Effects of norfloxacin on decomposition and nutrient release in leaves of the submerged macrophyte Vallisneria natans (Lour.) Hara.

It is well known that antibiotic residuals affect the composition and structure of microbial communities. However, the consequences of these biological changes in terms of ecosystem function remain poorly understood, particularly in aquatic ecosystems. Here, we investigated the impacts of norfloxacin (NOR, 0, 0.5, and 8 mg L-1), a widely used antibiotic, on the microbial community structure on leaf surfaces of the submerged macrophyte Vallisneria natans, and the corresponding variations in litter decomposition, litter nutrient release, and water properties. Results showed that after 40 days of exposure, bacterial richness consistently decreased with increasing NOR concentration, and that richness of fungi was significantly lower in treatments adding NOR than in the control treatment. Moreover, NOR shifted the community toward NOR resistant phyla and genera, especially in the bacteria community. These community shifts resulted in the inhibition of litter decomposition and nutrient release from leaf litter to system water, accompanied by increases in dissolved oxygen concentration and pH of system water. Our results indicate that, by affecting microbial communities, NOR had significant effects on litter decomposition, litter nutrient release, and water properties, highlighting the potential harmful effects of NOR on aquatic ecosystem function.

Pollutant removal from agricultural drainage water using a novel double-layer ditch with biofilm carriers.

Agricultural drainage ditches can prevent flooding and mitigate agricultural pollution; however, the performance is unsatisfactory in plateau areas like the Dianchi Lake basin. Thus, a novel double-layer ditch system (DDS) with a fibrous packing as biofilm carriers was developed to form the carrier-attached biofilms and enhance the pollutant removal. The results indicated the DDS performed better than a single-layer ditch system, and annual average removal efficiencies of TN, NO3--N, NH4+-N, TP, COD and SS were 18.61%, 17.13%, 7.74%, 11.90%, 11.95% and 23.71%, respectively. High amount and carbon, nitrogen and phosphorus contents of biofilms are favourable to pollutant removal by DDS. Although bacterial diversity of biofilms remained relatively stable throughout the year, the relative abundance of dominant assemblages varied greatly. Denitrifying microorganisms affiliated with Bacteroidetes might contribute to effective NO3--N reduction. This study demonstrates DDS performed well and provides a novel method for application of biofilm carriers in drainage ditches.