Influence of land cover types and phytoplankton community on the distribution and fate of dissolved organic matter in a typical river located in the semi-arid regions of China

•Dissolved organic matter (DOM) is associated with land-use and in-situ production.•Mediation analysis allowed disentangling the effects of land-use vs. phytoplankton.•Phytoplankton notably mediated land-use effects on the shift in DOM in urban areas.•Decreased humic-like DOM is mainly attributed to the reduced terrestrial loading. Land use can impact dissolved organic matter (DOM) dynamics directly by changing terrestrial loading in anthropogenic areas, and indirectly by promoting in-situ phytoplankton production due to the high load of nutrients. However, understanding how land use and phytoplankton community interact to affect DOM quantity and quality is deficient. To tease apart the synergistic effects of land use and phytoplankton on DOM dynamics, fluorescence spectroscopy with parallel factor analysis (PARAFAC) and mediation analysis was performed in this study. PARAFAC produced three components that had two humic-like (C1 and C2) and a protein-like (C3) fluorescent components, significantly related to anthropogenic land-use (cropland + urban area) and phytoplankton concentration (p