Impact of UV radiation on DOM transformation on molecular level using FT-ICR-MS and PARAFAC

Abstract

Dissolved organic matter (DOM) is an omnipresent constituent of natural water bodies. Reuse and transformation of DOM compounds in the water column is driven by physicochemical and biological processes leading to the production of refractory DOM. Typically, breakdown of DOM chemical compounds into smaller or more condensed fragments is triggered by ultraviolet (UV) radiation. Here, we present a study on the photodegradation of DOM produced during an incubation experiment with a natural microbial community. At the end of the first incubation without UV irradiation, the samples from 3 mesocosms were filtered to remove microbes and particles and continuously exposed to UV radiation (280-365 nm). We investigated DOM in depth via monitoring of dissolved organic carbon (DOC) concentrations, DOM molecular characterization by Fourier-Transform Ion Cyclotron Resonance Mass Spectrometry (FT-ICR-MS) and excitation emission matrix spectroscopy (EEMS). Analysis of variance indicated no significant differences in the DOC concentration between treatments. Main peaks in the fluorescent DOM (FDOM) were photo-bleached by UV radiation, and an increase in the fluorescent intensity of selected peaks was observed on irradiated samples toward the end of the experiment. Parallel factor analysis (PARAFAC) indicated the presence of three main components in all treatments: C1 (Marine humic M), C2 (Bacterial produced humic C), C3 (Tyrosine), and an additional component in the dark incubation of mesocosm 3, C4 (Tryptophan). Despite an intensive filtration protocol through 0.7, 0.2 and 0.1 μm filters, low bacterial abundances were determined (b2.5 × 10 −3 cells mL −1 ). We observed a direct correlation between structural indices and the intensity of PARAFAC components. Average double bond equivalent and aromaticity were strongly positively correlated with PARAFAC components C1 and C2 for one or more mesocosm. Moreover, FT-ICR-MS showed that under the tested conditions, the refractory character of the DOM assessed as the similarity to a deep ocean DOM reference did not increase on molecular level. Thus, mechanisms other than photochemical transformations of relatively recent DOM are likely necessary to facilitate long-term stability of DOM in the oceans.

Factors controlling the distributions of dissolved organic matter in the East China Sea during summer

“…Although the photodegradation could modify the FDOM indexes during the long-range transport from the Changjiang River, such as significant decreasing the degree of DOM humification and increasing the BIX value of DOM [50][51][52][53] , the values of the indexes between the surface (0 m) and subsurface water (> 0 m) depths in these well-stratified water columns showed no statistically differences (Student's t-test; p-value = 0.06 for HIX, 0.47 for BIX, and 0.35 for FI). In the previous studies, the relatively lower HIX values (< 2) and higher BIX values (> 0.8) already reported near the Changjiang River mouth 54,55 , indicating that the in-situ biological production seems to be a significant origin of DOM in the ECS.…”

A DOM continuum from the roof of the world – Tibetan molecular dissolved organic matter characteristics track sources, land use effects, and processing along the fluvial-limnic pathway

“…In a streamestuary-lake gradient the terrigenous brackish DOM likely underwent a transformation when entering deeper in the lake, leaving more recalcitrant DOM behind (Goldberg et al, 2015) as corroborated by the higher percentage of IoS compared to stream and brackish DOM (Table 2). Miranda et al (2020) found that highly unsaturated and aromatic compounds are not only degraded, but partly transformed to unsaturated (N-containing) compounds by UV radiation. This can further explain the increase in unsaturated and unsaturated N-containing compound classes and the more negative CHO with lower molecular mass (Fig.…”

Study on Dissolution Characteristics of Excess Sludge by Low-Temperature Thermal Hydrolysis and Acid Production by Fermentation

“… 30 , 31 C4(322 and 430 nm) is soil fulvic acid, which belongs to humic acid with a high molecular weight and is terrestrial in nature. 32 …”

“…It includes two protein-like (C1 and C3) and three humus-like (C2, C4, and C5) substances. Among them, C1 (310 and 364 nm) is a metabolic protein, belonging to tyrosine-like substances, usually related to microbial products. , C3 (282 and 334 nm) is a protein-like substance, belonging to tryptophan-like substance, mainly free or bound protein or amino acid, which can be used to indicate a complete protein. , C2 (418 and 470 nm) and C5 (314, 382, and 454/526 nm) are visible humic acids, usually derived from manmade sources such as sewage or agricultural waste. , C4­(322 and 430 nm) is soil fulvic acid, which belongs to humic acid with a high molecular weight and is terrestrial in nature …”

“…30,31 C4(322 and 430 nm) is soil fulvic acid, which belongs to humic acid with a high molecular weight and is terrestrial in nature. 32 Figure 5 shows the distribution of maximum fluorescence intensity of each component of thermally hydrolyzed sludge at different temperatures. It can be seen that different temperatures have a significant effect on the fluorescence intensity of sludge dissolution products, and the maximum fluorescence intensities at different temperatures are different, C3, C3, C1, C3, C3, C3, C3, respectively.…”