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Abstract Microplastics are emerging contaminants of increasing concern. Despite the occurrence of microplastics in farmland soils, the knowledge on microplastics in rice-fish co-culture ecosystems is limited. In this study, we investigated the distribution of microplastics in three rice-fish culture stations in Shanghai. During non-rice and rice-planting periods, microplastics in water, soils and aquatic animals (eel, loach and crayfish) were systematically assayed using methods of NaCl density extraction, H 2 O 2 digestion and micro-fourier transform infrared spectroscopy. Results showed that average microplastic abundances were 0.4 ± 0.1 items L−1, 10.3 ± 2.2 items kg−1, 1.7 ± 0.5 items individual−1 in water, soils and aquatic animal samples, respectively. We found an increasing trend in microplastic abundances in water, soil and animal samples from non-rice period to rice-planting period. Almost all of microplastics were found in digestive tracts of animals. Major microplastics were small (<1 mm) polyethylene and polypropylene fibers, with color of white and translucent. Size, shape, color and polymer type distributions of microplastics were similarly found in environmental and animal samples. Moreover, microplastic abundances in aquatic animals correlated to abundance in farmland soils. This study, for the first time, reveals the occurrence and characteristics of microplastic pollution in rice-fish culture ecosystem which suggests the potential ecological risks of microplastics in the agroecosystem. Graphical abstract Unlabelled Image Highlights • Microplastic pollution was studied in three rice-fish co-culture ecosystems. • Microplastics were found in water, soil and breeding aquatic animal samples. • An increasing trend of microplastics occurred from non-rice period to rice period. • Major microplastics were small (<1 mm) polyethylene and polypropylene fibers. • Microplastic abundances in aquatic animals were correlated to abundances in soils. [ABSTRACT FROM AUTHOR]

Dark carbon fixation (DCF) by chemolithotrophic microbes can make considerable contribution to inorganic carbon fixation in aquatic ecosystems. However, little is known about the importance and diversity of chemolithotrophic microbes in cascade reservoir sediments. In this study, we determined the potential DCF rates of sediments of three cascade reservoirs in Wujiang River basin by carbon isotopic labeling. The results showed that the DCF rates of the surface sediments ranged from 1.5 to 14.7 mmol C m−2 d−1. The ratio of DCF to mineralization rate of sediment organic matter of surface sediment was between 11.6%~60.9%. High-throughput sequencing analysis of cbbL and cbbM genes involved in Calvin Benson Cycle indicated that cbbL -carrying CO 2 -assimilating bacteria included diverse functional groups, while cbbM type was mostly involved in sulfur oxidation. The sediments of Hongfeng (HF) reservoir, which has much longer hydraulic residence time (HRT) and locates in most upstream of a major tributary of Wujiang River, have substantially higher DCF rates. The cbbL and cbbM communities in HF were dominated by sulfur oxidizing bacteria, and were largely different from that in the other two reservoirs. Our results suggested that chemolithotrophy plays an important role in carbon cycling of sediments in cascade reservoir. Meanwhile, HRT and relative location of cascade reservoirs are the key control factors of both DCF and composition of autotrophic microbial communities in cascade reservoir sediments. Unlabelled Image • First evaluation of chemolithotrophic activity in surface sediment of cascade reservoirs. • Chemolithotrophic carbon fixation was found to play an important role in carbon cycling of sediments in cascade reservoirs. • Hydraulic residence time and relative location of reservoirs are the key control factors of activity and composition of autotrophic microbial communities in cascade reservoir sediments. [ABSTRACT FROM AUTHOR]