Seasonal and anthropogenic factors-driven distribution of nutrient salts and microbial communities in the Pearl River Delta

The transformations of Iron (Fe), Phosphorus (P) and sulfide (S) has been previously investigated, but quantifying the effects of seasonal and anthropogenic influences on nutrient transformations and microbial community distributions is a major issue that requires urgent attentionin areas with serious anthropogenic disturbance. We used the diffusive gradients in thin-films (DGT) technique and 16S rRNA gene sequencing to determine spatial heterogeneity in nutrient distribution and microbial community structure in the overlying water and sediment in the Pearl River Delta (PRD), the sampling campaigns were conducted in summer and winter, respectively. The results show that the nutrient salts exhibited greater differences in time than in space, and the higher water pollution levels in winter than in summer. Sediment was identified as a potential source, especially in summer, due to the loose structure of sediment particles and diffusion fluxes of P, Fe, and NH ₄ ⁺ -N caused by rainfall and high temperature. Microbial diversity and abundance were also affected by seasonal and anthropogenic factors, with higher richness and diversity of microbial communities in summer than in winter, and high salinity and nutrient salts concentration had a significant inhibitory effect on microorganisms. Mantel test revealed that the spatiotemporal distribution patterns of dominant bacteria were closely related to the TOC and DO levels and play an important role in the P, Fe, S, and N cycle. These observations are important for understanding nutrient salts transformation and diffusion in the Pearl River Delta.