Amount Of Dissolved Organic Matter Research Articles

Vertical Profile Characteristics of Dissolved Organic Matter Biochemistry in the Tropical Reservoir Shaped by Hydrodynamic Forces

Dissolved organic matter (DOM) exerts a crucial role in biogeochemical processes and ascertaining water quality in reservoirs, where it is vulnerable to the dynamic impacts of surface water inflows. However, understanding how DOM quantity and biochemical features responds to hydrodynamic forces in tropical reservoirs remains limited. To enhance our understanding of the vertical profiles of DOM characteristics under varying hydrodynamic forces (strong, moderate, and weak regions) in the Chitian Reservoir (18°43′–18°42′ N, 109°68′–109°70′ E), in December 2023, we investigated the concentrations and biochemical characteristics of water column DOM samples using multispectral techniques, a parallel factor model, and two-dimensional correlation analysis. Our results indicated that DOM concentrations (4.34 ± 0.36 mg/L) are the highest in the reservoir center, whereas total nitrogen (0.52 ± 0.04 mg/L), total phosphorus (0.02 ± 0.03 mg/L), and nitrate nitrogen (1.01 ± 0.07 mg/L) present their highest values in the inlet region. As hydrodynamic force decreases, microbial activity increases, whereas DOM’s humification degree and molecular weight decline. DOM in the Chitian Reservoir comprises humic-like components, including three terrestrial sources (accounting for 85.38%~87.03%) and one microbial source, with dominant characteristics of allochthonous origin. The relative abundance of microbial components decreased from 14.62% to 12.97% with the increasing hydrodynamic force and increased with depth. DOM functional groups in the strong hydrodynamic force region and the reservoir’s upper layer show high consistency and uniformity. Phenolic O–H is the most reactive functional group concerning changes in water depth across all hydrodynamic areas, followed by polysaccharide C–O, owing to its high photoactivity. In contrast, aromatic C–H demonstrates the weakest reactivity. DOM’s spectral features are closely linked to nutrient form concentrations (N and P).

Manganese Dioxides Induce the Transformation and Protection of Dissolved Organic Matter Simultaneously: A Significance of Crystallinity.

Interactions between manganese dioxides (MnO2) and dissolved organic matter (DOM) have long been the subject of scientific inquiry. However, the effect of MnO2 crystallinity on the DOM fate remains unclear. Herein, we comprehensively investigate the adsorption, protection, and mineralization of DOM by MnO2 with various crystallinities (order of crystallinity: γ-30 < γ-90 < γ-120). The results show that DOM adsorption is positively correlated with the specific surface area (SSA) of MnO2; γ-30 with the largest SSA adsorbs the highest amount of DOM, resulting in DOM protection. However, γ-90 and γ-120 with a smaller SSA could induce the Maillard reaction and thereby promote the formation of geopolymerized organic matter, leading to reduced bioavailability of DOM. Furthermore, the capability of MnO2 to mineralize DOM decreases in the order γ-120 > γ-90 > γ-30, and it is determined by both Mn4+ and hydroxyl radical (·OH) content. In particular, the contribution of radical-based oxidation of ·OH to DOM mineralization is 64.8, 47.4, and 23.7% for γ-30, γ-90, and γ-120, respectively. We propose that crystallinity of MnO2 may have a significant but hitherto unexplored influence on the global carbon cycle over geological time.

Exploring the variations in molecular characteristics of dissolved organic matter driven by aquaculture types

In recent decades, global aquaculture has expanded rapidly, raising concerns about coastal environmental degradation due to unregulated or poorly regulated discharge of aquaculture tailwater. Despite the crucial role of dissolved organic matter (DOM) in biogeochemical processes and aquatic biodiversity, the influence of aquaculture type on the molecular characteristics of DOM remains largely unexplored. Herein, this study investigated the variations in chemical and spectroscopic properties as well as molecular characteristics and composition of DOM across different aquaculture types including crustacean, fish and shellfish. Our findings revealed notable differences in DOM quantities among different aquaculture types, with crustacean and fish aquaculture water containing higher DOM amount compared to shellfish aquaculture water. This disparity can be attributed to the more frequent formulated feeds of crustacean and fish in contrast to shellfish aquaculture. Furthermore, distinct differences were also observed in the characteristics and composition of DOM among the different aquaculture waters. Specifically, DOM in shellfish aquaculture water exhibited a higher abundance of unsaturated and reduced molecules as well as increased aromaticity compared to the other two aquaculture waters. Conversely, DOM from fish aquaculture water showed a greater contribution from terrestrial origin characterized by elevated levels of plant-based components such as lignin-like and tannin-like compounds. Interestingly, DOM from shellfish aquaculture water contained lower levels of microbial-derived components such as lipid-like and protein-like compounds, likely due to reduced microorganism populations resulting from lower nutrients availability and higher salinity. Overall, these significant variations in characteristics and composition of DOM underscore the potential impacts of aquaculture type on the DOM biogeochemical cycle and the environmental quality in aquatic ecosystems.

Four decades of changing dissolved organic matter quality and stoichiometry in a Swedish forest stream

Dissolved organic matter (DOM) concentrations have risen by a factor of two or more across much of Europe and North America during recent decades. These increases have affected the carbon cycle, light regime, drinking water treatability, and the energy and nutrient budgets of lakes and streams. However, while trends in DOM quantity are well characterised, information on how/whether qualitative properties of DOM have changed are scarce. Here, we describe over 40 years of monitoring data from a forested headwater stream in the Gårdsjön experimental catchment, southwest Sweden, which provides a unique record of biogeochemical change, including optical and stoichiometric DOM quality metrics, spanning the entire period of recovery from acidification. For the period 1980–2020 we find a 71% reduction in decadal mean sulphate concentrations, and a similar reduction in inorganic aluminium concentrations, alongside a 64% increase in dissolved organic carbon (DOC) concentrations. Over the same period, colour (absorbance at 420 nm) increased almost twice as much as DOC, whereas dissolved organic nitrogen (DON) increased by only one third as much. These results demonstrate a shift in stream water composition, with DOM becoming dominated by highly coloured, complex, nitrogen-poor compounds. This material is likely more resistant to biological degradation, but more susceptible to photochemical degradation. Changes in DOM stoichiometry could lead to intensified nitrogen and/or phosphorus limitation in surface waters, while increased colour/DOC ratios could intensify light-limitation of primary production beyond that expected from DOC increases alone. We observed increases in organic matter associated metals (iron 117%, organically complexed aluminium 85%) that exceeded the increase in DOC, consistent with their increased mobilisation by more aromatic organic matter. All observed changes are consistent with recovery from acidification being the primary driver of change, implying that past acidification, and ongoing recovery, have profoundly affected terrestrial and aquatic biogeochemistry, ecology and the carbon cycle.

Temporal Variations in Fire Impacts on Characteristics and Composition of Soil-Derived Dissolved Organic Matter at Qipan Mountain, China.

Dissolved organic matter (DOM), the most reactive fraction of forest soil organic matter, is increasingly impacted by wildfires worldwide. However, few studies have quantified the temporal changes in soil DOM quantity and quality after fire. Here, soil samples were collected after the Qipan Mountain Fire (3-36 months) from pairs of burned and unburned sites. DOM contents and characteristics were analyzed using carbon quantification and various spectroscopic and spectrometric techniques. Compared with the unburned sites, burned sites showed higher contents of bulk DOM and most DOM components 3 months after the fire but lower contents of them 6-36 months after the fire. During the sharp drop of DOM from 3 to 6 months after the fire, carboxyl-rich alicyclic molecule-like and highly unsaturated compounds had greater losses than condensed aromatics. Notably, the burned sites had consistently higher abundances of oxygen-poor dissolved black nitrogen and fluorescent DOM 3-36 months after the fire, particularly the abundance of pyrogenic C2 (excitation/emission maxima of <250/∼400 nm) that increased by 150% before gradually declining. This study advances the understanding of temporal variations in the effects of fire on different soil DOM components, which is crucial for future postfire environmental management.

Temporal variations in dissolved organic matter properties in a eutrophic lake under water dilution and aquatic plant litter decomposition: A simulated microcosm study revealing the environmental and microbial driving factors

Dilution by importing external clean water and restoration of aquatic vegetation are widely applied strategies for improving water quality of eutrophic lakes, while the influence of dilution or aquatic plant litter decomposition on dissolved organic matter (DOM) properties, which is closely associated with the health of aquatic ecosystems, is rarely known. In this study, the temporal variations of DOM properties in the overlying water of a eutrophic lake (Yilong lake in Yunnan, southwest China) under water dilution and aquatic plant litter decomposition were comparatively investigated via a simulated microcosm study using in situ samples. The results showed that water dilution reduced DOM concentration and bioavailability in the overlying water in a short term (about 45 d), and increased DOM humification, but such effect diminished over time. DOM concentration increased substantially during aquatic plant litter decomposition, and reed litter released much more amounts of DOM than that of cattail litter, which dominated by protein-like substances and characterized by high bioavailability and low humification degree. Nutrient (available phosphorus (AP), NH4+-N and TN) contents in the sediment indirectly affected DOM properties by remarkably influencing microbial community compositions and enzyme activities. The strong correlations between the relative abundances of dominant genera Bacillus and Clostridium and concentrations of DOM components implied the important roles of these taxa in DOM transformations. Our findings highlighted the effects and potential mechanisms of dilution and aquatic plant litter decomposition on DOM properties in eutrophic water bodies, and the necessity of proper water diversion and plant litter harvest to reduce endogenous organic pollution in lakes.

Long-term effects of nitrogen and phosphorus fertilization on profile distribution and characteristics of dissolved organic matter in fluvo-aquic soil

Dissolved organic matter (DOM) drives numerous biogeochemical processes (e.g. carbon cycling) in agro-ecosystems and is sensitive to fertilization management. Nevertheless, changes in the quantity and quality of DOM in the vertical soil profile following long-term continuous nitrogen (N) and phosphorus (P) inputs remain unclear. In this study, the contents and optical characteristics of DOM along a 2-m soil profile were investigated using a 40-year wheat/maize rotation combined with experiments using different N and P fertilization rates in the North China Plain. The results revealed that the dissolved organic carbon (DOC) content decreased with an increase in soil depths. Compared with that in the control (no fertilization), 40-year N, P, and N + P additions increased the soil DOC content by 26%–69%, except for 270-kg N, and 67.5-kg P treatments. N + P application resulted in higher DOC contents than N-alone and P-alone applications. N, P, and N + P inputs increased or did not affect the aromaticity and hydrophobicity of DOM at 0–40 cm but reduced them from 40 to 200 cm. Compared with that in the control, N, P, and N + P inputs enhanced the content of humic acid-like substances (C1+C2+C3+C4) and decreased the content of protein-like substance (C5). C1 was the dominant component among the five DOM, representing the microbial humic component. Optical indices also indicated that soil DOM primarily originated from microbial sources. Nutrient addition accelerated transformation between complex C1 and simple C5 via promoting microbial activities. These results imply that N and P fertilizers increased the DOM content and altered its composition, thereby potentially affecting the stability of soil organic matter in the agroe-cosystems.

Assessing the spatiotemporal variability of dissolved organic matter fluorescence composition in the Lake George, NY watershed

Lake George (LG) is a temperate, oligotrophic, medium-sized lake (114 km2) located in northeastern New York State (U.S.). Lakes are highly understudied environments where extensive dissolved organic matter (DOM) processing occurs. With this study we establish the foundation for researching the organic biogeochemistry of the LG watershed, in particular, the numerous tributaries flowing into the lake. Collected were 213 samples from 64 tributaries and 12 lake locations. Some of the tributaries had unique wastewater, agricultural, or wetland influences. We employed fluorescence spectroscopy, a common biogeochemical technique, to characterize the fluorescent DOM (FDOM) component. We developed a parallel factor analysis (PARAFAC) model for the deconvolution of FDOM data allowing to depict six underlying FDOM constituents, which varied in source and biogeochemical reactivity on spatiotemporal scales. Tributary DOM, in comparison to lake DOM, was much more aromatic, of larger molecular weight, more humic, and contained less protein-like material. The distribution of humic and protein-like PARAFAC components was impacted by land-use and wastewater influences. Supporting characterization of the chromophoric DOM (CDOM) and total DOM (on dissolved organic carbon basis) allowed differentiating the influence of wetlands, which could not be depicted by spatiotemporally assessing the variability of PARAFAC components. Temporal assessment revealed minor variabilities in tributary DOM quantity and quality except in cases of point sources such as wastewater treatment facilities. Overall, this primer study establishes baseline understanding of the baseflow levels of DOM constituents in the LG watershed, and more broadly, presents a PARAFAC model for the deconvolution of fluorescence spectra of DOM from temperate and oligotrophic lake watersheds such as LG.

The loss of dissolved organic matter from biological soil crust at various successional stages under rainfall of different intensities: Insights into the changes of molecular components at different rainfall stages

Biological soil crusts (BSCs) are typical covers in arid and semiarid regions. The dissolved organic matter (DOM) of BSCs can be transported to various aquatic ecosystems by rainfall-runoff processes. However, the spatiotemporal variation in quality and quantity of DOM in runoff remains unclear. Herein, four kinds of runoff plots covered by four successional stages of BSCs were set up on slopes, including bare runoff plot (BR), cyanobacteria crust covered runoff plot (CR), mixed crust covered runoff plot (MIR), and moss crust covered runoff plot (MOR). The quantity and quality of DOM in runoff during rainfall was investigated based on the stimulated rainfall experiments combined with optical spectroscopy and ultra-high resolution mass spectrometry analyses. The results showed that the DOM concentrations (i.e., 0.30 to 45.25 mg L−1) in runoff followed the pattern of MOR>MIR>CR>BR, and they were exponentially decreased with rainfall duration. The DOM loss rate of BR (8.26 to 11.64 %) was significantly greater than those of CR, MIR, and MOR (0.84 to 3.22 %). Highly unsaturated compounds (HUCs), unsaturated aliphatic compounds (UACs), saturated compounds (SCs), and peptide-like compounds (PLCs) were the dominated compounds of the water extractable DOM from the original soils. Thereinto, PLCs and UACs were more easily leached into runoff during rainfall. The relatively intensity of HUCs in runoff generally decreased with rainfall duration, while the relatively intensities of UACs, PLCs, and SCs slightly increased with rainfall duration. These findings suggested that the DOM loss rate was effectively decreased with the successional of BSCs during rainfall; meanwhile, some labile compounds (e.g., PLCs and UACs) were transported into various aquatic ecosystems by rainfall-runoff processes.

Optical properties and molecular compositions of dissolved organic matter in multiple runoff components during rainfalls on the karst hillslope

Understanding the chemical composition, origin, and molecular structure of dissolved organic matter (DOM) in multi-interface runoff is essential for comprehending the fate of laterally transported DOM in complex soil-epikarst systems of karst hillslopes. Limited information, however, is available for the optical properties and molecular compositions of the transported OM in multiple runoff components on the karst hillslope in relation to land-uses and soil thicknesses. In this study, we conducted a study to observe the changes in the quantity and quality of DOM in multiple interface flow (surface, subsurface, and epikarst) during natural rainfall events in 2022 in karst hillslopes that are covered by different land uses (cropland and shrubland) and soil thicknesses (with mean depths of 66.0 cm for deeper soil and 35.4 cm for shallower soil) in the karst region of southwest China. chemcial compositions of runoff DOM were determined by optical analysis and microbial compositions in runoff were inferred with high-throughput sequencing. The results showed that the soil-epikarst structure was controlling the runoff DOM quantity and quality during rainfall events. A decrease in the aromaticity, humification, unsaturation, and oxidation degree and an increase in carbohydrate, aminosugars, protein, and lipid compounds were found from surface to epikarst flow, indicating that plant-and soil-derived carbon decreased, while the microbially-derived carbon increased. The results were further comfirmed by the higher bacterial richness and diversity, along with fungal diversity in the epikarst flow compared to other runoff components. The bio-labile protein materials (C2) were the most important component of runoff DOM output in karst hillslopes. In surface and subsurface flow, rainfall amount, runoff rate, and discharge significantly affected the DOM concentration and quality during rainfalls, indicating that the dynamics of DOM in runoff from karst hillslopes were predominantly influenced by hydrological processes. Furthermore, the runoff DOM quality in cropland was dominated by lower unsaturation and oxidation degrees and higher protein component, compared to those in shrubland. The compositions of DOM in runoff from hillslope plots with thicker soils were primarily characterized by microbially-derived materials. Our findings were conducive to understanding the mechanism governing the migration of DOM quality and quantity in discharge during multi-interface hydrological processes on karst hillslopes.

Quantity and quality characteristics of DOM loss in sloping cropland under natural rainfall in Southwestern China

Rainfall events lead to dissolved organic matter (DOM) loss in sloping cropland, resulting in a high risk of soil carbon emissions and water pollution. However, limited studies have concentrated on the quality of DOM during different loss pathways in sloping cropland. In this study, the characteristics of DOM loss were explored during different loss pathways (surface runoff, interflow (0–20 cm), interflow (20–40 cm), and sediment) under different slope gradients (10° and 15°), based on natural rainfall. The results showed that surface runoff was the primary carrier of DOM in the sloping cropland, occupying 33 %-43 % of the total loss flux. The slope gradient significantly increased the DOM loss flux of surface runoff and sediment (p < 0.05). Parallel factor analysis (PARAFAC) analyses indicated that four fluorescent components of DOM were detected in both the runoff and sediment. The humic-like components (C1 and C2) accounted for higher than 70 % of the DOM in surface runoff. The protein-like components (C3 and C4) tended to dominate the DOM in the sediment and accounted for 63.02 %-66.93 %. An increased slope gradient exacerbated hydrophobic carbon loss in runoff. The hydrophobicity and aromaticity of DOM in sediment were higher than those in surface runoff. The molecular weight and bioavailability of DOM in sediment were lower than those in surface runoff. The range of humification index (HIX) was 0.63–0.70, indicating a low degree of DOM humification in sloping cropland. Our study clarified the differences between DOM quantity and quality during different loss pathways, which can provide a theoretical foundation for the effective prevention and control of DOM loss and the sustainable agricultural development of sloping cropland.

Anthropogenic dissolved organic matter accumulation fuels greenhouse gas diffusive emissions in urban lakes along trophic state levels

Lakes are an important reservoir of dissolved organic matter (DOM) and also emit large amounts of greenhouse gases (GHGs), such as carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O). Yet, the linkages between quantity and quality of DOM and GHGs emissions are still not well understood. Hence, we investigated how DOM optical properties mediated dissolved GHGs levels and diffusive fluxes along a trophic state level in subtropical urban lakes, China. Our study showed that anthropogenic protein-like DOM (tryptophan- and tyrosine-like components) dominated the DOM pools, comprising 62% of total fluorescence DOM (FDOM). Partial least squares path modeling (PLS-PM) showed that the direct contribution of relative abundance of DOM to CO2 and CH4 diffusion in the highly-eutrophic state was higher than in the mesotrophic and lightly/moderately-eutrophic states. In particular, protein-like DOM primarily accounted for CO2 variations (44%-49%), while humic- and protein-like DOM contributed comparably to CH4 variations (38%-40% vs. 36%-40%). Furthermore, in the lightly/moderately- and highly-eutrophic states, nutrients contributed to DOM, CO2 and CH4 in both direct and indirect ways, while phytoplankton (chlorophyll a, Chl-a) negatively and directly affected carbon emissions. However, only nitrogen content directly contributed to N2O production and diffusion in the mesotrophic and lightly/moderately-eutrophic states. We concluded that protein-like DOM enrichment had the potential to trigger CO2 and CH4 diffusion and this process was largely mediated by nutrient levels. N2O diffusion was found to be mainly influenced by nitrogen loadings and forms. Our findings highlight the urgency for effective strategies to reduce anthropogenic DOM inputs and control nutrient levels to reduce GHGs diffusion in highly human-impacted aquatic systems.

Dynamic Changes of Dissolved Organic Matter Derived from Algal Decomposition and the Environmental Effects in Eutrophic Lakes

The global occurrences of lake eutrophication have led to algal bloom and the subsequent algal decomposition, releasing high amounts of algae-derived dissolved organic matter (DOM) into the lake water. Algae-derived DOM could regulate the quantity and composition of DOM in lake water and further impact the biogeochemical cycles of multiple elements. In this study, the dynamic changes in the quantity and quality of DOM during algal decomposition under different eutrophic scenarios (e.g., from oligotrophication to severe eutrophication) were monitored, and the corresponding environmental effects (e.g., microbial responses and greenhouse gas emissions) caused by algal decomposition were further explored. The results showed that algal decomposition significantly increased the DOM levels, bioavailability, and intensities of fluorescent components in the water. The total DOM levels gradually decreased, whereas the average molecular weight increased along the decomposition process. Furthermore, unsaturated hydrocarbon and aliphatic compounds were preferentially utilized by microorganisms during algal decomposition, and some refractory molecules (e.g., lignin, condensed hydrocarbons, and tannin with high O/C values) were synchronously generated, as evidenced by the results from ultra-high-resolution mass spectrometry. The dominant bacterial species during algal decomposition shifted from Proteobacteria (46%) to Bacteroidetes (42%). In addition, algae addition resulted in 1.2-5 times the emissions of CO2 and CH4 from water, and the emission rates could be well predicted by the optical index of a254 in water. This study provides comprehensive perspectives for understanding the environmental behaviors of aquatic DOM and further paves the ways for the mitigation of lake eutrophication.

Hydrological alteration drives chemistry of dissolved organic matter in the largest freshwater lake of China (Poyang Lake)

As the largest reactive organic carbon pool, dissolved organic matter (DOM) plays an important role in various biogeochemical processes in lake ecosystems. Recently, climate change-induced extreme events (e.g., floods and droughts) have significantly modified the hydrological patterns of lakes worldwide, and regulated the quality and quantity of DOM. However, the responses of DOM chemistry to hydrological alteration in lakes remain poorly understood. Here we investigated the influences of hydrological alteration on sources, composition, and characteristics of DOM in Poyang Lake, the largest freshwater lake in China, using a combination of bulk chemical, optical and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) techniques. Results show various sources of DOM (autochthonous, allochthonous, and anthropogenic inputs) and significant variations in DOM chemistry across four hydrological periods (the retreating, dry, rising, and flooding periods) in Poyang Lake. During the retreating, rising, and flooding periods, DOM was characterized by higher aromaticity, humification degree, and recalcitrance, and exhibited pronounced allochthonous signatures. In contrast, DOM contained more S-containing molecules and aliphatic compounds during the dry period, displaying relatively stronger autochthonous features. Terrestrial inputs and the lignin-CHOS formation process are likely the primary underlying mechanisms shaping the differences in DOM chemistry in Poyang Lake. Our research demonstrates the significant impacts of hydrological alteration on DOM dynamics, and provides an improved understanding of DOM biogeochemical cycles and carbon cycling in large aquatic systems under global climate change.

Contrasting optical properties of dissolved organic matter between oceanic regions near the Getz and Dotson ice shelves in the Amundsen Sea, West Antarctica

The Amundsen Sea, located in West Antarctica, is experiencing rapid melting due to the intrusion of Circumpolar Deep Water, which is causing ice sheet thinning and basal melting. The resulting changes can affect the biogeochemical cycle of dissolved organic matter (DOM) by supplying iron from sea ice and/or glacier, thereby influencing primary production and ocean circulation. Therefore, it is crucial to understand the dynamics of the DOM in this region. In this study, our primary focus was to examine the optical properties of DOM in the oceanic regions adjacent to the West Getz Ice Shelf (WGIS) and the Dotson Ice Shelf (DIS). Significant differences in DOM optical properties, including the chromophoric DOM (CDOM) absorption coefficient at 350 nm (a350), spectral slope coefficient (S275–295), and specific UV absorbance at 254 nm (SUVA254), were observed between the WGIS and DIS regions (t-test, p < 0.05). Notably, the WGIS regions exhibited high a350 values. Additionally, the S275–295 and SUVA254 values, which serve as indices of molecular weight, indicated that the DOM pool in the WGIS regions was dominated by high molecular weight compounds with a substantial proportion of aromatic compounds. In contrast, the low values of a350 and SUVA254 along with the high S275–295 values in the DIS region suggested the dominance of low molecular weight CDOM associated with compounds of lower aromaticity. Furthermore, significant negative correlations were found between biomass of Phaeocystis antarctica (P. antarctica) and phosphate (PO4) in the WGIS regions (r2 = 0.82, p < 0.01 for WGIS 1 and r2 = 0.73, p < 0.01 for WGIS 2). However, no significant relationship was observed in the DIS region. These findings suggest that the high value and molecular weight of a350, extending from the surface layer to the deep layer, in the WGIS regions were associated with autochthonous sources, primarily driven by the colony-forming bloom of P. antarctica. These findings demonstrate that the quantity and quality of DOM in the Amundsen Sea are strongly affected by bloom conditions. The results emphasize that a combination of physical and biological processes interacts in complex ways to determine the characteristics of DOM in the Amundsen Sea.

MIEX resin and enhanced coagulation treatment of high-bromide natural water: Chlorine reactivity and DBP precursors removal

Both organic and inorganic constituents play a major role in the formation and speciation of disinfection by-products (DBPs) under chlorination. In this study, the removal of organic and inorganic precursors to DBPs by ion exchange and coagulation was examined, and the relationships between characteristics of dissolved organic matter (DOM), chlorine reactivity, and the formation of DBPs in high-bromide natural water were investigated. Formation potential tests were conducted for trihalomethanes (THMs) and haloacetronitriles (HANs) before and after the different treatments (coagulation, magnetic ion exchange (MIEX) resin, and combined MIEX/coagulation). At a low resin dose, MIEX was more effective than coagulation for DOM removal. The advantages of the MIEX resin were more prominent at a high resin dose because substantial amounts of DOM and bromide were simultaneously removed. The maximum bromide uptake on the MIEX resin was 0.02 mg-Br/mL. A 4-component PARAFAC model was developed using a dataset of 148 fluorescence excitation-emission matrices (EEMs) generated from pre-chlorinated and post-chlorinated samples. The maximum fluorescence intensities of humic-like components were found to be strongly correlated to THMs formation (R2 = 0.79–0.89). The MIEX treatment substantially lowered the formation of THMs (19–51%) and HANs (70–95%) due to its ability to remove humic-like DOM and bromide. The fluorescence loss for humic-like DOM was found to increase over a chlorination time of 3 days, suggesting that these compounds had stronger reactivity to chlorine compared to protein-like DOM. The chlorine reactivity of protein-like DOM increased after treatments as the residual chlorine was able to react with the less reactive fractions of DOM after chlorine-reactive compounds were removed.

Adsorption and thermal stability of dissolved organic matter on Ca- and Mg-exchanged montmorillonite: Implications for persistence in soils and sediments

Dissolved organic matter (DOM) represents a vital and highly dynamic component of organic matter in the environment. Despite its significance, there is still limited knowledge regarding how different base cations and chemical conditions influence the preservation of complex natural DOM through adsorption. This study aimed to investigate the adsorption of natural DOM onto montmorillonite (Mt) by systematically exploring the effects of exchanging cations (Ca2+ and Mg2+), pH levels (4 and 7), and DOM molecular weight (< 10, 10–100, and > 100 kDa) on the mechanisms and thermal stability of adsorbed DOM. To this end, we conducted a series of adsorption experiments, complemented by spectroscopic and thermal analyses. Our results revealed that lower pH and higher DOM molecular weight enhanced adsorption, with affinity for carbohydrate-like compounds. Notably, changes in d001 spacing and peak broadening indicated intercalation of DOM into the interlayer space of Mt, which was positively correlated with the amount of DOM adsorbed. Conversely, increased adsorption was found to negatively correlate with thermal stability. This was attributed to the prevalence of weaker DOM-DOM interactions occurring at higher DOM weight and lower pH, owing to reduced repulsion among protonated organic molecules, in contrast to stronger electrostatic interactions near the Mt surface that appeared to dominate at lower DOM weight and higher pH conditions. Intriguingly, no clear preference for DOM adsorption on Ca- or Mg-exchanged Mt was observed, suggesting similar efficiencies of these cations in stabilizing DOM through cation-bridging. Our findings provide significant insights into the mechanisms involved in mineral-organic associations and have implications for understanding the persistence of DOM in soils and sediments.

Dissolved organic matter and nutrient processing in organic-rich subterranean estuaries: Implications for future land use and climate scenarios

The subterranean estuary (STE) is a recognized reactive biogeochemical zone at the groundwater–seawater interface in coastal regions. However, few studies have explored dissolved organic matter (DOM) and nutrient processes in buried organic-rich STEs (with up to 20 % of organic matter content), despite their potential contributions to coastal water hypoxia and greenhouse gas emissions. This study conducted controlled laboratory experiments to investigate the physicochemical controls on DOM and nutrient processing in organic-rich STEs, considering variations in groundwater nitrate (NO3–) concentrations, salt concentration, seawater ions, and incubation times. Results showed elevated levels of dissolved organic carbon (DOC) and dissolved organic nitrogen (DON) in pore water, primarily from particulate organic matter (POM) degradation that originated from decayed vascular plants. POM-to-DOM degradations further resulted in the accumulation of ammonium (NH4+) and highly unsaturated compounds in all treatments. The addition of high-ionic-strength treatments (e.g., seawater and sodium chloride [NaCl] solution) reduced DOC solubility and selectively removed dissolved aromatic compounds in porewater. The cation-rich seawater shifted the porewater NH4+ generation pathway from predominantly biological (re)mineralization in freshwater to abiotic (desorption via ion exchange) pathways in the saline water setup. Orthophosphate (PO43−) dynamics were likely to be influenced by the iron-rich sediment surface in both freshwater and saline water scenarios. Our experiments further indicated that the long-term incubation enriched DOM concentration with a high degradation state. This work demonstrated that organic-rich STEs are significant sources of less labile DOM and NH4+ to coastal waters. In the context of global climate change, our results illustrate the sensitivity of DOM and nutrient biogeochemical cycling in STEs to salinization and altered residence time, consequently affecting the quantity and quality of DOM and nutrients transported to coastal waters.

Fluorescence spectroscopic characterization of dissolved organic matter in the wastewater treatment plant and hybrid constructed wetlands coupling system in winter: A case study in eastern China

Dissolved organic matter (DOM) in municipal wastewater can have a detrimental effect on aquatic ecosystems, as DOM can participate in the global carbon cycle and change the transport of other pollutants. The characteristics of DOM can also affect the utilization efficiency of dissolved organic carbon by microorganisms in water. In this study, variations in DOM quantity and quality in a full-scale wastewater treatment plant (WWTP) coupled with a hybrid constructed wetland (CW) system during cold periods were characterized by using excitation-emission matrix spectroscopy combined with parallel factor analysis (EEM-PARAFAC). The results showed that the DOM concentration significantly decreased after exiting the WWTP, while a slight increase was found in the CW. The coupled system could significantly eliminate influent DOM with a removal efficiency of 92.1%. The CW system could still remove DOM even in winter. Five fluorescent components, including three humic-like components, one protein-like component and one tyrosine-like component, were identified. Although the biological treatment process in the WWTP contributed a large number of protein-like substances, the optical indices showed that the bioavailability of wastewater was gradually reduced, indicating that DOM was selectively removed by the integrated system. Moreover, there were significant correlations between water quality parameters and DOM indices. This study could contribute to a better understanding of the elimination process of dissolved organic carbon in coupled systems of WWTPs and CWs and offer novel ideas for organic carbon resource recovery and water quality monitoring in watershed environments.

Unveiling temporal variation in dissolved organic matter (DOM) with high-frequency spectroscopic measurements in a shallow eutrophic lake

ABSTRACT Dissolved organic matter (DOM) plays an important role in biogeochemistry of lake ecosystems. Studies measuring DOM at short intervals in lakes are rare, and thus its short-term dynamics are largely unknown. We investigated DOM temporal variation in large, shallow, eutrophic Lake Võrtsjärv (Estonia) during one growing season (May–Sep 2016) using a field-deployable in situ spectrometer to measure absorbance spectra (wavelength range 200–708 nm) at a 2 h interval coupled with monthly discrete water sampling. Collected spectra were analyzed together with some in-lake variables, lake metabolic rates, and meteorological and hydrological data using boosted regression tree (BRT) and random forest (RF) models. Different spectral parameters were used to assess total and allochthonous DOM quantity and relative share of autochthonous DOM. All parameters (i.e., DOM quantity and quality) varied on a large scale. For example, dissolved organic carbon (DOC) concentrations ranged from 12.0 to 17.3 mg L−1. High levels of DOM were mainly of allochthonous origin, and a strong relationship with inflow indicated the same. The relative share of autochthonous DOM increased with rising air temperature as primary production rose in warm water; however, we found no direct relationships with gross primary production. RF and BRT models explained up to 38% and 63% of DOM temporal variability, respectively. Our results showed that monthly water samples did not capture large variation in DOM. Therefore, high-frequency measurements using in situ spectrometry improve temporal representativeness of DOM monitoring in lakes compared to traditional sampling methods.