Aquatic Biodiversity And Ecosystem Health Assessment In The Kaihua Section Of Majinxi River

In order to understand the current status of water ecological environment in the Kaihua section of the Majinxi River.In this study,water environment and aquatic organism surveys were carried out on the Kaijin section of the Majinxi River in 2017 and 2018.The current status of plankton,benthic and fish resources was analyzed,and the benthic integrity index was used to evaluate the health of river ecosystem.The main results are as follows:The results of water environment monitoring in 12 sampling sections showed that the water temperature of the mainstream in the dry season was generally higher than that in the tributary(P<0.05),but the difference of water temperature between the mainstream and the tributary was not significant in the wet season(P>0.05).The difference of p H and dissolved oxygen in both dry and wet season,as well as mainstream and tributary was not obvious(P>0.05).The conductivity indexes of Qixi reservoir,Gaoling and Hetian were significantly lower than those of other sections(P<0.05).A total of 223 speciesof phytoplankton were detected in all sections of the survey,belonging to 8 phylum.Diatoms were the most abundant,93 species were detected,accounting for 41.70% of the total species.The average density of phytoplankton in the dry season of the Majinxi River was 1.351×106 ind./L(0.270~5.565×106ind./L).The average biodiversity index(Shannon-Winner index)of phytoplankton in the Majinxi River basin was 2.70 nat(2.18-2.88 nat)in the wet season.The average density of phytoplankton in the wet season was 0.97 x 106 ind./L(0.13~2.45×106ind./L).The average biodiversity index of phytoplankton was 2.33 nat(1.53-2.88 nat).The results of analysis of similarity(ANOSIM)showed that the phytoplankton community structure had obvious seasonal differences(P<0.05),and the phytoplankton community structure of the mainstream and the tributaries also showed significant differences(P<0.05).A total of 96 species and belonging to 4 types were detected in zooplankton.The rotifers and protozoa were dominant taxa in both wet and dry seasons.There were 41 and 36 species of rotifers and protozoa were found,and account for 42.70% and 37.50% of the total species of zooplankton,respectively.A total of 10 species of cladocera were detected,which account for 10.4 of the total species of zooplankton.Only 9 species of copepoda were found and it was account for 9.40% of the total species of zooplankton.Rotifers and protozoa were the dominant species in both dry and wet season.The average density of zooplankton in the dry season was 307.94 ind/L(82.06-900.18 ind./L).The average biodiversity index of the zooplankton(Shannon-Winner index)in the Majinxi River basin during the dry season was 1.81 nat(1.57-2.18nat).The average density of zooplankton in the wet season was 408.08 ind/L(5.10-3192.80 ind./L).The average biodiversity index of the zooplankton(Shannon-Winner index)in the Majinxi River during the wet season was 1.47 nat(1.00-2.01 nat).The results of ANOSIM showed that there was a significant difference in zooplankton community structure between the mainstream and the tributaries(P<0.05),and between the dry and wet seasons(P<0.05).A total of 54 species,39 genera,11 families,4 order,and 2669 fish specimens and 68563.1g were found in the field catch surveys.There are 40 species of cypriniformes,accounting for 75.50% of the total species.There are 7 species and 6 species of scorpion perciformes and siluriformes,respectively,accounting for 12.96% and 11.1% of the total species.1 species of Synbranchiformes.The cyprinidae was the most abundant of the cypriniformes,a total of 36 species which accountting for 90.00% of the cypriniformes species.4 species from cobitidae,accountting for 10 of the cypriniformes species.The mainstream distributes 37 species of fish,and the tributaries distribute 48 species of fish.The analysis showed that there were significantly difference of fish assemblage structure for seasons(p<0.05)in the Majinxi River and the differences between the mainstream and tributaries(p<0.05).Analysis of the abundance biomass curve(ABC)showed that the miniaturization of fishes in Majinxi River has become more obvious.A total of 51 species from 16 orders and 4 phylum were detected of the benthic animals,including 25 mollusk animal,accounting for 49% of the total species.The average density of benthic animals in the wet season was 100.61 ind./ m2(22.22-181.4ind./m2).The average biomass of benthic animals in the wet season was 28.74g/ m2(1.41-108.2g/ m2).Using the ratio method and based on the benthic integrity index(B-IBI)evaluation system,the assessment of the river health level in the Majin River showed that the health status of the tributaries of the Majinxi(Kaihua section)was generally better than the mainstream.Two out of 12 sample sites in the Majinxi River basin were rated as health level,two were rated as sub-health level,four was rated as a general grade and four was rated as a poor grade.This study identified the basic situation of aquatic organisms in the Kaihua section of Majinxi River,and evaluated the river health level through the benthic integrity index.On the one hand,this study provides basic data on the aquatic organisms of the Majinxi River,and on the other hand it can provide basic information for the protection of aquatic resources in Majinxi River.