Spatiotemporal variability drives dissolved organic matter composition in a tropical river: Insights from PARAFAC and...

The dynamics of dissolved organic matter (DOM) in river systems are complex and influenced by spatial and temporal drivers such as land use and land cover (LULC) and hydrological conditions. Understanding these linkages is critical for water quality management, particularly in rapidly urbanizing and industrializing regions. In this study, the spatial and temporal effects of LULC on DOM optical characters and compositions along the Chao Phraya River, Thailand, were investigated during four sampling events between 2023 and 2024. Water samples were collected from five sites along with corresponding LULC data. DOM was characterized using fluorescent spectroscopy with parallel factor analysis (PARAFAC) and Orbitrap mass spectrometry (Orbitrap MS) with non-target analysis. Humic-like components (C1 and C2) were consistently correlated with molecular features associated with urban and miscellaneous land uses, with up to 492 components showing significant correlation during high-precipitation conditions. The components were composted of mainly chlorinated CHON and oxygenated CHOS compounds (O/C > 0.4), closely resembling signatures of anthropogenic DOM. Protein-like component (C3) correlated with up to 397 components dominated by lignin-like CHO and reduced CHOS compounds (O/C < 0.4) associated with agricultural land use. Notably, the number of correlations varied across different samplings, indicating seasonal fluctuation. These findings highlight the role of LULC and hydrological conditions in shaping DOM. The overlap with DBP precursors indicates the need for careful watershed management. The results provide valuable insights for land development planning, watershed protection, and mitigation of DBPs in downstream drinking water treatment.