Characterizing the Spatiotemporal Distribution of Dissolved Organic Matter (Dom) in the Yongding River Basin: Insights from Flow Regulation

Abstract

Dissolved organic matter (DOM) plays a vital role in the carbon cycle and manages biogeochemical and ecological processes in aquatic systems. The effects of human activities on DOM quality and quantity have been reported across spatial and temporal scales, but the influence of artificial regulation of river flows on fluvial DOM composition has received little attention. This study used the optical properties of DOM to explore the temporal and spatial distribution characteristics of DOM in the Yongding River basin, where artificial regulation of river flows by cross-basin and inner-basin water transfers are implemented. Excitation-emission matrix fluorescence spectroscopy coupled with parallel factor analysis (EEM-PARAFAC) identified four fluorescent substances of DOM, one microbial humic-like (C1), one terrestrial humic-like (C2), one non-point source pollution humic-like (C4) and one tryptophan-like substance (C3). Due to cross-basin water transfer from the Yellow River, the flow is the highest in spring, which caused the signal of terrestrial humic-like substances(C2) stronger in spring compared to summer and autumn. More microbial humic-like substances(C1) was present with higher temperatures in summer. Meanwhile, humic-like substances(C4) originated from urban and/or agricultural nonpoint source runoff increased because of more rainfall. The tryptophan-like substances(C3) derived from autochthonous sources was higher in autumn as a result of inner-basin water transfer from upstream reservoirs. The artificial regulation of river flows changed the hydrological characteristics, which in turn changed the temporal and spatial distribution characteristics of the quantity and quality of the DOM. This study is intended to help us understand the impact of artificial regulation of river flows on the source, migration, and transformation of DOM and promote the development of appropriate management strategies for artificial regulation of river flows in the basin.

Keywords: Dissolved organic matter, Flow regulation, Excitation-emission matrix fluorescence spectroscopy, Parallel factor analysis, Driving factors.