The Response Of Macroinvertebrates To Fluvial Geomorphological Feature In Typical Debris Flow Gullies Of The Xiaojiang River Basin In Yunnan Province

In the upper reaches of the Yangtze River,the river valleys are mostly in the shape of V or U.They have steep riverbed gradient and large flow energy.The riverbed is usually in the state of downward erosion.Under the action of riverbed erosion and heavy rain in flood season,natural disasters(i.e.,collapse,landslide,and debris flow)are easy to occur.The riverbed structure is formed by solid particles which has the function of resisting scour.When the riverbed structure is well developed,it can effectively inhibit the starting and transportation of riverbed sand.Riverbed structure help to improve the flow resistance,riverbed stability and reduce the impact of debris flow and other natural disasters.In April and September 2017,the river topography,aquatic environment,and macroinvertebrates of the Xiaojiang River Basin were investigated systematically.There are 3 research targets:(a)To lind out the composition and spatial pattern of benthic community structure and functional characters of debris flow gullies;(b)To explore the relationship between various environmental factors of debris flow gully and riverbed structure;(c)To revel the response relationship between macroinvertebrate standing stock,functional traits and riverbed structure.Based on the study of fluvial landform,a new fluvial landform parameter—concavity-convexity degree(W)is proposed to quantitatively calculate the riverbed structure.Through the study of benthic community structure,benthic function traits,water environment condition and riverbed structure,the response of macroinvertebrate standing stock,functional traits and environment factors to riverbed structure were reveled.The results showed that:(a)Macroinvertebrates were mainly composed of individuals with the ability of avoiding risks and recovering quickly in debris flow gullies;(b)The environmental factors affecting macroinvertebrates(i.e.,average particle size,velocity,flow rate,water depth,and gradient)had a great relationship with riverbed structure;(c)Species richness,density and biomass of macroinvertebrates in 5 debris flow gully were significantly positively correlated with the riverbed structure;(d)Only 3(trophic habit,attachment and drift)of the 10 benthic functional traits in the study area had a good correlation with riverbed structure.It was more suitable for macroinvertebrates of different species to live,and more conducive to the maintenance of ecological stability when the concavity-convexity degree value was about 0.075.In addition,we preliminarily explored the evaluation method of habitat heterogeneity.These results can provide scientific basis for ecological conservation and management in debris flow gullies where eco-environment is very fragile.For example,try to keep concavo-convex degree at about 0.075 to accommodate more kinds of aquatic organism by adding some large stones.