Cyclotron Resonance Research Articles

The unique biogeochemical role of carbonate-associated organic matter in a subtropical seagrass meadow

The particulate organic matter buried in carbonate-rich seagrass ecosystems is an important blue carbon reservoir. While carbonate sediments are affected by alkalinity produced or consumed in seagrass-mediated biogeochemical processes, little is known about the corresponding impact on organic matter. A portion of particulate organic matter is carbonate-associated organic matter. Here, we explore its biogeochemistry in a carbonate seagrass meadow in central Florida Bay, USA. We couple inorganic stable isotope analyses (δ34S, δ18O) with a molecular characterization of dissolved and carbonate associated organic matter (21 tesla Fourier-transform ion cyclotron resonance mass spectrometry). We find that carbonate-associated molecular formulas are highly sulfurized compared to surface water dissolved organic matter, with multiple sulfurization pathways at play. Furthermore, 97% of the formula abundance of surface water dissolved organic matter is shared with carbonate-associated organic matter, indicating connectivity between these two pools. We estimate that 9.2% of the particulate organic matter is carbonate-associated, and readily exchangeable with the broader aquatic system as the sediment dissolves and reprecipitates.

Backward test particle simulation of nonlinear cyclotron wave-particle interactions in the radiation belts

Wave-particle interaction plays a crucial role in the dynamics of the Earth’s radiation belts. Cyclotron resonance between coherent whistler mode electromagnetic waves and energetic electrons of the radiation belts is often called a coherent instability. Coherent instability leads to wave amplification/generation and particle acceleration/scattering. The effect of wave on particle’s distribution function is a key component of the instability. In general, whistler wave amplitude can grow over threshold of quasi-linear (linear) diffusion theory which analytically tracks the time-evolution of a particle distribution. Thus, a numerical approach is required to model the nonlinear wave induced perturbations on particle distribution function. A backward test particle model is used to determine the energetic electrons phase space dynamics as a result of coherent whistler wave instability. The results show the formation of a phase space features with much higher resolution than is available with forward scattering models. In the nonlinear regime the formation of electron phase space holes upstream of a monochromatic wave is observed. The results validate the nonlinear phase trapping mechanism that drives nonlinear whistler mode growth. The key differences in phase-space perturbations between the linear and nonlinear scenarios are also illustrated. For the linearized equations or for low (below threshold) wave amplitudes in the nonlinear case, there is no formation of a phase-space hole and both models show features that can be characterized as linear striations or ripples in phase-space.

Intrinsic Chemical Drivers of Organic Aerosol Volatility: From Experimental Insights to Model Predictions

AbstractAccurately predicting the volatilities of molecules in aerosols is challenging but crucial for understanding the atmospheric effects of aerosols. We used negative and positive ion electrospray ionization Fourier‐transform ion cyclotron resonance mass spectrometry (FT‐ICR MS) to identify differences in the molecular compositions of gas and particle phase samples from urban atmosphere. We aimed to identify intrinsic chemical parameters that determine and predict the organic aerosol volatility. We found higher average molecular weights, carbon mass percentages, and double bond equivalents (DBE) but lower average O/C ratios and oxygen mass percentages in the particle phase than the gas phase. We identified DBE, which display a significant negative correlation with volatility, as a key parameter. We proposed to improve the previous model for predicting organic aerosol volatility by incorporating DBE as a new variant; and the result showed that this subsequently improved the accuracy of the model, particularly for compounds with minimal or no heteroatoms (0–2) such as hydrocarbons (CH). The revised model offers insights into the contributions of DBE, carbon, nitrogen, oxygen, and sulfur atoms to the volatilities of diverse organic molecules in aerosols and could be applied to improve our understanding of the phase distributions of volatile organic compounds in the ambient air.

Electron temperature and ion density distribution on a vertical section in a weakly magnetized inductively coupled plasma

In this study, the distributions of electron temperature and ion density on a vertical section in a weakly magnetized inductively coupled plasma were measured using radially movable floating probes placed at different axial positions. The chamber used in this experiment included two cylindrical parts: a smaller radius top part with a planar antenna on the top quartz window and a larger radius downstream part. A magnet coil around the chamber top part maintained a divergent magnetic field in the discharge region. As the current in the magnet coil increased, the magnetic field also increased. Due to the variations of the radio frequency electric field in the plasma, the increase in electron temperature can be divided into different stages. At the higher magnetic field, the electric field of the electrostatic wave can increase electron temperature at the chamber center axial. Also, since the electron cyclotron resonance (ECR) heating in the chamber downstream part changed with the magnetic field, the maximum ion density was observed when the magnetic field around the bias electrode was slightly larger than the ECR magnetic condition. The reasons for these variations were verified in the plasma numerical simulations. The ion flux distribution measured on the bias electrode can change from a center-high distribution to an M-shape distribution with the increased magnetic field.

Molecular insights into the degradation of organic matter from secondary swine wastewater effluent: A comparative study of advanced oxidation processes

Advanced oxidation processes (AOPs) are promising for the treatment of secondary swine wastewater effluents, however, the molecular-level understanding of effluent organic matter (EfOM) removal and transformation during AOPs is limited. This study employed molecular-level characterization based on Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) and bulk characterizations to investigate these processes in various AOPs, including Cu-Fenton, UV-Cu-Fenton, Fenton, UV-Fenton, and UV/H2O2 treatments. Our findings revealed that the removal rates of dissolved organic carbon and EfOM molecules follow the sequence of UV-Fenton > Fenton > UV-Cu-Fenton > UV/H2O2 > Cu-Fenton, correlating with the rates of H2O2 decomposition during reactions. AOPs with faster H2O2 decomposition, indicative of higher reactive oxygen species generation, predominantly mineralize rather than transform EfOM. Linkage analysis highlighted oxygen addition and deamination as the primary transformation reactions, with variations in the dominance levels of these reactions across different AOPs. Recalcitrant molecule, particularly CHNO and CHO types, including low-molecular-weight carboxyl-rich alicyclic molecules, pose challenges in treatment. To enhance the efficacy of secondary effluent treatment, strategies focusing on the targeted removal of such recalcitrant EfOM should be developed. This study provided new insights into the selection and optimization of AOPs for secondary swine wastewater effluent treatment.

Unveiling the optical and molecular characteristics of aging microplastics derived dissolved organic matter transformed by UV/chlor(am)ine oxidation and its potential for disinfection byproducts formation

The investigations into the existence and behavior of microplastics (MPs) in water environment were widely conducted, while the characteristics of dissolved organic matter derived from MPs (MPs-DOM) during advanced oxidation have garnered comparatively little attention. In this study, Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) was employed along with multiple statistical analyses to gain a deeper understanding of the conversion of MPs-DOM in UV/chlor(am)ine advanced oxidation processes (AOPs). The diverse treatments exhibited varying degrees of augmentation in both aging and fragmentation of MPs with the order of UV/Cl2 > UV > UV/NH2Cl. The fragmentation degree of MPs upon two UV-based AOPs (UV-AOPs) was dependent on their monomer chemical structure. The highest TOC values of three MPs-DOM were observed after UV/Cl2 AOP and the lowest after UV/NH2Cl AOP. Polyvinyl chloride (PVC) displayed a greater release of MPs-DOM under varying leaching conditions. UV/Cl₂ AOP favored the reaction with saturated MPs-DOM, while UV/NH₂Cl AOP reduced unsaturated MPs-DOM, alleviating disinfection byproducts (DBPs) formation after chlorination. The precursors generated by UV/Cl₂ AOP owned lower H/C, higher modified aromatic index (AImod), and lower molecular weight (MW) products after chlorination. PVC-DOM with fewer CH₂ groups was more reactive. -H₂O, +O and -CH₂ reactions dominated in PVC-DOM (CHO compounds), while -2H, +O, -CH₂ did in PVC-DOM (CHON compounds). The dominant chlorine addition/substitution reactions occurred in PVC-DOM treated by UV/Cl₂ AOP, identifying 195 Cl-DBPs with 220 precursor-product pairs. Mass difference analyses showed that +2H and +O reactions were the most frequent of the 24 reaction types. Environmental ImplicationMicroplastics derived dissolved organic matters (MPs-DOM) transformed into disinfection byproducts (DBPs) under advanced oxidation processes (AOPs), heightening environmental risks. In this study, Fourier transform ion cyclotron resonance mass spectrometry was employed to gain a deeper understanding of MPs-DOM conversion in UV/chlor(am)ine AOPs. MPs fragmentation and fluorescent components varied with monomer chemistry and polymers. UV/Cl₂ AOP reacted with saturated MPs-DOM. UV/NH₂Cl AOP reduced unsaturated MPs-DOM, alleviating DBPs formation. DBPs precursors generated by UV/Cl₂ AOP owned higher modified aromatic index, lower H/C and molecular weight. Unveiling the MPs-DOM transformation during AOPs can mitigate the negative environmental impacts of MPs and their derivatives.

Multifluid Theory of Electrostatic Ion Cyclotron Waves in Partially Ionized Plasmas

Partially ionized plasmas universally exist in various astrophysical environments, such as the solar atmosphere and the E region of the ionosphere. In these contexts, the existence and propagation of waves in plasmas could be significantly influenced by effects of weakly ionized plasma (e.g., ion–neutral collisions). In this work, we investigate electrostatic ion cyclotron (EIC) waves in partially ionized plasmas based on the multifluid model with adiabatic electrons. Two distinct branches of EIC waves coexist in partially ionized plasmas: one branch is the conventional EIC waves; the other branch propagates around the “effective ion cyclotron frequency” which originates from self-consistent ion–neutral collisions. Furthermore, theoretical predictions in the new branch of EIC waves are qualitatively consistent with laboratory observations. In addition, a comparison between our theory and the previous work is also performed. This work can aid in understanding the acceleration and transverse heating of ions in partially ionized astrophysical plasmas where the ion–neutral collisions are frequent.

ON THE EFFICIENCY OF WAVE-PARTICLE INTERACTION

The efficiency of acceleration of charged particles during cyclotron resonances and acceleration of particles in a vacuum without an external magnetic field are considered. It is shown that the statement formulated in Lawson-Woodward theorem that relativistic particles do not exchange energy with an external electromagnetic wave in a vacuum is not sufficiently justified.

A fast solid-phase microextraction scheme for in vivo monitoring of bio-accumulation and bio-transformation of arbidol in living plants

Large quantity of the antiviral drug arbidol is used for resisting virus infection like the Corona Virus Disease 2019 and influenza, resulting in unanticipated environmental pollution. Herein, to investigate the environmental risks of the unanticipated arbidol contamination, a novel in vivo sampling probe was developed based on a bromo-substituted porous organic polymer (Br-POP) and then adopted for tracking the bio-accumulation and bio-transformation of arbidol in living plants by coupling with a nano-electrospray ionization fourier-transform ion cyclotron resonance mass spectrometry (Nano-ESI-FT-ICR-MS) method. The established method showed good extraction performance towards arbidol with limit of detection (LOD) of 0.48 ng g−1, and relative standard deviation (RSD) of single-and multiple- probe of 2.2 and 14 %. Owing to the interactions between the Br-POP and the target analytes, as well as the fast analysis process of Nano-ESI-FT-ICR-MS, <6 min was cost for total sampling and analysis duration, achieving hourly tracking of arbidol and its metabolites in this work. During 21-d in vivo tracking, the concentration of arbidol in living plant stems increased rapidly within 6 h and peaked at 413.93 ± 47.09 ng g−1. Meanwhile, it was found that dissolved organic matters (DOM) had significant effect on arbidol behaviors in living plants, resulting in a decrease of the maximum concentration of arbidol in plant stems (152.70 ± 42.44 ng g−1) and the change of dominant metabolite of arbidol that the S-oxidation rather than N-demethylation product of arbidol was dominant with DOM participation. Additionally, the plant root secretion was found to be significantly altered by arbidol exposure. To summarized, the combination of in vivo SPME and the FT-ICR-MS analysis provide new and important information regarding arbidol contamination and related alternation of plant root metabolism.

Compositional Analysis of Oxygenates and Hydrocarbons in Waste and Virgin Polyolefin Pyrolysis Oils by Ultrahigh-Resolution Fourier Transform Ion Cyclotron Resonance Mass Spectrometry

Compositional Analysis of Oxygenates and Hydrocarbons in Waste and Virgin Polyolefin Pyrolysis Oils by Ultrahigh-Resolution Fourier Transform Ion Cyclotron Resonance Mass Spectrometry

Model-predictive kinetic control with data-driven models on EAST

Abstract In this work, model-predictive control (MPC) was combined for the first time with singular perturbation theory, and an original plasma kinetic control method based on extremely simple data-driven models and a two-time-scale MPC algorithm has been developed. A comprehensive review is presented in this paper. Slow and fast semi-empirical models are identified from data, by considering the fast kinetic plasma dynamics as a singular perturbation of a quasi-static equilibrium, which itself is governed, on the slow time scale, by the flux diffusion equation. This control technique takes advantage of the large ratio between the time scales involved in magnetic and kinetic plasma transport. It is applied here to the simultaneous control of the safety factor profile, q(x), and of several kinetic variables, such as the poloidal beta parameter, βp, and the internal inductance parameter, li, on the EAST tokamak. In the experiments, the available control actuators were lower hybrid current drive (LHCD) and co-current neutral beam injection (NBI) from different sources. Ion cyclotron resonant heating (ICRH) and electron cyclotron resonant heating (ECRH) are used as additional actuators in control simulations. In the controller design, an observer provides, in real time, an estimate of the system states and of the mismatch between measured and predicted outputs, which ensures robustness to model errors and offset-free control. A number of control applications are described in the paper, either in nonlinear simulations with EAST-like parameters or in real experiments on EAST. Various controller configurations were tested, with up to three controlled variables chosen among q0 = q(x=0), q1 = q(x=0.5), βp and li. Both the extensive nonlinear simulations and the experiments described in this paper have demonstrated the relevance of combining model-predictive control, data-driven models and singular perturbation methods for plasma kinetic control.

Enhanced hydrothermal liquefaction of tires using zinc and MoS2

This study introduces a novel approach for tire liquefaction employing zinc and unsupported catalyst MoS2 to mitigate oxygen, nitrogen, and sulfur content, while inhibiting poly-aromatic formation. Autoclave experiments were conducted under subcritical water conditions at 360 and 410 °C. Comprehensive characterization of char and oil was performed, encompassing elemental analysis, functional-group assessment, and composition analysis using gas chromatography-mass spectrometry (GC-MS) and Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR MS). During the liquefaction, zinc metal pellets react with water to form ZnO and hydrogen, aiding hydrogenation, and MoS2 preserves its catalytic stability. ZnO shows a catalytic effect on deoxygenation, desulfurization, and denitrification reactions. However, the reaction between ZnO and H2S is not favorable under hydrothermal conditions. Zinc and MoS2 synergistically promote cracking of heavier compounds into lighter ones, particularly evident at higher temperatures, without diminishing the overall oil yield. Incorporating zinc pellets and MoS2 slightly facilitates sulfur and oxygen migration from liquid to solid and gas phases. FT-ICR MS analysis reveals oxygen, sulfur, and nitrogen-containing compounds in heavy fraction of oils. The oxygen-containing compounds, predominantly comprised of stearic acid and its derivatives, are identified. Concurrently, the nitrogen-containing compounds manifest primarily as basic nitrogen compounds. MoS2 possesses the capability of forming more N-containing compounds, leading to the generation of a broader spectrum of N-containing compounds. This work elucidates the synergistic role of zinc-assisted catalysis and MoS2, offering insights into tire liquefaction mechanisms and product composition, vital for sustainable waste management and resource recovery.

Cyclotron resonance imaging at cryogenic temperatures enabled by electric field modification in a microwave cavity

Abstract Cyclotron resonance (CR) is a standard but emerging technique for investigating carrier properties of semiconductors. We have succeeded in CR measurements by employing a microwave cavity designed for electron paramagnetic resonance (EPR). Here, we demonstrate CR imaging to visualize the spatial distribution of carriers at cryogenic temperatures for the first time. To realize CR imaging, it is necessary to account for the electric field modification in the microwave cavity of a cylindrical TM110 mode, which is designed for EPR imaging and is inherently unsuitable for CR measurements. CR detection requires the oscillating electric field perpendicular to the external static magnetic field (B0) at the sample position, which is not designed for the unloaded cavity. It has been challenging to verify the electric field distribution inside the cavity experimentally, but we show that the observation of the CR signals provides evidence of modification in the electric field. Analysis of the electromagnetic field explains the results, revealing a field distribution whose strength and direction are perturbed due to the lensing effect by the inserted dielectric materials.

The consequences of tritium mix for simulated ion cyclotron emission spectra from deuterium-tritium plasmas

Abstract Measurements of ion cyclotron emission (ICE) are obtained from most large magnetically confined fusion (MCF) plasma experiments, and may be used in future to quantify properties of the fusion-born alpha-particle population in deuterium-tritium (DT) plasmas in ITER. ICE is driven by spatially localised, strongly non-Maxwellian, minority energetic ion populations which relax collectively under the magnetoacoustic cyclotron instability (MCI). ICE spectral peaks are typically observed at, near, or separated by, integer harmonics of the energetic ion cyclotron frequency. Here, for the first time, we study how simulated ICE spectra from DT plasmas vary with tritium concentration and compare with an observed JET DT ICE spectrum. We incorporate a population of thermal tritons, in addition to thermal deuterons and an energetic minority population of fusion-born alpha-particles, in simulations with the kinetic particle-in-cell (PIC) code EPOCH. This code has previously been used extensively for interpretation of ICE observations in terms of the self-consistent gyro-resolved collective Maxwell-Lorentz dynamics of tens of millions of simulation particles. Our simulation parameters are relevant to the ICE-generative outer midplane edge region of JET DT plasma 26148, which included 11% tritium. Quantifying the variation of simulated ICE power spectra with tritium concentration reveals that our simulation with 11% tritium concentration most accurately represents the observed ICE spectrum from this plasma. This outcome is encouraging for the diagnostic application of ICE to fusion plasmas containing two thermal ion species, including future DT plasmas.

Characterization of natural and anthropogenic dissolved organic matter in the yangtze river basin using FT-ICR MS

Dissolved organic matter (DOM) is a complex mixture that plays a crucial role in global carbon cycling and climate dynamics. Understanding the chemical composition of DOM is crucial for studying its biogeochemical behavior. However, identifying individual DOM molecules is challenging. Here, using ultrahigh-resolution Fourier transform ion cyclotron resonance mass spectrometry and an in-house database, we developed a framework to investigate DOM characteristics in natural water. Through the developed approach, we successfully identified thousands of individual DOM molecules in the water bodies of the Yangtze River Basin. For the first time, the proportions of natural and anthropogenic organics within DOM were revealed. In total, 9006 unambiguous molecular formulas were assigned to DOM in the Yangtze River Basin. The proportions of CHNO and CHOS compounds increased from upstream to downstream regions. Moreover, 1099 DOM compounds were tentatively identified, with 85 % being endogenous organics and 15 % being exogenous organics. Notably, lipids and pharmaceuticals and personal care products were the most frequently detected endogenous and exogenous compounds. The spatial variation of the identified DOM indicated anthropogenic discharges considerably increased both the number and abundance of DOM in the downstream Yangtze River Basin. This study highlighted the importance of anthropogenic impacts on DOM in water.

Electromagnetic Surface Waves in a Relativistic Magnetized Plasma Propagating in a Cylindrical Column

Dispersion relations of electromagnetic surface waves in a magnetized relativistic plasma propagating in a cylindrical column surrounded by vacuum are derived by means of the relativistic fluid equations. The zero order relativistic beam is assumed to stream along the direction of the axial magnetic field. The coupled equations of the E- and B-wave modes are solved analytically in terms of the cylindrical coordinates in weak or intermediate values of the magnetic field in which the cyclotron frequency is much smaller than the relativistic Doppler-shifted frequency. The entangled field components of the E- and B-waves are decoupled by assuming that the flow is incompressible. The surface wave dispersion relations of the E- and B-wave modes show a strong similarity and symmetry. The static magnetic field splits the E- and B-waves, thus doubling the modes in unmagnetized plasma. By taking the radius of the cylinder infinite, the dispersion relations in a semi-infinite plasma are derived.

VOCs conversion in He/H2O plasma produced in a micro-capillary tube at atmospheric pressure

Abstract A non-equilibrium plasma is created in a micro-capillary quartz tube (800 µm of internal diameter), by a DC-pulsed micro-dielectric barrier discharge (micro-DBD) and the propagation of an ionisation wave, in mixtures of He/H2O/VOC at atmospheric pressure where the studied volatile organic compounds (VOCs) are representative of molecules belonging to different chemical families: alcohols (methanol, ethanol, isopropanol, tert-butanol), ketones (acetone), nitriles (acetonitrile), and aromatic hydrocarbons (toluene). The conversion efficiency of these VOCs is studied as a function of the applied voltage on the micro-DBD (or electrical energy deposited in the plasma) and of the initial concentration of the molecules in the range from 1 ppm up to 3000 ppm (depending on the molecule), with the help of high-resolution real-time mass spectrometry Fourier transform ion cyclotron resonance associated to chemical ionisation (CI-FTICR) using H3O+ as precursor ion. A variety of by-products resulting from the conversion of VOCs are identified and quantified, emphasising that the micro-capillary plasma is able to induce a complex chemical reactivity. A qualitative analysis of the involved kinetics, based on the existing literature, reveals that helium species (ions and metastable states) and radicals coming from the dissociation of the water molecules (O and OH) are the most probable candidates to explain the formation of all compounds detected by the CI-FTICR apparatus. Quenching processes of the metastable He(23S) by the VOCs, leading to the dissociation of the molecules, are suggested to explain some of the experimental results.

Observation of high frequency Alfvén eigenmodes excited by RF-accelerated minority hydrogen ions in the EAST tokamak

Abstract The paper presents the original observation of high frequency Alfvén eigenmode excited by fast minority hydrogen ions accelerated by ion cyclotron range of frequency waves in EAST. The frequency of high frequency Alfvén eigenmodes is around 0.75~8*Ω H, where Ω H is the cyclotron frequency of hydrogen ions evaluated at the low-field side plasma edge. It tracks the on-axis magnetic field B t and the edge plasma electron density n e via the Alfvenic relation ω~ B t *n e -1/2. The high frequency Alfvén eigenmodes are always accompanied by sub-cyclotron modes in several experiments at EAST, consistent with the high frequency Alfvén eigenmode detected on other conventional tokamaks, namely ASDEX Upgrade and DIII-D. Based on the previous study, these sub-cyclotron modes are consistent with the spectrum splitting produced by toroidal mode numbers[Nuclear Fusion 43, 228 (2003)]. We also found that the location of eigenmode excitation of high frequency Alfvén eigenmode driven by RF-accelerated minority hydrogen ions remains unchanged even though the cyclotron resonance location of hydrogen ions varies with B t.

Thermal Denaturation of Fresh Frozen Tissue Enhances Mass Spectrometry Detection of Peptides.

Thermal denaturation (TD), known as antigen retrieval, heats tissue samples in a buffered solution to expose protein epitopes. Thermal denaturation of formalin-fixed paraffin-embedded samples enhances on-tissue tryptic digestion, increasing peptide detection using matrix-assisted laser desorption ionization imaging mass spectrometry (MALDI IMS). We investigated the tissue-dependent effects of TD on peptide MALDI IMS and liquid chromatography-tandem mass spectrometry signal in unfixed, frozen human colon, ovary, and pancreas tissue. In a triplicate experiment using time-of-flight, orbitrap, and Fourier-transform ion cyclotron resonance mass spectrometry platforms, we found that TD had a tissue-dependent effect on peptide signal, resulting in a (22.5%) improvement in peptide detection from the colon, a (73.3%) improvement in ovary tissue, and a (96.6%) improvement in pancreas tissue. Biochemical analysis of identified peptides shows that TD facilitates identification of hydrophobic peptides.

Long-Term Photochemical and Microbial Alterations Lead to the Compositional Convergence of Algal and Terrestrial Dissolved Organic Matter.

Lakes are expected to become more active in processing dissolved organic matter (DOM), but the fate of DOM with different origins remains poorly constrained. We conducted long-term incubation experiments (∼1 year) with sole light, sole microbial, and combined light and microbial treatments using DOM from algal and terrestrial sources (DOMa and DOMt, respectively). Fourier transform ion cyclotron resonance mass spectrometry and 16s rRNA were used to analyze the DOM molecular composition and bacterial community, respectively. We observed that DOMa and DOMt converged toward a similar composition under the combined light and microbial treatment, driven by the removal of source-specific compositions along with the production of refractory, carboxylic-rich alicyclic molecules (CRAM). For CRAM enrichment, microbial processes played a greater role for DOMa, while phototransformation was more important for DOMt. The co-occurrence patterns between DOM molecules and bacteria showed that DOM molecular composition influenced the bacterial community. More complex DOM-bacteria interactions were observed for DOMt compared to DOMa, suggesting that greater bacterial cooperation was necessary for transforming DOMt. Collectively, these findings offer new insights into the mechanisms underlying the uniformity of DOM from various sources through prolonged environmental transformations in lakes.