FLUORESCENCE TRACKING COMPONENTS AND HUMIFICATION OF DISSOLVED ORGANIC MATTER UNDER DIFFERENT LAND USES OF TAIHU LAKE WETLAND, CHINA

摘要

The fluorescent components and humification degree of dissolved organic matter (DOM) extracted from wetland soils under different types of land use were studied using fluorescence emission, excitation, synchronous, excitation-emission matrix spectra with PARAFAC model. Composite soil samples of different depths (0-10, 10-20 and 20-30 cm) were collected from four different wetland ecosystems along a disturbed-impact and land-use gradient in Taihu Lake wetland, i.e. cinnamomum camphora field (CFD), grassland (GLD), paddy field (PFD), and soybean field (SFD). Fifteen humification indices (HLXs) (A_4/A_1, A_(465), I_(445)/I_(340), I_(370)/I_(338), I_(440)/I_(338),I_(440)/I_(370),S_(338-370),S_(338-440),S_(370-440),A_2/A_1,A_3/A_1, A_3/A_2, C_1,C_2 and C_3), deduced from fluorescence spectra of DOM, were very feasible to indicate humification degree, except A_4/A_1 and C_2. The aromatic contents and molecular weights of DOM were the highest in the CFD soils, while land-use intensity was the lowest, followed by the GLD, PFD and SFD. Humification degree of DOM within the CFD soil profile was the highest, followed by the GLD, PFD and SFD. Due to good linear correlations of electric conductivity (EC) with HIXs, EC could indirectly suppress humification processes through adverse effect on microbial and biochemical activity. Obviously fluorescence can be used as an effective method to indicate soil DOM humification, and also be used as a predictive tool to indicate secondary salinization.