The Effects Of Ecotechnological Engineering On Improving Water Quality And The Dynamical Characteristics Of Phytoplankton In Dajingshan Reservoir

Reservoirs are man-made water bodies in which hydrodynamics are strongly regulated by humans.Dajingshan Reservoir,located in the southern subtropics of China,is of great importance for supplying drinking water to Zhuhai city and Macao,but its water quality is worsening,while its trophic state index increases,threatening the supply of safe drinking water.Improving water quality and controlling algal blooms in reservoirs are now of great importance in China.In this thesis,we analyze the response of phytoplankton and physical-chemical indexes to water quality engineering by ecotechnological techniques,as well as to the ecological characteristics of the phytoplankton community.We attempt to gain insight into the factors influencing phytoplankton composition and seasonality in a southern subtropical region of China,to serve as a useful baseline for the management of other reservoirs in this region.The dynamics of water quality show that water quality is better in summer than in winter and spring.The phytoplankton community is dominated by Cyanophyta.Phytoplankton abundance and biomass are high,typical of a mesotrophic to eutrophic state.Pumped-water from a nearby river and precipitation affect water quality directly.By applying ecotechnological engineering,the concentrations of total nitrogen,total phosphate,orthophosphate,nitrate nitrogen,nitrite nitrogen, ammonia nitrogen,and chlorophyll a decreased while Secchi disk depth increased.The phytoplankton community structure changed:abundance and biomass decreased.Generally speaking,the trend of eutrophication was efficiently controlled and water quality improved.Comparing the ecotechnological engineering of two regions,A to B,we found that the effects were better in region B than in region A.In region B,comparing the years 2007 to 2006,the concentrations of total nitrogen,ammonia and total phosphate decreased with 8%,70%,30%, respectively.The concentration of chlorophyll a decreased by 30%to 40%.Phytoplankton abundance and biomass decreased 20%to 180%,20%to 50%,respectively.The trophic state index decreased by 5%,secchi disk depth increased by 50%.At the boundary of the ecotechnological engineering,water quality was enhanced and improved.Total nitrogen here was the lowest of the three samplings(boundary of the ecotechnological engineering,middle-let and inlet).Comparing years 2007 to 2006,the concentration of total phosphate,chlorophyll a,phytoplankton abundance and trophic state index decreased by 10%,35%,30%and 9%,respectively,while Secchi disk depth increased by 40%.In all,116 taxa of phytoplankton were identified from 580 samples.Cyanophyta,Chlorophyta and Bacillariophyta were the most important groups by number of species.Pseudanabaena limnetica was the dominant species in years 2005 and 2006,but in year 2007,Cyanophyta, Chlorophyta and Bacillariophyta periodically became the dominant algae.Phytoplankton abundance ranged from 1.24×10⁶ to 106.17×10⁶ cells L^-1.Abundance changes in individual phytoplankton taxa varied widely.Total biomass varied from 0.87 to 16.8 mg L^-1.Abundance and biomass showed seasonal patterns of change,with two peaks.From March to May,the peak was highest,followed by a peak in November to December,but in July to September,a minimum was reached.Margalef's Index changed from 0.99 to 3.42.It had a strong connection with number of species,abundance of Cyanophyta,total phytoplankton abundance,nitrate nitrogen,precipitation and total phosphorus.Evenness and Shannon-Weaver Index of diversity were from 0.03 to 0.72, 0.09 to 2.54,respectively.They confirmed that water quality was worse in 2006 than in 2007,and the trend of eutrophication had been controlled in 2007.Theβdiversity index changed from 0 to 1.88,and it reflected that the composition of Cyanophyta was single,the number of species changed little and pelagic water bodies were relatively stabilization.In 2007,the moreβdiversity index changed,the more obvious was discrepancy of environmental grades was.The number of Chlorophyta and Bacillariophyta increased,a major change in the phytoplankton community structure and composition.The phytoplankton showed a steady-state phase in summer each year.The functional groups S₁ and L₀ were dominant.Pseudanabaena limnetica and Peridinim sp.were in steady-state from June to August in 2005,Pseudanabaena limnetica,Peridinim sp.and Limnothriox redekei were in steady-state from August to October in 2006,Peridinim sp.,Lyngbya sp.and Limnthriox redekei were at steady-state from July to September 2007.The steady-state reflected the changes in the water environment,a moderate disturbance of water level was the main cause.Canonical correspondence analysis(CCA) was used to investigate the environment-phytoplankton relationship.Ordination by CCA divided all samples into four groups, distributed in the four districts forming axis 1 and axis 2,corresponding to the seasons:winter, spring,summer and autumn.Most samples were located in the districts of summer and autumn,and 54 main species were selected for performing of a CCA.The Cyanophyta,Bacillariophyta and Euglenophyta were restricted to the districts at the left of axis 1,while most of the Chlorophyta, Chrysophyta,and Cryptophyta were to the right of axis 1.Canonical correspondence analysis revealed that temperature,precipitation and water-level were most important for species composition and phytoplankton dynamics.Chlorophyll-a is a well-accepted index of phytoplankton abundance and population density of primary producers in an aquatic environment.The relationship between Chlorophyll-a and 11 chemical,physical and biological water quality variables was studied by using principal component scores(PCs) in stepwise linear regression analysis(SLR) to predict Chlorophyll-a and phytoplankton abundance levels.Principal component analysis was used to simplify the complexity of the relationships between water quality variables.Score values obtained by PC scores were used as independent variables in multiple linear regression models.The following models were used to predict Chlorophyll-a,abundance of Cyanophyta,Chlorophyta,Bacillariophyta and Pyrrophyta, respectively:Chlorophyll-a=31.230-4.977(score 2),log₁₀(Cyanophyta)=7.247-0.147(score 1),log₁₀(Chlorophyta)=5.270-0.302(score 2),log₁₀(Bacillariophyta)=5.555-0.501(score 2), log₁₀(Pyrrophyta)=4.109-0.468(score 3).Models could be used to predict Chlorophyll-a and phytoplankton abundance levels successfully.These models revealed that temperature,pH value, precipitation and nitrogen were the most important factors regulating the composition and dynamics of Cyanophyta;Secchi disk depth,water-level and total phosphate were the most important factors regulating the composition and dynamics of Bacillariophyta,Chlorophyta and Chlorophyll-a. Orthophosphate was the main factor affecting the Pyrrophyta.