Research Of Water Enviroment And Carring Capacity In The West Yangcheng Lake

As one part of Yangcheng Lake,the west is an important standby water source of Suzhou.Because of the barriernet culture,west Yangcteng Lake eutrophication had been accelerated for decades.In order to control eutrophication of west Yangcheng Lake,Suzhou goverment dismantled the barriernet in 2008,and had carring out fish multiplication from 2009.In our thesis,an investigation was conducted in west Yangcheng Lake from March to November,2014,including time-space distribution of water quality;the contentof TN,IP of mud;community structure of phytoplankton,zooplankton,macroinvertebrates.We syste-matically studied spatial and temporal characteristics of environment,and comprehensively estimated the carrying capacity of west Yangcheng Lake through natural carrying capacity,pollution load estimate on TN,TP and water environmental capacity.The results showed that:1.142 species 68 genera and 8 phyla were identified,including Chlorophyta(63 species,accounting for 44.37%),Bacillariophyta(27 species),Cyanophyta(22 species).The dominant species were Melosira granulata var,Cryptomonas ovata Her,and Merismo-pedia tenuissima Lemm,and varied obviously as the season changed.The annual abundan ce and biomass of phytoplankton were(3.999±4.00)×106 cell/L and(1.41±1.05)mg/L,respectively.The annual diversity indexes of Shannon,Pielou and Margalef were 2.97,0.66,1.11,respectively.The results of Pearson correlation analysis showed that the primary factors affecting the structure of phytoplankton community were identified to be pH,Tem and the content of TN,TP,whereas RD A results indicated that the key environmental factors influencing the phytoplankton assemblages were Tem,pH,DO and the content of TN,TP.2.92 species 49 genera and 4 phyla were identified,including protozoa(36 species,accounting for 40.00%),rotifer(34 species),cladocera(13 species)and copepod(7 species).Micro-zooplankton dominated obviously,with the density ranging from 342.15 to 97597.16 cell./L and the biomass varying from 0.08 to 198.72 mg/L.Besides,the annual diversity indexes of Shannon,Pielou and Margalef were 2.84-4.45,0.63-0.89,1.46-3.69,respectively.The results of Pearson correlation analysis agreed with RDA analysis,showing that water temperature,SD and nutrient were the main environmental factors afecting the spatial distribution of zooplankton comnmunity.3.35 species and 3 phyla were identified,including Annelida(16 species,accounting for 45.71%),Arthropoda(6 species)and Mollusca(13 species),among which,Corbicula fluminea,Limnodrilus hoffmeisteri,Lumbriculus variegatus,Limnodrilus grandisetosus and Bellamya aeruginosa were dominanted.The annual density and biomass of macroinverteb-rates were 117.46-770.67 ind/m2 and 79.28 to 373.03 g/m2,respectively.The annual diversity indexes of Shannon,Margalef and Goodnight-Whitley averaged 1.66,0.43 and 0.50,respectively.The results of Pearson correlation analysis showed that pH,water temperature,DO and nutrient were the main environmental factors affecting the spatial distribution of macroinvertebrates community.Meanwhile,RDA results indicated that Arthropoda fovored high alkalinity,high dissolved oxygen and high nutrient levels,but Annelida and Mollusca prefered to low transparency,low CODMn,and low nutrient.4.In the research,natural carrying capacity in the condition of stocking was 4336 t,and the real stocking amount was far less than scientific stocking amount.Considering the result of the model of pollution load,we found that the TN load was-2 × 107 kg and the TP load was-5 × 106 kg,indicating the stocking model has no negative effect on the environment of west Yangcheng Lake.The water environmental capacity estimated by Dillion model was 137 t/a,which according to the principle of sensitive factor.Finally,studies showed the carrying capacity was 137 t in west Yangcheng Lake.