Origins of Organic Matter in Tuo River Sediments

Ultraviolet-visible (UV-Vis) and three-dimensional excitation emission matrix fluorescence (3D-EEM) spectroscopies were conducted to investigate the structure and origin of dissolved organic matter (DOM) from soils around the Tuo river in Suzhou city in different season. The results showed that the characteristics of all samples, UV-Visible spectra were similar and the relative concentrations of DOM showed an overall increasing trend in the middle and upper reaches of the Tuo River and reached a maximum in the middle reaches of the river. In particular, the aromaticity (A250/A365) of DOM in sediments at the midstream point of the Tuo River and the degree of humification degree (SUVA254) were higher than those in other river sections. The 3D-EEM fluorescence spectra showed that fulvic acid-like peaks in the visible region, fulvic acid-like peaks in the UV-visible region, and two humic acid-like peaks were reflected in the dissolved organic matter of the Tuo River sediments. Combining the three-dimensional fluorescence spectrum with the fluorescence index (fluorescence index, FI) and autochthonous index (autoch-thonous index, BIX) of DOM in the sediments of the Tuo River in different seasons, it shows that the exogenous input of DOM in the sediments of each section of the Tuo River is extremely obvious and less bioavailable. The aromaticity of DOM molecules is enhanced after the Tuo River flows through urban areas. The present study can provide a reference for the future management of the water environment of related rivers.