In this study, microplastics in the surface water in the Pearl River Delta during different seasons were studied to analyze their temporal and spatial distribution, morphological characteristics, related socio-economic indicators, and potential ecological risks. Based on an analysis of surface water samples from 13 sampling sites, we found that the temporal and spatial distribution of microplastics in the Pearl River Delta were unbalanced. The microplastic abundances at the Qingqi, Chencun, Zuotan, and Beijiao sites were tremendously higher than those at other sites. Nevertheless, the abundance of microplastics at most sites was tremendously higher in the rainy season than dry season. Meanwhile, the morphological characteristics of microplastics had a strong correlation with the changes of season and site location. During the rainy season, the major color, shape, and size distribution of microplastics were gray (38.64%), strip (78.29%), and 100–500 μm (57.38%), respectively. The most usual color, shape, and size distribution of microplastics in the dry season were black (38.64%), granular (78.29%), and 0–100 μm (70.29%), respectively. As for the socio-economic indicators, including the degree of afforestation as well as the extent of industrial, transportation, and other human activities, all had varying degrees of impact on microplastic abundances. The potential ecological risk assessments demonstrated that most sites in the Pearl River Delta had a high potential for ecological risk related to microplastic pollution, which should be given more attention in the future. In summary, our investigations offer a theoretical basis for research related to microplastics in the Pearl River Delta and can further improve our understanding of the need to protect aquatic environments by exploring the overall ecological risks posed by microplastics.

Pulsed aerial exposure (PAE) is a major stressor for submerged macrophytes in tidal river networks, yet species-specific physiological mechanisms remain unclear. We conducted a 7-day PAE mesocosm experiment using Hydrilla verticillata (L.f.) Royle and Vallisneria denseserrulata (Makino) Makino to compare their photosynthetic performance, pigment retention, and oxidative defense. Hydrilla maintained lower baseline Y(II) and reliable EC₅₀s (64.6–85.7 min/d). In contrast, Vallisneria showed higher baseline Y(II) but a transient Y(NPQ) increase peaking at 120 min/d that subsequently collapsed, greater pigment loss (total chlorophyll −68% vs. −44%), and highly uncertain or out-of-range EC₅₀s. Although antioxidant enzyme activities were higher in Vallisneria, MDA accumulation was comparable between species. Principal component analysis (87.14% total variance) revealed that PC1 (42.03%) separated pigments from antioxidant enzymes, and PC2 (26.46%) captured photochemical efficiency. PC3 (18.65%) further indicated a transient oxidative burst and subsequent defense breakdown in Vallisneria under severe stress. These results suggest that Hydrilla exhibits a low light-capture strategy to mitigate PAE pressure, while Vallisneria exhibits an inducible defense that becomes overwhelmed. The quantitative parameters provide baseline data for macrophyte growth models, though field validation is required to confirm long-term ecological implications.