Relationship Between Fish Community And Environmental Factors And Biotic Integrity Evaluation In The Lower Reaches Of Jialing River

In recent years,the assessment method to river health base on biotic integrity index of fish(F-IBI)have been promoted and perfected,some scholars put forward,except the biotic integrity of fish,should also focus on the relationship between fish community and environmental factors.This study investigated fish community and water quality of the lower reaches of the Jialing River,in August 2015 to July 2016.The relationship between the fish community at each site and environmental factors was analyzed by canonical correspondence analysis(CCA).Biotic integrity index of fish(F-IBI)evaluation system was established,based on the initial selection,distributing range,discriminatory power and Pearson's correlation analysis.Main results were obtained as follows:(1)According to statistics,8848 fish were collected in the survey,and the results showed that there were 62 fish species(did not include exotic species)belonging to 5 orders and 9 families found in the investigating region.Percent of Cyprinidae species ranked first place,and far more than other families,accounting for 60.32% of the total number of categories.According to the catches and economic value,main economic fish of the lower reaches of the Jialing River include Cyprinus carpio,Pelteobagrus nitidus,Mystus macropterus,Culter alburnus,Rhinogobio typus,Carassius auratus and Pelteobagrus vachelli et al.Middle-lower and bottom fish was the main species in the lower reaches of the dam,species was relatively rich,number of species was evenly distributed,and the fish community structure more stable.On the contrary,the main species was upper-middle and bottom fish in the reservoir area,with single species and simple community structure.According to Shannon-winner index,Pielou index and Margalef index,the differences of the fish community diversity in the up and down of dam had appeared.(2)The main physical and chemical factors include DO,CODMn and NH4+-N were identified by principal component analysis in the lower reaches of the Jialing River.The main hydrological landscape factors include flow velocity and the width of the river was identified by the same method.Canonical correspondence analysis showed that CODMn,NH4+-N,flow velocity and DO were the main environmental factors.According to the CCA biplot of environmental factors and sampling sites in the lower reaches of Jialing River,fish communities were significantly different between Shui Tu,Ci Qikou and Jin Zi,Yan Jing because of the dam separating.The dam cut the lower reaches of the Jialing River into two parts,and changed the physical and chemical factors and hydrological situation,especially the nutrient salts and flow velocity.According to the results of the study,it can be concluded that dam construction was the main reason for the change of ecological environment in the lower reaches of the Jialing River,and it was also the main factor affecting the fish community diversity.(3)And based on the initial selection,distributing range,discriminatory power and Pearson's correlation analysis of the 38 candidate indexes,seven metrics,including Shannon-Wiener index,number of Cypriniformes species,number of Siluriformes species,percent of middle-lower fish species,percent of intolerant species,percent of omnivorous individuals,percent of drift eggs spawning individuals were selected to establish biotic integrity index of fish(F-IBI)evaluation system.The traditional step method and ration scoring method were used separately to calculate the value of each metric and IBI,and the results showed that Jin Zi in the state of health,Shui Tu and Ci Qikou in the health to sub-health transitional phase,He Chuan in the state of sub-health,Yan Jing in the state of good-fair.In general,the fish-based biotic integrity index was the best in Jin Zi,by the smallest human disturbance;however,Yan Jing was the worst,by the largest human disturbance.