汉江(丹江口坝下-兴隆段)水体中微塑料的赋存特征

河流作为内陆微塑料进入海洋的重要途径，其微塑料污染问题受到广泛关注. 为了解南水北调中线一期工程调水及梯级水利枢纽运行条件下，汉江(丹江口坝下-兴隆段)水体中微塑料的赋存状况，以该河段河道的表层水体以及王甫洲、崔家营、兴隆水利枢纽库区的表层、中层、底层水体为研究对象，通过野外采样调查，分析水体中微塑料的赋存特征. 结果表明:①汉江(丹江口坝下-兴隆段)表层水体中微塑料丰度的范围为4 467~8 400 n/m3，平均值为(6 260±1 431) n/m3，崔家营和兴隆水利枢纽库区中层水体中微塑料丰度均显著高于表层和底层水体. ②汉江(丹江口坝下-兴隆段)表层水体中微塑料粒径主要分布在200, 500) μm，占比为42.5%；且随水深增加，微塑料粒径有增大趋势，崔家营水利枢纽库区底层水体、兴隆水利枢纽库区中层及底层水体中微塑料粒径均以500, 1 000) μm为主. ③汉江(丹江口坝下-兴隆段)表层水体中观测到的微塑料以纤维状为主，占比为65.2%，但微塑料形状在水利枢纽库区随水深发生显著性变化，即随水深增加，纤维状的微塑料占比下降，碎片状的微塑料占比增加. ④汉江(丹江口坝下-兴隆段)表层水体中微塑料聚合物类型以尼龙为主，占比约为65.9%，但王甫洲、崔家营、兴隆水利枢纽库区中层及底层水体中尼龙的占比均有所下降，平均值分别为57.3%和43.1%. 研究显示，水利枢纽库区中的微塑料有在水体中层聚集的趋势，其粒径、形状和材质在不同水层的分布也有所不同，今后还需要对微塑料在水利枢纽库区中的沉降机制进行深入研究，以系统揭示微塑料在水利枢纽运行条件下的环境行为与输移规律. 

Characteristics of Microplastics in Water of the Hanjiang River (Below the Danjiangkou Dam-Xinglong Section)

River as an important pathway for inland microplastics to enter the ocean, their microplastic pollution has received extensive attention. In order to understand the occurrence of microplastics in water of the Hanjiang River (Below the Danjiangkou Dam-Xinglong Section) under the conditions of the first phase of the South-North Water Transfer Project and the operation of the cascade water conservancy projects, the surface water of the Hanjiang River (Below the Danjiangkou Dam-Xinglong Section) and the surface, middle and bottom water of the Wangfuzhou, Cuijiaying and Xinglong Water Conservancy Projects were sampled, and the characteristics of microplastics in water were analyzed. The results showed that the abundance of microplastics in the surface water of the Hanjiang River (Below the Danjiangkou Dam-Xinglong Section) ranged from 4467 n/m3 to 8400 n/m3, with an average of (6260±1431) n/m3. The abundance of microplastics in the intermediate water of Cuijiaying and Xinglong Reservoir was significantly higher than that of surface and bottom water. The particle size of microplastics in surface water of Hanjiang River (Below the Danjiangkou Dam-Xinglong Section) was mainly distributed in 200, 500) μm, with a proportion of 42.5%. With the increase of water depth in the reservoirs, the particle size of microplastics tends to increase, and the particle size of microplastics in the middle and bottom water bodies of the Cuijiaying and Xinglong Water Control Project are mainly 500, 1000) μm.The microplastics in the surface water were mainly fibers, with a proportion of 65.2%, but the shape of the microplastics changed significantly with the water depth of the reservoirs. The proportion of fibers decreased, and the proportion of fragments increased with the water depth. The microplastics in surface water of the Hanjiang River (Below the Danjiangkou Dam-Xinglong Section) were mainly composed of nylon, with a proportion of 65.9%; but the proportion of nylon in the middle and bottom water bodies of the Wangfuzhou, Cuijiaying and Xinglong Water Conservancy Projects decreased, with an average of 57.3% and 43.1%, respectively. The results of this study indicated that microplastics tend to accumulate in the intermediate layer in the reservoir, and the distribution of particle size, shape and material in different water layers are different. Further studies are recommended to investigate the settlement mechanism of microplastics in the reservoir and systematically reveal the environmental behavior and transport pattern of microplastics under the operating conditions of water conservancy projects.