Applying EEM Coupled with 2D-COS to Character Structural Composition of DOM and Its Spatial Variations in an Urban River

Three-dimensional excitation-emission matrix (EEM) fluorescence spectroscopy combined with parallel factor analysis (PARAFAC) and two-dimensional correlation spectroscopy (2D-COS) was applied to characterize structural composition and changes of the dissolved organic matter (DOM) in the urban river in Shenyang City. Water samples were collected from Puhe River, where the sampling sites 1# to 3# were located in the clean region, the sampling sites 4# to 6# in the industrial region, and the sampling sites 7# to 9# in the residential area. The EEMs of DOM were measured, from which fluorescence index (FI), autochthonous index (BIX) and humification index (HIX) were deduced. Based on the analysis of FI, BIX and HIX, DOM was mainly autotrophic source, while DOM in the industrial and the residential regions were also affected by terrestrial sources, and the degree of humification was relatively weak. Using PARAFAC, the six fluorescent components were extracted, i. e. fulvic-like (C1 and C2), humic-like (C3), tryptophan-like (C4 and C6) and phenolic substances (C5), of which fulvic-like (37.91%-43.82%) and tryptophan-like (23.64%-33.60%) were the main components. Based on 2D-COS, the variation order of fulvic-like and tryptophan-like in the industrial region was tryptophan-like → fulvic-like, so was the residential region. However the change order in the clean region was opposite to the industrial and residential regions, indicating that the variations of the tryptophan-like in the former were larger than those in the latter. This indirectly verified that there was a large amount of domestic sewage and industrial wastewater entering into the river from the industrial and the residential region. Based on the principal component analysis (PCA), C1-C5 were the main potential factors affecting DOM (55.15%). The scores of the sampling sites were the highest in the industrial region, followed by the residential region and the clean region. It showes that the river sections in the industrial and the residential regions were deeply affected by human activities, while the river sections in the clean region were less affected by human activities.