Evaluation Of Eutrophic Condition And Analysis Of The Relations Between Algae And Environmental Factors Using Stepwise Multiple Regression In Xiliu Lake

With the advance in industry and agriculture and the increase of population, the demanding amount of water resources of people is increasing. And the eutrophic condition of polluted water body is also more serious. It was reported that individually 53, 28,48, and 41 percent lakes in Europe, Africa, North America and South America exist different degree eutrophication. And 54 percent lakes in Asian Pacific Area are under eutrophic condition. Eutrophic condition of freshwater in China has been more serious since 1990. And the eutrophic range is involved Yangtze River, Yellow River, Taihu Lake and Chaohu Lake etc.When eutrophic condition of water body is serious, algae on water surface proliferate and cover the water surface flakily to form water blooms or red tides. Generant frequency and serious degree of cyanophyta water blooms have been increasing in freshwater lakes all over the world since mid-twenty century. Cyanophyta water blooms happened in Taihu Lake of China earlier. The harm of poisonous water blooms and red tides that result in the death of aquatic animals, avifauna, drove and human is very serious. There are many reports about algae and toxins, but no reports about analysis of the relations between proliferation of algae and environmental factors in Henan are found. So scientific data for safe water supply for residents in Zhengzhou are supplied by studies on eutrophic condition and the relations between algae and environmental factors in living water resources ofZhengzhou.Materials and methods1. Two sampling sites were designed in Xiliu Lake. The first was at the entrance of storage pool of Shiyuan water factory, the second was 1000 meters far from storage pool. The monitoring time was from March to October in 2004, rain was avoided while sampling, and the sampling time was at 8:00~9:00. While sampling, a total of 12L water was collected at five meters under water surface using collecting water device of 2.5L, then put into worked polythene bottles and glass bottles and determined quickly. At the same time, air temperaturewas determined. Total sampling number was 25. The sampling number was 10, 9, 6 in spring, summer, autumn respectively.2. Water temperature (WT) was determined by using deep water thermometric. Secchi-depth (SD) and water depth (WD) were determined by using Saishi disc. Chemical oxygen demand (CODmiO was determined using the method of acidic potassium permanganate. Total nitrogen (TN) was determined using the method of alkaline potassium persulphate digestion UV-spectrophotometric. Total phosphorus (TP) was determined using the method of ammonium molybdate spectrophotometric. Chlorophyll-a (Chla) was determined using the method of spectrophotometric. Algae cell density (ACD) and cyanophyta cell density (CCD) were determined by using accounting blood corpuscle disc.3. Trophic level index (E) (TLI(E)), linear correlation analysis and stepwise multiple regression analysis were used in the statistical test. The significant level is 0.05.Results1. SD concentration of two sampling sites exceeded the III standard of environmental quality standard for surface water in three seasons, and the super-standard multiple increased along with the seasonal subrogation gradually. CODmh concentration reached the II standard in spring and exceeded the III standard in summer, which exceeded the standard 0.07 and 0.12 multiple respectively. In autumn CODMn concentration of the first sampling site remained steadiness,however, that of the second sampling site fell lightly. TN concentration exceeded the III standard in three seasons, and the super-standard multiple increased in autumn obviously, which were 0.81 and 0.94 multiple respectively. TP concentration of the first sampling site exceeded the III standard in three seasons, and the super-standard multiple increased from 0.02, 0.62 to 1.86 multiple; however, the super-standard multiple of the second sampling site increased from 0.40 to 0.56 multiple. The super-standard multiple of Chla concentration of the first sampling site increased from 2.97 to 7.47 multiple, which of the second sampling site increased from 0.03, 3.71 to 5.67 multiple in three seasons. In three different seasons, the super-standard multiple of SD concentration increased from 0.55, 0.69 to 0.72 multiple respectively. CODmii, TP, Chla concentration reached the II standard in spring and exceeded the III standard in summer and autumn respectively; the super-standard multiple were 0.10, 0.52, 3.34 multiple and 0.03, 1.22, 6.57 multiple respectively. The super-standard multiple of TN concentration were from 0.75,0.74 to 0.88 multiple.2. Nutritive condition of two sampling sites were the maximum of mesotropher in spring, the maximum of light eutropher in summer and the minimum of middle eutropher in autumn. TLI( E) of the second sampling site was higer than TLI( E) of the first sampling site in spring and summer, however, TLI(E) of the first sampling site was higer than that of the second sampling site in autumn. In three different seasons, nutritive condition of Xiliu Lake was from the maximum of mesotropher, the maximum of light eutropher to the minimum of middle eutropher.3. The primary algae of two sampling sites were bacillariophyta, chlorophyta, cyanophyta and euglenophyta, while other algae were few. The dominant algae were bacillariophyta and chlorophyta in the first sampling site and euglenophyta and chlorophyta in the second sampling site in spring, cyanophyta and chlorophyta in two sampling sites in summer, cyanophyta and chlorophyta in the first sampling site and cyanophyta and bacillariophyta in the second sampling site in autumn. The dominant algae of Xiliu Lake were chlorophyta and bacillariophyta in spring and cyanophyta and chlorophyta in summer and autumn.4. Positive correlations were found between the standardized Chla and WT,n, TP, and negative correlations were found between the standardized Chla and SD in Xiliu Lake. The results of stepwise multiple regression showed that three correlated factors were selected in the first sampling site. WT and TP were positive correlated factors, SD was negative correlated factor. Two correlated factors were selected in the second sampling site. WT and TP were positive correlated factors. WT. TP, CODmii were correlated factors to the standardized Chla of Xiliu Lake. Positive correlations were found between the standardized ACD, CCD and WT, TP, and negative correlations were found between the standardized ACD, CCD and SD, WD in Xiliu Lake. The results of stepwise multiple regression on ACD showed that three correlated factors were selected in the first sampling site. WT and TP were positive correlated factors, SD was negative correlated factor. Two correlated factors were selected in the second sampling site, TP was positive correlated factor, WD was negative correlated factor. WT, TP were correlated factors to the standardized ACD of Xiliu Lake. The results of stepwise multiple regression on CCD showed that two correlated factors were selected in two sampling sites, WT and TP were positive correlated factors. WT, TP were also correlated factors to the standardized CCD of Xiliu Lake.Three regressive equations of the standardized Chla, ACD, CCD and environment factors are listed respectively:(l)ln(Chla+l)=-0.114+8.348xl0"2WT+6.874TP+0.193CODMn;/><0.01. (2)ln(ACD+l)=4.524+0.140WT+15.071TP;/><0.01. (3)ln(CCD+l)=1.004+0.232WT+22.364TP;P<0.01.The inspective results of three regressive equations showed that the coincidence of practical value and predictive value of the standardized Chla was good. And the coincidence of practical value and predictive value of the standardized ACD and CCD was better, only the value of 17~23 samples was different. The contents of Chla, ACD and CCD could be predicted by the multiple equations.5. TN/TP fell along with the seasonal subrogation of two sampling sites and Xiliu Lake, TN/TP was about 20 in summer and between 10 and 20 in autumn. TN/TPof 17~24 samples were steady and about 20 in Xiliu Lake. The contents of Chla, ACD and CCD increased along with the seasonal subrogation in Xiliu Lake, the contents of 19~24 samples increased obviously, and TN/TP was steady about 20. Conclusions1. Nutritive condition of Xiliu Lake is eutropher and aggravates from spring to autumn.2. The dominant algae change along with the seasonal change in eutrophic water body.3. The basal material to monitor the eutrophic condition of surface water is supplied by three regressive equations of the standardized Chla, ACD, CCD and environment factors.4. Phosphorus is primarily limiting salt affecting the eutrophic condition of water body and algous cell vicissitude.