怒江源区不同层级河流底栖动物群落结构特征及影响因子分析

Characteristics of benthic community structure and their relationships with environmental factors in rivers at different orders within the source area of the Nu River

基于2021年4—5月和9—10月对怒江源区1~6级河流29个河段的底栖动物调查,分析了不同层级河流上底栖动物群落结构特征与环境因子的关系.两次调查共计监测到底栖动物59个分类单元,分属3门4纲8目26科.怒江源区不同层级河流上的底栖动物群落结构特征具有空间差异,总体呈现物种数、物种丰富度、物种多样性与河流层级成反比.1~2级源头河流底栖物种数最多,达到了48种,其次是3~4级中型支流和5~6级干流,分别为44种和29种.底栖动物的优势种群均为水生昆虫,其中,源头河流优势种中蜉蝣目、襀翅目和毛翅目3类种群占比75%,显著高于中型支流的25%和干流的33%.所有监测点中,物种密度最高的为源头河流藏曲,最低的为干流怒江,分别为116.67 ind.·m^(-2)和2.22 ind.·m^(-2).在生物多样性方面,源头河流和中型支流的Margalef丰富度指数和Shannon-Wiener多样性指数均高于干流.水环境因子CCA分析表明,源头河流关键环境因子为溶解氧,干流则主要受流速、河宽、砷和总溶解固体影响.不同层级河流的生境差异是造成底栖动物群落结构差异的主要原因,源头河流水温低、溶氧高且营养物质来源丰富,相较于干流而言,更加有利于襀翅目稚虫等喜冷水、清洁物种的生存和繁衍.

Benthos from 29 sites of rivers in the source area of the Nu River were investigated from April to May and from September to October 2021,and the relationship between benthic community structure characteristics and environmental factors of rivers at different stream orders was analyzed.A total of 59 taxonomic units of benthos from 3 phyla,4 classes,8 orders and 26 families were identified in the two surveys.The results showed that the benthic community structure in rivers at different orders was spatially different in the study area,and the number of species,species richness and species diversity were inversely proportional to stream order.Headwater streams had the highest number of species with 48,followed by medium-sized tributaries and mainstreams with 44 and 29 species,respectively.The dominant species of benthos were all aquatic insects,with 75%of the dominant species in the headwater streams being Ephemeroptera,Plecoptera,and Trichoptera,greater than 25%of the medium-sized tributaries and 33%of the mainstreams.Among all monitoring sites,the highest density was in the headwater stream Zangqu and the lowest was in the main stream Nu River,with 116.67 ind.·m^(-2) and 2.22 ind.·m^(-2),respectively.The Margalef richness index and Shannon-Wiener diversity index of headwater streams and medium-sized tributaries were higher than those of mainstreams.CCA analysis of hydro-environmental factors showed that headwater streams were most responsive to dissolved oxygen,while mainstreams was mainly affected by velocity,river width,arsenic and total dissolved solids.Habitat differences in rivers at different orders were the main reasons for the differences in benthic community structure.The headwater streams had lower water temperature,higher dissolved oxygen and richer sources of nutrients,which is more conducive to the survival and reproduction of cold water-loving and clean species such as plecoptera larvae than the mainstreams.