Community Structure Of Cave Benthos And Its Relationship With Environmental Factors In Niuchang Township,Liuzhi County,Guizhou Province

Karst cave is a special underground ecosystem,which is considered as the"extreme bottom of the ground biodiversity"gathering place,and has a high scientific research value.Benthos is an important part of cave aquatic ecosystem.The study on the community structure of zoobenthos plays an important role in understanding the ecological process of cave aquatic ecosystem.In this study,the zoobenthos in five typical karst caves,including Longjing Dayan Cave,Chuan Cave,Yingjiayan big Cave,Yangjiaxia Cave and Lanba Dayan Cave in Niuchang Township of Liuzhi,were investigated and sampled in August 2019(summer)and January 2020(winter),the distribution of species number,standing stock,dominant species and biodiversity of zoobenthos were analyzed.The relationship between zoobenthos structure and environmental factors was discussed by Pearson correlation analysis and Multivariate analysis(CCA,RDA),the water quality of 5 karst caves was evaluated by Single factor evaluation and Benthic biological index.The main results are as follows:(1)A total of 98 species of benthos were collected in summer and winter,belonging to 4 phyla,7 classes,13 orders and 57 families.Among them,75 species belong to Arthropoda,accounting for 76.53%;20species belong to Mollusca,accounting for 20.41%;2 species belong to Annelida,accounting for 2.04%;1 species belongs to platyhelma,accounting for 1.02%.The single factor variance showed that there was no significant difference in the number of benthos species between the caves in summer and winter(summer:F=0.297,P=0.872;winter:F=0.837,P=0.535),and there was no significant difference in the number of benthos species among the light bands(F=1.833;P=0.206).The number of individuals in summer(2730)was higher than that in winter(1316).(2)The dominant species of cave Zoobenthos vary according to season,8 dominant species in summer,3dominant species in winter,Ephemera sp.and Perlidae were dominant species in summer and winter;The distribution of dominant species of Zoobenthos varies from cave to cave,in all caves,Hydropsyche sp.and Baetis sp.were dominant species in 60%of caves.(3)The total density and biomass of cave Zoobenthos in summer and winter were 6.9883 ind·m^-2 and 0.1810 g·m^-2.,respectively,the density and biomass of each group of Zoobenthos were arthropods>mollusks>flat animals>annelids.The density of Zoobenthos in each cave is also shown as arthropods>mollusks>flat animals>link animals.(4)The diversity characteristics of Zoobenthos Community in the same cave in summer and winter are different.Among them,the diversity index(H')of Longjing Dayan Cave,evenness index(J)and richness index(D)of yangjiaxia Cave are higher in winter than in summer,while the diversity index(H'),richness index(D)and evenness index(J)of other caves are higher in summer than in winter.Among them,the average diversity index(H'),average richness index(D)and average evenness index(J)of Lanba Cave are the highest,the average diversity index(H')and average richness index(D)of Yingjiayan Cave are the lowest,and the lowest average evenness index(J)appears in Yangjiaxia Cave.(5)Pearson correlation analysis showed that the main environmental factors affecting the diversity of benthos community in different seasons were different,p H and Do in summer,Do,TN,SOM and Chl-a in winter,Do,NH₃-N,TN,SOM,som-a in summer and winter,and DO,NH₃-N,TN,SOM,WT in summer and winter WT and Chl-a.Based on the multivariate analysis of different benthos species and environmental factors,it is found that the main environmental factors affecting the distribution of cave benthos species in different seasons are different,including TN in summer,COD_Mnand SOM in winter;Chl-a and COD_Mn in summer and winter.(6)Based on the physical and chemical indexes and biological indexes of the karst caves,the water quality evaluation of karst caves shows that the water quality of karst caves in Niuchang Township of Liuzhi is in good condition in summer and winter.Except for the TN being class II water,other projects meet the class I water quality standards,and the water quality is in good condition;the results of diversity index(H?),richness index(D)and evenness index(J)showed that the cave water was clean,clean and slightly polluted respectively;the results of FBI index showed that the cave water was clean;the carlander biomass index showed that the nutrient water of cave water was in an average oligotrophic state.The water quality of karst caves in Niuchang Township of Liuzhi is generally in good condition.