Microplastics distribution characteristics in typical inflow rivers of Taihu lake: Linking to nitrous oxide emission and microbial analysis

The microplastics in nature water are important for the environmental fate of nitrous oxide (N2O). This study investigated the influence and microbial mechanism of microplastic abundance to the N2O flux in typical inflow rivers of Taihu lake. The microplastic abundance were in a range of 160-700 particles/m3 surface water, and 514-3018 particles/kg dry sediment. The highest percentage of microplastic color was transparent, significantly higher than other color (p<0.0001) in both surface water and sediment. The dominant microplastic size was 500-5000 μm in surface water, while size lower than 1000 μm was dominant in sediment. The microplastic abundance in sediment was negatively correlated with the concentration of suspended sediments (SPS) (p<0.05), Chl-a (p<0.05), NH4+-N (p<0.05) and TP (p<0.01) in inflow river surface water. The dissolved N2O concentration were 45.71-132.42 nmol/L, and the N2O fluxes were 29.85-276.60 μmol/m2/d. The dissolved N2O concentration was significantly correlated with the nirK abundance and nirK/nosZI ratio negatively (p<0.05), revealed that sediment nirK-type denitrification was the main driver of dissolved N2O. Meanwhile, the N2O flux (water-air interface) was significantly correlated with nosZI, napA, narG and nirS negatively, implied that nitrification and denitrification interaction in sediment is the main influence factor. The denitrification process in sediment was the main driven factor of N2O releasing. Mantel-test shows that microplastic abundance in surface water was significantly correlated with nitrification (p = 0.001∼0.01) and denitrification (p = 0.01∼0.05) genera in water. The dominant denitrification microorganism was Dechloromonas in sediment and Flavobacterium in surface water. These results provided new insight into the fact that plastisphere which comprises microbial community on microplastic could affect the N2O emission in aquatic system.