Community Structure Characteristics Of Zoobenthos In Karst Cave Of Songtao County,Guizhou Province And Its Relationship With Environmental Factors

The benthic survey was carried out in the light zones of the 5 karst caves of Shuidong,Xiadong,Qiandong,Lianjiadong and Liangfengdong in Songtao County of Guizhou Province in three water periods（normal-water period,high-water period,low-water period）the study,Redundancy analysis（RDA）was used to study the relationship between benthic community structure and environmental factors,and the health risk assessment model recommended by the US Environmental Protection Agency（US EPA）was used to assess the health risk of water and heavy metals.The aim is to understand the community structure characteristics of cave benthos in the study area,the main environmental factors that affect the community structure of cave benthos,and the health risks of heavy metals in the cave water.It aims to understand the community structure characteristics of cave benthos in the study area and the main environmental factors that affect the community structure of cave benthos and the health risks of heavy metals in the Songtao Karst cave water in Guizhou,for the protection of cave benthic diversity and the development of cave resources Provide scientific basis and theoretical guidance to provide basic data and background information for the material circulation and energy flow of the cave water ecosystem.The main results of the research are as follows:（1）A total of 3218 specimens,93 species or groups were collected from 5 caves in 3 water periods,belonging to 4 phylums,7 classes,16orders,60 orders and 82 families.The main groups are molluscas and aquatic insects.The seasonal variation in the numbers of species is in the order of high-water period（56）>normal-water period（53）>low-water period（51）,respectively.There are 23 dominant species in 5 caves during normal-water period,18dominant species in 5 caves during high-water period and 20 dominant species in 5 caves during low water period.The average density and biomass of benthic animals are 10.5688ind./m² and 1.3112g/m²,respectively.The number of mollusc species in the dominant species of zoobenthos is in the order of high-water period>normal-water period>low-water period,respectively.（2）The highest value of Shannon Wiener diversity index,Margalef richness index,Pielou evenness index and dominance index all appeare in the normal-water period,which are 2.3579,3.9136,0.961 and 1.1294respectively.The single factor analysis shows that low-water period is significant difference with Margalef richness index of zoobenthos in normal-water period and high-water period.（3）Redundancy analysis（RDA）shows that the adaptability of benthic community structure to environmental factors in different seasons is obvious.During the high water period,the number of individual benthic species,the number of species,obviously increases with the increase of air humidity and air temperature.The richness and diversity index are positively correlated with the content of O₂,CO₂ and air humidity in the cave air.Uniformity is positively correlated with dissolved oxygen,water temperature,water pressure,and organic matter content.During the normal-water period,pH,water temperature,turbidity10,turbidity 100,O₂,dissolved oxygen,air temperature are positively correlated with dominance and benthic density,richness,diversity index,uniformity,species number,biomass are obvious It is proportional to chlorophyll a,CO₂ content,flow rate,sediment organic matter content,and total nitrogen.During the low-water period,the flow rate,chlorophyll a,CO₂ concentration,total phosphorus and benthic density,biomass,species number and species are directly proportional.（4）Redundancy analysis（RDA）shows that different types of heavy metal factors obviously affect the structure of different benthic communities.During the high-water period,the number of species and the density of benthic animals were positively correlated with Cd,Pb,Cr and Ni,and negatively correlated with Mn and Cu.In the normal-water period,the number of species,diversity index,richness,number of individuals,evenness,benthic biomass are positively correlated with As and Pb,and the density and dominance of benthic fauna are positively correlated with Zn and Hg.During the low-water period,the number of species,the number of species,and the degree of dominance are positively correlated with As,Ni,Cd,Pb,Cr,Zn.（5）The content of heavy metal caves in the five cave waters in the three water periods is lower than the surface water and groundwater outside the caves,and none of them has exceeded the Class III water standard of the"Groundwater Quality Standard"（GB/T14848-2017）.Spearman correlation analysis shows that heavy metals Cd,Pb,and Zn have significant differences in low-water period,high-water period,and normal-water period,indicating that Zn and Cd,Pb,Ni,As,and Cu may undergo similar environmental geochemistry.（6）Health risk assessment shows that as for the total health risk,the total carcinogenic risk of each cave in normal-water period greater than high-water period and low-water period.Cr and As have the greatest contribution to total risk and the contribution rate is as high as 96%.Cr and As should be taken as the priority management control pollutant.