Dissolved Organic Matter Sources Research Articles

Karenia brevis and Pyrodinium bahamense Utilization of Dissolved Organic Matter in Urban Stormwater Runoff and Rainfall Entering Tampa Bay, Florida

This study investigated how nitrogen and dissolved organic matter (DOM) from stormwater runoff and rainfall support the growth of Karenia brevis and Pyrodinium bahamense. Excitation–emission matrix spectroscopy coupled with parallel factor analysis tracked changes in the optical properties of DOM in each bioassay, revealing greater reactivity of terrestrial humic-like DOM. Significant increases in cell yield and specific growth rates were observed upon additions of runoff for both species, with significant increases in specific growth rates upon the addition of a 2 in simulated rain event for P. bahamense only. By hour 48, 100% of the dissolved organic nitrogen (DON) in each treatment was utilized by P. bahamense, and by hour 72, over 50% of the DON was utilized by K. brevis. The percentage of bioavailable dissolved organic carbon (DOC) was greater for P. bahamense compared to K. brevis, suggesting a greater affinity for DOC compounds by P. bahamense. However, the bioavailability of DOM for each species could be owed to distinct chemical characteristics of labile DOM conveyed from each site. This study demonstrates that stormwater runoff and rainfall are both sources of labile DOM and DON for K. brevis and P. bahamense, which has implications for blooms of these species in Tampa Bay waters.

Impact of Hill Fires on Dissolved Organic Matter in Watersheds of Karst Areas Based on Three-Dimensional Fluorescence-Parallel Factor Analysis

Hill fires have the potential to influence dissolved organic matter (DOM) in water bodies, yet fewer studies have investigated the effects of hill fires on DOM within watersheds in karst areas. In this study, we employed the three-dimensional fluorescence-parallel factor analysis (EEM-PARAFAC) method to analyze the DOM fluorescence peaks, component compositions, fluorescence indices, and sources within the water body of the Yuanteng River sub-basin, which was impacted by the hill fire, serving as our primary research focus. The results indicate the presence of three primary fluorescent fractions in the water body of the Yuanteng River: C1, resembling humic acid (fulvic acid); C2, consisting of biopolymers and microbial by-products; and C3, containing proteins such as tyrosine and tryptophan. The Yuanteng River exhibited elevated levels of humus-like substances, diminished concentrations of protein-like substances, and demonstrated higher biogenic, freshness, and humification indices compared to unaffected water samples, reflecting the impact of the hill fire. Elevated levels of exogenous humic acid-like inputs into the waters of the Yuanteng River, along with exogenous inputs of DOM, were primarily influenced by stable, high-molecular-weight organic matter. Additionally, agricultural effluent, domestic sewage, and anthropogenic activities contributed to these inputs to a lesser degree. The impacts of endogenous inputs are mainly related to the restoration of ecosystems. The occurrence of hill fires has significantly influenced the composition of dissolved organic matter in the waters of the Yuanteng River. A comprehensive analysis of the impacts of hill fires on dissolved organic matter in water bodies can serve as a valuable reference for characterizing DOM in the water bodies of the Yuanteng River. Furthermore, it can inform strategies for environmental protection, facilitate the traceability of pollutants in water bodies, and contribute to environmental and ecological restoration efforts following hill fires in the region.

Role of low-proportion, hydrophobic dissolved organic matter components in inhibiting methylmercury uptake by phytoplankton

Uptake of methylmercury (MeHg), a potent neurotoxin, by phytoplankton is a major concern due to its role as the primary pathway for MeHg entry into aquatic food webs, thereby posing a significant risk to human health. While it is widely believed that the MeHg uptake by plankton is negatively correlated with the concentrations of dissolved organic matter (DOM) in the water, ongoing debates continue regarding the specific components of DOM that exerts the dominant influence on this process. In this study, we employed a widely-used resin fractionation approach to separate and classify DOM derived from algae (AOM) and natural rivers (NOM) into distinct components: strongly hydrophobic, weakly hydrophobic, and hydrophilic fractions. We conduct a comparative analysis of different DOM components using a combination of spectroscopy and mass spectrometry techniques, aiming to identify their impact on MeHg uptake by Microcystis elabens, a prevalent alga in freshwater environments. We found that the hydrophobic components had exhibited more pronounced spectral characteristics associated with the protein structures while protein-like compounds between hydrophobic and hydrophilic components displayed significant variations in both distributions and the values of m/z (mass-to-charge ratio) of the molecules. Regardless of DOM sources, the low-proportion hydrophobic components usually dominated inhibition of MeHg uptake by Microcystis elabens. Results inferred from the correlation analysis suggest that the uptake of MeHg by the phytoplankton was most strongly and negatively correlated with the presence of protein-like components. Our findings underscore the importance of considering the diverse impacts of different DOM fractions on inhibition of phytoplankton MeHg uptake. This information should be considered in future assessments and modeling endeavors aimed at understanding and predicting risks associated with aquatic Hg contamination.

Soil source, not the degree of urbanization determines soil physicochemical properties and bacterial composition in Ningbo urban green spaces

Urban green spaces provide multiple ecosystem services and have great influences on human health. However, the compositions and properties of urban soil are not well understood yet. In this study, soil samples were collected from 45 parks in Ningbo to investigate the relationships among soil physicochemical properties, heavy metals and bacterial communities. The results showed that soil dissolved organic matter (DOM) was of high molecular weight, high aromaticity, and low degree of humification. The contents of heavy metals were all below the China's national standard safety limit (GB 3660–2018). The bioavailability of heavy metals highly correlated with soil pH, the content of DOC, the fluorescent component, the degree of humification and the source of DOM. The most abundant genera were Gemmatimonadaceae_uncultured, Xanthobacteraceae_uncultured, and Acidothermus in all samples, which were related to nitrogen cycle and bioavailability of heavy metals. Soil pH, bioavailability of Zn, Cd, and Pb (CaCl2 extracted) were the main edaphic factors influencing bacterial community composition. It should be noted that there was no significant impact of urbanization on soil physicochemical properties and bacterial composition, but they were determined by the source of soil in urban green spaces. However, with the passage of time, the effect of urbanization on urban green spaces cannot be ignored. Overall, this study provided new insight for understanding the linkage among soil physicochemical properties, heavy metals, and bacterial communities in urban green spaces.

Differences in dissolved organic matter and analysis of influencing factors between plantations pure and mixed forest soils in the loess plateau

The dissolved organic matter (DOM) in forest ecosystems significantly impacts soil carbon cycling due to its active turnover characteristics. However, whether different plantation forest soil profiles exhibit distinct DOM characteristics remains unclear. Hence, utilizing fluorescence spectroscopy and the parallel factor analysis (PARAFAC) method, a 1-meter soil profile analysis was carried out on three distinct artificial forests (Pinus tabuliformis (PT), Quercus crispula (QC), and a mixed forest of PT and QC (MF)), concurrently assessing the impact of soil chemical properties and enzyme activity on dissolved organic matter (DOM). The findings indicated that the mean concentration of dissolved organic carbon (DOC) was greatest in the MF and lowest in PT, exhibiting considerable variation with soil depth, suggesting that mixed tree species may promote the discharge of organic matter. The fluorescence spectra revealed two distinct peaks: humic-like fluorescence peaks (Peaks A and C) and a protein-like fluorescence peak (Peak T), with the most intense fluorescence observed in MF soil. As the soil depth increased, the fluorescence intensity of Peaks A and C steadily declined, while the intensity of Peak T rose. Four DOM components were identified in three types of plantations forests: surface soil was dominated by humic acid-like fluorescent components (C1 and C2), while the deep soil was primarily characterized by protein-like fluorescence components (C3 and C4). Different soil profile fluorescence parameter indices indicated that the source of DOM in the surface soil (i.e., 0–20 cm) was mainly allochthonous inputs, whereas, in the deep soil (i.e., 60–100 cm), it was mainly autochthonous, such as microbial activity. The findings from the partial least squares path modeling (PLS-PM) revealed that TP, aP, NH4+-N, and the combined impact of soil enzymes were influential in shaping the diversity of DOM attributes. Put differently, alterations in DOM concentration were concomitantly influenced by forest classification, soil characteristics, and depth. It has been demonstrated that, in contrast to monoculture forests, the establishment of mixed forest models has been more advantageous in enhancing the soil dissolved organic matter (DOM). These discoveries offer innovative perspectives on the dynamic characteristics of DOM in soil profiles and its influencing factors under different plantations forest planting patterns.

Storm-driven hydrological, seasonal, and land use/land cover impact on dissolved organic matter dynamics in a mid-Atlantic, USA coastal plain river system characterized by 21 T FT-ICR mass spectrometry

Introduction: Dissolved organic matter (DOM) as primary and secondary energy sources can be transported via rivers to estuaries and impact coastal biogeochemical cycles. Storm-induced high discharge events can alter the dominant river flow paths and enhance leaching of shallow organic-rich soil layers, leading to elevated terrestrial DOM export. Land use/land cover (LULC) and associated anthropogenic interventions (including artificial reservoirs and agricultural irrigation) can control sources and transformation processes of exported DOM along with hydrologic factors. The relative significance of LULC, hydrological factors, and temperature variations with seasons will differ depending on geographical locations and complicate their incorporation in biogeochemical models of DOM dynamics. This study investigates the role of LULC, seasonality, and storm events on DOM concentrations and molecular composition in the Murderkill River system.Method: Surface water samples were collected seasonally and before/after storm events from 6 sites representing forested, agricultural, and developed LULC units. The DOM was characterized via parallel factor analysis of excitation-emission matrix data and electrospray ionization 21 T Fourier-transform ion cyclotron resonance mass spectrometry to determine potential DOM sources and enable the development of a conceptual model for DOM dynamics in rivers impacted by anthropogenic reservoirs.Result and Discussion: Our results suggest that storm-induced shallow and overland flow paths can increase surface-vegetation/plant-litter derived DOM based on atomic ratios associated with specific biogenic precursors (i.e., lignin, tannins, and/or oxygenated aromatic DOM), particularly in winter when autochthonous production was suppressed due to reduced temperatures. We further demonstrate that the damming effects of artificial reservoirs enhance the role of seasonal patterns of autochthonous production, disrupting storm-shunt process and stimulating significantly more bio-produced DOM export during spring and summer (i.e., tryptophan/tyrosine-like. N- and S- containing, phytoplankton-derived compounds). Collectively, these results demonstrate how artificial reservoirs alter the characteristics of DOM exported from rivers with implications for understanding carbon export and fate at river-estuary interfaces.

Characteristics of DOM and Their Relationships with Potentially Toxic Elements in the Inner Mongolia Section of the Yellow River, China.

The characterization of dissolved organic matter (DOM) is important for better understanding of the migration and transformation mechanisms of DOM in water bodies and its interaction with other contaminants. In this work, fluorescence characteristics and molecular compositions of the DOM samples collected from the mainstream, tributary, and sewage outfall of the Inner Mongolia section of the Yellow River (IMYR) were determined by using fluorescence spectroscopy and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). In addition, concentrations of potentially toxic elements (PTEs) in the relevant surface water and their potential relationships with DOM were investigated. The results showed that the abundance of tyrosine-like components increased significantly in downstream waters impacted by outfall effluents and was negatively correlated with the humification index (HIX). Compared to the mainstream, outfall and tributaries have a high number of molecular formulas and a higher proportion of CHOS molecular formulas. In particular, the O5S class has a relative intensity of 41.6% and the O5-7S class has more than 70%. Thirty-eight PTEs were measured in the surface water samples, and 12 found above their detective levels at all sampling sites. Protein-like components are positively correlated with Cu, which is likely indicating the source of Cu in the aquatic environment of the IMYR. Our results demonstrated that urban wastewater discharges significantly alter characteristics and compositions of DOM in the mainstream of IMYR with strongly anthropogenic features. These results and conclusions are important for understanding the role and sources of DOM in the Yellow River aquatic environment.

The specific molecular signature of dissolved organic matter extracted from different arctic plant species persists after biodegradation

Dissolved organic matter (DOM) is a small but very reactive pool of organic matter (OM) in the environment. Its role is related to its composition, which depends on its source. In soils, vegetation is the main source of DOM, and biodegradation is the main regulating mechanism. This study aims to characterise DOM produced by contrasted arctic vegetation species and their biodegradation products.The water-extractable organic matter (WEOM) was produced from C. stellaris (lichen), E. vaginatum (sedge), A. polifolia (dwarf evergreen shrub) and B. nana (deciduous dwarf shrub). The WEOM were inoculated with a common aerobic heterotrophic soil bacteria (P. aureofaciens) and incubated for 7 days. During the experiment, WEOM was characterised through a wide range of analytical methods (TOC, UV–Vis absorbance, high-performance ion chromatography and HRMS Orbitrap).The results showed bacteria consumed a significantly greater proportion of WEOM produced by C. stellaris than by A. polifolia and B. nana at the end of the experiment (p < 0.05). Furthermore, the number of features in WEOM decreased for C. stellaris and E. vaginatum, whereas it increased for B. nana. These findings shed light on the species-specific biodegradation processes that rely on the initial composition of DOM, specifically influenced by the vegetation's capacity to produce recalcitrant compounds. Furthermore, our results emphasised that even though bacterial activity greatly impacted molecular characteristics, the WEOM produced by different vegetation species maintained their distinct molecular signatures. As a result, it can be inferred that the DOM found in natural environments directly reflects the relevant vegetation cover despite the strong influence of biogeochemical processes on DOM molecular composition. This should be considered when developing models to assess the influence of climate change on vegetation cover composition and its subsequent effects on DOM dynamics in soil and surface waters.

Mass variations and transfer process of shrimp farming pollutants in aquaculture drainage systems: Effects of DOM features and physicochemical properties

The expansion of aquaculture produces increasing pollutant loads, necessitating the use of drainage systems to discharge wastewater into surface water. To assess the mass variations and transfer process of aquaculture wastewater, an entire aquaculture drainage investigation lasting for 48 h was conducted, focusing on the nutrients, heavy metals, dissolved organic matter (DOM), and physicochemical properties of drainage in a commercial shrimp farm. The findings revealed that early drainage produced more heavy metals, total nitrogen (TN), dissolved organic nitrogen (DON), and feed-like proteins from aquaculture floating feed and additives, whereas late drainage produced more PO43--P and total dissolved phosphorus (TP). A few pollutants, including DON, Cu, and feed-like proteins, were effectively removed, whereas the contents of TN, dissolved inorganic nitrogen, and Zn increased in the multi-level aquaculture drainage system. Limited dilution indicated that in-stream transfer was the main process shaping pollutant concentrations within the drainage system. In the lower ditches, NO3--N, heavy metals, and feed-like proteins exhibited evident in-stream attenuation, while TN and NH4+-N underwent significant in-stream enrichment processes, especially in ditch C, with the transfer coefficient values (vf) of –1.74E-5 and –2.04E-5. This indicates that traditional aquaculture drainage systems serve as nitrogen sinks, rather than efficient nutrient purge facilitators. Notably, DOM was identified as a more influential factor in shaping the in-stream transfer process in aquaculture drainage systems, with an interpretation rate 40.79% higher than that of the physiochemical properties. Consequently, it is necessary to eliminate the obstacles posed by DOM to pollutant absorption and net zero emissions in aquaculture drainage systems in the future. Environmental implicationsNutrients, heavy metals, and dissolved organic matter are hazardous pollutants originating from high-density aquaculture. As the sole conduit to natural waters, aquaculture drainage systems have pivotal functions in receiving and purifying wastewater, in which the in-stream transfer process is affected by ambient conditions. This field study investigated the spatial variations, stage distinctions, effects of physicochemical properties, and dissolved organic matter (DOM) features. This finding suggests that the aquaculture drainage system as a nitrogen sink and DOM source. While the DOM is the key factor in shaping the in-stream transfer process, and obstacles for pollutant elimination. This study helps in understanding the fate of aquaculture pollutants and reveals the drawbacks of traditional aquaculture drainage systems.

Unraveling the photochemical behavior of dissolved organic matter derived from hydrothermal carbonization process water: Insights from molecular transformation and photoactive species

Hydrothermal carbonization process water (HTPW) has been utilized as a substitute for chemical fertilizers in agricultural applications. However, the input of HTPW into paddy water, particularly the significant proportion of dissolved organic matter (DOM) in HTPW (DOM-HTPW), directly engages in photochemical transformations, a phenomenon often overlooked. This study observed a consistent decrease in humification (SUVA280, 7.7–53.9%) and aromaticity (SUVA254, 6.1–40.0%) of DOM-HTPW after irradiation. The primary active photobleaching components of DOM-HTPW varied depending on the feedstock, such as protein for chicken manure DOM-HTPW and lignin for rice straw DOM-HTPW. The photochemical activity of DOM-HTPW was augmented by its lower molecular weight and higher hydrophilic composition, particularly evident in chicken manure DOM-HTPW, which exhibited higher generation rates for 1O2 (35.1–37.1%), 3DOM* (32.8–43.9%), and O2•− (28.6–48.8%) as measured by molecular probes. DOM-HTPW effectively facilitated the phototransformation of tetracycline, with the contribution of O2•− being more significant than 3DOM* and 1O2. These findings shed new light on the understanding the photochemical processes of DOM-HTPW as exogenous DOM and the interconnected fate of contaminants in aquatic environments.

Investigating the impacts of solid phase extraction on dissolved organic matter optical signatures and the pairing with high‐resolution mass spectrometry data across a freshwater stream network

AbstractAdvancing our understanding of dissolved organic matter (DOM) chemistry in aquatic systems necessitates the integration of data streams from multiple analytical platforms. Some measurements require pretreatment with solid phase extraction (SPE), while others are performed directly on whole water samples. Evidence has suggested that SPE will be biased against select DOM fractions, leading to concerns over the ability to establish data linkages across platforms with variable needs for SPE pretreatment, such as those from optical measurements and those that provide high‐resolution molecular information. Here, we directly addressed this concern by assessing the impact of SPE on DOM optical properties through excitation–emission matrices with parallel factor analysis (PARAFAC) for 47 samples across a stream network within a single watershed reflective of variable DOM sources. PARAFAC data was further paired with molecular information obtained by Fourier transform ion cyclotron resonance mass spectrometry (FTICR‐MS). A comparison of PARAFAC models first revealed no systematic qualitative differences in major components between whole water DOM and DOM isolated by SPE (SPE‐DOM); however, quantitative biases against select components were observed. Further linkages with FTICR‐MS data revealed that the molecular fingerprint associated with each PARAFAC component was consistent between the whole water DOM and SPE‐DOM. Our results suggest that bulk scale linkages across these analytical platforms could be inferred irrespective of the observed quantitative biases resulting from SPE for samples within this example watershed. This work represents a key step toward the systematic evaluation of linkages between optical and high‐resolution mass spectrometry datasets in freshwater lotic environments.

Dynamic distribution and photochemical-microbial coupling degradation of dissolved organic matter in a large river-Influenced Bay

A large river-influenced offshore area is the junction where land and open sea meet, which is important in the biogeochemical processes of dissolved organic matter (DOM). Because hydrodynamic and biogeochemical processes are complex, processes such as the photochemical and microbial degradation of DOM are poorly understood. In this study, to further understand the degradation mechanisms of DOM from different sources, water was sampled from three cruises during autumn 2018 and spring and summer 2019 in Laizhou Bay (LZB), as this bay is greatly influenced by the Yellow River. Field incubation experiments examining the riverine, mixed, and marine DOM photochemical and microbial degradation processes alone or in combination were conducted onboard. Due to the dual influence of the Yellow River input and phytoplankton autogenous production, dissolved organic carbon (DOC) and chromophoric DOM (CDOM) show relatively conservative mixing behaviour with maximum values in summer, and the S275–295 gradually increases from the river to nearshore. In addition, it is indicated that higher primary productivity from large nutrient inputs in areas with moderate salinity during the summer is often accompanied by higher bioavailability DOM based on field investigation results. Various sources of DOM have different sensitivities to photochemical and microbial degradation due to their components and properties. Riverine DOM is susceptible to photochemical degradation, while marine DOM is more susceptible to microbial degradation. Moreover, the low-molecular-weight organic matter produced by photochemical degradation effectively promotes the microbial degradation of DOM from riverine sources, whereas photodegradation from mixed and marine sources do not significantly increase the biodegradation efficiency due to the low content of aromatic substances. Furthermore, photoammonification and bioammonification of autochthonous and allochthonous DOM may be the potential processes driving ammonia regeneration.

Bacteria Affect the Distribution of Soil-Dissolved Organic Matter on the Slope: A Long-Term Experiment in Black Soil Erosion

Soil erosion results in dissolved organic matter (DOM) loss and is one of the main paths of soil carbon loss. Bacteria affect the generation and transformation of DOM. However, the effect of bacteria on the composition and slope distribution of DOM has rarely been investigated under field conditions. Based on a long-term experiment of three gradients (3°, 5°, 8°) in a black soil erosion area of Northeast China, the content, composition, and source of DOM were studied. The results showed that the DOM of the 3° and 5° slope was enriched midslope, and the DOM of the 8° slope was enriched downslope. Parallel factor (PARAFAC) analysis indicated that the main substances in DOM were fulvic-like acid, humic-like acid, tryptophan-like protein, and soluble microbial metabolites. The upslope and downslope soils of 3° and 5° slopes showed high DOM bioavailability, while the downslope soil of the 8° slope showed high DOM bioavailability. The content of new DOM in downslope soil increased with the gradient. Bacteria played an important role in the synthesis and transformation of DOM and affected its composition and slope distribution. Verrucomicrobiota, Firmicutes, Planctomycetota, and Gemmatimonadota were the main factors affecting soil DOM. The results could be helpful in understanding the loss mechanism of DOM in eroded black soil and provide support for soil carbon sequestration.

Effect of UV-LED Wavelength on Reactive Species Photogeneration from Dissolved Organic Matter

The photogeneration of reactive species from dissolved organic matter (DOM) plays a crucial role in the photochemical and photobiochemical processes in natural aquatic systems. However, the impact of the ultraviolet (UV) wavelength on the photogeneration of reactive species by different sources of DOM remains unclear. In this study, UV light at four wavelengths (365 nm, 310 nm, 280 nm, and 260 nm) provided by UV-LEDs were irradiated onto three types of DOM: humic acid (HA), fulvic acid (FA), and effluent organic matter (EfOM). Three reactive species produced by DOM, including excited triplet-state DOM (3DOM*), singlet oxygen (1O2), and hydroxyl radicals (•OH), were determined. UV365 proved to be the most efficient wavelength for generating 1O2 and •OH, with formation rates of 3.47 × 10−6 M s−1 and 1.67 × 10−8 M s−1, respectively, with the addition of FA and EfOM. The highest steady-state concentrations of all three reactive species were also generated under UV365, reaching 3.00 × 10−13 M (3DOM*) and 1.64 × 10−11 M (1O2) with the FA addition, and 1.44 × 10−10 M (•OH) with the EfOM. Across the different DOM sources, UV365 obtained the maximum quantum yields of reactive species, indicating the stronger effect of UV365 on inducing the photosensitization of DOM compared to the other shorter wavelengths. This study expands our understanding of the photochemistry of DOM in aquatic environments.

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.

Outwelling of reduced porewater drives the biogeochemistry of dissolved organic matter and trace metals in a major mangrove‐fringed estuary in Amazonia

AbstractMangrove‐fringed estuaries are intertidal ecosystems discharging significant amounts of dissolved organic matter (DOM) into coastal oceans. DOM in these ecosystems is derived from autochthonous production, fluvial input, and mangrove porewater outwelling; however, differentiating between these sources remains challenging. Our incomplete understanding of the biogeochemical factors controlling DOM dynamics and its relationship with nutrient and trace metal cycling still hinders the formulation of elemental budgets in coastal environments. Here, we relate the DOM composition in a mangrove‐fringed estuary in North Brazil (Amazonia) to the redox conditions at the formation sites. We combined molecular DOM analyses via ultrahigh‐resolution mass spectrometry (FT‐ICR‐MS) with parallel factor analysis of excitation–emission fluorescence matrices (EEM‐PARAFAC), nutrient and redox‐sensitive trace metal analyses. During low tide, the influx of oxygen‐depleted porewater carried terrigenous DOM, inorganic nutrients, and trace metals into the mangrove‐fringed creeks. Precipitation of metal(hydr)oxides and microbial turnover controlled nutrient and trace metal dynamics in the estuary. The highest inorganic nitrogen concentrations within the upper mangrove‐fringed estuary indicated outwelling from mangrove sediments as an essential source. Phosphate concentrations were highest within the lower mangrove‐fringed estuary, where available phosphate likely exceeded precipitation with iron(hydr)oxides. We tracked the DOM transport to the coastal ocean using a novel molecular index derived from sulfidic porewater (ISuP). Outwelling of recalcitrant DOM from mangrove habitats is relevant in the context of blue carbon storage. Therefore, applying our molecular proxy (ISuP), together with trace‐metal and optical DOM analyses, is a powerful approach for differentiating contributions of diverse DOM sources in highly complex coastal ecosystems.

Stratification of dissolved organic matter in the upper 5000 m water column in the western Pacific Ocean

Marine dissolved organic matter (DOM) is a principal reservoir involved in biogeochemical cycles and exerts a pivotal influence on global carbon flux dynamics. In this study, excitation-emission matrix fluorescence spectroscopy combined with parallel factor analysis (EEM-PARAFAC) was conducted on 230 DOM samples collected from 21 sites between February and April 2022 in the Western Pacific Ocean (WPO). We identified five distinct fluorescence peaks (peaks B, T, A, C, and M), predominantly protein-like and humic-like components. These findings, marked by significant differences (p < 0.01) in fluorescence intensities and spectral indices, characterized the transformation of DOM with ocean depth, illustrating a transition from active to recalcitrant forms. Additionally, random forest analysis (RFA) identified depth as a key factor influencing marine dissolved organic carbon (DOC), with a 32.59% importance value. Correlations between hydrological and fluorescent parameters underscored the complexity of DOM sources and influencing processes. Overall, this work broadens our understanding of DOM variability in the upper 5000 m of the WPO, enhancing our knowledge of the marine environment's role in the global carbon cycle.

Characteristics and Influencing Factors of Dissolved Organic Matter in Cave Drip Water—A Case Study from Furong Cave, Southwest China

Understanding the hydrological processes of dissolved organic matter (DOM) in the surface karst zone is crucial for the utilization and safety of groundwater resources. However, research on DOM in drip water from karst caves is limited. In this study, continuous monitoring was conducted for four years at four drip water monitoring sites (MP1, MP2, MP3, and MP9) in Furong Cave, Southwest China. The three-dimensional fluorescence excitation–emission spectroscopy (3D-EEM) and fluorescence region integration (FRI) methods were employed, along with correlation analysis, to investigate the spectral characteristics, composition, sources, and influencing factors of the DOM in the drip water of Furong Cave. The results indicated that (1) the three-dimensional fluorescence peaks in the drip water were classified into six categories: A, B, C, T, Ti, and M. (2) The dominant source of the drip water DOM is endogenous organic matter. (3) The FRI analysis indicates a relatively high proportion of Type II substances in the drip water, predominantly composed of tryptophan-like substances. (4) The DOM in the drip water of Furong Cave was influenced by various factors, including the mixing effect of “new” and “old” water, water residence time in karst systems, and water–rock interactions (WRI), resulting in the complex responses of drip rates and DOM to surface precipitation and temperature at different drip water sites. This study provides a reference for comparative research on DOM in cave drip water in karst regions, which contributes to a better understanding of the migration mechanism of DOM in karst aquifers under different climate and karst ecological conditions.

Exploring the diversity of dissolved organic matter (DOM) properties and sources in different functional areas of a typical macrophyte - derived lake combined with optical spectroscopy and FT-ICR MS analysis

Lake Baiyangdian is one of China's largest macrophyte - derived lakes, facing severe challenges related to water quality maintenance and eutrophication prevention. Dissolved organic matter (DOM) was a huge carbon pool and its abundance, property, and transformation played important roles in the biogeochemical cycle and energy flow in lake ecosystems. In this study, Lake Baiyangdian was divided into four distinct areas: Unartificial Area (UA), Village Area (VA), Tourism Area (TA), and Breeding Area (BA). We examined the diversity of DOM properties and sources across these functional areas. Our findings reveal that DOM in this lake is predominantly composed of protein - like substances, as determined by excitation - emission matrix and parallel factor analysis (EEM - PARAFAC). Notably, the exogenous tyrosine-like component C1 showed a stronger presence in VA and BA compared to UA and TA. Ultrahigh - resolution mass spectrometry (FT - ICR MS) unveiled a similar DOM molecular composition pattern across different functional areas due to the high relative abundances of lignan compounds, suggesting that macrophytes significantly influence the material structure of DOM. DOM properties exhibited specific associations with water quality indicators in various functional areas, as indicated by the Mantel test. The connections between DOM properties and NO3N and NH3N were more pronounced in VA and BA than in UA and TA. Our results underscore the viability of using DOM as an indicator for more precise and scientific water quality management.

Organic matter biofiltration performance modeling: Influence of influent water quality, operating conditions, and biomass

The impact of source water dissolved organic matter (DOM) origin, empty bed contact time (EBCT), temperature, and pretreatment methods on biofiltration performance was evaluated and predictive models based on experimental data were developed. Three DOM source water types, terrestrial, microbial, and treated wastewater (WW) effluent, were utilized. A model was developed to predict biofilter performance for dissolved organic carbon (DOC) removal based on the influent biodegradable DOC (BDOC) fraction, a single active biomass measurement from the top of the filter and the filter EBCT. A biomass distribution model was developed to predict total active biomass throughout the filter based on a single biomass measurement from the top of the filter. The measured BDOC fractions were 21 % for the nonWW impacted source waters, 36 % for the WW effluents and 62 % for the ozonated WW effluents. At an EBCT of 15 min, biofilters removed between 7 and 21 % of the DOC (19 to 50 % for BDOC) depending on the DOM type and use of ozonation. When the EBCT decreased to 5 min DOC removal decreased by 40 % and when increased to 30 min removal increased by 42 %. When the temperature decreased from 22 °C to 6 °C DOC removal was 33 % lower and when increased to 28 °C removal was 42 % higher. ATP values were found to be a function of temperature and DOM origin, as the average ATP values from the WW effluent biofilters were almost double that of the non-WW impacted sources and pre-ozonation of the WW effluent yielded values three times higher. The model was applied to the results of 27 different biofilter runs at three EBCTs yielding one distinct rate constant for the non-WW impacted source waters and one rate constant for the WW effluents. The model was successfully applied to the results of 19 filter runs from the literature and to those from a pilot plant over 6 months of operation.