| The Lancang-Mekong River originates from the northeastern of the Tanggula Mountains in Qinghai Province,flows through Yunnan and Tibet provinces of China and Laos,Myanmar,Thailand,Cambodia and Vietnam of Southeast Asia,and then flows into the South China Sea.The Lancang-Mekong River is an important international river in China and Southeast Asia,and is also one of the basins with the highest biodiversity in the world.In recent years,with the increase of hydropower development intensity in the basin,the water environmental conditions of the basin have been significantly changed,the survival and reproduction of aquatic organisms have been affected,and the health of aquatic ecosystems in the basin has been threatened.Understanding the impact law of the dam on macroinvertebrates(hereinafter referred to as zoobenthos)not only provides a basis for using zoobenthos to indicate environmental impact,but also a scientific basis for water ecological environment protection and management of hydropower development rivers.In this study,the Nanla River(with dams)and Buyuan River(without dams),two adjacent primary tributaries in the lower reaches of the Lancang River,are taken as the study area.By comparing the differences in density,biomass,species diversity,functional traits and functional diversity between rivers with dams and rivers without dams in different seasons(dry season and wet season),this study explored the significant environmental and spatial factors affecting the composition of the zoobenthos community,and revealed the role of different ecological processes(deterministic processes dominated by environmental filtration and stochastic processes dominated by dispersal effects)in the composition of zoobenthos community.The main results are as follows:In terms of species diversity of the two tributaries:the number of zoobenthos in the Buyuan River is higher than that in the Nanla River.In different seasons,a total of150 species of zoobenthos were collected in the Buyuan River and 123 species in the Nanla River.The average density and biomass of zoobenthos in the dry season of the Nanla River are 476.23ind/m~2 and 11.52g/m~2,and the average density and biomass of zoobenthos in the wet season of the Nanla River are 631.68ind/m~2 and 17.53g/m~2.The density and biomass of zoobenthos in the wet season of the two tributaries are higher than those in the dry season.The results of PERMANOVA test of zoobenthos community structure show that the community structure of the Nanla River shows significant differences in different seasons,and the zoobenthos community structure of the Buyuan River shows no significant differences in different seasons.The Margalef diversity index,Shannon diversity index and species richness of the Buyuan River in dry season and wet season are significantly higher than those of the Nanla River,while Simpson diversity index and Pielou diversity index have no significant difference between the two rivers.The composition of functional traits of zoobenthos in Nanla River and Buyuan River showed great differences in different seasons,which are mainly reflected in:in the dry season,the diversity of rheophily(deposition and erosional),adult lifespan(short),oviposition(stone)and dispersal(very strong)in the Buyuan River is significantly higher than that in the Nanla River,and the diversity of habits(sprawl),tolerance(tolerant),adult lifespan(long)oviposition(other)and dispersal(very weak)are significantly lower than those of the Nanla River;In wet season,rheophily(erosional),habits(skate),voltinism(semivoltine)and oviposition(stone)of the Buyuan River are significantly higher than those of the Nanla River,and oviposition(free)is significantly lower than that of the Nanla River.Among the 14 functional traits selected,7 functional traits including rheophily,adult lifespan,oviposition,dispersal ability,habits,voltinism,and tolerance are more vulnerable to dam construction.The Buyuan River(without dams)is more suitable for the survival of zoobenthos such as depositional and erosional flow regimes,short lifespan,spawning on stone,strong dispersal ability,skating,semivoltine,and poor tolerance.The Nanla River(with dams)is more suitable for the survival of zoobenthos like depositional flow regime,long lifespan,free spawning,weak dispersal ability,sprawl,univoltine or bi-or multivoltine,and strong tolerance.For the functional diversity index,the FRic of the Buyuan River in the dry season is significantly higher than that of the Nanla River,the FRic,FDiv and RaoQ of Buyuan river in wet season are significantly higher than that of the Nanla River,but the FEve is lower than that of the Nanla River.Environmental factors play an important role in driving the differences in zoobenthos community structure,and spatial factors also play an important role.The main manifestations are as follows:the pure environmental factor(8%)explained more community structure difference of zoobenthos in the dry season of Nanla River than the pure spatial factor(0.5%).On the contrary,the pure spatial factor(9.3%)explained more community structure differences of zoobenthos in the dry season of Buyuan River than the pure environmental factor(4.1%);pure environmental factor(7.7%)and pure spatial factor(6.2%)are similar in explaining the difference of zoobenthos community structure in the wet season of Nanla River;the pure environmental factor(9%)explained more differences in community structure of zoobenthos in the wet season of Buyuan River than the pure spatial factor(4.0%).Through a comparative study on the diversity of zoobenthos in the Nanla River(with dams)and Buyuan River(without dams)in the lower reaches of the Lancang River,especially related research on functional traits and functional diversity,this study will help to use zoobenthos to indicate and evaluate the impact of dam construction on river aquatic environment in the future,which can also provide scientific basis for the protection and management of water ecological environment and zoobenthos diversity in the Lancang River basin. |
