Study The Dynamic Distribution Characteristics Of Plankton Community Structure And Water Quality In Upper And Lower Reaches Of Changsha Complex Hub Of Xiangjiang River

The Changsha Complex Hub of Xiangjiang River has changed the Xiangjiang River from a seasonal river to a reservoir,changing the original pattern of water environment,thus affecting the structure and di-stribution of aquatic communities.For understand the character-istics of plankton communities and water environments after major projects,from January to November 2018,an ecological survey was conducted on the 6 monitoring points upstream and downstream of the Xiangjiang Changsha Integrated Hub.In order to discuss the impact of"dam"on aquatic community,and to provides theoretical basis for monitoring and harnessing water environment in river basins,the physical and chemical properties of the water body and the characteristics of the plankton community was evaluated comprehensively.The main results are as follows:?1?The annual water temperature is 10²9.50°C,which is a weakly alkaline water body.Among the measured parameters,petroleum,Vol-P,Hg,Pb,Cu,Zn,Fluoride,Se,Cd and SAA are all reach Category I.The parameters decreased significantly and the water quality improved.TP,COD and NH₃-N are the main pollution indicators affecting the water quality of the basin,and there are accumulation phenomena in the lower reaches of tributaries and junctions.?2?A total of 196 species?including varieties and variants?belonging to 69 genera and 7 phyla were detected in planktonic algae.The species composition is the largest in diatoms,followed by green algae,and there is a tendency for diatomic-green algae to evolve into green algae from the upstream to the downstream of the hub.There are73 genera and 123 species of zooplankton,with rotifers the most,protozoa the second,and species composition tending to be miniaturized.Compared with previous studies,the number of species of phytoplankton and zooplankton increased,and the community structure changed.?3?The abundance of phytoplankton algae is between 9900 and688,500 ind./L,and the biomass is between 0.09 and 4.75 mg/L.The main contributors to the current stock of phytoplankton algae are diatoms and green algae Gates.The distribution is seasonal,and the upstream of the hub reflects the stock lower than the downstream.The abundance of zooplankton is between 42 and 651ind./L,and the biomass is between 0.16 and 13.41 mg/L.The main contributors to the abundance and biomass of zooplankton are protozoa and rotifers,branchlets and copepods,respectively.The distribution of existing stocks is seasonal,the upstream abundance of the hub is higher than the downstream,and the downstream biomass is lower than the downstream.The dominant species have seasonal succession characteristics,and the various points are basically the same.Compared with the previous studies,the current stocks of plankton in the basin have increased,and the main contributors to the existing stocks are basically the same as those of previous studies.?4?The phytoplankton Shannon-Wiener diversity index?H?is between 1.87 and 3.47,the Margalef richness index?D?is between 1.13and 4.62,and the Pielou uniformity index?J?is between 0.23 and 0.65.?-diversity was higher in summer and autumn than in spring and winter,and higher in the upstream than in the downstream of the hub.The Shannon-Wiener diversity index?H?of zooplankton is between 1.89 and3.63,the Margalef richness index?D?is between 1.22 and 5.35,and the Pielou evenness index?J?is between 0.45 and 0.68.The H and D diversity indices show that spring and summer are higher than autumn and winter.The J value is overall stable,and the upstream diversity of the hub is higher than the downstream.?5?Comprehensive analysis showed that the rising of water level of Xiangjiang River makes pollutants be fully settled and diluted.Pollutants influx from upstream and tributaries of the hub is an important cause of pollution downstream of the hub.The results of biological evaluation and physical and chemical evaluation are basically the same:the water quality is slightly to moderately polluted,which is between class III and V.The water quality of the sample points near the tributaries into the estuary is worse,and the water quality of the downstream of the hub is inferior to that of the upstream.