Chemogeography of Dissolved Organic Matter in Lake Sediments Structured by Climatic and Geochemical Factors

Abstract

Dissolved organic matter (DOM) plays a key role in lake carbon cycling, yet the geographic patterns and environmental associations of sediment DOM chemodiversity remain poorly understood. Here, we analyzed sediment DOM from 92 lakes across China spanning a broad latitudinal gradient of 23–50°N using Fourier‐transform ion cyclotron resonance mass spectrometry (FT‐ICR MS). Sediment DOM was dominated by aliphatic‐like compounds, with CHO formulas representing the major elemental class. DOM molecular richness decreased significantly with increasing latitude and elevation, and molecular composition exhibited a significant distance‐decay relationship. Distance‐decay slopes varied among compound classes, with peptide‐like and aliphatic‐like compounds showing stronger spatial turnover than unsaturated and aromatic compounds. DOM molecular richness and composition were associated with geographic, climatic, water, and sediment variables. Among these variable groups, sediment properties explained the largest unique fractions of variation in DOM chemodiversity, and sediment total organic carbon (TOC) showed the strongest associations with both molecular richness and composition. At the molecular level, molecules positively associated with sediment TOC were larger, more oxygenated, and less aromatic than negatively associated molecules. Geographic and climatic variables were associated with DOM chemodiversity mainly through indirect pathways involving water and sediment variables in the structural equation models. These findings highlight a strong association between sediment carbon status and DOM chemodiversity across broad environmental gradients and provide a continental‐scale basis for investigating DOM transformation and persistence in lake sediments.