Characteristics and significance of dissolved organic matter in river sediments of extremely water-deficient basins: A Beiyun River case study

Abstract

The characteristics of dissolved organic matter in river sediments, affected by microorganisms, are of great significance to water management strategies. Based on three-dimensional excitation and emission matrix fluorescence, ultraviolet–visible spectroscopy, and high-throughput sequencing technology, this study jointly analyzed the composition and transformation mechanisms of dissolved organic matter as well as the microbial community structure in sediments of the Beiyun River, the main river within a basin with extreme water shortages. Moreover, we evaluated N and P contents in sediments to identify parameters to reflect potential eutrophication risks. Our results demonstrated that the content of dissolved organic matter in sediments was between 30.2 and 49.9 g/kg in the Tongzhou area of the Beiyun River. Humic substances were the largest components of dissolved organic matter in the sediments, followed by protein-like substances and soluble microbial byproducts. Furthermore, the proportion of humic matter decreased from upstream to downstream. The proportion of carbonyl, carboxyl, hydroxyl, and ester substituents on the aromatic structures of dissolved organic matter was significantly higher in the upstream, whereas the proportion of substances with aliphatic chain substituents on their aromatic structures was relatively low. The variation in downstream sediment microbial communities was much greater than that in the upstream (analyzed at the phylum level). Proteobacteria was the most abundant phylum (47.97%), which was closely related to the aromaticity of the dissolved organic matter in sediments. The N and P contents in the sediments of the Beiyun River were high and exhibited active transformation. The maximum fluorescence intensity of fulvic-acid-like components in the sediments [Fmax(C4)] can indirectly reflect the potential risk of eutrophication in the Beiyun River. Therefore, our results provide a theoretical basis for the assessment of water quality and pollution control in the Beiyun River and other water-deficient regions worldwide.