Influence of Human Activities on Bacterial and Fungal Communities in Urban Rivers

Environmental microorganisms are sensitive indicators of aquatic ecosystem disturbance, yet their links with river eco-health remain poorly understood. We investigated water quality, bacterial and fungal communities and socioeconomic factors across source, suburban and urban sections of the Minjiang River. Water quality and microbial diversity exhibited clear spatial gradients consistent with agricultural, industrial and residential activities. Proteobacteria dominated urban bacterial communities, Actinobacteria prevailed in suburban areas and Armatimonadetes were associated with intensive human activities. Fungal assemblages also showed spatial differentiation, with Chytridiomycota dominating upstream, Ascomycota midstream and Basidiomycota downstream. At the genus level, CL500-29 marine group and hgcI-clade were enriched upstream, whereas Limnohabitans and Flavobacterium dominated downstream; Septoria prevailed upstream, while Mycosphaerella, Didymella and Ampelomyces were more abundant downstream. Multivariate analyses (PCA, RDA, Mantel tests) identified TP, TN and DO as key drivers of bacterial communities, while COD, BOD₅ and DO primarily shape fungal distributions. Socioeconomic factors, including GDP per capita and population density, also contributed significantly. Predicted functional profiles based on OTUs showed spatial differences in microbial metabolic potential. This study provides a preliminary spatial analysis linking water quality, human activities and microbial communities in an urban river system.