The molecular characterization, source identification and biogeochemical processes of DOM derived from diverse sources in aquatic ecosystems

Dissolved organic matter (DOM) plays an essential role due to its high activities in freshwater systems, which exert significant influence on carbon cycling, nutrient dynamics, and migration of pollutants. However, due to the complexity of chemical composition, sources and biogeochemical processes of DOM, the understanding of their migration, transformation and fate within freshwater ecosystem remains limited. Specially in the context of global warming and eutrophication, the sources and fate of DOM will also undergo significant dynamic changes. Therefore, in this study the extraction and characterization strategy, source identification method and biogeochemical processes of DOM were systematically explored. Firstly, we optimized the extraction methods of organic matter from diverse sources, and thus identified their specific molecular fingerprint of organic matter in multiple medium. For example, the results showed that the optimized PPL solid-phase extraction at a 1:500 PPL/DOC ratio with dual ESI mode coupled with FT-ICR-MS enabled effective full-component molecular characterization of algae-derived DOM. And then based on this, we established a quantitative source apportionment model for aquatic DOM by integrating spectroscopic, molecular (FT-ICR-MS), and isotopic fingerprints. Refractory molecules were identified as the stable, source-diagnostic fraction of DOM, and then applied random forest importance ranking to quantify how optical and molecular parameters explain the variability of these signatures, allowing us to select the key tracers for model input and develop a new multi-proxy method for DOM source apportionment. This model has successfully applied in several lakes such as Lake Erhai and Caohai. Moreover, the biogeochemical processes including degradation, precipitation and environmental effect were also explored. Mineral adsorption exhibited distinct fractionation: terrestrial DOM (rich in aromatic compounds) was strongly adsorbed, while algal DOM (aliphatic-rich) showed weaker, reversible adsorption, thus eutrophication might potentially weaken carbon sink potential in lakes. Degradation experiments indicated that aliphatic compounds were readily bio-degraded, whereas aromatic, highly unsaturated compounds persisted, forming a refractory carbon sink. Furthermore, the molecular fingerprint and potential risk of anthropogenic microplastic-derived DOM (MP-DOM) were also explored. The results showed that MP-DOM was more aliphatic, oxygenated and lower aromaticity and they also showed higher potential for generating toxic disinfection by-products compared to natural organic matter with protein-like substances identified as key precursors. This research provides critical methodological advances for the characterization and source identification of DOM, and also provide theoretical insights for the precise management of lake organic pollution and proactive risk assessment and control of microplastics.

Presentation Preference: Standard Oral (12 Minutes)

Primary Presenter: Shasha Liu, University of Science and Technology Beijing (liushashajida@163.com)

Authors:

Shasha Liu, University of Science and Technology Beijing  (liushashajida@163.com)