Identifying the reactivity of photochemically produced reactive intermediates with dissolved organic matter

Abstract

Photolysis of dissolved organic matter (DOM) is a critical pathway in the carbon cycle of inland lakes. Complete photooxidation releases carbon dioxide (CO2), while partial photooxidation results in the incorporation of oxygen (O2) into DOM and subsequent transformation of DOM. Both complete and partial photooxidation can be highly influenced by indirect photolysis, which occurs when photochemically produced reactive intermediates (PPRI) transform DOM. However, which PPRI and reaction mechanisms are most important to DOM photooxidation remains unclear. In this study, DOM was collected from 11 inland lakes of differing trophic status to investigate the role of PPRI in complete and partial photooxidation of DOM. Quencher studies of singlet oxygen (¹O2), hydroxyl radical (•OH), and triplet DOM (³DOM), along with Fourier transform-ion cyclotron resonance mass spectrometry (FT-ICR MS) analysis, were used to identify the roles of these PPRI in the partial and complete photooxidation of DOM. Consequently, all PPRI investigated were found to play a role in complete and partial photooxidation in a diverse set of DOM. For example, O2 contributed to the oxidation of DOM, •OH participated in oxidation and complete photooxidation in some samples, and DOM played a role in complete photooxidation. Overall, these results give insight into how DOM reactivity influences CO2 production in inland lakes.