DOM Characteristics Analysis of Surface Sediment-overlying Water in Suzhou Landscape River Course

Abstract

In order to understand the characteristics and interrelationship of dissolved organic matter (DOM) in interstitial water and overlying water of a landscape river in Suzhou, the characteristics of DOM in interstitial water and overlying water of landscape river sediments in the urban area of Suzhou from July to September after the 2020 flood season were analyzed using the UV-Vis absorption spectrum, high-performance liquid chromatography(HPLC), and fluorescence spectrum combined with the fluorescence region integration method. The results showed that the relative molecular weight of DOM in both the interstitial water and the overlying water was about 1000, and the relative molecular weight tended to increase in the same way over time. Both interstitial water and overlying water had the highest DOM of protein-like content, with a mass fraction that reached 68%-79%. By contrast, the content of humus-like substances was lower, with a mass fraction accounting for approximately 21%-32%, and both were dominated by low-excitation tryptophan. From July to September, a large increase in DOM levels appeared in the interstitial water, followed by a gradual increase in DOM levels in overlying water. These increases might have come from the deposition of algae on the river bottom after summer outbreaks, likely followed by cleavage and release into the interstitial and overlying water. The fluorescence indices (FI) of the interstitial water and overlying water differed more in July and then increased and decreased following the same trend; however, both were greater than 1.2. The authigenic indicator BIX indicator values were all greater than 0.8 and tended toward 1. The humification index (HIX) values were all less than 4; moreover, the interstitial water and overlying water became smaller in the same trend. The same positive correlation was present between the six fluorescent components of DOM (P<0.05), with a significant correlation between low-excitation tyrosine, α254, and HIX. The relationship between interstitial water and DOM in the overlying water in the Suzhou landscape river was closely related, and the interstitial water may be a potential source of DOM in overlying water.