Molecular Diversity of Dissolved Organic Matter Reflects Macroecological Patterns in River Networks

Understanding the molecular complexity of dissolved organic matter (DOM) is crucial for deciphering ecosystem function and predicting responses to environmental change. Using a continental-scale dataset of molecular formulae generated by Fourier-transform ion cyclotron resonance mass spectrometry through the WHONDRS Project, we reveal fundamental scaling patterns of DOM diversity across watershed characteristics. We show that both local and regional watershed features across latitude reveal universal scaling patterns across compound classes. Our analysis demonstrates that local and regional watershed features—including drainage area, land use, land cover, and water temperature—significantly influence DOM diversity, quantified through DOM richness and chemodiversity. Notably, we document one of the first observed latitudinal gradients in freshwater chemodiversity, suggesting that macroecological factors orchestrate molecular diversity similarly to organismal distributions. These findings offer more than descriptive insights. By identifying universal scaling laws, we propose that simple predictive models can forecast compound responses to climate change, providing critical understanding of watershed functional dynamics under emerging environmental conditions. The research contributes a novel perspective on ecosystem molecular complexity, bridging biogeochemical processes with broader ecological principles and offering a quantitative framework for anticipating ecosystem molecular transformations across scales.