Unveiling environmental dynamics of dissolved and particulate organic matter in high-sediment waters

Dissolved organic matter (DOM) serves as the largest reservoir of organic carbon in the hydrosphere and plays a crucial role in global climate change. However, limited research has been conducted on the interactions between dissolved organic matter (DOMw) and particulate organic matter (DOMp) in high-sediment waters and their relationships with environmental factors. This study utilized ultraviolet-visible spectroscopy (UV-vis) and three-dimensional fluorescence excitation emission matrix spectroscopy (3D-EMMs) techniques to investigate the optical properties of DOMw and DOMp in the water section from Xiaolangdi to Kaifeng along the Yellow River, examining their spatiotemporal heterogeneity, and establishing quantitative relationships between environmental factors and DOMw and DOMp. The research findings suggest that the concentrations of DOMw, DOMp, and biodegradable dissolved organic carbon (BDOC) in the water segment from Xiaolangdi to Kaifeng along the Yellow River exhibit fluctuating spatial variation, showing an overall trend of DOCw > BDOC > DOCp. Minimum and maximum concentrations of DOMw, DOMp, and BDOC were recorded in April and June. The sources of DOMw and DOMp in this water section are a combination of terrestrial input and internal sources (phytoplankton, algae). The cluster analysis and partial least squares path modeling (PLS-PM) showed that nitrogen-phosphorus nutrients and sediment particle size significantly impact the river compositional features of DOMw and DOMp, and in both the DOMw and DOMp models, it is evident that water quality parameters and nutrient concentrations directly influence the concentration, sources, and composition of dissolved organic matter. This, in turn, indirectly affects the molecular characteristics of DOM, thereby exhibiting a pathway-dependent nature. • DOMw and DOMp are a combination of terrestrial inputs and endogenous sources. • DOMw consists of humic-like components, DOMp consists of protein-like components. • Nutrients and sediment particle size significantly impact the compositional characteristics of DOMw and DOMp.