Comparison of organic matter (OM) pools in water, suspended particulate matter, and sediments in eutrophic Lake Taihu, China: Implication for dissolved OM tracking, assessment, and management

Biological and terrestrial influences on dissolved organic matter in Antarctic surface waters: Insights from mass spectrometry and metagenomic analysis

Global warming increases the surface waters and biodiversity in polar regions. However, the intrinsic biological sources of dissolved organic matter (DOM) in Antarctic surface waters remain poorly understood. This work evaluated the sources and driving mechanisms of DOM in Antarctic lakes systematically, based on fluorescence excitation-emission matrices, ultrahigh-resolution mass spectra, biological detection, and metagenomic analyses. The most abundant DOM in the water was peptides (37.02%), which differed from those in soil (lignins: 26.33%) and penguin guano (lipids: 50.71%). The relative abundance of CHON and CHOP compounds in water was significantly correlated with the distance from the penguin colony (p < 0.05). Both the fluorescence and mass spectrum fingerprints of water and soil/faeces showed low similarities using end-member source tracking methods. This could be attributed to the facilitation of guano-derived nutrients to phytoplankton proliferation, whereas the concentrations of NH4+-N, NO3--N, total phosphorus, and total organic carbon were significantly higher in the penguin-intensive area than in the other areas. Algae had significant positive effects on carbohydrates and amino sugars and positive effects on lignins, compared to zooplankton and bacteria. Zooplankton had significantly more positive effects on peptides than phytoplankton. Secondary bacterial metabolic activity can be positively linked with CHO compounds. Carbohydrates and amino sugars co-occurred with carbohydrate-active enzyme genes and nitrogen cycling genes in one module of the co-occurrence network, whereas the other module was characterised by the co-occurrence patterns of condensed aromatic structures with carbohydrate-active enzyme genes and nitrogen cycling genes. These results emphasise the roles of secondary metabolites from algae and bacteria in species-specific sources of DOM, shedding light on the driving mechanisms of the biogeochemical cycling of DOM in the Antarctic water environment.

Cascading microbial regulation of autochthonous DOM stability in a picocyanobacteria-dominated estuarine reservoir

Estuaries serve as vital interfaces in the global carbon cycle by mediating land-ocean exchange and regulating dissolved organic matter (DOM) dynamics. However, the role of microbial communities in regulating autochthonous DOM under phosphorus-limited estuarine conditions remains insufficiently understood. This study explored the biogeochemical parameters, inorganic carbon dynamics, DOM optical properties, and algal-bacterial community composition in a picocyanobacteria-dominated estuarine reservoir subject to seasonal salinity and nutrient fluctuations. Samples were classified into three groups based on DOM compositional features: pristine autochthonous group (PG), high allochthonous group (HG), and balanced group (BG). In BG, picocyanobacteria, particularly Cyanobium PCC-6307, promoted the accumulation of labile tryptophan-like DOM (component C4), which was associated with the lowest autochthonous DOM stability ratios (AuSR). In HG, terrestrial runoff led to a decline in C4 and an increase in DOM stability, reflecting rapid microbial degradation and partial transformation. In BG, colder temperatures and elevated microbial α-diversity facilitated the conversion of DOM into more humified forms, as indicated by higher proportions of humic-like components and AuSR. Key microbial taxa showed substrate-specific metabolic traits related to amino acid, polysaccharide, and one-carbon compound processing. By integrating DOM-defined groupings, fluorescence-derived stability metrics, and microbial marker analysis, this study reveals a sequential cascade of microbial regulation in DOM production, transformation, and stabilization. These findings offer the first detailed evidence of such processes in a phosphorus-limited estuarine system and provide a new framework for linking DOM properties with microbial ecological functions in dynamic aquatic environments.

Seasonal hydrological variation impacts nitrogen speciation and enhances bioavailability in plateau lake sediments

Global warming has intensified the distinction between dry and wet seasons in monsoonal climates. The synergistic effect of high temperatures and rainfall during the wet season promotes the release of endogenous nitrogen (N) and eutrophication within lake ecosystems. However, the seasonal variations in sediments N speciation and bioavailability, and their intrinsic connection to release potential, remain unclear. This study employed sequential extraction method and Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (FT-ICR MS) to characterize extractable N (Ex-N) in Erhai Lake sediments during dry and wet seasons. The results indicated that ion-exchangeable organic form N (IEF-ON) serves as a substrate for microbial mineralization, with the highest proportion of protein-like substances (26.2%). The influx of N-containing polysaccharides and poly-N glycoproteins during the wet season further increased its bioavailability. Algal-derived N exists as the weak acid-extractable organic form N (WAEF-ON), which has the highest lipid proportion (11.7%) and the lowest double bond equivalent (DBE) values. Overall, elevated water temperatures and N input during the wet season accelerate both the mineralization rate of organic N (ON) and the content of labile N components. This potentially triggers a "priming effect" that could further activate the refractory N components in the sediments. Additionally, the wet season reduces sediment pH and redox potential, making WAEF-ON and strong alkali-extractable form N (SAEF-N) more labile and susceptible to release. This study reveals the adverse effects of seasonal variations on N sequestration in lake sediments, complicating the control of endogenous pollution release under the backdrop of climate change.

Influencing Factors of Phosphorus Mobility and Retention in the Sediment of Three Typical Plateau Lakes

The mechanisms driving changes in the stability of phosphorus (P) in sediments under lake ecosystem degradation remain poorly understood. This study investigated the P-binding forms in sediments from three plateau lakes with different trophic states in Yunnan Province, China, aiming to elucidate the responses of sediment P compositions to human activities, lake trophic status, and dissolved organic matter (DOM) characteristics. The results showed that human activity directly contributed to sediment P retention. The trophic type of lake exerted a discernible effect on P mobility in the sediments, as eutrophic algae-type lakes had a higher content of sediment mobile-P. Moreover, the sediment DOM promoted the adsorption of BD-P and NH4Cl-P. Generally, exogenous pollution caused by human activity leads to lake eutrophication and a decline in lake ecosystem stability. This variation was largely influenced by water depth. A decrease in lake ecosystem stability leads to increased P mobility in sediments, which increases the risk of endogenous pollution. The DOM plays an important role in the mobility of sediment P. These insights offer a novel perspective for understanding how lake ecosystem characteristics are related to endogenous P loads in lakes.

Polystyrene microplastics enhanced the photo-degradation and -ammonification of algae-derived dissolved organic matters

Algae-derived organic matter (ADOM) is a key source of chromophoric dissolved organic matter (CDOM) in natural waters. When exposed to solar irradiation, ADOM undergoes gradual degradation and transformation. The escalating presence of microplastics (MPs) can act as a novel type of environmental photosensitizer, however its impacts on ADOM photodegradation remains largely unexplored. Thus, in this study, ADOM were extracted from four common algal species (Microcystis aeruginosa, Synechococcus sp., Chlorella pyrenoidosa and Scenedesmus obliquus) and exposed to UV irradiation with or without polystyrene (PS) MPs, namely ADOM+PS groups and ADOM groups, respectively. The results indicated that a more rapid degradation of amino acid-like substances (∼38 % vs. ∼22 %) and more ammonia products (1.86 vs. 1.21 mg L-1) were observed in the ADOM+PS groups compared to the ADOM groups after a five-day exposure. This enhanced photodegradation might be attributed to the production of environmentally persistent free radicals and reactive species during the photoaging of PS. Furthermore, PS-derived high electron transfer belt activity of ADOM led to the production of highly aromatic and humified products. These humic-like products could potentially accelerate the degradation of amino acid-like compounds by exciting the generation of excited triplet CDOM. This study underscores the role of MPs as environmental photosensitizers in promoting ADOM degradation and ammonia generation, providing insights on the transformation of ADOM mediated by emerging pollutants and its impact on aquatic carbon and nitrogen cycles.

Cyanobacteria decay alters CH4 and CO2 produced hotspots along vertical sediment profiles in eutrophic lakes

Cyanobacteria-derived organic carbon has been reported to intensify greenhouse gas emissions from lacustrine sediments. However, the specific processes of CH4 and CO2 production and release from sediments into the atmosphere remain unclear, especially in eutrophic lakes. To investigate the influence of severe cyanobacteria accumulation on the production and migration of sedimentary CH4 and CO2, this study examined the different trophic level lakes along the middle and lower reaches of the Yangtze River. The results demonstrated that eutrophication amplified CH4 and CO2 emissions, notably in Lake Taihu, where fluxes peaked at 929.9 and 7222.5 μmol/m2·h, mirroring dissolved gas levels in overlying waters. Increased sedimentary organic carbon raised dissolved CH4 and CO2 concentrations in pore-water, with isotopic tracking showing cyanobacteria-derived carbon specifically elevated CH4 and CO2 in surface sediment pore-water more than in deeper layers. Cyanobacteria-derived carbon deposition on surface sediment boosted organic carbon and moisture levels, fostering an anaerobic microenvironment conducive to enhanced biogenic CH4 and CO2 production in surface sediments. In the microcosm systems with the most severe cyanobacteria accumulation, average CH4 and CO2 concentrations in surface sediments reached 6.9 and 2.3 mol/L, respectively, surpassing the 4.7 and 1.4 mol/L observed in bottom sediments, indicating upward migration of CH4 and CO2 hotspots from deeper to surface layers. These findings enhance our understanding of the mechanisms underlying lake sediment carbon emissions induced by eutrophication and provide a more accurate assessment of lake carbon emissions.

Effects of wet-dry alternation on organic phosphorus dynamics and sediment characteristics in the intertidal zone of Nansi Lake

The study of the fractions and distribution characteristics of organic phosphorus in the sediment of the water level fluctuating zone of Nansi Lake is conducive to revealing the transformation of phosphorus in the lake, and has important scientific significance for controlling the eutrophication of Nansi Lake. Based on the sediment of the water level fluctuation zone of Nansi Lake. The improved Hedley continuous grading extraction, ultraviolet-visible spectroscopy and three-dimensional fluorescence spectroscope were used to characterize the structural characteristics and stability of organic molecules in the sediment, and to reflect the differences in the structure and stability of organophosphate in the water level fluctuating zone. Principal component analysis (PCA), Redundancy analysis (RDA) and correlation heat map analysis were used to analyze the correlation between phosphorus and physicochemical index. The results showed that the alternation between wet-dry conditions was more favorable for the release of phosphorus from sediment, compared to continuous inundation conditions. Moreover, the higher the frequency of wet-dry alternations, the greater the release of phosphorus in different forms from the sediment. Wet-dry alternation resulted in a reduction of substituent on the aromatic rings of sediment DOM (dissolved organic matter), and the continuous drying would increase the molecular weight and humidification degree of DOM in the sediment. Correlation analysis showed that NaOH-Po content in sediment was significantly negatively correlated with TP, IP, OP and various organophosphorus forms, indicating a close transformation relationship between phosphorus forms in sediment. The results can provide a scientific basis for controlling the release of endogenous phosphorus and the risk of eutrophication in Nansi Lake.

Optimizing sustainable agriculture: A comprehensive review of agronomic practices and their impacts on soil attributes

This study explores agronomic management (AM) effects on soil parameters under diverse conditions. Investigating tillage practices (TP), nutrient management (NM), crop rotation (CR), organic matter (OM), irrigation management (IM), and mulching (MS), it aims to reveal impacts on soil productivity, nutrient availability, microbial activity, and overall health. Varied TP affect soil quality through compaction, porosity, and erosion risk. Proper NM is vital for nutrient cycling, preventing imbalances and acidification. CR disrupts pest cycles, reduces weed pressure, and boosts nutrient recycling. OM management enhances soil quality by influencing organic carbon, nutrient availability, pH, fertility, and water retention. Optimizing IM regulates soil water content without inducing waterlogging. MS contributes to OM content, nutrient retention, soil structure, and temperature-moisture regulation, benefiting soil biota, aggregation, soil health and agricultural productivity. The review emphasizes integrated nutrient, CR, and OM management's positive impact on fertility and microbial activity. Different TP and IM variations impact soil health and crop production. Judicious implementation of these practices is essential for sustainable agriculture. This synthesis identifies uncertainties and proposes research directions for optimizing productivity while ensuring environmental sustainability. Ongoing inquiry can guide a balanced approach between yields and resilient soil stewardship for future generations.

Co-influence of biochar-supported effective microorganisms and seasonal changes on dissolved organic matter and microbial activity in eutrophic lake

DOM (dissolved organic matter) play a crucial role in lakes' geochemical and carbon cycles. Eutrophication evolution would influence nutrient status of waters and investigating the DOM variation helps a better understanding of bioremediation on environmental behavior of DOM in eutrophic lakes. In our study, the contents, compositions and characteristics of systematic DOM&SOM (sediment organic matter) were greatly influenced by seasonal changes. But the effective bioremediations obviously reduced the DOM concentration and thus mitigated the eutrophication outbreak risks in water bodies due to the increased MBC (microbial biomass carbon), microbial activity and metabolism. In early summer, the overall DOM in each treatment were readily low levels and derived from both autochthonous and exogenous origins, dominated by fulvic acid-like. In midsummer, the DOM contents and characteristics in each treatment increased significantly as phytoplankton activity improved, and the majority of DOM were humic acid-like and mainly of biological origin. The greatest differences of enzymes, MBC, microbial metabolism and DOM&SOM removal among different treatments were observed in summer months. In autumn, the systematic DOM&SOM slightly reduced due to the deceased microbial activity, in which the microbial humic acids were main component and derived from endogenous sources. Additionally, the gradually decreased SOM with cultivated time in each treatment was a result of microbiological conversion of SOM into DOM. For various treatments, BE, BE.A, BE.C and BE.E increased the MBC, enzymatic and microbial activities due to the application of biochar-supported EMs. Among these, BE and BE.A, especially BE.A with oxygen supplement, achieved the most desirable effect on reducing systematic DOM&SOM levels and increasing enzymatic and microbial activities. The group of EM also reduced the levels of DOM&SOM as improved degradation of EMs for DOM. However, BC, BE.C and BE.E finally did not achieved the desirable effect on reducing DOM&SOM due to the suppression of microbial activities, respectively, from high dose of biochar, weakening of dominant species and additional introduction of EMs in low liveness.

Biological activity and molecular mechanism of inactivation of Microcystis aeruginosa by ultrasound irradiation

Harmful algal blooms (HABs) significantly impact on water quality and ecological balance. Ultrasound irradiation has proven to be an effective method for algal control. Nevertheless, the molecular mechanisms underlying the inactivation of M. aeruginosa by ultrasound are still unknown. In this study, the physiological activity and molecular mechanism of algal cells exposed to different frequencies of ultrasound were studied. The results indicated a pronounced inhibition of algal cell growth by high-frequency, high-dose ultrasound. Moreover, with increasing ultrasound dosage, there was a higher percentage of algal cell membrane ruptures. SEM and TEM observed obvious disruptions in membrane structure and internal matrix. Hydroxyl radicals generated by high-frequency ultrasound inflicted substantial cell membrane damage, while increased antioxidant enzyme activities fortified cells against oxidative stress. Following 2 min of ultrasound irradiation at 740 kHz, significant differential gene expression occurred in various aspects, including energy metabolism, carbohydrate metabolism, and environmental information processing pathways. Moreover, ultrasound irradiation influenced DNA repair and cellular apoptosis, suggesting that the algal cells underwent biological stress to counteract the damage caused by ultrasound. These findings reveal that ultrasound irradiation inactivates algae by destroying their cell structures and metabolic pathways, thereby achieving the purpose of algal suppression.

Distribution pattern of dissolved organic matter in pore water of sediments from three typical areas of western Lake Taihu and its environmental implications

The migration, transformation, and accumulation of dissolved organic matter (DOM) in pore water of sediment cores play a pivotal role in lacustrine carbon cycling. In order to understand the dynamics of DOM in the sediments of large shallow eutrophic lakes, we examined the vertical profiles of DOM and the benthic fluxes of dissolved organic carbon (DOC) in sediment cores located in algae accumulated, dredged, and central areas of eutrophic Lake Taihu, China. Optical properties showed the significant influence of terrestrial inputs on the DOM components of pore water in the algae accumulated area but an abundant accumulation of autochthonous DOM in the central area. The benthic fluxes of DOC ranging from -458.2 to -139.4 mg·m-2·d-1 in the algae accumulated area displayed an opposite diffusion direction to the other two areas. The flux ranges of 9.5-31.2 mg·m-2·d-1 in the dredged area and 14.6-48.0 mg·m-2·d-1 in the central area were relatively smaller than those in the previously reported lake ecosystems with low trophic levels. Dredging engineering disturbed the pre-dredging distribution patterns of DOM in sediment cores. The deposition, accumulation, and transformation of massive algae scums in eutrophic lakes probably promoted the humification degree of sediments.

The Effects and Mechanisms of pH and Dissolved Oxygen Conditions on the Release of Arsenic at the Sediment-Water Interface in Taihu Lake

The pH and dissolved oxygen (DO) conditions are important environmental factors that control the migration of arsenic (As) at the sediment-water interface. This study investigates the distribution differences of reactive iron, manganese, and arsenic at the sediment-water interface under anaerobic and aerobic conditions at different pH levels. The strong buffering capacity of sediment to water pH results in a shift towards neutral pH values in the overlying water under different initial pH conditions. The level of DO becomes a key factor in the release of As from sediment, with lower DO environments exhibiting higher release quantities and rates of As compared to high DO environments. Under low DO conditions, the combined effects of ion exchange and anaerobic reduction lead to the most significant release of As, particularly under pH 9.5 conditions. The formation of amorphous ferrous sulfide compounds under low DO conditions is a significant factor contributing to increased arsenic concentration in the interstitial water. Therefore, the re-migration of endogenous arsenic in shallow lake sediments should consider the combined effects of multiple driving forces.

Controlled and driving mechanism of the SPM variation of shallow Brackish Lakes in arid regions

Suspended particulate matter (SPM) in the brackish Ebinur Lake of arid northwest China profoundly affect its water quality and watershed habitat quality. However, the actual driving mechanisms of the Lake's SPM changes remain unclear. Therefore, the purpose of this study is to explore the controlling factors driving the variability of SPM in the Ebinur Lake. This study constructed month-by-month SPM maps of Ebinur Lake based on time-series remote-sensing imageries and SPM inversion model. Thirty-four factors that might influence SPM changes were extracted, and the Partial Least Squares Structural Equation Modeling (PLS-SEM), suitable for complex relationships and factor interactions, was applied to identify the relative influence of each factor quantitatively. The results showed: (1) a clear increasing trend of SPM concentration in Ebinur Lake from 2011 to 2020; (2) that SPM changes were influenced by external and internal factors, explaining 48.2 % and 46.9 % of the changes, respectively; (3) that, to the external factors, meteorological factors exerted the greatest influence on SPM (relative contribution of 38.9 %); that, to the internal factors, water salinity imposed the greatest influence on SPM (relative contribution of 43.3 %); (4) that, among the meteorological factors, the measured variable Alashankou wind speed expressed the most significant positive effect on SPM (weighting coefficient of 0.894), and sulfate generated the strongest positive effect on SPM (weighting coefficient of 0.791) among the water salinity factors. Hence, the quantitative identification of drivers of SPM changes in Ebinur Lake could provide a new perspective to investigate the driving mechanisms of lake water quality in arid areas and inform their sustainable restoration and management.

Sediment-seawater exchange altered adverse effects of ocean acidification towards marine microalgae

Ocean acidification (OA) exhibits high threat to marine microalgae. However, the role of marine sediment in the OA-induced adverse effect towards microalgae is largely unknown. In this work, the effects of OA (pH 7.50) on the growth of individual and co-cultured microalgae (Emiliania huxleyi, Isochrysis galbana, Chlorella vulgaris, Phaeodactylum tricornutum, and Platymonas helgolandica tsingtaoensis) were systematically investigated in the sediment-seawater systems. OA inhibited E. huxleyi growth by 25.21 %, promoted P. helgolandica (tsingtaoensis) growth by 15.49 %, while did not cause any effect on the other three microalgal species in the absence of sediment. In the presence of the sediment, OA-induced growth inhibition of E. huxleyi was significantly mitigated, because the released chemicals (N, P and Fe) from seawater-sediment interface increased the photosynthesis and reduced oxidative stress. For P. tricornutum, C. vulgaris and P. helgolandica (tsingtaoensis), the growth was significantly increased in the presence of sediment in comparison with those under OA alone or normal seawater (pH 8.10). For I. galbana, the growth was inhibited when the sediment was introduced. Additionally, in the co-culturing system, C. vulgaris and P. tricornutum were the dominant species, while OA increased the proportions of dominant species and decreased the community stability as indicated by Shannon and Pielou's indexes. After the introduction of sediment, the community stability was recovered, but remained lower than that under normal condition. This work demonstrated the role of sediment in the biological responses to OA, and could be helpful for better understanding the impact of OA on marine ecosystems.

Integrated evaluation of the reactive oxygen species (ROS) production characteristics in one large lake under alternating flood and drought conditions

Reactive oxygen species (ROS) are omnipresent in natural aquatic environments, and play an important role in biogeochemical cycles. One of the dominant sources of ROS in surface waters was thought to be from dissolved organic matter (DOM) interacting with photochemical process. The properties of DOM were different between the flood and drought periods in lakes; yet, information on how these variations influence ROS photoproduction is unknown. Through a three-year study, the photochemical properties of DOM and the resultant ROS photoproduction between the flood and drought period were determined in the largest freshwater lake in China (Lake Poyang). Results found that quantum yield coefficients of excited triplets (³CDOM*), apparent quantum yields of singlet oxygen (¹O₂) and hydroxyl radicals (•OH) were holistically higher in the flood period than those in the drought period. The optical properties of DOM showed that DOM in the flood period featured an allochthonous input, accompanied by higher molecular size (E2/E3), aromatic content (SUVA₂₅₄), humification degree (HIX), while DOM in the drought period was mainly internal input. Fourier transform ion cyclotron resonance mass spectrometry (FI-ICR MS) further revealed that some refractory components, such as lignin-like and carboxyl-rich alicyclic molecules (CRAM) presented higher abundance in the flood period, and played the positive impacts on ROS production. Orthogonal partial least squares (OPLS) were used to build novel multivariate predictive models for indicating the spatio-temporal ROS production. Also, the relatively higher steady-state concentrations of ³CDOM* and ¹O₂ in the flood period could significantly diminish the half-lives of acetochlor. Considering the photochemical activity of DOM varied considerably at different periods, this study provided a new method to predict ROS production and contributed to a new insight into stage-specific emerging contaminants removing in natural aquatic environments.