Organic carbon drives the microbial-mediated blackening and odorization of urban rivers

As the rapid global urbanization, massive anthropogenic inputs of mineral nutrients and organic pollutants result in severe pollution of urban rivers, and consequently alter the structure and function of their aquatic microbial communities. In a one-year field study on the composition, function and spatiotemporal dynamics of water and sediment microbial communities in seven black-odorous urban rivers in a megacity in southern China, combined with laboratory water-sediment column experiments, we identify organic carbon as the key parameter to drive overgrowth of heterogeneous microorganisms, and further form suspended black flocs in water phase under redox conditions, resulting in the blackening and odorization of urban rivers.