Abstract
Dissolved humic substances in the river waters of Sanjiang Plain, which has undergone a land-use change from wetland marsh to cultivated land, were studied by three-dimensional excitation emission matrix spectroscopy and high-performance size exclusion chromatography to characterize the dissolved organic matter in the river systems. River water samples were collected at 14 points from nine rivers in the summer in 2005. Fulvic like fluorescence maxima were detected for the river waters at an excitation wavelength (Ex.) in the range of 315-335 nm and an emission wavelength (Em.) in the range of 410-430 nm and at an Ex. in the range of 235-260 nm and an Em. in the range of 410-440 nm. The relative fluorescence intensity of fulvic like materials in the river waters from wetlands in the August samples was lower than those of the September samples, but that of the river waters from the cultivated area was higher than those of the September samples. The fluorescent properties of humic substances can be divided into three groups on the basis of river water pH, the relative fluorescence intensity of fulvic like materials and its peak positions. These groups correspond to the land-use types such as wetlands, dry lands and their mixture in the watershed of rivers.
