Non-point source pollution from human activities increasing the biotic homogenization in urban river network system

Abstract

AbstractRivers have been a preferred location for human settlements throughout history. Human activities were believed to affect the assembly and biogeographic pattern of river microorganisms, while the underlying processes are not sufficiently understood yet. Comparing the river microbial communities in highly urbanized rivers and undisturbed natural rivers could expand our understanding of the river ecosystem responses to environmental changes resulting from human activities. Here, 28 urban and 24 nature reserve river surface sediment samples were collected in a highly connected river network spanning ∼400 km located in the Qinling Mountains, Northwest China, and their geobiochemistry profiles and microbial populations were investigated. The results showed that human activities resulted in significant increases in organic/inorganic nutrients, microbial population size and diversity in urbanized rivers. The structure of the microbial communities in the surface sediments had distinct relationships with environmental factors and their co-occurrence networks exhibited a clear spatial pattern. Redundancy and correlation analysis together indicate that nitrogen was the major environmental attribute that affected the community structure and assembly process. High abundances of nitrogen transformation microorganisms, pathogens, antibiotic-resistant bacteria and PAHs-degrading bacteria were observed in urbanized areas. The neutral community model and null model revealed community composition to be predominant governed by homogeneous selection in urban river areas, suggested the non-point source pollution led to significantly increased biotic homogenization.