River restoration changes distributions of antibiotics, antibiotic resistance genes, and microbial community.

ABSTRACT

Although river restoration has been increasingly implemented to restore water quality in ecosystems, its effect on the removal of emerging pollutant antibiotics, and their resultant influence on microbial community structure and functions in river water is still unclear. This study investigated the changes of antibiotics, antibiotic resistant genes (ARGs), microbial communities, and their spatial distributions in a megacity river before and after river restoration. Results indicated that although the restoration activities including riverbed dredging, riverbank hardening, sewage and storm water separation and re-pipelining improved water quality such as by decreasing total phosphorus (TP) content from 4.60 ± 6.38 mg/L in 2018 to 0.98 ± 0.44 mg/L in 2020, the antibiotic concentrations in river water increased. Total antibiotic concentrations in the water samples were higher in 2020 (506.89-6952.50 ng/L) than those in 2018 (137.93-1751.51 ng/L), likely caused by increased usage of antibiotics in 2020 for COVID-19 treatment. The spatial distributions of antibiotics were less varied likely as a result of less retardation and fast mixing during antibiotic transport. The result also found that the abundance of Actinobacteria and Proteobacteria, and their correlations with ARGs increased. The spatial distributions of ARGs and microbial communities became less varied in the river water, consistent with the antibiotic variations before and after river restoration. Physicochemical changes such as decreased TP and dissolved organic carbon content may also be a factor. The results indicated that the current river restoration efforts were not effective in removing antibiotics, and implied that further studies are needed to investigate their subsequent transformation and transport, and to assess their risks to the health of ecosystems.