Study And Analysis Of Eutrophication Assessment In Chaohu Lake Based On Interpretative Structural Modeling

The study and analysis of eutrophication assessment in Chaohu Lake wereconducted based on the water quality data of12monitoring points seted bygovernment from2000to2009. The main content and methods were summarized asfollowed:Firstly, Integrated structure analysis of the factors that affected the algalbloom and the eutrophication was conducted using interpretative structuralmodeling method based on the reason of the eutroophication.Secondly, structural equation model was used to model the eutrophicationfactors on chlorophyll a（chla） in order to analyzed quantitatively the relationshipbetween the factors and chlorophyll a（chla） based on the water quality data of12monitoring points seted by government from2000to2009.Thirdly, Chose total phosphorus, Chemical Oxygen Demand, total nitrogen,transparency and chlorophyll a（chla） as the evaluating indicators, thecharacteristics of the temporal and spatial variation of the eutrophication in ChaohuLake was analyzed with Kriging interpolation based on GIS.Fourthly, scoring method,set pair analysis method and comprehensivenutrition state index method were used to evaluate eutrophication in east-half aswell as west-half of Chaohu Lake,and the evaluation results were compared.Finally, comprehensive trophic state index for all the sampling sites wasanalyzed in order to assess the eutrophication degree.The main conclusions were summarized as followed:1. Integrated structure analysis of the18factors that affected the algal bloomand the eutrophication was conducted using interpretative structural modelingmethod, the result showed that wind field, Chaohu Lake sluice, temperature andlight had important influence on the eutrophication and the algal bloom; nutrienthad the most impact factors, among which strictly decreasing and controling inputnutrient were under artificial control.2. Structural equation modeling showed that the effect on chlorophyll a（chla）of the mentioned factors in the order of TP>COD_Mn>TN>SD>T, Chaohu Lake was a Phosphorus controlling lake. Contour plotting of TP, COD_Mnand chlorophylla（chla） indicated that concentration of chlorophyll a（chla） increased more quicklywhen concentrations of COD_Mnwas aboult7.5mg/L～10ml/L; concentration ofchlorophyll a（chl-a） increased more quickly when TP had a higher concentrationthan0.3mg/L; the maximum point of concentration of chlorophyll a（chla） did notmatch with the maximum point of concentration of COD_Mnand TP.3.Chose total phosphorus, Chemical Oxygen Demand, total nitrogen,transparency and chlorophyll a（chla） as the evaluating indicators, thecharacteristics of the temporal variation of the eutrophication in Chaohu Lake wasanalyzed with Kriging interpolation based on GIS. Combined with thecharacteristics of the spatial variation of eutrophication in Chaohu Lake from2000to2009, the result showed that the eutrophication degree of north-west was worsethan the south-east part, large-scale algal bloomed in west-half lake in2003; thedistribution of measure indexes of all evaluating indicators was “west high, eastlow”.4. Scoring method, set pair analysis method and comprehensive nutrition stateindex method were used to evaluate eutrophication in east-half as well as west-halfof Chaohu Lake, the result showed that west-half was worse than east-half,large-scale algal bloomed in west-half lake in2003, and water quality of ChaohuLake improved in2009, which indicated that water quality had a reduce trend.5.Comprehensive trophic state index for all the sampling sites was analyzedwith Kriging interpolation, the result showed that the simulation had stable results,the distribution of eutrophication degree was in agreement during the recent10years.