Quantitative Analysis Of The Impact Factors On The Eutrophication Of Western Chaohu-Lake

The lake eutrophication,becoming a major factor hampering economic and social sustainable development,is a serious national environmental problem.The Chaohu-Lake is one of the most serious eutrophication lakes in China . Considering the Zhongmiao-Mushan-Qitouzui as the boundary,the Chaohu-Lake has been divided into two parts,west and east.In this paper,using SPSS 13.0 for windows and other statistical software,we study the west part with ecological principles and methods.On this basis, we use SPSS statistical software to analyze the comprehensive effect of the multi-factors on the eutrophication,screen data and establish multi-regression models to explore the western Chaohu-Lake eutrophication and its development law and evolutional trends.In that case,we can forecast the degree of the western Chaohu-Lake eutrophication and put forward control rational proposals to prevent and control it.The conclusions of the western Chaohu-Lake analysis are as follows:According the analysis of the western Chaohu-Lake's monitoring data (2001~2007), we study and evaluate the extent of eutrophication comprehensively.The results show that: chlorophyll-a,total nitrogen,total phosphorus content and other factors maintain a high level while the water quality has been maintained at heavy eutrophic to extremely eutrophic level.During 2001-2007,the western Chaohu-Lake's chlorophyll-a content maintain at a high level.The annual average content rose gradually,from 25.50mg/m3 to 75.22 mg/m3 (2001~2003),then it showed a gradual downward trend.However,the overall level was still beyond the criterion of Chaohu-Lake's eutrophication (20.00 mg/m3).The content of chlorophyll a had seasonal variation significantly.Under a certain temperature range,water temperature and chlorophyll a were positively correlated (r = 0.255).With the rising of water temperature,algae growth had accelerated,increasing the concentration of chlorophyll-a.Therefore,water temperature is the main factor of algae growth (chlorophyll a).The total nitrogen,total phosphorus concentration of the western Chaohu-Lake had always been in a high level.During 2001-2007,the lowest annual average concentration of total nitrogen and phosphorus content were 1.551mg/L and 0.190mg/L respectively.According to the criteria of the lake's eutrophication,we could get that Chaohu-Lake's water quality had been maintained at heavy eutrophic to extremely eutrophic level.Basing on the correlation analysis of the total nitrogen,total phosphorus,ammonia nitrogen with the chlorophyll,we knew that total nitrogen,total phosphorus and ammonia nitrogen were positively correlated with chlorophyll-a (the first two index were significant).It represented that total nitrogen and phosphorus were the limiting factors for algae growth in the western Chaohu-Lake.The mass ratio of N,P in the lake was 11.66:1.In light with the Redfield ratio,N was relatively abundant in Chaohu-Lake and the algae growth speed was determined by the P concentration,showing Chaohu-lake belonged to P-controlled lakes.The content of organic matter was also a main factor of Chaohu-Lake eutrophication.The lake's average content of CODMn maintained at 5.55-7.00mg /L, which was relatively stable.The two important factors of the lake's eutrophication (CODMn and chlorophyll a) were positively correlated . The CODMn concentration , hardly decomposed by the micro-organisms,affected the chlorophyll-a significantly and affected the environment greater.BOD5 and chlorophyll-a were negative correlated.They were not the limiting factors of the western Chaohu-Lake.The water's pH value was between 6.9 and 9.1 , the average was 7.9 (micro-alkaline).The Chaohu-Lake dissolved oxygen (DO) average was 8.02 mg /L. The correlation between chlorophyll-a and the pH value,DO were not significant,it manifested that the quantity and distribution of the algae affected the pH value and DO concentration.Therefore,pH value and the DO were algae (Chl-a) passive factors,rather than the limiting factors of the western Chaohu-Lake.Based on the analysis of chlorophyll-a concentration and ecological factors, we established multi-regression model using SPSS statistical software.And the results are as follows:Y=-16.276+0.653 X1+1.853 X2+23.727 X3+1.853 X4In this regard,Y is chlorophyll-a;X1 is water temperature(℃);X2 is total Nitrogen (mg/L);X3 is total Phosphorus (mg/L);X4 is CODMn(mg/L).The Analysis of variance and significance test showed that the model is highly significant (p= 0.006 <0.01),model and all coefficients were statistically significant, residuals were approximately a normal distribution,the model is credible,it could better predict the chlorophyll content in the Chaohu-Lake.Considering the results and the situation of the Western Chaohu-Lake,from the ecological angle,we put forward warning systems strengthening the Western Chaohu-Lake eutrophication prediction and the establishment of algae bloom; adopted control measures combining with the project management and ecological restoration.We should make a strong bid for the development of eco-agriculture,improve the utilization of chemical fertilizer,soil and water conservation,reconstruct and rehabilitate aquatic ecosystems, reducing agricultural non-point pollution and inner source pollution, maintain the sustainable development of the western Chaohu-Lake eutrophication control.