Composition and lability of photochemically released dissolved organic matter from resuspended estuarine sediments

Photodissolution of Rare Earth Elements and Dissolved Organic Carbon from Subbituminous Coal: Effects of Environmental Variables and Implications for Biogeochemical Cycling

“…The maximum DOC produced in the irradiated samples was 30.5 ± 5.69 mg/L (765 W/m 2 , 5.5 °C, Day 4) and 1.74 ± 0.155 mg/L (5.5 °C, Day 1) for the dark treatment groups. These results agree with previous studies that report the photochemical formation of DOC from particulate organic matter. − , The relatively small concentration of DOC in the dark controls represents the readily water-soluble organic matter in coal. An increase in DOC after irradiation could be explained by the photooxidation of hydrocarbons in coal that produces water-soluble organic compounds.…”

“…79−83 Metal complexation can affect DOM-mediated processes, 84−88 and photochemistry is an environmental driver of DOM composition. 38,51,64,89,90 There is considerable uncertainty over how boreal soil−aquatic−marine system interactions will change over the coming years due to onset of rapid deglaciation and permafrost thaw. 91−95 As new stores of subbituminous coal are released from landslides and terrestrial throughfall into the marine environment, photochemistry, as a process, may affect increased REE bioavailability in the oceans.…”

Characterizing Dissolved Organic Matter Across a Riparian Soil–Water Interface: Preliminary Insights from a Molecular Level Perspective

“…The variation of molecular groups in S-DOM resulted from water submerging was also uncovered. Higher averaged relative abundances of peptides and unsaturated aliphatic compounds but lower averaged relative abundances of polyphenols, highly unsaturated compounds, and CRAM were observed in SS-DOM than those in S-DOM (Figure ) This indicates that after the riparian soils were submerged in water, S-DOM underwent specific changes in molecular groups, including (i) labile compounds were synthesized or photodissolved from the particulate phase; and (ii) relatively more aromatic compounds were partially removed in SS-DOM, because after submerging, water could act as a medium in which photoproduced reactive oxygen species can be generated and facilitate photodegradation of highly aromatic compounds (most sensitive to photodegradation). − Therefore, the variation of DOM on the molecular level across the soil–water interface further demonstrates that instead of simple “release of dissolved molecules from soils to rivers”, active removal and production processes are simultaneously involved.…”

“…The travel of organic matter from soil to water can be affected by several processes: physical processes (i.e., desorption , ), photodissolution (i.e., DOM released from particles induced by sunlight , ), and microbial processing of particulate organic matter (POM) to DOM. , Adsorption experiments have found that relatively high molecular weight (>500 Da) and highly aromatic compounds (SUVA 254 > 3.2 L mg C –1 m –1 ) are preferentially adsorbed on mineral surfaces. − Nevertheless, whether the findings from ideal lab incubation experiments can be applied to the field studies are less understood. Some field studies have compared DOM composition in water and adjacent soils to deduce the DOM compounds mobilized across the soil–water interface. − Although the similarity and difference in DOM composition between riparian soils and water support the presence of “selective” transport mechanisms, these studies usually neglected potential changes in DOM composition of soils after water submergence .…”

Exploring the Complexities of Dissolved Organic Matter Photochemistry from the Molecular Level by Using Machine Learning Approaches

“…Dissolved organic matter (DOM) is one of the largest reactive carbon pools on the earth, and its chemical composition and reactivity are closely associated with aquatic carbon and nutrient cycling, , trace-element transport, microbial metabolism, and reactions with environmental contaminants . Photochemical reactions (photoproduction and photodegradation) are essential components altering DOM chemistry, by directly mineralizing it to CO 2 or indirectly inducing its biogeochemical function changes for subsequent microbial mediation. − The state-of-the-art ultrahigh resolution mass spectrometry, Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS), can unprecedentedly provide thousands of molecular formulas (MFs) within one DOM sample and provide an opportunity to directly link the molecular chemical composition and photochemical reactivity. , Previous studies demonstrated significant DOM compositional conversions after photoirradiation, , and the MFs linked to photochemical processing are operationally classified as photoresistant, photolabile, and photoproduct types according to their occurrence before and after irradiation experiments. , …”