Reclaimed water use improved polluted water's self-purification capacity--Evidenced by water quality factors and bacterial community structure

Reclaimed water is increasingly adopted around the world to relieve water resource crisis induced by accelerated urbanization process. Compared with natural water bodies, aquatic ecosystems replenished with reclaimed water are usually enriched with organic matter, total nitrogen (TN) and phosphorus (TP). However, whether and how nutrient stoichiometric characteristic can impact receiving waters' self-purification remains poorly addressed. Here, we evaluated the effects of reclaimed water use on water's self-purification capacity in terms of water quality, sedimentary bacterial diversity, bacterial community structure and function. Results showed that reclaimed water use has improved water quality of domestic polluted urban rivers and increased bacterial genus-level abundance, but failed to directly affect bacterial biodiversity indexes and evenness of receiving waters. Water organic matter input from reclaimed water was the decisive factor in shaping sedimentary bacterial community structure rather than temperature. Meanwhile, compared with non-reclaimed water, reclaimed water replenishment enhanced polluted waters' carbon (C)-, N-and P-removing functions, suggesting an improvement of self-purification capacity. Our findings could improve the understanding of the ecological impact of reclaimed water on urban aquatic ecosystem, and inform the rational use of reclaimed water in urban rivers.