Abstract: Based on analysis of dissolved organic carbon (DOC),with the techniques of UV-visible absorption and three-dimensional excitation emission matrix (3DEEM),distribution and origin of chromophoric dissolved organic matter (CDOM) in Lake Qianwei,Chongming Island at the Yangtze River Estuary were explored. In the surface layer of the water body,DOC was evenly distributed,with concentration ranging from 5.87 to 7.02 mg·L^-1 and averaging 6.35 mg·L^-1. The UV-visible absorption revealed that the calibrated absorption coefficient a₃₅₅ was the highest in the fish-culturing zone,reaching 4.58 m^-1,and declining towards either side,which implied that there were other sources of CDOM besides terrestrial sources. Fluorescence index (f_450/500) analysis proved presence of aquatic biological sources,and also indicated that the CDOM in the waterbody of Lake Qianwei did not show any significant trace of terrestrial or aquatic biological origin. However,the ratio of a₃₅₅ and DOC showed a significant positive correlation with fluorescence index (r=0.787,n=10,P<0.01),suggesting a strong biological signal existed in the aquicultural zone,and it might come from phytoplankton production. 3-DEEM analysis show that humic-like components commonly existed in CDOM in this lake,and did not vary much in spatial distribution,while protein-like components did and presumably were the major factor affecting spatial distribution of CDOM.

Key words: chromophoric dissolved organic matter(CDOM), fluorescence index, specific absorption coefficient, biological production