Study On The Change Structure Of Phytoplankton Community And Water Quality Evaluation In Danjangkou Reservoir

Danjiangkou Reservoir is the water source of Central Line Project of South-to-North Water Diversion,covering Hubei province and Xichuan county in Henan province.Danjiangkou reservoir not only the water conservation district but also the largest artificial lake in Asian.At present the reservoir water quality is well,but because of the existence of all kinds of pollution will cause hidden danger security,and it solved the problems of many cities in the domestic water and both ecological environment and agricultural water,so the reservoir water quality have the direct bearing on the success of South-to-North Water Diversion.The paper was under monitoring the plankton and physical and chemical indicator in Danjiangkou Reservoir from July 2013 to July 2015.We study on the biomass index and diversity indexes from January 2014 to analyze and discuss the plankton communities of Danjiangkou Reservoir primarily and the impact of top-down effect on plankton communities,This paper offers the detail list of plankton in Danjiangkou Reservoir,biology proof to comprehensive assessment the water quality.1. There are 609 species of phytoplankton in Danjiangkou Reservoir during July 2013 from July 2015,which belong to 173 genera of 10 phyla.Of all species there are 13.91% in Cyanophyta,35.80% in Chlorophyta,37.39% in Bacillariophyta,5.65% in Euglenophyta,3.19% in Dinophyta,The species number of Charophyta,Rhodophyta and Xanthophyta is less.Phytoplankton species number has obvious change with seasons,more in sunmmer,less in winter.The samples contained 117 species(varieties),58 genus,8 doors of saprobic indicate plankton.Of all species there are 12.82% in Cyanophyta,57.27% in Chlorophyta,13.68% in Bacillariophyta,5.13% in Euglenophyta,1.71% in Dinophyta,only one specie in Rhodophyta. with 32.48% of β- mesotrophication and 39.32% of α-β-oligosaprobic nutrient,.In general evaluation Danjiangkou Reservoir belongs to α-β-oligosaprobic nutrient.2. There are 151 species of Zooplankton was identified in the surrounding waters from July 2013 to July 2015,which belong to 83 genera of 5 phyla,of all zooplankton the Rotaria contribute the most for 41.06%.The Protozoa the second place with 28.48%.Cladoceran and Copepod respectively with 25 species and 17 genera.With 8 species and 6 genera saprobic indicate of zooplankton was identified in Danjiangkou Reservoir for nearly two years,there are 4 species belong to Protozoa and 2 species to Rotaria. The species number of zooplankton in Danjiangkou Reservoir is much in summer and little in winter.From the standpoint of the saprobic indicate of zooplankton show that the Danjiangkou Reservoir is geared to oligosaprobic nutrient water.3. The dominant species plankton in Danjiangkou mainly lies Cyanophyta,Chlorophyta and Bacillariophyta.Such as Aphanizomenon flos-aquae Ralfs,Pandorina morum,Fragilaria Lyngbye and Cryptomonas erose Ehr. Bacillariophyta and Cryptophyta is the dominant species in winter and springtime, Chlorophyta as dominant species in summer.Zooplankton only has 10 dominant species in the past two years,and it changes in different seasons.4. The average density of phytoplankton is 969 cell/L,and the average biomass is 7.65 mg/L,they have diffierent variation tendency.The average abundance of phytoplankton is 21 ind/L,and the average biomass is 3.30 mg/L,the tributary’s biomass condition is most,then the Dan reservoir and the Han reservoir is minimal.The seasonal variation from large to small is summer,autumn,spring and winter in turn.5. The average value of H’,d,and J of planktonic algae were 1.94,3.86 and 0.59 respectively and the diversity indexes of H’,d,and J of zooplankton were 1.82,3.23 and 0.88 respectively.All of these diversity indexes had remarkable seasonal variation,the seasonal variation of H’and J had the similar trend,they were all higher in summer and autumn,lower in winter and spring,on the contrary,the seasonal variation of d is different. The seasonal variation same as planktonic algae.6. The average concentration of Chl(a) was increase in turn among Hanku,Tributary and Danku reservoirs.In Hanku Chl(a) had a significant or very significant positive correlation with temperature and NH4+-N.while in Danku it had a significant or very significant negative correlationwith SD. The Chl(a) had a significant positive correlation with temperature,TN and TP in Tributary,which indicated that nutritive N was the major environmental factors that influenced water Chl(a) concentration.7. Use single factor evaluation method and comprehensive evaluation to assessment water environmental evaluation,the pollution level of Danku was clean,TN concentration was over the surface water quality standard.Tributary was of middle level pollution,NH4+-N concentration was over the surface water quality standard Ⅲ.CODMn concentration was over the surface water quality between Ⅰ and Ⅲ.and Hanku was from clean to low level pollution.8. The average value of Carlson and index of comprehensive nutrition of Danjiangkou Reservoir were 36.76 and 42.54 respectively.All of these indexes had the same seasonal variation,They were higher in summer and autumn,lower in winter and spring.The results showed that the comprehensive index of the Reservoir nutrient condition was at semi-eutrophic level.