Study On The Difference Of Water Quality And Phytoplankton In Water Source Reservoirs In North And South China

Reservoir is one of the important water sources,the problem of eutrophication and water quality of reservoir has become increasingly prominent.In order to solve the problem of reservoir pollution in different regions,This article takes Xi’an Jinpen Reservoir（April 2019 to February in 2020）and Shenzhen Xikeng Reservoir（May to December in 2020）as examples.Through in-situ and laboratory monitoring in the two reservoirs,the seasonal changes of thermal stratification and phytoplankton,water quality response in the two reservoirs were systematically studied.Finally,the operation of lifting aeration was taken as the breakthrough point to analyze inhibition effect on algae in Jinpen Reservoir.The main research results were as follows:（1）The thermal stratification of Jinpen reservoir and Xikeng reservoir showed obvious seasonal variation.The seasonal variation of Jinpen Reservoir was mainly affected by air temperature,and the thermal stratification formation period（April to June in 2019）,thermal stratification stabilization period（July to September in 2019）,artificial forced mixing period（October in 2019）and natural mixing period（November in 2019 to March in 2020）.The seasonal variation of thermal stratification in Xikeng Reservoir was affected by air temperature and water transfer,and the thermal stratification was weaker than that in Jinpen Reservoir.The seasonal variation was as follows:thermal stratification period（May to September in 2020）and mixing period（October to December in 2020）.（2）Under the influence of thermal stratification,the distribution of dissolved oxygen,chlorophyll a and pH showed seasonal variations in Jinpen Reservoir and Xikeng Reservoir.In the thermal stratification period of Jinpen reservoir,there appeared obvious anaerobic zone in the bottom layer.Due to the growth of algae,chlorophyll a and pH in the surface reached the peak in August to September.However,due to the water depth and water diversion in Xikeng Reservoir,the anaerobic area was small and the range of variation was large.The growth of surface algae led to the peak value of chlorophyll a and pH in June and July,which was earlier than that in Jinpen reservoir.After mixing,the vertical distribution of dissolved oxygen,chlorophyll a and pH in the two reservoirs was basically the same in the two reservoirs.（3）The nutrient concentrations were both affected by endogenous and exogenous sources in Jinpen and Xikeng reservoirs.The exogenous pollution of the golden basin mainly came from the pollution brought by the upstream runoff.For the endogenous pollution,the nutrients were constantly released into the overlying water under the anaerobic environment in the bottom water during the thermal stratification period.The exogenous pollution source of Xikeng Reservoir was mainly from the diversion of Dongjiang River.During the flood season,the concentration of various pollutants increased correspondently,leading to the corresponding increased of nutrient concentration into the reservoir.For endogenous pollution,similar to the Jinpen reservoir,the formation of the bottom anaerobic zone continuously accelerated the release of nutrients from sediments during the thermal stratification period.After water mixing,the nutrient concentration of the two reservoirs decreased to a stable level.（4）A total of 92 species,59 genera and 8 phyla of planktonic algae were found during the survey in Jinpen Reservoir.The abundance and population of planktonic algae showed seasonal variations.The dominant population distribution was mainly Cyanophyta and Chlorophyta in the thermal stratification period in spring and summer,and the dominant population distribution was mainly Chlorophyta and Bacillariophyta in the mixed period in autumn and winter.A total of 149 species,75 genera and 8 phyla of planktonic algae were found during the survey in Xikeng Reservoir,compared to Jinpen reservoir has higher species diversity.During the thermal stratification period,the disturbance of water body caused by water diversion and the influx of nutrients made Bacillariophyta easily burst.During the mixing period,the density of algae decreased,and Chlorophyta and Bacillariophyta became the dominant algae species.（3）The phytoplankton monitored by the Jinpen Reservoir belonged to 15functional groups,of which 10 were dominant functional groups.The seasonal change were as follows:B+X₁+X₃in April→B+X₁+F+J+M in May→B+X₂+X₁+F+M in June→B+X₁+E+M in July→X₁+M in August→B+P+M_P+X₁in September→B+P+X₁+M from October to February next year.The phytoplankton detected in Xikeng reservoir belonged to 20 functional groups,of which there were 10 dominant functional groups.The weak thermal stratification ecological environment in Xikeng Reservoir led to the difference of functional group succession from that in Jinpen Reservoir Their seasonal distribution characteristics were as follows:B+N+X₁+G+J+K in May→B+N+X₁+G+J in June→B+N+M_P+X₁+J+M in July→B+N+X₁+J+M in August→B+D+N+X₁+J+M in September→B+D+N+P+M_P+X₁+J from October to December.（4）During the thermal stratification period of the Jinpen Reservoir,the operation of lifting water aeration reduced the temperature difference between the surface and the bottom of the water body,weakened the thermal stratification,and the mixed aeration made the dissolved oxygen concentration in the bottom layer increase continuously,and destroyed the original anaerobic state of the bottom layer during the thermal stratification period.At the same time,the density of algae was reduced to below 5 million/L,which inhibited the growth of Cyanobacteria and Chlorophyta.During the extinction period of thermal stratification,the opening of water lifting aeration completely destroyed the thermal stratification of water body,accelerated the transition from thermal stratification period to mixing period,the dissolved oxygen was saturated,and the algae density remained at a low level.