Temperature-driven mechanisms involving complex feedback and lag that affect the evolution of hydrological processes and ecological functions in cold- and arid-region lakes represent a core scientific issue in current hydrology and lake ecology research. In this study, based on month-scale temperature and environmental factor data from Daihai Lake in Inner Mongolia from January to December 2023, statistical methods (redundancy analysis, Tukey's test analysis, correlation analysis, structural equation modeling), time series analysis methods (dynamic time warping), and machine learning methods (random forest) were combined. A hierarchical and phased response framework was constructed that encompassed driver identification, path tracing, lag characterization, and contribution quantification. The framework was used to explore the short-term response mechanisms of environmental factors to temperature, analyze the response degrees of different environmental factors to temperature changes, and investigate the driving mechanism of temperature fluctuations on lake environmental factors. The results showed that the temperature (T), lake area (Z), wind speed (WS), and precipitation (P) explained 31.35%, 23.38%, 15.35%, and 22.09% of the variations in the water environmental factors, respectively (p < 0.05), with temperature being the primary driver of Daihai's water environment changes.

Natural rainfall drives dramatic changes in the hydrology and ecosystems of lakes in cold-arid regions through complex cascading and lagged pathways. Our understanding of these processes remain a key scientific challenge in current hydrology and lake ecology research. This study is based on monthly-scale rainfall and environmental factor data from Chagannaoer Lake, Inner Mongolia, for the period from January to December 2024. We used a redundancy analysis, correlation analysis, structural equation modeling, dynamic time warping, and Random Forest algorithms to construct a systematic analytical framework that encompassed “driver identification-pathway tracing-contribution quantification.” The results of the study showed that changes in the water environment of Chagannaoer Lake were primarily influenced by rainfall. The study revealed the “four-level cascading response system” and the “three-stage lagged response mechanism” triggered by rainfall, and we quantified the rainfall contribution rate to water environmental factors. The tiered and staged theoretical framework proposed in this study overcomes the limitations of traditional single linear response models, with the aim to provide scientific evidence for algal bloom risk warnings and ecologically precise management in cold-arid region lakes.

The discharge of Municipal wastewater treatment plant (WWTP) is one of the important ways for microplastics (MPs) to enter the natural environment. Therefore, this study conducted in depth research on a combined sewer treatment plant, exploring the occurrence characteristics, migration mechanisms, and correlation with climate factors of MPs in activated sludge(AS), and conducting traceability analysis of MPs in AS. Research has shown that the main forms of MPs in AS are small-sized fragments (0.25-0.50 mm) and large-sized fibers (1.00-5.00 mm), with polyester (PES) and polypropylene (PP) as the main components. The Positive Matrix Factorization (PMF) model was applied to analyze the four main sources of MPs, which are household sources (15.88 %), textile sources (48.7 %), agricultural sources (21.95 %), and industrial sources (13.47 %); The Absolute Principal Component Score-Multiple Linear Regression (APCS-MLR) model source analysis shows that the proportion of mixed sources of industrial, agricultural activities, and residential life is 62.71 %, and the proportion of textile activities is 28.31 %. Our research has validated the good applicability of PMF and APCS-MLR models for MPs source apportionment, which can provide important theoretical support and technical guidance for WWTP to analyze the main sources of MPs from different perspectives.

As an emerging pollutant， microplastics （MPs） pose significant threats to agricultural ecosystems globally. This study investigates the occurrence， spatial distribution， migration mechanisms， and ecological risks of MPs in arid irrigated farmlands， focusing on the Urad Irrigation area-a critical agricultural zone in the Hetao Irrigation District of Inner Mongolia， China. Given intensive plastic mulching （annual application： ~45 kg·hm-2）， deep tillage practices （up to 40 cm）， and saline-alkaline soil conditions， this region offers a unique model for understanding MPs behavior in water-scarce environments. A total of 69 stratified soil samples （0-10， 10-20， and 20-30 cm） were collected from 23 monitoring sites along irrigation-drainage networks， combined with Fourier transform infrared spectroscopy （FTIR）， Mantel test， and other multi-index risk assessment methods， to reveal the distribution characteristics， migration mechanism， and ecological risk of soil MPs in the irrigation area. The results showed that： ① The abundance of MPs showed significant spatial heterogeneity （2.42×104-1.28×105 n·kg-1）， which was at a high level in China， and the horizontal distribution was driven by irrigation retreat， which was in the eastern &gt; western upper layer， the eastern &gt; western middle layer， and the northern/southern western lower layer &gt; western lower layer. The vertical distribution showed surface enrichment （8.92×104 n·kg-1 in the upper layer &gt; 6.18×104 n·kg-1 in the middle layer &gt; 5.43×104 n·kg-1 in the lower layer）， but 21.7% of the sites had lower layer &gt; middle layer due to agricultural tillage （depth up to 40 cm） anomalous enrichment of the middle layer. ② The polymer composition was mainly polyethylene （PE， 37%， proportion， the same below）， polystyrene （PS， 27%）， and polypropylene （PP， 26%）， and morphological analysis showed that PE was mainly film/fibrous， and PS was mostly block， which was consistent with the characteristics of local agricultural mulch film. At the same time， a variety of plastic additives （such as benzyltriethylammonium chloride） were detected， suggesting the risk of MPs aging. ③ Mantel test identified soluble salts （r=-0.43） and pH （r=-0.41） as inhibitors of MPs mobility， promoting aggregation via ionic strength； specific surface area （r=0.44） and organic matter （r=0.29） enhanced MPs retention； middle-layer moisture （r=0.42） facilitated vertical transport via irrigation leaching； and coarse-textured soils （D50 &gt; 50 μm） in deeper layers reduced MPs retention （r=-0.44）. ④ PHI indicated low-to-moderate risk （I-II grade）， inversely correlated with MPs abundance due to localized PS enrichment （high toxicity coefficient=30）； RI reached "strong risk" levels （RI=106） at drainage hubs （e.g.， T17）， reflecting hydrological "pollution traps；" and Igeo demonstrated significantly higher accumulation in middle/lower layers （moderate-to-heavy） than in surface soils （light-to-moderate）， with spatial gradients （east &gt; west） mirroring irrigation flow paths. This study establishes a tripartite driving model （"hydraulic-salinity-tillage"） unique to arid irrigated agroecosystems in which hydraulic processes （irrigation return flow） govern horizontal MPs distribution， soluble salts inhibit MPs mobility via aggregation， and deep tillage （≥30 cm） induces subsoil MPs enrichment. The results highlight the urgent need to optimize mulch film recovery （&lt;30% currently） and regulate drainage management to mitigate MPs export to downstream sinks （e.g.， Wuliangsuhai Lake）. The risk assessment framework underscores the necessity of polymer-specific toxicity evaluation beyond abundance metrics. This work provides a scientific foundation for MPs pollution control in global arid irrigation zones， supporting sustainable agriculture in the Yellow River Basin.

Groundwater accounting in arid and semi-arid well-irrigated areas is often constrained by difficulties in water-meter installation and maintenance, as well as variability in well-pump operation, thereby limiting refined agricultural water-use management. The electricity-to-water conversion coefficient (Tc) can be used to estimate groundwater abstraction from electricity consumption; however, the applicability of empirical models developed for plain irrigation districts remains uncertain in plateau regions characterized by pronounced topographic relief and complex aquifer conditions. This study examined 56 typical irrigation wells in Chayouzhongqi on the Inner Mongolia Plateau. Based on pumping-test data and using correlation analysis, structural equation modeling, redundancy analysis, and random forest analysis, we investigated the spatial distribution of Tc and its associated mechanisms. Tc ranged from 0.08 to 3.88 m3 kWh-1, with a mean of 1.62 m3 kWh-1, and exhibited a pattern of higher values in the north, lower values in the south, and the lowest values in the western part of the study area. Electricity consumption, rated flow rate, and actual discharge were the principal associated variables, with relative importance values of 43.0%, 21.6%, and 15.7%, respectively. Topographic and aquifer conditions imposed regional constraints on spatial variation in Tc by influencing well-pump operating states. These findings indicate that Tc estimation in plateau well-irrigation districts should not directly adopt empirical relationships developed for plains, but should instead be calibrated according to regional hydrogeological and engineering operating conditions, thereby providing a basis for improved groundwater accounting and water-saving management in arid and semi-arid regions.

Lake sediments act as important sinks for heavy metals and microplastics, yet the mechanisms governing their enrichment, coexistence, and combined ecological risks remain insufficiently understood. This study investigated sediments from Daihai Lake, China, systematically characterizing the occurrence features of microplastics (morphology, size, and composition) and their associated heavy metal contents. A composite pollution risk framework (Multi Feature Potential Ecological Risk Index) was developed to evaluate microplastics–heavy metals interactions using correlation analysis, principal component analysis, and cluster analysis. In addition, a two-dimensional pollution index was applied to assess combined ecological risks. Results showed that MP abundance ranged from 6.60 to 26.80 n·g−1, with a decreasing trend from southwest to northeast. Microplastics were dominated by fragments, with a high proportion of small particles (<0.25 mm), and were mainly composed of polyethylene terephthalate and polypropylene. The average concentrations of heavy metals in sediments were ranked as follows: Mn (863 ± 78 mg·kg−1); Cr (124 ± 28 mg·kg−1); Zn (86 ± 17 mg·kg−1); Ni (43 ± 10 mg·kg−1); Cu (36 ± 0.1 mg·kg−1); Pb (23 ± 5 mg·kg−1); As (15 ± 4 mg·kg−1); and Cd (0.20 ± 0.04 mg·kg−1). The two-dimensional comprehensive index values ranged from 124 to 1032, with an average value of 365.0, exceeding the risk threshold (>100). Approximately 70% of sampling sites exhibited high composite pollution risks. Small-sized and fibrous microplastics showed significant positive correlations with multiple heavy metals, indicating strong carrier effects.

Conventional coagulation processes exhibit limited efficiency for microplastics (MPs) removal in wastewater treatment plants (WWTP). They also face two major challenges: high dosages of inorganic flocculants and potential secondary pollution caused by residual metal ions. To address this issue, this study systematically evaluated the removal efficiency of single and composite systems for MPs by combining cationic grafted starch (CGS) with polyaluminum chloride (PAC) and polyferric sulfate (PFS), respectively. Multidimensional statistical analysis and multiscale characterization were used to reveal the synergistic removal mechanism. The results showed that: (1) the introduction of CGS significantly improved the removal rate of MPs, from 60.0% of the single flocculant to over 90.0%, while reducing the dosage of inorganic flocculant, resulting in larger floc size and denser structure; (2) the removal behavior of MPs was regulated by its own characteristics, with density, surface functional groups and particle size all significantly affecting the flocculation effect, and the removal rate was positively correlated with particle size; (3) pH was identified as the key control factor through orthogonal experiments, grey relational analysis (GRA) and response surface methodology (RSM), and the optimal coagulation window was determined. The synergistic mechanism was revealed by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and Zeta potential characterization. This study systematically elucidated the enhanced removal mechanism of MPs by the composite system under the coupling effect of multiple factors, providing mechanistic insights and a potential approach for developing efficient MPs control technologies.

Microplastics in the environment can age under the influence of light， high temperature， and mechanical forces， releasing nanoplastics and soluble organic matter， which in turn have more severe impacts on the environment. In cold regions， microplastics in water and soil surfaces are usually affected by both light and freeze-thaw cycles， but the aging mechanism and the release characteristics of solubles under their combined effects remain unclear. This study investigated the apparent characteristics， changes in functional groups， and release characteristics of solubles of polypropylene microplastics （PP-MPs） under different durations of light， freeze-thaw， and combined aging treatments through a freezing simulation experiment. The results showed that after light aging treatment， holes and wrinkles appeared on the surface of PP-MPs， while after the freeze-thaw treatment， cracks and peeling occurred. After the combined aging treatment， the degree of damage on the surface of PP-MPs was significantly greater than that under the single-factor aging treatments. The increase in the hydroxyl and carboxyl indices of PP-MPs was higher after freeze-thaw and combined treatments. Under light， freeze-thaw， and combined treatments， the order of the five typical peaks of PP-MPs was： -CH3 → -OH → C=O → C-C → -CH2， -CH3 → C-C → -CH2 → C=O → -OH， and -CH3 → C-C → -CH2 → C=O → -OH， respectively. The concentration of DOC released by PP-MPs changed within the ranges of -0.076 mg-1.843 mg， -0.076 mg-1.778 mg， and 0.086 mg-1.803 mg， respectively， showing an initial increase followed by a decrease. The abundance of nanoplastics released by PP-MPs changed within the ranges of 1.16×109-4.34×1010 particles·mL-1， 1.87×109-3.12×1010 particles·mL-1， and 1.87×109-3.12×1010 particles·mL-1， respectively. Under light conditions， the abundance of nanoplastics increased with time， and the particle size decreased with time. Under freeze-thaw and combined treatments， the abundance of nanoplastics decreased， and the particle size increased. This study can provide a theoretical basis for clarifying the environmental effects and aging mechanisms of microplastics in cold regions.

Analyzing the sources of nitrogen and phosphorus pollution in atmospheric deposition is crucial for protecting the surface water environment in vulnerable areas. This study focused on the Dahekou Reservoir, Shayuan District, Xilin Gol League, Inner Mongolia, China. It established 12 monitoring sites, conducted one-year monitoring, and collected 144 samples. The concentrations of nitrogen, phosphorus, and water-soluble ions in atmospheric wet sedimentation were measured. This study identified atmospheric precipitation types, revealed seasonal variations in nitrogen and phosphorus concentrations, assessed the contribution of atmospheric wet sedimentation to reservoir water quality. Utilizing the air mass backward trajectory (HYSPLIT) model and PMF model, the main pollution sources were analyzed. The results were as follows. 1) During the observation period, the atmospheric precipitation types were nitric acid rain in spring, sulfuric acid rain in winter, and mixed acid rain in summer and autumn. 2) The monthly concentrations of nitrogen and phosphorus of various forms varied significantly, with NH4+-N peaking in spring, NO3--N and DOP in autumn, and DIP and DON in summer. Annual pollution loads of atmospheric nitrogen and phosphorus precipitation into the reservoir were 35.77 and 4.17 t/a, respectively, severely impacting reservoir water quality. 3) Precipitation was negatively correlated with TN concentration, particularly with the NO3--N/TN ratio, and positively correlated with TP and DIP concentrations. 4) The analysis of pollution sources indicated that the sources of atmospheric nitrogen and phosphorus wet deposition pollution in the study area included agricultural, anthropogenic, dust, and coal sources, with contribution rates of 32.4 %, 25.6 %, 21.0 %, and 21.0 %, respectively.

The riparian zone, located between agricultural region and aquatic environments, is a hotspot for microbe-driven nitrogen (N) reduction. However, the impact of seasonal and spatial variations on the N-cycling microbial community and the underlying mechanisms in riparian soils remain poorly understood. This study took the riparian zone of the North Canal in Hebei Province, China, as an example. Four sampling profiles (A, B, C, and D) were established at 1, 20, 40, and 50 m from the water body, respectively. Each profile was divided into 0-20, 20-40, 40-60, and 60-80 cm layers, and soil properties and microorganisms were investigated to reveal the seasonal and spatial dynamics of microbial N-cycling communities and denitrification potential (DP). The most pronounced disparities were observed across soil profiles, with significant variations in the abundance of most N-cycling genes and DP. Both rivers and agricultural fields affect neighbouring riparian zones, leading to a decline in soil DP. Moreover, the waterside profile A displayed the most distinct N-cycling microbial composition, along with significantly higher network complexity and stronger deterministic assembly processes. Vertical stratification analysis revealed that N-cycling microbial diversity and DP decreased significantly with soil depth, with topsoil layers exhibiting greater network complexity and stronger deterministic processes. Seasonal comparisons showed that microbial diversity, network complexity, and deterministic processes were markedly enhanced during the wet season. Multiple physicochemical factors collectively regulated N-cycling community and DP, with soil nitrate and moisture content emerging as the most influential drivers. These findings enhance our mechanistic understanding of microbial N removal processes in riparian ecosystems.

Underlying surface in lake watersheds and mercury concentrations in lake inflows are key factors affecting the accumulation of mercury in lake sediments. Lake characteristics play a crucial role in the process of mercury methylation in sediments. Lakes in cold regions have unique environmental features, including a long ice-cover period, during which mercury undergoes complex physicochemical processes. However, the extent of mercury accumulation and methylation in cold region lake sediments remains unclear. We studied the concentrations, pollution levels, and ecological risks of mercury and methylmercury in surface sediments from six lakes in China's cold regions, and analyzed the mechanisms by which lake characteristics influence mercury methylation. The results indicate significant mercury enrichment in surface sediments of typical lakes in Inner Mongolia, with some regions exceeding the average mercury levels found in lakes across China. Mercury concentrations in surface sediments of lakes from different land use types within their watersheds show considerable spatial variability, with the following pattern: agricultural irrigation areas > agro-pastoral transition areas > grassland and sand areas. Agricultural activity intensity in lake watersheds has the most pronounced impact on the spatial heterogeneity of surface sediment mercury concentrations and their associated ecological risks. Lake water input and geographical location can indirectly control the spatial distribution of mercury concentrations and ecological risks in Inner Mongolia lakes by affecting external mercury inputs. The methylation process in lake surface sediments during the ice-cover period is significant. Based on a correlation analysis model, water depth was found to be a key factor controlling methylmercury content and mercury methylation rates in lake sediments during the ice-cover period. Deep water lakes promote the conversion of mercury into methylmercury in sediments. Water depth influences the redox conditions of sediments and the amount of light radiation received by the sediments, thereby affecting the methylation and demethylation processes of mercury, ultimately controlling the levels of methylmercury in sediments.

Microplastics, characterized by their small size, chemical stability, and significant environmental risks, pose a challenge for removal through natural decomposition processes, making them an urgent environmental concern. This study outlines the synthesis of a metal-organic framework (MOF), MIL-101(Fe), combined with Fe3O4 particles via a solvothermal method and further modified with Mg and Zn doping. The resulting MOFs, Mg/MIL-101(Fe)@Fe3O4 and Zn/MIL-101(Fe)@ Fe3O4 exhibited enhanced adsorption properties with increased active sites for removing polystyrene (PS) from water, achieving maximum removal rates of 92.89 % and 94.46 %, respectively. These materials demonstrated several advantages, including strong magnetic separation capabilities, minimal interference from co-existing anions, a broad operational pH range, and excellent recyclability for adsorption. The adsorption mechanisms and attachment properties were thoroughly analyzed using SEM, BET, XRD, FTIR, XPS, and other characterization techniques, as well as kinetic, isothermal, and thermodynamic modeling. The adsorption process was determined to be governed by hydrogen bonding, it-it interactions, electrostatic attraction, and complexation. It proceeded spontaneously, aligning with the Langmuir isotherm and the pseudo-second-order kinetic model. The maximum adsorption capacities, estimated using the Langmuir model, were 878.24 mg/g and 1365.20 mg/g for Mg/MIL-101(Fe)@Fe3O4 and Zn/MIL-101(Fe)@Fe3O4, respectively. The synthesized MOFs provide a highly effective and reusable solution for PS removal from water. This study highlights the potential of these novel materials for practical applications in microplastic remediation and provides a useful perspective regarding the development of advanced adsorption technologies for water purification.

Fluoride pollution is a serious global environmental issue that has attracted widespread attention due to its toxicity, persistence, and tendency to accumulate in ecosystems. In certain lakes and groundwater bodies located in the arid and semi-arid regions of northern and northwestern China, the problem of localized fluoride contamination has become particularly severe, highlighting the urgent need for systematic research and scientific forecasting to identify its causes and understand its evolution. This study focuses on the Daihai Lake Basin in Inner Mongolia, northern China, where 530 samples were collected, including 370 surface water samples and 160 groundwater samples from surrounding areas. By applying hydrogeochemical methods, the study systematically analyzes the hydrochemical characteristics of lake surface water and adjacent groundwater. ArcGIS software was used to map the spatiotemporal distribution patterns of fluoride (F-) concentrations in Daihai Lake and its surrounding groundwater. Correlation and statistical analyses were then performed to investigate the underlying causes and main driving factors of fluoride pollution. On this basis, multiple machine learning models-including K-Nearest Neighbors (KNN), Backpropagation (BP) Neural Network, Gradient Boosting Decision Tree (GBDT), Random Forest (RF), and Grey Relational Analysis-Random Forest-were developed and compared.The results indicate that the surface water in Daihai Lake predominantly exhibits SO4 & centerdot;Cl--Ca & centerdot;Mg and SO4 & centerdot;Cl--Na hydrochemical types, whereas the surrounding groundwater is primarily characterized by the HCO3--Ca & centerdot;Mg type. Surface water fluoride concentrations display clear seasonal variation, following the order: summer > winter > spring > autumn. Spatially, fluoride concentrations are lowest in the western estuary, moderate in the central region, and highest in the northern area. Groundwater fluoride concentrations show no significant temporal variation but exhibit a spatial trend of higher values in the northeast and lower values in the southwest. Fluoride enrichment is mainly controlled by evaporation concentration, fluorite dissolution, and Na+/Ca2+ ion exchange; alkaline conditions with low Ca2+ and high HCO3- concentrations promote fluoride release. The grey correlation-random forest model demonstrated superior performance in predicting fluoride concentrations, achieving RMSE values of 0.916 for surface water and 0.579 for groundwater, and MAE values of 0.690 and 0.429, respectively-significantly outperforming traditional single models. This study provides a scientific basis for the prevention and control of fluoride pollution in the Daihai Basin and offers methodological insights for environmental risk assessment and prediction in similar semi-arid closed-basin lakes.

Excessive fluoride levels have become a critical concern in contemporary society, with China ranking among the nations most severely affected by fluoride pollution. To investigate the health and ecological risks associated with excessive fluoride, 80 surface water samples, 80 sediment samples, 152 groundwater samples from rural drinking wells surrounding the lake, and 64 tributary samples flowing into Lake Daihai were consecutively collected between 2023 and 2024. A comprehensive spatiotemporal analysis of fluoride concentrations in Lake Daihai's water body, sediments, and surrounding groundwater was conducted using ArcGIS and Origin software. The potential ecological risks of Lake Daihai's surface water and sediments were evaluated using the integrated pollution index method, the entropy method, and the modified Nemero index method. A human health risk model was applied to evaluate the health risks of groundwater around Lake Daihai. Monte Carlo uncertainty analysis and the Crystal Ball sensitivity analysis system were combined to estimate the probability of exceeding non-carcinogenic risk thresholds and to identify sensitivity levels for fluoride-related ecological risks across different population groups. The results indicate that the average fluoride concentration in Lake Daihai's water bodies is 6.22 mg/L, while groundwater in surrounding rural drinking wells ranges from 0.11 to 3.78 mg/L, exceeding the national average of 0.66 mg/L. Surface water fluoride concentrations exhibited an overall seasonal pattern of spring increase, summer decrease, and autumn rebound. Sediment fluoride concentrations showed a gradient pattern of higher in the northwest, lower on the east/southwest shores. Groundwater fluoride concentrations generally followed a pattern of higher on the east/west shores, lower on the north shore. The surface water bodies of Lake Daihai face potential ecological risks, with over 99 % of samples exhibiting a hazard quotient (HQ) greater than 1 and an average HQ of 3.12. This finding indicates a state of moderate risk and high instability, characterized by potential mobility and bioavailability. The ecological risk of fluoride in sediments is generally classified as mild to moderate contamination. For groundwater samples, the non-carcinogenic risk threshold exceeded standards in 85 % of infants (THQ > 1.0), 60 % of adults, and 30 % of children and adolescents. Uncertainty model analysis indicates non-carcinogenic health risk exceedance probabilities of 74.25 % for infants, 28.18 % for children, 24.82 % for adolescents, and 42.47 % for adults, with infants facing the highest non-carcinogenic fluoride risk. Sensitivity analysis reveals F- contribution as the primary factor for non-carcinogenic risks in infants (73.9 %) and children (30.6 %).

Nitrogen and phosphorus play pivotal roles in determining the eutrophic conditions and nutrient provision in lakes. However, the mechanisms and processes of nutrient release at the sediment-water interface of shallow lakes in cold regions remain unclear, especially under the complex environmental conditions of freezing and open-water periods. Therefore, Diffusive Gradients in Thin-films (DGT) and High-resolution Peeper technologies (HR-Peeper) were used to investigate the nitrogen and phosphorus characteristics of the sediment water interface, and the process of bacteria affecting the nitrogen and phosphorus cycle was clarified by the high-throughput sequencing technology. The results indicated that sediment phosphorus (PO43-) flux ranged from -1.39 to 3.6 mg/m2·d, with the interstitial water-Soluble Reactive PO43- presenting notable fluidity and potential bioavailability. The ammonia nitrogen (NH4+-N) flux varied from -4.71 to 3.65 mg/m2·d. The nitrate nitrogen (NO3--N) flux varied from -11.64 to 1.18 mg/m2·d, exhibiting an opposite trend to NH4+-N, which was released into water bodies during the freezing period and migrated to the sediments in the open water period. Common metabolic pathways and functional genes for nitrogen and phosphorus were identified in Methylomicrobium, Marinobacter, and Psychrobacter. The dissimilatory nitrate reduction to ammonium (DNRA) facilitated the transformation of polyphosphates and the release of phosphorus. Water temperature indirectly regulated the fluxes of nitrogen and phosphorus at the sediment-water interface (SWI) by modulating the microbial abundance and dissolved oxygen (DO) content.

Ice, water, and sediment represent three interconnected habitats in lake ecosystems, and bacteria are crucial for maintaining ecosystem equilibrium and elemental cycling across these habitats. However, the differential characteristics and driving mechanisms of bacterial community structures in the ice, water, and sediments of seasonally frozen lakes remain unclear. In this study, high-throughput sequencing technology was used to analyze and compare the structure, function, network characteristics, and assembly mechanisms of bacterial communities in the ice, water, and sediment of Wuliangsuhai, a typical cold region in Inner Mongolia. The results showed that the bacterial communities in the ice and water phases had similar diversity and composition, with Proteobacteria, Bacteroidota, Actinobacteria, Campilobacterota, and Cyanobacteria as dominant phyla. The bacterial communities in sediments displayed significant differences from ice and water, with Chloroflexi, Proteobacteria, Firmicutes, Desulfobacterota, and Acidobacteriota being the dominant phyla. Notably, the bacterial communities in water exhibited higher spatial variability in their distribution than those in ice and sediment. This study also revealed that during the frozen period, the bacterial community species in the ice, water, and sediment media were dominated by cooperative relationships. Community assembly was primarily influenced by stochastic processes, with dispersal limitation and drift identified as the two most significant factors within this process. However, heterogeneous selection also played a significant role in the community composition. Furthermore, functions related to nitrogen, phosphorus, sulfur, carbon, and hydrogen cycling vary among bacterial communities in ice, water, and sediment. These findings elucidate the intrinsic mechanisms driving variability in bacterial community structure and changes in water quality across different media phases (ice, water, and sediment) in cold-zone lakes during the freezing period, offering new insights for water environmental protection and ecological restoration efforts in such environments.

Mercury and arsenic are two highly toxic pollutants, and many researchers have explored the effects of the two substances on the environment. However, the research content of toxic substances in frozen periods is relatively small. To explore the spatial and vertical distribution of mercury and arsenic in the ice, water, and sediments of Wuliangsuhai Lake under ice conditions, and to assess the harm degree of the two toxic substances to human beings. We collected the ice, water, and sediments of the lake in December 2020, and tested the contents of Hg and As. The single-factor pollution index method, the local cumulative index method, and the ecological risk coding method were used to assess the pollution status in these three environmental media, and the Monte Carlo simulation combined with the quantitative model recommended by USEPA was used to assess the population health risk. The results showed that (1) The average single-factor pollution values of Hg and As in water were 0.367 and 0.114, both pollutants were at clean levels during the frozen period. (2) The mean Igeo values of Hg and As were 0.657 and −0.948. The bioavailability of Hg in the sediments of Wuliangsuhai Lake during the frozen period was high, and its average value was 7.8%, which belonged to the low-risk grade. The bioavailability of As ranged from 0.2% to 3.7%, with an average value of 1.3%. (3) Monte Carlo simulation results indicate acceptable levels of health risks in both water and ice. This study preliminarily investigated the distribution characteristics of toxic substances and their potential effects on human health in lakes in cold and arid regions during the frozen period. It not only clarified the pollution characteristics of lakes in cold and arid regions during the frozen period, but also provided beneficial supplements for the ecological protection of lake basins. This study lays a foundation for further environmental science research in the region in the future.

Ecological pollution caused by heavy metals released from sediments is a worldwide concern. However, the effect of changes in sediment speciation on their release of heavy metals has not been adequately reported. In this study, the research focused on Pb and Cr in the ice period of Wuliangsuhai. This study analyzed changes in the sediment speciation of Pb and Cr before and after a release experiment using four risk assessment methods while varying the temperature, pH, and salinity of the water column. The results indicated that the total concentration of Pb ranged from 11.17 to 24.25 mg/kg, while for Cr it ranged from 42.26 to 69.68 mg/kg. Both elements exhibited mild contamination. The release of Pb and Cr from sediments increases with increasing water temperature, mainly due to the conversion of the residual fraction of Pb to the Fe–Mn oxide fraction and Cr converting more residual fraction to the organic matter and sulfide fraction. The release of sediment Pb and Cr decreased with increasing pH, with Pb converting more acid extractable fraction to the residual fraction and Cr converting more organic matter and sulfide fraction to the residual fraction. In contrast, the release of Pb and Cr increased and then decreased with increasing salinity. For Pb, the acid extractable fraction was more susceptible to conversion to the residual fraction by environmental influences, whereas for Cr, the organic matter and sulfide fraction were susceptible to conversion to the residual fraction.