Multi-Media Distribution and Sources of Dissolved Organic Matter in Subtropical Watershed: Insights into Impact of Sediment Grain Size

The multi-media environmental behavior of dissolved organic matter (DOM) is closely related to biogeochemistry and water quality. In this study, we characterized the multi-media distribution patterns and sources of DOM in a human-intensive watershed based on fluorescence measurements and fluorescence quotient (FQ) methods. Clay showed higher proportions in urban areas compared with rural areas. The biological index decreased with the increased similarity of DOM between sediment and a wastewater treatment plant (WWTP)/domestic sewage. The similarity of DOM between sediment and aquaculture was negatively related to coarse silt (Pearson, p < 0.05). In the water, C2 was more abundant in urban areas than in rural areas; among all sources, the WWTP exhibited the highest similarity (98.04%) of DOM with water, which was higher than that between sediment and the WWTP. The fluorescence index decreased with the increased similarity of DOM between waters and the WWTP/domestic sewage. The FQs for some amino acid-like materials and microbial byproducts between sediment and water were negative, while those for humic-like and fulvic-like materials between sediment and water were positive. Structure equation model (SEM) results showed that sediment grain size exerted positive effects on the distribution of C1 between sediment and water and negative effects on the distribution of C3 between sediment and water. The results demonstrated that the distribution of DOM between sediment and water, as well as the source contribution to DOM in sediment, was related to the sediment grain size, revealing the impact of sediment on the multi-media environmental behavior of DOM.