct land-based source nutrients (river source, domestic source, aquaculture source, and industrial source) remains limited, constraining accurate assessment of bay’s self-purification capacity. This study conducted incubation experiments in Tieshan Bay (TSB) during Summer (June 2023) and winter (January 2024), systematically analyzing the self-purification process of nutrients and associated environmental drivers. Distinct source-specific patterns emerged: river inputs exhibited maximal dissolved inorganic nitrogen (DIN) 1.390 ± 0.74 mg/L, whereas industrial discharges showed peak dissolved inorganic phosphorus (DIP) 4.88 ± 1.45 mg/L. Chlorophyll a (Chl-a) concentrations varied markedly across sources, ranging from 34.97 ± 23.37 μg/L (domestic source) to 86.63 ± 77.08 μg/L (river source). First-order kinetics demonstrated significant source differentiation (p < 0.05). River-derived DIN exhibited the highest attenuation coefficient (−0.3244 ± 0.17 d⁻¹), contrasting with industrial-sourced DIP showing maximum depletion (−0.4332 ± 0.20 d⁻¹). Correlation analysis indicated that summer was significantly associated with the impacts of three key control factors pH, dissolved oxygen, and turbidity on nutrient dynamics (p < 0.05), whereas winter exhibited a stronger dependence on salinity. These parameters collectively may modulate microbial degradation pathways and particulate matter adsorption capacities. These findings establish quantitative thresholds for coastal nutrient buffering mechanisms, highlighting the necessity for source-specific eutrophication mitigation frameworks. The differential self-purification efficiencies underscore the importance of calibrating pollution control strategies according to both anthropogenic discharge characteristics and regional hydrochemical resilience, which is of key importance for ensuring the traceability and control of land-based sources of pollution into the sea and the scientific utilization of the self-purification capacity of the bay water body.

The natural radioisotopes ⁷Be, ²¹⁰Pb, and ²¹⁰Po, with different half-lives, are all particle-reactive and serve as natural tracers to study sources and transportation of sediments, sedimentation rates, and sediment chronology. Atmospheric deposition of these radioisotopes is the premise and foundation of their tracing application. The Maowei Sea is a semi-closed bay along the Beibu Gulf, which is an important gulf in the northwest of the South China Sea, but the atmospheric deposition of the abovementioned radioisotopes has not been systematically reported along the coast. In this research paper, the atmospheric depositional fluxes of ⁷Be, ²¹⁰Pb, and ²¹⁰Po were observed over a period from June 2018 to December 2021 on the coast of the Maowei Sea. The annual atmospheric depositional fluxes (Bq m^-2 yr^-1) of ⁷Be, ²¹⁰Pb, and ²¹⁰Po on the coast of the Maowei Sea were 496.80, 201.72, and 58.08, respectively. The distributions for ⁷Be and ²¹⁰Pb depositional fluxes during a whole year (years 2019 and 2021) followed a bimodal pattern, with one peak from February to April and another peak from August to October, while the distribution for ²¹⁰Po depositional flux showed only one peak during the year of 2019 and another during 2021. The deposition flux and activity of ⁷Be showed a strong positive correlation with the deposition flux and activity of ²¹⁰Pb, respectively; the deposition flux and activity of ²¹⁰Po also showed positive correlations with the deposition fluxes and activities of ²¹⁰Pb and ⁷Be, respectively, indicating a similarly scavenging behavior from the atmosphere. A Pearson correlation matrix was used to illustrate the factors influencing the atmospheric depositions and found that precipitation, air quality index (AQI), and PM (both PM_2.5 and PM₁₀) were the major factors that influenced the deposition of these three radionuclides. Precipitation had significant positive correlations with the deposition fluxes of all three radionuclides, indicating that, for these radionuclides, rainfall was the main scavenging way from the atmosphere. The observations for specific single rainfall events and their air mass backward trajectory analyses showed that the air masses movement during the rainfall may be another important factor that impacted the depositional fluxes for ⁷Be, ²¹⁰Pb, and ²¹⁰Po.

To understand how coastal microbial communities adapt to seasonal environmental shifts, we investigated the community structure and potential metabolic functions of surface water microbiomes in the Maowei Sea (Beibu Gulf) during the summer and winter of 2024 using Illumina sequencing. Significant seasonal variations were observed in both composition and function. Proteobacteria, Actinobacteriota, and Bacteroidota were the dominant phyla; Actinobacteriota was enriched in summer (10.80%, p < 0.05), while Bacteroidota peaked in winter (16.71%, p < 0.05). At the species level, the uncultured Mediterranean phage uVMED, a core viral population, dominated both seasons but declined from 29.88% in winter to 15.89% in summer (p < 0.05). Functional predictions indicated that amino acid metabolism was enriched in summer, whereas carbohydrate metabolism and membrane transport significantly increased in winter (p < 0.05). These structural and functional shifts were driven by different environmental parameters, temperature(T), salinity(S), and pH primarily shaped the community structure (p < 0.01), whereas pH and the dissolved inorganic nitrogen to phosphorus (DIN/DIP) ratio governed potential metabolic functions. This separation of structural and functional responses demonstrates how subtropical coastal microbiomes adapt to environmental stress by synergistically adjusting species composition and metabolic strategies, providing a theoretical foundation for the ecological health management of coastal bays.