| The concentration and spatio-temporal distribution of Chromophoric Dissolved OrganicMatter（CDOM）are not only important parts of the carbon cycle,but also significant factors in environmental assessment,which are greatly affected by land use types and human activities.Therefore,it is conducive to analyze the influences quantitatively by human activities based on the study of the optical properties and spatio-temporal distribution of CDOM in lakes.CDOM optical properties in Taihu Lake were analyzed based on the data collected from three field samplings from 2016 to 2017.Then,CDOM concentration（the absorption coefficient of CDOM at 443nm）of Taihu Lake was caculated based on the the remote sensing inversion algorithm.Meantime,the data of OLCI（Ocean and Land Colour Imager）from November 2016 to January 2018 is used to construct a long-term sequence data set of CDOM in the Taihu Lake based on the inversion algorithm in order to analyze the spatio-temporal distribution of CODM.Finally,the influencing factors affected on the spatio-temporal distribution of CDOM in Taihu Lake are analyzed from both natural and human aspects,which will provide referenced information for carbon cycle,carbon estimation and Taihu Lake water quality management.Results are obtained in the following aspects.（1）In general,the concentration of suspended particulate matters（SPM）,chlorophyll-a （Chla）and CDOM in Taihu Lake are high.And suspended particulate inorganic matters（SPIM）concentration is slightly higher than the suspended particulate organic matters（SPOM）,indicating that the SPIM are the main optically active substance in Taihu Lake.There is almost no correlation between CDOM and other water color parameters such as SPM and Chla,indicating that the sources of CDOM are mainly from the exogenous input including production domestic sewage and industrial wastewater.According to the optical characteristics of lake water CDOM,an optimized semi-analytical inversion model（QAA709 algorithm）is established.The results of verification accuracy are reasonable(R2=0.432,RMSE=0.117m-1,MAPE=25.277%),which can be used in Taihu Lake water body.（2）CDOM concentration of long-term sequence data set of the Taihu Lake was established based on the OLCI satellite data with optimized QAA709 algorithm from November2016 to January 2018 in order to analyze the spatio-temporal distribution of CDOM.The spatial distribution of CDOM shows a clear gradual change,gradually decreasing from the north to the south of Taihu Lake.CDOM concentration in autumn is the highest in the year,following by spring and sunmer,and CDOM concentration in winter is the lowest.CDOM concentration in the Zhushan Bay is higher than in the Meiliang Bay and the Northwest Lake District,and CDOM concentrations in the Huxin District,Gonghu Bay and Southwest Lake District are lower than the regions mentioned above.In addtion,except for Gonghu Bay and Huxin District,the other lake areas showed significant seasonal differences.（3）The natural factors are the objective reason for the spatio-temporal distribution of CDOM in Taihu Lake.Dilution effects of water and the pollutants brought by rivers make the CDOM concentration of the whole lake is higher in fall than that in summer.Moderate wind speed in spring and winter results that the spatial distribution of CDOM in Taihu Lake is relatively uniform,but wind speed fluctuates greatly in summer and autumn leading to the great variation of CDOM spatial distribution.Human factors are important external factors affecting the spatio-temporal distribution of CDOM in Taihu Lake.Human activities lead to increased emissions of various pollutants,which are finally reflected in the CDOM of Taihu Lake.The eutrophication distribution is consistent with the spatial distribution of CDOM in the whole lake.Large areas of cultivated land and forest land have been converted into construction land in the past seven years of land use type in the Taihu Basin.The usage of chemical fertilizers and pesticides in agriculture and the discharge of wastewater from industrial production have affected the spatio-temporal distribution of CDOM in Taihu Lake.The positive coupling of industrial agglomeration and water environmental pollution in the secondary industry in the social economy is one of the important reasons that affect the spatio-temporal distribution and concentration of CDOM in Taihu Lake. |
