The molecular characteristics of dissolved organic matter in urbanized river sediments and their environmental impact under the action of microorganisms

Destabilization mechanisms of Semi-aerobic aged refuse biofilters under harsh treatment conditions: Evidence from fluorescence and microbial characteristics

Semi-aerobic aged refuse biofilters (SAARB) are commonly-used biotechnologies for treating landfill leachate. In actual operation, SAARB often faces harsh conditions characterized by high concentrations of chemical oxygen demand (COD) and Cl-, as well as a low carbon-to-nitrogen ratio (C/N), which can disrupt the microbial community within SAARB, leading to operational instability. Maintaining the stable operation of SAARB is crucial for the efficient treatment of landfill leachate. However, the destabilization mechanism of SAARB under harsh conditions remains unclear. To address this, the study simulated the operation of SAARB under three harsh conditions, namely, high COD loading (H-COD), high chloride ion (Cl-) concentration environment (H-Cl-), and low C/N ratio environment (L-C/N). The aim is to reveal the destabilization mechanism of SAARB under harsh conditions by analyzing the fluorescence characteristics of effluent DOM and the microbial community in aged refuse. The results indicate that three harsh conditions have different effects on SAARB. H-COD leads to the accumulation of proteins; H-Cl- impedes the reduction of nitrite nitrogen; L-C/N inhibits the degradation of humic substances. These outcomes are attributed to the specific effects of different factors on the microbial communities in different zones of SAARB. H-COD and L-C/N mainly affect the degradation of organic matter in aerobic zone, while H-Cl- primarily impedes the denitrification process in the anaerobic zone. The abnormal enrichment of Corynebacterium, Castellaniella, and Sporosarcina can indicate the instability of SAARB under three harsh conditions, respectively. To maintain the steady operation of SAARB, targeted acclimation of the microbial community in SAARB should be carried out to cope with potentially harsh operating conditions. Besides, timely mitigation of loads should be implemented when instability characteristics emerge, and carbon sources and electron donors should be provided to restore treatment performance effectively.

Elucidating the Composition and Transformation of Dissolved Organic Matter at the Sediment-Water Interface Using High-Resolution Mass Spectrometry

The exchange and transformation of dissolved organic matter (DOM) at the sediment-water interface are crucial factors in regulating watershed biogeochemistry, with the molecular composition of DOM serving as a pivotal determinant in elucidating this process. High-resolution mass spectrometry (HRMS) is an effective tool for resolving the composition of DOM. By analyzing the compositional characteristics of DOM at the sediment-water interface under three different salinities at the same latitude region in northern China, the findings indicate certain variations in component characteristics of DOM between low-salinity inland waters and high-salinity seawaters, with the former exhibiting greater molecular diversity and higher molecular weights, whereas the latter displayed a higher saturation and bioavailability. Notably, the presence of more CHOS substances in the low-salinity inland waters underscores the transformation of the DOM influenced by terrestrial inputs and anthropogenic activities. Conversely, the presence of more CHO and CHNO substances in high-salinity seawater underscores the microbial effects. The chemical transformation process from overlying water to pore water to sediments was characterized by methylation, hydrogenation, decarboxylation, and reduction, as determined by calculating the relations between the H/C and O/C ratios of different compound types. These findings indicate that HRMS can yield more refined results in revealing the process of DOM at the sediment-water interface under different environments, which provides a more reliable basis for a deeper understanding of the source-sink mechanism of sediment organic matter.

Advancing fluorescence tracing with 3D-2D spectral conversion: A mixed culture on microbial degradation mechanisms of DOM from a large-scale watershed

Fluorescence tracing, known for its precision, rapid application, and cost-effectiveness, faces challenges due to the microbial degradation of dissolved organic matter (DOM) in aquatic environments, altering its original spectral fingerprint. This study conducted a 15-day microcosm experiment to examine the effects of biodegradation on the spectral properties of DOM from various sources: livestock excrement (EXC), urban sewage (URB), industrial wastewater (IND), and riparian topsoil (tDOM). Our findings show that while the spectral structures of DOM from different sources change during 15 days of microbial degradation, these changes do not overlap or interfere with each other. However, distinguishing between tDOM and URB in the presence of both IND and EXC is only possible at high resolution. Spectral index calculations revealed significant fluctuations and interference in FI and BIX indices among samples from different sources due to microbial degradation. In contrast, the HIX index exhibited independent fluctuations and remained a reliable spectral index for tracing. LEfSe (Linear discriminant analysis Effect Size) identified characteristic bio-indicators (CBI) for each DOM source. The CBI for tDOM and URB differed significantly; tDOM showed a marked CBI only within the first four days of microbial degradation, with a sharp decline in abundance thereafter, while URB's CBI remained abundant for 12 days. Similarly, IND's CBI maintained high relative abundance for the first 12 days. EXC's CBI was unique, showing a distinct and stable community only after six days of degradation, likely due to its high bioavailability and initial rapid microbial utilization. This study addresses the temporal variability in spectral tracing techniques caused by pollutant biodegradation. We developed a combined spectral-biological tracing technique using the "three-dimensional to two-dimensional" method along with bio-indicators, enhancing the accuracy and timeliness of spectral tracing.

Phosphorus mining from marine sediments adopting different carbon/nitrogen strategies driven by anaerobic reactors: The exploration of potential mechanism and microbial activities

To investigate the possibility of phosphorus (P) recovery from marine sediment and explore the role of the carbon: nitrogen ratio in affecting the internal P release under anaerobic conditions, we experimented with the external addition of carbon (acetic acid and glucose) and ammonia nitrogen (NH4-N) to expose P release mechanisms. The 24-day anaerobic incubations were conducted with four different carbon: nitrogen dosing groups including no NH4-N addition and COD/N ratios of 100, 50, and 10. The P release showed that extra NH4-N loading significantly suppressed the decomposition of P (p < 0.05) from the marine sediment, the maximum P release was 4.07 mg/L and 7.14 mg/L in acetic acid- and glucose-fed systems, respectively, without extra NH4-N addition. Additionally, the results exhibited that the imbalance of carbon: nitrogen not only failed to induce the production of organic P mineralization enzyme (alkaline phosphatase) in the sediment but also suppressed its activity under anaerobic conditions. The highest enzyme activity was observed in the group without additional NH4-N dosage, with rates of 1046.4 mg/(kg∙h) in the acetic acid- and 967.8 mg/(kg∙h) in the glucose-fed system, respectively. Microbial data analysis indicated that a decrease in the abundance of P release-regulating bacteria, including polyphosphate-accumulating organisms (Rhodobacteraceae) and sulfate-reducing bacteria (Desulfosarcinaceae), was observed in the high NH4-N addition groups. The observed reduction in enzyme activity and suppression of microbial activity mentioned above could potentially account for the inhibited P decomposition in the presence of high NH4-N addition under anaerobic conditions. The produced P-enriched solution from the bioreactors may offer a promising source for future recovery endeavors.

Spatial gradients and molecular transformations of DOM, DON and DOS in human-impacted estuarine sediments

Dissolved organic matter (DOM) constitutes the most active fraction in global carbon pools, with estuarine sediments serving as significant repositories, where DOM is susceptible to dynamic transformations. Anthropogenic nitrogen (N) and sulfur (S) inputs further complicate DOM by creating N-bearing DOM (DON) and S-bearing DOM (DOS). This study delves into the spatial gradients and transformation mechanisms of DOM, DON, and DOS in Pearl River Estuary (PRE) sediments, China, using combined techniques of UV-visible spectroscopy, Excitation-emission matrix (EEM) fluorescence spectroscopy, Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS), and microbial high-throughput sequencing. Results uncovered a distinct spatial gradient in DOM concentration, aromaticity (SUVA254), hydrophobicity (SUVA260), the content of substituent groups including carboxyl, carbonyl, hydroxyl and ester groups (A253/A203) of chromophoric DOM (CDOM), and the abundances of tyrosine/tryptophan-like protein and humic-like substances in fluorophoric DOM (FDOM). These all decreased from upper to lower PRE, accompanied by a decrease in O3S and O5S components, indicating seaward reduction in the contribution of terrestrial OM, especially anthropogenic inputs. Additionally, sediments exhibited a reduction in molecular diversity (number of formulas) of DOM, DON, and DOS from upper to lower PRE, with molecules tending towards a lower nominal oxidation state of carbon (NOSC) and higher bio-reactivity (MLBL), molecular weight (m/z) and saturation (H/C). While molecular composition of DOM remained similar in PRE sediments, the relative abundance of lignin-like substances decreased, with a concurrent increase in protein-like and lipid-like substances in DON and DOS from upper to lower PRE. Mechanistic analysis identified the joint influence of terrestrial OM, anthropogenic N/S inputs, and microbial processes in shaping the spatial gradients of DOM, DON, and DOS in PRE estuarine sediments. This study contributes valuable insights into the intricate spatial gradients and transformations of DOM, DON, and DOS within human-impacted estuarine sediments.

Differential Adsorption of Dissolved Organic Matter and Phosphorus on Clay Mineral in Water-Sediment System

Lake sediments connection to the biogeochemical cycling of phosphorus (P) and carbon (C) influences streamwater quality. However, it is unclear whether and how the type of sediment controls P and C cycling in water. Here, the adsorption behavior of montmorillonite (Mt) with different interlayer cations (Na+, Ca2+, or Fe3+) on dissolved organic matter (DOM) and P was investigated to understand the role of Mt in regulating the organic carbon-to-phosphate (OC/P) ratio within freshwater systems. The adsorption capacity of Fe-Mt for P was 3.2-fold higher than that of Ca-Mt, while it was 1/3 lower for DOM. This dissimilarity in adsorption led to an increased OC/P in Fe-Mt-dominated water and a decreased OC/P in Ca-Mt-dominated water. Moreover, an in situ atomic force microscope and high-resolution mass spectrometry revealed molecular fractionation mechanisms and adsorptive processes. It was observed that DOM inhibited the nucleation and crystallization processes of P on the Mt surface, and P affected the binding energy of DOM on Mt through competitive adsorption, thereby governing the interfacial P/DOM dynamics on Mt substrates at a molecular level. These findings have important implications for water quality management, by highlighting the role of clay minerals as nutrient sinks and providing new strategies for controlling P and C dynamics in freshwater systems.

Molecular insights into microbial transformation of bioaerosol-derived dissolved organic matter discharged from wastewater treatment plant

Wastewater treatment plants (WWTP) are important sources of aerosol-derived dissolved organic matter (ADOM) which may threaten human health via the respiratory system. In this study, aerosols were sampled from a typical WWTP to explore the chemical molecular diversity, molecular ecological network, and potential toxicities of the ADOM in the aerosols. The high fluorescence index (>1.9) and biological index (0.66-1.17) indicated the strong autogenous microbial source characteristics of the ADOM in the WWTP. DOM and microbes in the wastewater were aerosolized due to strong agitation and bubbling in the treatment processes, and contributed to 74 % and 75 %, respectively, of the ADOM and microbes in the aerosols. The ADOM was mainly composed of CHO and CHOS accounting for 35 % and 29 % of the total number of molecules, respectively, with lignin-like (69 %) as the major constituent. 49 % of the ADOM transformations were thermodynamically limited, and intragroup transformations were easier than intergroup transformations. Bacteria in the aerosols involved in ADOM transformations exhibited both cooperative and divergent behaviors and tended to transform carbohydrate-like and amino sugar/protein-like into recalcitrant lignin-like. The microbial compositions were affected by atmosphere temperature and humidity indirectly by modulating the properties of ADOM. Tannin-like, lignin-like, and unsaturated hydrocarbon-like molecules in the ADOM were primary toxicity contributors, facilitating the expression of inflammatory factors IL-β (2.2-5.4 folds), TNF-α (3.5-7.0 folds), and IL-6 (3.5-11.2 folds), respectively.

Spatial dynamics and risk assessment of phosphorus in the river sediment continuum (Qinhuai River basin, China)

This study investigated the concentration and fractionation of phosphorus (P) using sequential P extraction and their influencing factors by introducing the PLS-SEM model (partial least squares structural equation model) along this continuum from the Qinhuai River. The results showed that the average concentrations of inorganic P (IP) occurred in the following order: urban sediment (1499.1 mg/kg) > suburban sediment (846.1-911.9 mg/kg) > rural sediment (661.1 mg/kg) > natural sediment (179.9 mg/kg), and makes up to 53.9-87.1% of total P (TP). The same as the pattern of IP, OP nearly increased dramatically with increasing the urbanization gradient. This spatial heterogenicity of P along a river was attributed mainly to land use patterns and environmental factors (relative contribution affecting the P fractions: sediment nutrients > metals > grain size). In addition, the highest values of TP (2876.5 mg/kg), BAP (biologically active P, avg, 675.7 mg/kg), and PPI (P pollution index, ≥ 2.0) were found in urban sediments among four regions, indicating a higher environmental risk of P release, which may increase the risk of eutrophication in overlying water bodies. Collectively, this work improves the understanding of the spatial dynamics of P in the natural-rural-urban river sediment continuum, highlights the need to control P pollution in urban sediments, and provides a scientific basis for the future usage and disposal of P in sediments.

Characterizing photochemical production carboxyl content of dissolved organic matters using absorbance spectroscopy combined with FT-ICR MS

Irradiation can significantly impact the structure, reactivity and environmental behavior of dissolved organic matter (DOM). The extent of these processes remains to be ascertained in more detail but the heterogeneity and site-specificity of DOM, and the lack of methods to characterize DOM at its environmentally-relevant concentrations make it a challenge. In this study, the differences of DOM response to photodegradation in four typical origins (i.e., surface water, sediment and intracellular and extracellular algal DOM) were tracked on the molecular-level using Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (FT-ICR MS). Changes of the carboxyl and phenolic DOM moieties induced by irradiation were quantified by spectroscopic titrations, and the mechanism of functional groups affecting the changes of specific molecular composition was qualitatively proposed. The results demonstrated that intracellular algal organic matter (I-DOM) was most susceptible to photodegradation (ca. 63% DOM loss), then came extracellular algal organic matter (E-DOM) and surface water DOM (W-DOM) (ca. 15% DOM loss). Sediment DOM (S-DOM) was most resistant to irradiation, with a very small level of its mineralization. Lipids, lignin-like compounds and tannin-like compounds in I-DOM and E-DOM were relatively photo-labile. The photodegradation of lipids was related to the decarboxylation of carboxyl functional groups, while the photodegradation of tannin-like compounds was related to the rupture of phenolic functional groups. In comparison, the molecular composition of W-DOM and S-DOM was less affected by irradiation, which was also reflected in the fact that the carboxyl and phenolic functional groups were highly photo-resistant. This study showed that the photoactivity of DOM in surface water was closely related to the abundance of algae, so controlling the excessive reproduction of algae may have a positive effect on stability of quality and quantity of organic matter in surface water.

Assessing the impacts of fine sediment removal on endogenous pollution release and microbial community structure in the shallow lakes

Resuspension is a crucial process for releasing endogenous pollution from shallow lakes into the overlying water. Fine particle sediment, which has a higher contamination risk and longer residence time, is the primary target for controlling endogenous pollution. To this end, a study coupling aqueous biogeochemistry, electrochemistry, and DNA sequencing was conducted to investigate the remediation effect and microbial mechanism of sediment elution in shallow eutrophic water. The results indicated that sediment elution can effectively remove some fine particles in situ. Furthermore, sediment elution can inhibit the release of ammonium nitrogen and total dissolved phosphorous into the overlying water from sediment resuspension in the early stage, resulting in reductions of 41.44 %-50.45 % and 67.81 %-72.41 %, respectively. Additionally, sediment elution greatly decreased the concentration of nitrogen and phosphorus pollutants in pore water. The microbial community structure was also substantially altered, with an increase in the relative abundance of aerobic and facultative aerobic microorganisms. Redundancy analysis, PICRUSt function prediction, and the correlation analysis revealed that loss on ignition was the primary factor responsible for driving changes in microbial community structure and function in sediment. Overall, the findings provide novel insights into treating endogenous pollution in shallow eutrophication water.

Sedimentary organic matter molecular composition reveals the eutrophication of the past 500 years in Lake Daihai, Inner Mongolia

Lake eutrophication seriously threatens water quality and human health. Under continuous global warming and intensified human activity, increasing attention is being paid to how lake trophic status responds to climate change and anthropogenic impacts. Based on the sedimentary organic matter (SOM) molecular composition determined by the Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) technology, and combined with the SOM stable nitrogen isotopes (δ¹⁵N_org), we studied how lake trophic status and ecology respond to both climatic changes and anthropogenic impacts of the past 500 yrs at Lake Daihai, Inner Mongolia. The results show that the relative abundance of lipids, proteins, and carbohydrates in lake sediments kept relatively low before AD ∼1850, and increased gradually thereafter, especially after AD ∼1950, suggesting that the lake trophic status was low before AD ∼1850, but obviously increased during the past one more century. On the other hand, the relative abundance of allochthonous condensed aromatics and vascular plant-derived polyphenols compounds gradually decreased after AD ∼1850, which is most likely due to the intensified land-use changes in the catchment. Our results show that the SOM molecular composition is more sensitive to trace the land-use changes than the δ¹⁵N_org ratios, suggesting a potential use of this technique to trace even earlier human land uses (e.g., during the prehistorical times) in a catchment. The results of this study suggest that intensified land-use change, increased discharges of human sewage and industrial wastewater, cropland runoff, and concentrated effects caused by lake level drops may have combinedly increased nutrient concentration and accelerated lake eutrophication at Lake Daihai. Therefore, proper policy is necessary to slow down anthropogenic impacts and limit further eutrophication for lakes like Lake Daihai.

Optical properties of sedimentary dissolved organic matter in intertidal zones along the coast of China: Influence of anthropogenic activities

The intertidal zone, due to its location in the transition zone of terrestrial and marine ecosystems, is seriously disturbed by anthropogenic activities such as fuel combustion and industrial production, causing significant increase in dissolved organic matter (DOM). However, the distribution and properties of DOM in intertidal sediments at the large scale and their correlations with local socio-economic indicators remain unclear. In this study, we collected sediment samples from 13 intertidal zones across 11 coastal provinces in China and analyzed optical properties and compositions of sedimentary DOM. The results showed that the physico-chemical properties of sediment, such as pH and texture, affected the content of organic matter, thereby influencing the concentration of sedimentary DOM indirectly. The contents of fulvic acid- and protein-like components were relatively higher than humic acid-like component at all sampling sites. Moreover, urbanization could lead to the release of aromatic and humified organic matters into intertidal zones. Unlike coal, oil consumption exhibited positive correlation with SUVA₂₅₄, indicating that the combustion of oil released more aromatic compounds. These findings revealed the impact of anthropogenic activities on sedimentary DOM and provided theoretical basis for predicting and regulating intertidal carbon sink.

Chromophoric dissolved organic compounds in urban watershed and conventional water treatment process: evidence from fluorescence spectroscopy and PARAFAC

This study aimed to investigate the origin, quantity, and composition of chromophoric dissolved organic matter (CDOM) from two urbanized watersheds (Cikapundung and Cimahi River), examine how CDOM compounds and absorbances change along the process of two different conventional WTPs (WTP Dago and Cimahi) using PARAFAC, and identify absorbance as potential surrogate parameters for CDOM compounds. Samples were collected from intake, secondary treatment, and filter outlets. PARAFAC was conducted based on two data scenarios: (1) from rainy and dry seasons in Cikapundung river and WTP Dago and (2) from the two rivers and two WTPs during rainy season. Tryptophan-like (C1A) and humic-like (C2A) compounds were identified based on scenario-1 analysis. For scenario-2, humic-like (C1B), peak-M (C2B), and tryptophan-like (C3B) were the main compounds. CDOM compound quantity is consistent with the fluorescence index (FI) and biological index (BIX) which confirmed sewage and animal manure pollution in both watersheds. The best overall removal of CDOM compound occurred in WTP Dago in rainy season. The high concentration of tryptophan-like in Cikapundung River in dry season and in Cimahi River in rainy season has worsen the WTP capability to reduce CDOM. Scenario-1 has shown that in WTP Dago, the potential surrogate parameter for C1A was A240 in rainy season (r = 0.60; p < 0.01) and A410 in dry season (r =  - 0.43, p < 0.05). Based on scenario-2, for the WTP Dago in rainy season, C1B strongly correlated with A254 (r = 0.86; p < 0.01), C2B has the strongest correlation with A298 (r = 0.93; p < 0.01), and C3B correlated well with A240 (r = 0.59; p < 0.01). In WTP Cimahi, during rainy season, all compounds correlated well with all measured absorbances, with the strongest correlation with A298.

Regulation of the Nutrient Cycle Pathway and the Microbial Loop Structure by Different Types of Dissolved Organic Matter Decomposition in Lakes

To explore the effect of different types of dissolved organic matter (DOM) decomposition on nutrient cycling pathways and the microbial loop, four lakes with different DOM sources were investigated monthly. In Lake Tangxun, Dolichospermum decay released highly labile dissolved organic nitrogen into the water column. This induced bacterial organic nitrogen decomposition, as indicated by the increased abundance of gltB, gltD, gdh, and glnA as well as aminopeptidase activity. Genes associated with dissimilatory nitrate reduction to ammonium further fueled ammonium accumulation, driving Microcystis blooms in the summer. In Lake Zhiyin, fish bait deposits (high nitrogen, similar to Dolichospermum detritus) also caused Microcystis blooms. Detritus from Microcystis decomposition then produced high levels of labile dissolved organic phosphorus, inducing phosphatase activity and increasing soluble reactive phosphorus concentrations from September to April in Lakes Tangxun and Zhiyin. The high refractory DOM from macrophytes in Lake Houguan led to insufficient nutrient availability, leading to nutrient mutualism between algae and bacteria. The high levels of labile dissolved organic carbon from terrestrial detritus in Lake Yandong increased bacterial biomass and production, resulting in low chlorophyll content due to the competitive relationship between algal and bacterial nutrient requirements. Therefore, different DOM compositions induce unique connections among available nutrients, algae, and bacteria in the microbial loop.

Bacterial diversity in surface sediments of collapsed lakes in Huaibei, China

The collapse lake area due to coal mining in Huaibei shows high biodiversity, but the bacterial community composition and diversity in the lake sediments are still rarely studied. Therefore, based on 16S rRNA high-throughput sequencing and combined with analysis of environmental factors, we comparatively analyzed the bacterial community composition and diversity of surface sediments from East Lake (DH) and South Lake (NH) and Middle Lake (ZH) in the collapse lake area of Huaibei. The bacterial community compositions are significantly different in the sediments among Huaibei collapsed lakes, with DH having the largest number of species, and NH having a higher species diversity. Pseudomonadota is the most abundant phylum in the sediments of DH and NH, while the most abundant phyla in ZH are Bacteroidales, Chloroflexales, Acidobacteriales, and Firmicutes. Anaerolineae (24.05% ± 0.20%) is the most abundant class in the DH sediments, and Gammaproteobacteria (25.94% ± 0.40%) dominates the NH sediments, Bacteroidia (32.12% ± 1.32%) and Clostridia (21.98% ± 0.90%) contribute more than 50% to the bacteria in the sediments of ZH. Redundancy analysis (RDA) shows that pH, TN, and TP are the main environmental factors affecting the bacterial community composition in the sediments of the collapsed lake area. The results reveal the bacterial community composition and biodiversity in the sediments of the Huaibei coal mining collapsed lakes, and provide new insights for the subsequent ecological conservation and restoration of the coal mining collapsed lakes.