Upstream contributions to the chromophoric dissolved organic matter in the Taihu Lake during summer rainy seasons

The spectral absorption and the three-dimensional fluorescence of chromophoric dissolved organic matter (CDOM)in three rivers (Zhihugang,Dapukou,and Changdougang)located upstream of the Taihu Lake are deter-mined.Such an upstream contribution to CDOM in the lake during the summer rainy season of 2008 is analyzed.It is found that the Zhihugang River has the highest CDOM absorption value,and followed by Dapukou.The lowest CDOM value is found in the Changdougang River.This result indicates that the allochthonous pollutant of the north river up-stream of the Taihu Lake contributes the most CDOM in the lake.Our results also show that the mean value of (4.76±0.79)m^-1 is found for the absorption coefficient of CDOM at 355 nm in the three rivers,which is significantly lar-ger than that of (3.62±0.84)m^-1 in the Taihu open water.Furthermore,CDOM absorption decreases gradually from the upstream of rivers to the river mouths,and to the Taihu Lake.It is thus clear that the three rivers are the major sources of allochthonous pollutants in the Taihu Lake during summer rainy seasons.In addition,the parallel factor analysis of the three-dimensional CDOM fluorescent excitation-emission matrix spectra reveals the presence of four fluorescent components.The component 1 and component 2 can be characterized as the protein-like fluorescence,and the rests are the humic-like fluorescence.The intensity of the latter decreases gradually from the river mouth to the open water of the lake,and the opposite is true for the protein-like fluorescence intensity.This analysis shows that the humic-like fluorescent dissolved organic matter in the Taihu comes mainly from the upstream rivers.