Characterizing molecular fingerprint of dissolved organic matter shaped by natural and anthropogenic factors in a large macrophytic shallow lake wetland

Dissolved organic matter (DOM) participates in and affects many biological processes in aquatic ecosystems, altering nutrient cycling, bioavailability and toxicity of pollutants. Lake water contains thousands of DOM molecules, which largely originate from natural sources and are greatly influenced by external inputs through anthropogenic activities. To elucidate the shaping mechanism of the DOM composition under complex habitat conditions and anthropogenic disturbances, the characteristic molecular fingerprint of DOM was determined based on chemodiversity information obtained via ultrahigh-resolution mass spectrometry for the Baiyangdian wetland (a typical large macrophytic shallow lake in North China). In the Baiyangdian wetland, the DOM composition exhibited high complexity and spatial heterogeneity, and more recalcitrant DOM molecules were identified in summer than in spring. Although multiple natural factors (nutrient concentration, depth of water and quality of submerged macrophytes) and anthropogenic factors (different land uses and discharge of pollutants) were associated with the relative abundance of various DOM molecules, only the influences from the anthropogenic factors were statistically significant. The alpha diversity index of DOM could reflect variations in both the natural factors (total dissolved phosphorus) and the anthropogenic factors (discharge of nitrogen and phosphorus). Furthermore, the DOM composition in each group were clustered according to the ecological functions (natural reserves, tourism, breeding, and domestic supply functions), and exhibited molecular fingerprint features. This study provides an effective approach to characterize the molecular fingerprint features of DOM and critical information to better understand the shaping mechanism of the DOM composition under complex habitat conditions and anthropogenic disturbances.