Lijun Xiong

The South China Sea, a semienclosed marginal sea and global hotspot for plastic pollution, presents complex hydrodynamics and pronounced water column stratification, offering a unique setting to investigate the vertical behavior of microplastics. This study examines vertical distribution, environmental drivers, and ecological risks of microplastics using water samples collected from 15 stations across 5 depth layers. Microplastic abundance significantly decreased with depth, accompanied by a compositional shift from low-density, small-sized, fibrous polyethylene and polypropylene at surface to higher-density, larger-sized, granular polyvinyl chloride and polyester in deeper layers. Principal component analysis and stratification index analysis revealed that gradients in temperature, salinity, density, and pressure jointly drive microplastic vertical differentiation. Notably, water column stability─primarily controlled by density gradients─plays a pivotal role in limiting microplastic vertical transport, as evidenced by a strong positive correlation between stratification index and vertical abundance gradient. A species sensitivity distribution model based on representative Chinese coastal species yielded a hazardous concentration for 5% of species of 12.3 items/L and a predicted no-effect concentration of 6.15 items/L. Moderate ecological risks were observed in surface waters, particularly for bivalves and planktonic crustaceans. These findings highlight the critical role of stratification in modulating microplastic exposure risks in marginal seas.

Paddy fields account for 10% of global CH₄ emissions, and the application of manure may increase CH₄ emissions. In this study, high-throughput sequencing technology was used to investigate the effects of manure application on CH₄ emissions and methanogens in paddy soil. Three treatments were studied: a controlled treatment (CK), pig manure (PM), and organic fertilizer (OF). The results showed that the contents of Zn, Cr and Ni in paddy soil increased with the application of manure, but the contents of heavy metals gradually decreased with the growth of rice. The Shannon index and Ace index showed that the application of pig manure and organic fertilizer less affected the diversity and richness of soil Archaea. The results of community composition analysis showed that Methanobacterium, Methanobrevibacter, Methanosphaera, Methanosarcina and Rice_Cluster_I were the main methanogens in paddy soil after manure and organic fertilizer application. Soil environmental factors were changed after applied manure, among which total potassium (TK) and total nitrogen (TN) were the main environmental factors affecting methanogens in paddy soil. The changes of soil environmental factors affected the community composition of methanogens, and the increase of the relative abundance of methanogens maybe the main reason for the increase of CH₄ emission flux. The relative abundance of methanogens and CH₄ emission flux in paddy soil were increased by both pig manure and organic fertilizer application, and pig manure had a bigger impact than organic manure.

For storm drainages inappropriately connected with sewage, wet weather discharge is a major factor that adversely affects receiving waters. A study of the wet weather influences of rainfall-discharge variables on storm drainages connected with sewage was conducted in the downtown Shanghai area (374 ha). Two indicators, event mean concentration (EMC) and event pollutant load per unit area (EPL), were used to describe the pollution discharge during 20 rain events. The study showed that the total rainfall and discharge volume were important factors that affect the EMCs and EPLs of the chemical oxygen demand, total phosphorus, and especially those of NH₄⁺-N. The pollutant concentrations at the beginning of the discharge and the discharge period were also major factors that influence the EMCs of these three pollutants. Regression relationships between the rainfall-discharge variables and discharge volume/ EPLs (R² = 0.824–0.981) were stronger than the relationships between the rainfall-discharge variables and EMCs. These regression equations can be considered reliable in the system, with a relative validation error of less than ±10% for the discharge volume, and less than ±20% for the EPLs. The results presented in this paper provide guidance for effectively controlling pollution in similar storm drainages.