Influence Of Cascade Damming On Plankton Community Structure And Water Quality

Phytoplankton is an important part of river ecosystem.They can indicate the ecological status of rivers,reservoirs and lakes,and have important guiding significance for protecting water environment.The South Pan River Basin is rich in hydropower resources and has a cascade dam group,but the construction of cascade dams has a certain impact on the aquatic ecosystem.In order to explore the influence of cascade damming on plankton community and water quality in South Pan River Basin,six samplings were carried out in South Pan River in Guizhou Province from October 2020 to July 2022,which were divided into dry season,normal season,wet season.A total of 22 sampling sites were set up.108 samples of physical and chemical indicators,phytoplankton and metazooplankton were collected respectively.The main results are as follows:1.The physical and chemical factors of the water body in the South Pan River Basin are affected by dam interception and season,showing certain spatial and temporal differences.In terms of time,TN,NO₂^-,TP,PO₄^3-,COD_Mn,Chl.a,pH and ORP showed significant differences between the three hydrological periods（P<0.05）.Spatially,NH₄⁺,NO₂^-,TP,PO₄^3-,ORP showed significant differences between reservoirs and rivers（P<0.05）.The water environment of the reservoir is more stable than that of the river,and the environmental factors are more closely related.2.Phytoplankton are affected by nutrient distribution and hydrological characteristics,and show different response relationships in different habitats.A total of 87 species（genus）of metazooplankton,61species（genus）of rotifers,9 species（genus）of copepods and 17 species（genus）of cladocerans were identified in the South Pan River.74 species（genus）of metazooplankton were identified in the river ecosystem,and62 species（genus）of metazooplankton were identified in the reservoir ecosystem.The density and biomass of metazooplankton both show that the reservoir is larger than the river.The density was the highest in the wet periods(266.88 ind·L^-1)and the lowest in the dry periods(22.32ind·L^-1).The biomass was also the highest in the wet periods(0.4165mg·L^-1)and the lowest in the dry periods(0.0640 mg·L^-1).A total of 84species（genus）of 7 phyla were identified,including 13 species of Cyanophyta,36 species of Chlorophyta,21 species of Bacillariophyta,6species of Dinophyta,3 species of Euglenophyta,2 species of Chrysophyta and 3 species of Cryptophyta.75 species of phytoplankton were detected in the river ecosystem,and 74 species of phytoplankton were detected in the reservoir ecosystem.The density and biomass shows that the reservoir is larger than the river.The phytoplankton density（1.50×10⁶cells/L）and biomass(2198.73μg·L^-1)were the highest in the wet periods,and the density（5.3×10⁵cells/L）and biomass(377.99μg·L^-1)were the lowest in the dry periods.3.The dominant species and niche characteristics of plankton were different in different hydrological periods.A total of 7 dominant species of metazooplankton were identified in the South Pan River.Keratella cochlearis,Nauplius and Mesocyclops leuckarti were the dominant species in the three hydrological periods.As the indicator species of eutrophic water.There were 10 dominant species of phytoplankton.Cyclotella sp.and Crytomonas sp.were dominant species in the three hydrological periods.In the wet periods,the dominant species of plankton were the most and dominated by narrow niche populations（84.62%）,and the niche overlap value is larger,the plankton community structure was more complex in the wet periods,and the competition among dominant species was fierce.In the dry periods,the dominant species were less,mainly in the middle niche population（44.44%）,the niche breadth was higher,and the niche overlap value was lower,the plankton community structure was relatively simple in the dry periods.4.The cascade dams makes the dominant species and niche patterns of plankton in rivers and reservoirs different.The dominant species of phytoplankton and metazooplankton in the reservoir were more than those in the river.The phytoplankton dominance of the reservoir was high（Y=0.12）,indicate that the community structure of phytoplankton in the reservoi was complex and stable,the river water flow rate was fast,the phytoplankton community was not stable enough,and the dominance was low（Y=0.09）.The water environment of the reservoir is more stable than that of the river,the dominant species are transferred to a wider area,and the niche width of the dominant species of the reservoir（Bi=0.178）is greater than that of the river（Bi=0.088）.The niche overlap value of dominant species in rivers（Oik=0.692）was greater than that in reservoirs（Oik=0.375）,and the interspecific competition of dominant species in rivers was stronger than that in reservoirs.Metazooplankton is more sensitive to the influence of cascade damming than phytoplankton.