The Response Of Benthic Macroinvertebrate To The Fluvial Processes Of Meandering Rivers In Baihe River Basin In The Source Region Of The Yellow River

Fluvial processes of meandering rivers not only contribute to diverse fluvial geomorphology,but also nurture abundant aquatic biological resources.In September 2019(normal water period)and June 2020(flood water period),we conducted a systematic river geomorphology-environmental-aquatic organisms survey in the Baihe River Basin which was located in the source area of the Yellow River,and then we determined the hydrological connectivity of different water bodies,analyzed the benthic community characteristics and environmental characteristics under different habitat conditions,and identified the key environmental factors that affected the characteristics of the benthic community.This study aims to reveal the response of benthic community characteristics to fluvial processes of meandering rivers in the Baihe River Basin in the source region of the Yellow River.According to the landscape connectivity of the water bodies,we divided the water bodies of the oxbow lake into connected oxbow lakes,semi-connected oxbow lakes and isolated oxbow lakes.Combining the main stream and tributaries,we divided the water bodies of the Baihe River Basin into five categories.According to this classification,we conducted research on the characteristics of the water environment and benthic communities in this area.There were significant differences in five types of water bodies and two sampling seasons,which were mainly reflected in the flow velocity,particle size and dissolved oxygen.In terms of the community characteristics of macroinvertebrates,altogether 127 species of benthic animals were identified,including 87 species in the normal water period(47 species in main streams,57 species in tributaries,47 species in oxbow lakes),and 92 species in the flood water period(47 species in main streams,64 species in tributaries,51 species in Oxbow Lake).Among them,there are 109 species of Arthropoda,14 species of Annelida,3 species of Mollusca and 1 species of Platyhelminthes.The dominant species in the main stream and tributaries were mainly species preferring running water,while the oxbow lake was mainly composed of species preferring static water.The canonical correspondence analysis showed that flow velocity,altitude,turbidity,silicon and nitrous acid were the key environmental factors affecting the distribution of benthic macroinvertebrate in the normal water period,and the flow velocity,river width,pH,dissolved oxygen and total nitrogen were the key environmental factors affecting the benthic community in the flood season.During the fluvial processes of meandering rivers,we found that as the connectivity weakened,the diversity of benthic animals first decreased and then increased,reaching a maximum in the isolated oxbow lakes.However,the trends of density and biomass were inconsistent in the two sampling seasons.In the normal water period,with the connectivity weakening,the density decreased,while the biomass first increased and then decreased.In the flood period,both the density and biomass first decreased and then increased when the connectivity was weakening.The dominant species were the succession aquatic insects(eg.Baetis sp.and Amphinemura sp.)preferring running water to snails(eg.Radix sp.)and aquatic insects(eg.Chironomidae and Coeixidae)preferring static water.From the normal period to the flood period,we found that the density of benthic animals in the water body of oxbow lake obviously increased,while the proportion of biomass decreased,but the density and biomass of benthic animals in isolated oxbow lakes were greatly increased.