Ecology Of Benthic Macroinvertebrates In Nanxi River

Benthic macroinvertebrates are an important component of aquatic organisms in river ecosystems.As consumers and decomposers in ecosystem,macroinvertebrates play important roles in the material cycle and energy flow of freshwater ecosystems.Benthic macroinvertebrates were sensitive to water environmental changes,and their diversity could reflect the health of rivers and played an important role in the biological evaluation of river water quality.Nanxi River,an important tributary of Yuanjiang Honghe River system,is located between Dawei mountain and Wenshan National Nature Reserves in Honghe and Wenshan Prefecture of Southeast Yunnan Province.The biogeographic fauna of this area was ancient origin and special with rich biodiversity..It was also one of the important ecologically fragile areas in Yunnan Province.However,little was known about the aquatic fauna in the region,especially the benthic macroinvertebrates.To understand the community structure and function of macroinvertebrates in Nanxi River,bentic macroinvertebrates in 35 sampling sites of Nanxi River Basin were investigated by standard sampling method in high water period(August)and low water season(November)in 2020.Based on the survey results,the water quality and health status of Nanxi River were evaluated.To clarify benthic macroinvertebrate diversity of river ecosystem,spatio-temporal pattern and dynamics of feeding function group,combined with the effects of environmental factors on feeding function groups was of great significance in understanding the roles of benthic macroinvertebrate in material circulation and energy flow of the river ecosystem.The results of the research could also provide basic information for the ecological environment monitoring and protection of Nanxi River and Yuanjiang River Basin,as well as the development and utilization of aquatic resources.The research on benthic macroinvertebrates in the Nanxi River had come to the following results:1.A total of 208 species(taxon)of benthic macroinvertebrates were identified from 9421 specimens collected in the two surveys,which belonged to 4 phylum,7 classes,73 families,including Insecta,Malacostraca,Gastropod,Lamellibranchia,Oligochaeta,Hirudinea,and Turbellaria.Aquatic insects were the dominant groups,The biodiversity index of benthic macroinvertebrates was at a high level in most sample sites of Nanxi River.The community structure and quantity of benthic macroinvertebrates had no significant seasonal changes,and the main dominant groups in the basin had remained little seasonal changes.The composition of benthic macroinvertebrates in the middle reaches of Nanxi River was more complex than that in the upper and lower reaches,and the number and species diversity of benthic macroinvertebrates in the lower reaches of Nanxi River were lower in the high flow period.2.The results of functional feeding group analysis showed that among the five functional groups,scrapers and predators accounted for the highest proportion in species richness,while gatherers,scrapers and collector-gathers accounted for 91.83% of the total abundance,while shredders were less.In the high flow period,the biomass and density of the predators in le Level 1 tributary were significantly higher than those in other levels,indicating that there were more Coarse Particulate Organic Matter input in level 1 tributary.Canonical correspondence analysis(CCA)showed that altitude and latitude were the main environmental factors affecting the functional feeding groups of benthic macroinvertebrates.The distribution of benthic macroinvertebrates during the low water period was mainly affected by river depth and water surface width,and the physical and chemical factors such as HN4+ and p H also had some influence on the distribution of benthic macroinvertebrates.3.The results of biological evaluation of water quality based on the pollution tolerance value showed that the health status of the river ecosystem in Nanxi River was in good condition as a whole.ASPT index,BMWP index and Shannon-Wiener index of benthic macroinvertebrate in Nanxi River were consistent,and EPT-FA index was not suitable for water quality biological assessment in Nanxi River.Both species number and quantity of Benthic macroinvertebrates in Nanxi River were large,which reflected the rich biodiversity in this basin.The distribution of feeding function groups was more closely related to the physical characteristics of the river,but less affected by chemical factors,which reflected the low chemical pollution in Nanxi River to some extent.At the same time,the results of water quality biological evaluation also showed that the overall health condition of Nanxi River was good.