Research On The Community Structure Of Rotifers In Gaoyou Lake And Its Correlation With Environmental Factors

Located in the middle of Jiangsu Province,Gaoyou Lake is located between 119o 06 ?~119o 25?,32o 42?~33o 41?,48 kilometers long and 28 kilometers wide,with a total area of 760.67 square kilometers,second only to Taihu Lake and Hongze Lake.It is the third largest lake in Jiangsu Province.It connects with Shaobu Lake through Xinmin Beach in the South and enters the Yangtze River through Beijing-Hangzhou Canal and Liaojiagou in the north,Hongze Lake in the north and Lianhuai River in the east,and Beijing-Hangzhou Canal in the east.Gaoyou Lake is the waterway of Huaihe River.It is both a lake and a river,and has the function of flood discharge.In order to study the Rotifer Community structure,spatial and temporal dynamic distribution and its relationship with environmental factors in Gaoyou Lake,the water quality was evaluated biologically.From January to December 2017,the community structure of rotifers in Gaoyou Lake,including species composition,population dynamics,dominant species,biomass,diversity index and water physical and chemical factors,was systematically investigated for one year.The relationship between Rotifer Community Structure and environmental factors was analyzed by correlation analysis,CCA(canonical correlation analysis)and diversity index.The water quality and eutrophication level were evaluated comprehensively by biodiversity index method and comprehensive nutritional status index method.The results are as follows.1.Rotifer species and dominant speciesThis research identified 31 species of rotifers belonging to 18 genera and 12 dominant species in the whole year.The dominant species of rotifers include Brachionus calyciflorus,Keratella valga,Keratella cochlearis,Brachionus angularis,Keratella quadrata,Brachionus diversicornis,Brachionus urceus,Asplanchna priodonta,Trichocerca similis,Polyarthra trigla,Conochilus unicornis,Trichocerca pusilla,Lecane closterocerca.The common species of rotifers in each season is the Keratella cochlearis,Polyarthra trigla,Asplanchna priodonta.Brachionus calyciflorus are dominant species in each season.In the samples of each season,brachionus rotifers accounted for a large proportion of the total density,ranging from the lowest 12.1 % to the highest 85.1 %.The dominance degrees of Keratella cochlearis and Keratella valga were 0.693 and 0.105,respectively.The dominant species appeared in different seasons during the survey period.The dominant species in January are Keratella cochlearis,Trichocerca pusilla and Asplanchna priodonta.The main dominant species in May were Keratella cochlearis,Polyarthra trigla and Conochilus unicornis.The main dominant species of rotifers in August were Polyarthra trigla,Keratella cochlearis and Brachionus angularis.The occurrence frequency of Brachionus diversicornis in August was higher than that in January.T he main dominant species of rotifers in October in autumn are Asplanchna priodonta,Keratella cochlearis and Keratella valga.2.Rotifer density and biomassDuring the survey period,the average annual density of rotifers in Gaoyou Lake was 331 ind./L,and the average annual biomass was 0.338mg/L.The seasonal variation trend of the average density of rotifers in Gaoyou Lake is in the order of autumn,winter,spring and summer.The lowest density of rotifers was 11.0 ind/L in winter,and the highest density was 153 ind/L in autumn.The highest value was 153ind/L in autumn.Among them,41.6 %,13.1 % and 21.8 % were Keratella cochlearis,Asplanchna priodonta and Polyarthra trigla,respectively.The results showed that the average density of rotifers in Gaoyou Lake increased gradually from January to March,decreased from April to May,and reached its peak in July.After June,it fell again.The density in February was close to that in January.The lowest rotifer biomass was 0.016 mg/L in April in Gaoyou Lake.The average biomass in July was 0.832 mg/L.Keratella cochlearis and Brachionus calyciflorus accounted for 41 % and 34 % respectively.The biomass of rotifers increased gradually from February to March,and the seasonal trend was that the biomass of rotifers in winter was smaller than that in autumn,and that in spring was smaller than that in summer.3.Shannon-wiener diversity indexThe Shannon-Wiener diversity index of rotifers in Gaoyou Lake ranged from 0.64 to 2.76.The Margalef index D was 0.21-2.25,The Pielou index of rotifers in Gaoyou Lake ranged from 0.51 to 0.88.Shannon-wiener diversity index H' indicated that the whole lake was a-medium pollution level in all seasons.Margalef richness index D indicated that the spring and summer in the surveyed area of Gaoyou Lake were of multiple pollution types.In autumn and winter,it belongs to the a-medium pollution level,and the annual average belongs to the a-medium pollution level.4.The relationship between the dynamic change of rotifer community structure and environmental factorsAccording to the investigation,the water in Gaoyou Lake is alkaline,and the range of pH is between 8.42 and 9.75.The highest water temperature occurs at 32 ? in August.The lowest water temperature occurs at 9 ? in February.As a shallow lake,the water depth of Gaoyou Lake has little change [61],and its range and average value are 1.15-3.8 m and 1.65 m,respectively.The water of Gaoyou Lake is turbid all year round with transparency ranging from 0.15 m to 1.31 m.Dissolved oxygen is usually higher in the range of 5.71-16.91 mg/L with an average of 11.35 mg/L.The average concentrations of TN and TP were 1.69 mg/L and 0.071 mg/L,respectively.Pearson correlation analysis results showed that there was a significant negative correlation between rotifer density and pH value in Gaoyou Lake.There was a significant negative correlation between rotifers biomass and dissolved oxygen.The biodiversity index was positively correlated with water temperature and pH.Rotifer biomass was positively correlated with Chla and total dissolved nitrogen,and negatively correlated with dissolved oxygen.Potassium permanganate index was negatively correlated with rotifer density and rotifer biomass.Rotifer biomass was significantly correlated with total soluble nitrogen and total soluble phosphorus.The species diversity of rotifers was significantly correlated with ammonia nitrogen.CCA analysis of rotifers and environmental factors showed that rotifers in Gaoyou Lake had a strong response to water temperature,chlorophyll,ammonia nitrogen,total soluble phosphorus,pH,potassium permanganate index and dissolved oxygen.The main environmental factors affecting the rotifers in gaoyou lake are: dissolved oxygen,pH,total phosphorus,ammonia nitrogen,chlorophyll and so on.5.Water pollution level and eutrophication evaluationThe water pollution level and eutrophication of Gaoyou Lake were evaluated by comprehensive nutrient status index,water quality factor evaluation,diversity index and rotifer pollution indicator species.According to the comprehensive results,the water quality of Gaoyou Lake in 2017 was at the level of-medium pollution,and the nutrient level was moderate eutrophication.