Study On The Spatia-Temporal Changes Of Water Quality And Ecology Of Drinking-Water Reservoirs In Guangdong Province

Liuxihe Reservoir in Guangzhou City,Gaozhou Reservoir in Maoming City and Hedi Reservoir in Zhanjiang City are three important reserve-water and drinking-water reservoirs in Guangdong Province.With the rapid development of the economy and the increasing pollution load in the basin,the water qualities of the reservoirs has been declined in recent years.The cyanobacteria blooms in the Gaozhou Reservoir and the Hedi Reservoir have threatened the safety of water supply.In this study,three water source reservoirs in Guangdong Province were selected,and the water quality of the three water source reservoirs and the temporal and spatial changes of phytoplankton water ecology in 2017 were investigated,Furthermore,the environmental factors affecting the distribution of phytoplankton community were analyzed.The water quality and water ecology of the reservoir were evaluated using the Carlson Integrated Nutritional Status Index and the Shannon-Wiener Diversity Index.Multivariate statistical analysis was used to identify the key environmental factors affecting algal blooms in each reservoir,and preliminary measures were proposed for the risks faced by the reservoirs,which provided a basis for water environmental protection and water bloom prevention.The main findings are as follows:(1)The annual average concentrations of total nitrogen and total phosphorus in the Liuxihe Reservoir were 1.20 and 0.03 mg/L,The comprehensive nutrient status index of the reservoir varies from 27.45 to 54.11.Except for the rivers in the early stage of the flood season,they are all below the medium nutrient state,and the water quality is relatively good.In the temporal and spatial distribution,the seasonal variation of total nitrogen total phosphorus in the Liuxihe Reservoir is characterized by the initial period of the wet season>dry season>flat water period>abundant water period,and the spatial variation is characterized by higher concentration in the inflow river basin and lower transition zone and reservoir area.The phytoplankton of the Liuxihe Reservoir is green algae--diatom--cyanobacteria in the species composition.However,with the change of time,the species of phytoplankton in the reservoir changes,and the species in the wet season are relatively more.The total density of phytoplankton cells in the reservoir The range of variation is 0.26×10~6 cells/L~1.52×10~7 cells/L.In terms of time,the total density of phytoplankton cells in Liuxihe Reservoir is9.93×10~6 cells/L,followed by 1.53×10~6 cells/L in the flat water period,0.96×10~6cells/L in the early wet season,and the lowest in the dry season is 0.75×10~6cells/L,the spatial variation is that the density of phytoplankton cells in the Lvtian River and Yuxi River is higher than that in the reservoir area,and the reservoir may have diatom and cyanobacteria blooms.(2)The annual average concentrations of total nitrogen and total phosphorus in the Gaozhou Reservoir were 0.58 and 0.03 mg/L,respectively.The comprehensive nutritional status index of the reservoir ranged from 30.50 to 44.53,both in the middle nutrient state,and the water quality was relatively good.In the time and space changes,the Gaozhou Reservoir The seasonal variation of total nitrogen and total phosphorus was higher in the wet season and the lowest in the dry season.The spatial variation was better in the Liangde reservoir than in the Shigu reservoir area.The phytoplankton in the Gaozhou reservoir was green algae--diatom--cyanobacteria in the species composition.The number of plant species was higher during the high water period,mainly due to the increase in the number of cyanobacteria species.The total density of phytoplankton cells in Gaozhou Reservoir was 3.28×10~6 cells/L~1.63×10~7 cells/L.In terms of time,the total density of phytoplankton cells in Gaozhou Reservoir was 8.36×10~7 cells/L,followed by 7.90×10~7 cells/L in the flat water period,5.20×10~7 cells/L in the early wet season,and 4.94×10~7 cells in the dry season.L,the spatial change is the density of algae cells in the Liangde reservoir area is lower than that in the Shigu reservoir area,and the reservoir may have cyanobacterial blooms.(3)The annual average concentrations of total nitrogen and total phosphorus in Hedi Reservoir were 1.87 and 0.09 mg/L,respectively.The concentration of nitrogen and phosphorus in Hedi Reservoir was the highest among the other three reservoirs.The comprehensive nutrient status index of the reservoir ranged from 35.80 to 60.71,which was a medium nutrient state.Above,the water quality is poor.In terms of temporal and spatial variation,the seasonal variation of total nitrogen in total phosphorus in Hedi Reservoir was in the dry season>flat water period>early wet season>high water period,and the spatial variation showed the highest concentration of stone angle in the inflow river.The green algae in Hedi Reservoir is in an absolute advantage in the species and quantity of phytoplankton.The total density of phytoplankton cells in Hedi Reservoir ranges from 3.11×10~6 cells/L~3.37×10~8cells/L.In terms of time,the total density of phytoplankton cells in Hedi Reservoir was 2.08×10~8 cells/L in the high water period,followed by 1.58×10~8 cells/L in the flat water period,6.4×10~7 cells/L in the early dry season,and the lowest in the dry season was 4.80×10~7 cells/L;spatial change is the density of algal cells in the reservoir area is higher than that of the inflow river,and the reservoir may have cyanobacterial blooms.(4)SPSS correlation analysis showed that the nitrogen and phosphorus in the Liuxihe Reservoir have a great influence on the growth and reproduction of phytoplankton.However,the effects of pH,DO,T and SD on the growth of the Gaozhou Reservoir and Hedi Reservoir are more prominent due to the sufficient nitrogen and phosphorus in the water,It can be seen that the genesis of cyanobacterial blooms in Gaozhou Reservoir and Hedi Reservoir is complicated.