Responses Of Fish Traits And Functional Diversity To Cascade Hydropower Development In The Langcang River

Cascade hydropower development has become one of the main factors threatening fish diversity because of its immediate impact on river environment and fish habitat conditions and consequently the loss of indigenous fish species.Functional traits of fish refers to any measurable properties that affect their biological functions,which is the basis of adaptation to habitats for fish and closely related to the environment.Studying the functional traits and functional diversity of fish is a pivotal approach to reveal the mechanism of which the cascade developments has impacted on fish.In this study,We divided Lancang River Basin into 12 reaches according to the planning and development of hydropower stations,and studied spatial and temporal distribution pattern and measured the changes of fish functional traits and functional diversity of different reach before and after the establishment of cascade hydropower,and revealed the influence of cascade development on fishes in the main stream of Lancang River.Furthermore,by studying the Nanla River(built dam)and the Buyuan River(unbuilt dam)in the lower tributaries of the Lancang River,we compared the divergence in fish functional traits and functional diversity between the two rivers,and clarified the impact of tributary cascade development on fish.The main results are as follows:(1)Before the cascade development,the functional composition of the fish assemblage in the Lancang River alter regularly along with the longitudinal gradient: the upper high-altitude reach was dominated by inhabit in demersal(55.0%),non-migratory(80%),position of mouth is superior(95 %)and small and medium-sized fish(average maximum body length 19.66cm),most of which are are elongated(95%),with long caudal peduncles,and mostly feed on invertebrates or algae(50%).In the middle and lower reaches of low-elevation rivers,fish are mainly inhabit in benthopelagic(59%),their body types are normal(35.2%)elongated(61.5%),with large body length(average maximum body length 29.51cm)and diverse feeding and oral positions.While after the cascade development,the upstream(unbuilt dam)is unaffected by invasive species,and all species(including invasive species)and native species have the consistent change.The average body length increased(from 19.66 cm to 22.21mm),the shape of the normal,the sub-inferior fish disappeared,and the proportion of omnivorous fish increased(from 35.5% to 44.2%).In the middle and lower reaches of the dam construction area,the average body length of the native species increased(from 29.51 cm to 34.59mm),the shape of the elongated increased(from 61.5% to 66.7%),and the mobility decreased(non-migratory increased from 68.9 % to 72.8%),and position of mouth is superior vanished.The average body length of all species increased(from 29.51 cm to 35.12mm),and position of mouth is inferior decreased(from 67.2% to 64.1%),subtropical fish increased(from 38.1% to 52.2%).The historical spatial distribution pattern of fish functional characteristics is mainly attributed to the remarkable vertical environmental gradient of lancang river,which is mainly the vertical gradient of altitude and latitude.After the cascade development,the change of water environment and river connectivity led to the change of functional structure of fish in Lancang river.(2)Before the cascade development,the functional ? diversity of fish in lancang river showed a regular change from upstream to downstream: Function richness accumulate;The discrepancy of functional evenness is unconspicuous in the upper reaches,but dropped first and then rises in the middle and lower reaches.The difference of functional dispersion is unapparent in the upper reaches,but decreased first and then increased in the middle and lower reaches.While after the cascade hydropower development,the overall functional richness(historical period: 2.40E-08,current period: 1.84E-05)and functional evenness(historical period: 0.916,current period: 0.929)of the indigenous species are higher than the historical period and functional dispersion(historical period: 0.894,current period: 0.892)is lower than the historical period.After cascade development,the functional ? diversity of native species in the upper reaches is 0.016,mainly determined by the nested part;the middle and lower reaches are 0.120,mainly determined by the nested part;the functional ? of all species in the upper reaches The diversity is 0.000,which is mainly determined by the nested part,and the middle and lower reaches of the river is 0.134,which is mainly determined by the nested part.Comparing the two periods,the functional ? diversity in unbuilt dam areas did not decrease significantly(p = 0.231),while the functional ? diversity of native species and all species in dam built areas increased significantly(p <0.01).The cascade hydropower construction result in the habitats fragmentation,Some peculiar traits and community heterogeneity of unbuilt dams have peter out,leading to a decline in functional ? diversity.However,due to the invasion of exotic species and the loss native species,the composition of the functional traits of the different river sections has changed,increasing the functional ? diversity.(3)Compared with the Nanla River(built dam)and the Buyuan River(unbuilt dam),in terms of functional ? diversity,the functional richness of the upper Nanla River is lower than that of the Buyuan River,the middle and lower reaches is also lower(Buyuan River : 50;Nanla River: 28.5);The functional evenness of the upper Nanla River is higher than that of the Buyuan River,the middle and lower reaches is also higher(Buyuan River: 0.972;Nanla River: 0.977);The functional dispersion of the upper reaches of the upper Nanla River is higher than that of the Buyuan River,and that of the middle and lower reaches is lower than that of the Buyuan River(Buyuan River: 0.543;Nanla River: 0.528).In terms of functional ? diversity,the Nanla River has a higher functional ? diversity(Buyuan River: 0.039,Nanla River: 0.034),mainly determined by the turnover part caused by the two ecological processes of function loss and acquisition.Cascade hydropower leads to the increase of functional richness,functional evenness,functional dispersion and functional diversity of fish species in the dam-building reach of the Lancang river.The comparative study of the tributaries shows that hydropower development has led to an increase in the functional evenness,while the functional richness and dispersion have decreased,while the ? diversity has increased.In this paper,through the study of the functional characteristics and the alpha and beta diversity levels of the functional diversity,we analyzed the response of the fish communities in the main and tributary of the Lancang River Basin to hydropower development and expands the research scope of the fish diversity in the Lancang River.The research results can provide a scientific evidence for the fish management of the Lancang River Basin and formulate fish diversity protection strategies properly,meanwhile it can be an effective basis of evaluating the impact of cascade hydropower development on freshwater ecosystems.