Influence of dissolved organic matter origin on hydrogen peroxide concentration in aquatic environments of southern Florida

Environmental context Characterizing dissolved organic matter (DOM) is important for understanding its quality, which is highly linked to its reactivity. The DOM acts as a substrate for the abiotic production of hydrogen peroxide (H2O2). In southern Florida aquatic environments, we found that the origin of DOM has a profound effect on the H2O2 concentrations. Rationale Dissolved organic matter (DOM) is a complex mixture of compounds that is ubiquitous in aquatic ecosystems and is involved in multiple biogeochemical processes. The degradation of DOM due to exposure to solar radiation can produce reactive photoproducts. Among these, reactive oxygen species (ROS), particularly hydrogen peroxide (H2O2), are strong oxidizing agents. We aim to expand our understanding of the complex relationship between DOM and H2O2 in tropical and subtropical aquatic systems in Florida. Methodology Using absorbance and fluorescence-based methods, we characterized the DOM quality. Additionally, we measured H2O2 concentrations in 42 aquatic systems. Results Freshwater aquatic ecosystems showed a broad variation in DOM quantity and quality. Based on their origin, the water samples can be grouped int three categories: autochthonous, recently produced allochthonous and allochthonous DOM. Using parallel factor analysis modeling (PARAFAC), we validated five fluorescent components: three humic-like components, one fulvic-component and one protein-like component. Notably, the humic-like component C4 (A), autochthonous and fresh allochthonous DOM, showed a significant direct relationship with H2O2 concentrations. Conversely, in water bodies primarily characterized by allochthonous DOM origin, a significant direct linear relationship was observed between chlorophyll-a and H2O2 concentrations. Discussion Overall, our results support the idea that reactive humic compounds serve as a primary substrate for H2O2 production. However, in the absence of reactive compounds, the biological processes also play a crucial role in the H2O2 production.