| Lake eutrophication mainly caused by exceeded nutrient has affected the aquaticecosystems balance and use value seriously, which has also drew much attention bythe government and the public. It’s significantly important to search the limitingphysical and chemical factor in order to mitigate the eutrophication effects. In thispaper, spatiotemporal distribution characteristics and correlations of water qualityindexes as well as different forms of phosphorus both in overlying water and sedimentwere analyzed. In addition, GA-SVM model was applied in predicting the content ofBAP. The main results are as follows:(1) The seasonal changes of water indexes in Xiaonanhu Lake were obvious.During the monitoring period, the maximum values of TN, TP and CODMn allexceeded lever Ⅴ of the surface water environmental quality standard and NH3-Nexceeded lever Ⅲ. Great correlations existed among all the water indexes. It showedthat pH, DO and EC had significantly negative correlations to water temperaturewhile DO, CODMn, NH3-N, TP and Chla had significantly negative correlations to pH.TP had less correlation to TN but much positive correlation to Chla. In most cases, thewater quality of Xiaonanhu Lake was in the middle eutrophication situation, butdeterioration in summer. P was the limiting factor of the lake. The content order ofthree kinds of P is TDP＞PP＞PO43--P. TDP and PP approximately took50%of TPrespectively. The maximum value of TDP/TP was near70%during April to Augustand the mean value of PO43--P/TDP was45.4%.(2) The mean content of TP in the surface sediment was635.0mg/kg, which wasabove average comparing with some other lakes in China. The mean content of IP inthe sediment was434.9mg/kg which took68.5%of TP while OP took the rest31.5%(200.1mg/kg). IP was mainly composed of HCl-P and NaOH-P. The content order offour kinds of IP was HCl-P> NaOH-P> BD-P> NH4Cl-P. NaOH-P was significantlycorrelated to NH4Cl-P (0.604, P<0.05). HCl-P was of high stability while other formswere easily affected by pH, temperature, DO, hydrodynamic condition, redoxpotential and many other factors in the overlying water. The different contents of TPin different sampling points were closely related to the physicochemical property ofsediment as well as the domestic sewage and other human activities.(3) The content variation range of BAP in sediment was220.57~281.80mg/kgand the mean value was245.34mg/kg which represented33.04%~44.26%of TP. NaOH-P contributed most to BAP. The Phosphorus migration and transformationexisted between BAP and PO43--P in the overlying water. Among the basic waterquality indexes, BAP had significant correlations to pH, CODMn and DO. Among thechemical water quality indexes, BAP had significant correlations to NH3-N, PO43--Pand N/P. That indicated the Phosphorus adsorption and desorption of BAP affected thecontent and distribution of nutrient in overlying water, which lead to theeutrophication situation.(4)7water quelity indexes (pH、CODMn、TUB、NH3-N、PO43--P、TN、N/P)which had the most significant correlations to BAP were employed to predict thecontent of BAP in sediment by the GA-SVM model.110groups of experiment datawere trained by crossover method and the key parameters C andσin the model wereoptimized by the GA method. The result showed that this model had a stronggeneralization ability. The correlation is significant between measured values andpredicted values (0.095) and the mean relative error was only18.1%. The modelprediction effect was within the allowed limits in consideration of the independentvariables chosen from overlying water and the complexity of aquatic ecologicalenvironment as well as eutrophication of lakes. |
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