Complete and Partial Photo-oxidation of Dissolved Organic Matter Draining Permafrost Soils

Abstract

Photochemical degradation of dissolved organic matter (DOM) to carbon dioxide (CO2) and partially oxidized compounds is an important component of the carbon cycle in the Arctic. Thawing permafrost soils will change the chemical composition of DOM exported to arctic surface waters, but the molecular controls on DOM photodegradation remain poorly understood, making it difficult to predict how inputs of thawing permafrost DOM may alter its photodegradation. To address this knowledge gap, we quantified the susceptibility of DOM draining the shallow organic mat and the deeper permafrost layer of arctic soils to complete and partial photo-oxidation and investigated changes in the chemical composition of each DOM source following sunlight exposure. Permafrost and organic mat DOM had similar lability to photomineralization despite substantial differences in initial chemical composition. Concurrent losses of carboxyl moieties and shifts in chemical composition during photodegradation indicated that photodecarboxylation could account for 40-90% of DOM photomineralized to CO2. Permafrost DOM had a higher susceptibility to partial photo-oxidation compared to organic mat DOM, potentially due to a lower abundance of phenolic moieties with antioxidant properties. These results suggest that photodegradation will likely continue to be an important control on DOM fate in arctic freshwaters as the climate warms and permafrost soils thaw.

Modeling CO2 emissions from Arctic lakes: Model development and site‐level study

“…The parameters in equations and , i.e., SUVA 305 , s g , m 1, and m 2, are lake specific (see Table ). We obtained or fitted them for yedoma, thermokarst, and glacial lakes, respectively, based on the published work [ Shirokova et al ., ; Cory et al ., ; Manasypov et al ., ; Ward and Cory , ]. It should be noted that the AQY parameter fitted from the work of Cory et al .…”

“…[] would yield low DOC photolability in yedoma lakes, which is consistent with other investigations [ Ward and Cory , ; Stubbins et al ., ]. In contrast, tundra and thermokarst lakes, which are mainly fed by terrigenous modern‐age DOC, would likely have much higher photochemical activities [ Cory et al ., ; Ward and Cory , ]. Unlike DOC tr , DOC aq is assumed to be little susceptible to sun‐induced mineralization [ Obernosterer and Benner , ].…”

Oxygen Isotopes (δ18O) Trace Photochemical Hydrocarbon Oxidation at the Sea Surface

“…A similar observation was made with regard to photo-production of fatty acids during the IXTOC-I oil spill (Overton et al, 1980). This result is surprising because the initial sensitizers for crude oil (polycyclic aromatic hydrocarbons, resins, and asphaltenes; Payne & Phillips, 1985) are different than for DOC (tannins, lignin, pigments, and thermally altered organic matter; Ward & Cory, 2016;Ward et al, 2017), and thus the major photo-oxidation pathways are expected to differ considerably. This result is surprising because the initial sensitizers for crude oil (polycyclic aromatic hydrocarbons, resins, and asphaltenes; Payne & Phillips, 1985) are different than for DOC (tannins, lignin, pigments, and thermally altered organic matter; Ward & Cory, 2016;Ward et al, 2017), and thus the major photo-oxidation pathways are expected to differ considerably.…”

Changes in dissolved organic matter quality in a peatland and forest headwater stream as a function of seasonality and hydrologic conditions

“…Aromatic structures of DOM could cause disinfection by-product (DBP) generation during drinking water treatment (Korshin et al, 1997). More aromatic, humic DOM also decreases light penetration and DOM photo-degradation potential in surface waters (Cory et al, 2007;Ward and Cory, 2016). The easily biodegradable DOM (BDOM) fraction -mainly fresh, protein-like DOM, derived from root or leaf exudates, litter decay, or leachates -can be readily utilized and serves as important nitrogen and phosphorus source in aquatic systems (Fellman et al, 2009).…”