Zooplankton In The Wuding River Basin:Community Structure Characteristics And Assessment Of Water Ecological Health

The main stream of Wuding River is a first-order tributary of the Yellow River,located in the ecologically fragile northwest of China.Due to its unique geographical location and climate conditions,coupled with the rapid development of industry and agriculture,the river basin faces ecological environmental problems such as soil erosion,land desertification,and reduced water quantity.In order to explore the current water ecology status of the Wuding River basin,a systematic water ecology investigation was conducted on the typical main and tributary streams and impoundments during the spring and autumn seasons of 2021.A total of 40 sampling sections were set up in the Wuding River basin,and the main conclusions are as follows:1.During the study,a total of 125 species of zooplankton were identified in the Wuding River Basin,including 40 species of protozoa,54 species of rotifers,15 species of cladocerans,and 16 species of copepods,with small,zooplankton being predominant.Among them,31 species were dominant,with nutrient-rich water indicators such as armoured tail spines and turtle carapace rotifer being the majority.Additionally,the dominance of spring species was higher than that of autumn species.The average density(360.9 individuals/L)and biomass(0.600 mg/L)of zooplankton were higher in spring than in autumn(83.6 individuals/L,0.298 mg/L).NMDS analysis indicated differences in the distribution of zooplankton communities between river and sedimentation pond water.RDA was used to further explore the main differences between the two types of water.It was found that different driving factors operated in the distribution of zooplankton communities in river and sedimentation pond water,including chemical indicators(dissolved oxygen,salinity,nitrite nitrogen,nitrate nitrogen,dissolved phosphorus,and chlorophyll a)and physical indicators(water depth,transparency,and turbidity).The result of water quality biological evaluation showed that the water quality was the best in the dry Wuding River in both seasons,followed by the tributary.The water quality was the worst in the sedimentation pond water,and the water quality of the downstream section of the dry Wuding River was better than that of the upstream section.2.Based on the data of zooplankton and water quality from 40 sampling sites in the Wuding River basin,and using zooplankton as an indicator organism,reference points and damaged points were determined for each season(13 reference points for spring,and 12 reference points for autumn),and core candidate biological indicators were screened out for each season.Then,the Z-IBI evaluation system for the Wuding River basin was established.The biological index values were calculated using three methods(tri-class method,quadripartite method,and ratio method)to obtain the Z-IBI index value for the Wuding River basin.Discriminant ability analysis and correlation analysis between diversity and Z-IBI value were used to select the tri-class method as the method for evaluating river health.The evaluation results showed that among the 40 sampling sites in the Wuding River basin,15 were in a healthy state,10 were in a sub-healthy state,4 were in a general state,and 1 was in a poor state in spring,while in autumn,32 were in a healthy state,5 were in a sub-healthy state,and 3 were in a general state.Overall,the health status of the river was better in autumn than in spring.3.Using zooplankton as the zoning object,principal component analysis(PCA)was conducted with the help of the physically-chemical parameters of the water in the Wuding River basin.This helped to identify the differences in the environmental factors of the region.Subsequently,aquatic ecological functional zones were established by combining the data of the planktonic community,the biological integrity index,and the aquatic habitat.The results revealed three aquatic ecological functional zones in the Wuding River basin.Zone A corresponds to the protection and industrial water district of the water function zoning,and includes the upper reaches of the Wuding River,Yuxi River,and Dali River source area.Zone B corresponds to the drinking water source area and protection area of the water function zoning,and includes the middle and upper reaches of the Wuding River and Lu River.Zone C corresponds to the reserve and buffer areas of the water function zoning,and includes the lower reaches of the Wuding River,Mahuyu River,the middle and lower reaches of the Dali River,and Huaining River.