Search Results (939)

The efficiencies of the restoration of three lakes of varied water dynamics—the polymictic Mielenko Lake (7.8 ha; 1.9 m), the meromictic Klasztorne Małe Lake (13.7 ha; 20.0 m), and the holomictic Klasztorne Duże Lake (57.5 ha; 8.5 m)—with the use of the phosphorus inactivation method and with the sequential application of iron and aluminum compounds have been compared. The full dose of the Fe coagulant used for the restoration of these lakes varied between 9 and 93 tons (littoral zone). The full dose of the Al coagulant applied in the studied lakes ranged between 9 and 148 tons (profundal zone). After the application of the reagents, greater efficiency in phosphate removal from the water column was observed in the stratified Klasztorne Małe and Klasztorne Duże lakes. Notably, in both lakes, inhibition of the internal loading process was observed. Research carried out several years after the completion of lake restoration showed that the obtained effects persist quite well in Klasztorne Małe Lake and Klasztorne Duże Lake, and in the case of the shallow-water Mielenko Lake, there was a significant increase in the concentration of phosphorus compounds in the bottom parts of the water. This phenomenon may be related to the shallow depth of the lake, high coupling between water and bottom sediments, and the large surface area of the active bottom. The results obtained for the Klasztorne Lakes show that the use of two types of compounds makes it possible to reduce the cost of restoration, and moreover, the dosing of iron salts in the coastal areas of the lakes ensures a higher level of ecological safety. Full article

Glacial lakes are sensitive indicators of climate-driven cryospheric change, and their accurate mapping provides fundamental spatial information for water-resource assessment and glacial lake outburst flood (GLOF) hazard assessment. In southeastern Tibet, automatic extraction remains difficult because glacial lakes are small and easily confused with snow, mountain shadows, dark bedrock, riverine wetlands, and non-glacial water bodies. In this study, we integrate optical bands and water indices from Sentinel-2, topographic information derived from a digital elevation model, and radar backscatter from Sentinel-1 into a nine-channel multimodal dataset, and develop an improved YOLO11-seg model that combines spatial-to-depth downsampling, multi-scale attention, long-range context modeling, and content-aware upsampling to enhance small-lake detection, background suppression, and boundary delineation. Compared with U-Net, DeepLabV3+, YOLOv8-seg, YOLO11-seg, YOLO12-seg, and YOLO26-seg, the proposed model achieved the highest F1-Score of 0.9205 and an mAP50(M) of 0.9331, while its F1-Score and IoU on the independent test set reached 0.9209 and 0.8533, respectively. Using remote sensing imagery acquired in 2024, the model extracted 4766 glacial lakes in southeastern Tibet, covering 428.13 km²; 80.84% of these lakes were smaller than 0.10 km². The results demonstrate an effective and reproducible framework for automatic glacial lake mapping in complex alpine environments. Full article

Supraglacial lake depth is a key variable for quantifying surface meltwater storage and assessing ice-shelf stability, yet spatially continuous and reliable bathymetric information remains difficult to obtain in polar regions because in situ measurements are scarce and optical imagery cannot directly provide water depth. This study develops an integrated framework for supraglacial lake identification and bathymetry retrieval by combining ICESat-2 ATL03 photon-counting lidar data with Sentinel-2 multispectral imagery. ICESat-2 lake photons were used to constrain lake-region extraction from Sentinel-2 imagery, and the photon-derived along-track depths were corrected for scattering and refraction before being converted into Sentinel-2 pixel-level depth labels. Based on these labels, four retrieval models were constructed and evaluated, including an empirical model, CatBoost, a convolutional neural network (CNN), and a residual dense network (RDN). CatBoost generated initial depth estimates, while CNN and RDN further incorporated the CatBoost-derived depth prior and Sentinel-2 multispectral features for pixel-level depth prediction. Experiments over four investigated supraglacial lakes showed that RDN achieved the best average performance across the investigated lakes, with mean R², RMSE, and MAE values of 0.927, 0.187 m, and 0.144 m, respectively. For the investigated lakes, the integration of ICESat-2 and Sentinel-2 extended discrete along-track reference-depth observations to spatially continuous bathymetry maps. Because the training and validation samples were obtained from different spatial blocks within the same four lake scenes, the reported performance primarily reflects within-lake spatial generalization under the investigated conditions, and transferability to unseen lakes remains to be evaluated. These maps may provide inputs for future lake-volume estimation and ice-shelf hydrological analyses, while their applicability to lakes with different morphological and optical conditions requires further evaluation. Full article

Small lakes are widespread, yet their biogeochemistry, particularly regarding greenhouse gases, remains insufficiently studied. This article presents the findings from an investigation of six small lakes in the Southern European part of Russia, conducted from September to October 2024. The primary aim was to examine the coupled distribution of methane (CH₄) and sulfide sulfur (a key metabolite of H₂S) in the lake sediments, in relation to geochemical parameters such as pH, Eh, sediment density, moisture, and the contents of sulfate ions (SO₄²⁻), organic matter, and granulometric composition. The studied sediment layers, reaching depths of up to 110 cm, consist primarily of silty clay. The lakes studied represent both freshwater (0.2–0.7 g/L) and brackish (1.3–24.2 g/L) systems. During the study period, the water column exhibited temperatures of 10.4–22.1 °C, pH values of 7.36–8.53, and dissolved O₂ concentrations ranging from 3.16 mg/L (34% saturation) to 11.79 mg/L (125% saturation). Methane concentrations in the water varied widely, from 1.6 µL/L to 37,380 µL/L. The lowest values were found in the highly mineralized Lake Bolshoy Tambukan (1.6–2.0 µL/L), while exceptionally high concentrations were detected in the bottom waters of the thermally stratified freshwater Lake Staroe. In the shallow, productive freshwater lakes, a significant portion of the organic matter undergoes limited mineralization in the water column and settles to the sediments as partially decomposed remains of sand- and coarse-silt-sized organisms. The subsequent degradation of this labile organic matter reduces bottom-water oxygen, triggering intense anaerobic processes in the upper sediment layer. In these freshwater sediments, where sulfate concentrations are relatively low, sulfate reduction is typically suppressed. Combined with an abundance of labile substrates, this condition fosters intensive methanogenesis, resulting in maximum CH₄ concentrations (33–179 µg/g). Under stable thermal stratification, such high CH₄ concentrations can also accumulate in the bottom water (e.g., up to 37. 4 mL/L in Lake Staroe), posing a risk of significant pulse emissions during autumn mixing. Conversely, the brackish Lake Bolshoy Tambukan exemplifies the crucial role of sulfate reduction, which is stimulated by sulfate-dependent anaerobic oxidation of CH₄. This process acts as a powerful natural biogeochemical barrier that curtails the emission of a major greenhouse gas. The sediments of this lake exhibited minimal CH₄ content (0.14–0.57 µg/g) alongside maximal sulfide sulfur concentrations (1.06–8.57 mg/g). Overall, this theoretical and experimental analysis demonstrates that sulfate reduction is a key determinant of redox potential, acid–base conditions, and the vertical distribution of CH₄ in the anaerobic sediments of small lakes in Southern Russia. Given the projected salinization of lakes in steppe and arid landscapes under climate change, a reduction in CH₄ emissions to the atmosphere is likely due to the enhanced sulfate-dependent anaerobic CH₄ oxidation associated with sulfate reduction in the sediments. Full article

Climate warming can alter lake zooplankton through changes in thermal structure, oxygen availability, nutrient cycling, and phytoplankton dynamics, but decadal evidence from African lakes remains scarce. We compared zooplankton size structure and biomass in Lake Bosumtwi, Ghana, between 2005–2006 and 2018–2020, using harmonised historical data and recent observations of zooplankton, temperature, dissolved oxygen, nutrients, chlorophyll a, and water transparency. Water temperatures increased across all depth strata, with the largest increase in the epilimnion (+0.30 °C), while dissolved oxygen declined by approximately 27%. Epilimnetic total nitrogen, total phosphorus, and chlorophyll a increased, and water transparency decreased. Chlorophyll a rose by 142% between periods, while mean total zooplankton biomass increased 2.33-fold, mainly because of higher copepod biomass. Mean body length decreased in nauplii but increased in copepodites and adult copepods, indicating contrasting stage-specific shifts in size structure. The median zooplankton biomass-to-chlorophyll a ratio increased from 59.46 to 79.24 (Mann–Whitney U = 210, p = 0.032). Biomass differed significantly among years for copepods, rotifers, and total zooplankton, but not for cladocerans. These findings show that warmer and less oxygenated conditions with higher chlorophyll a concentrations were accompanied by a substantial increase in copepod-dominated biomass and stage-specific changes in zooplankton size structure. Full article

To improve the quality of detection of envelope modulation on noise (DEMON) spectra extracted from ship-radiated noise under noisy conditions, a noise-robust DEMON spectrum extraction method incorporating adaptive decomposition and sparse reconstruction is proposed. Ensemble empirical mode decomposition (EEMD) is employed to adaptively select the effective frequency band, while the diagonal slice of the third-order cumulant is utilized to suppress Gaussian noise and enhance modulation characteristics. Subsequently, sparse Bayesian learning (SBL) is introduced to reconstruct the DEMON spectrum and improve the spectral resolution. The effectiveness of the proposed method is validated through numerical simulations and lake-trial experiments. The results show that the proposed method produces cleaner spectral backgrounds and improves the clarity of the shaft frequency and its harmonics compared with the conventional EMD-based method, especially under low modulation-depth conditions. These results demonstrate that the proposed method provides an effective solution for robust DEMON spectrum extraction from ship-radiated noise in complex underwater acoustic environments. Full article

Alpine karst lakes in Jiuzhaigou exhibit spatial variations in optical properties associated with differences in water depth, underwater substrates, and travertine distribution. Conventional satellite observations may not provide sufficient spatial resolution to resolve the small-scale optical variations present in these shallow and heterogeneous lakes. In this study, UAV-based hyperspectral imagery was used to quantify spatial optical variations among three representative cascade lakes located in the “Y-shaped” valley network of Jiuzhaigou, China. Hyperspectral reflectance data were transformed into the CIE L*a*b* color space to quantify perceptual color variability, while the Euclidean color difference metric (ΔE) was used to assess relative spatial heterogeneity. In addition, seven empirical optical proxies were developed to describe spatial variations in apparent optical properties without attempting absolute retrieval of water constituents. A tiered unsupervised K-means clustering approach was applied to resolve optical heterogeneity across multiple spatial scales. Global-scale clustering separated the major optical differences among lakes, whereas lake-specific clustering revealed distinct intra-lake optical zones, including areas with stronger benthic influence, transitional optical conditions, and zones dominated by water-column signals. Non-parametric Kruskal–Wallis H tests showed significant differences among optical zones, indicating that the selected proxies can distinguish spatial optical variability. The results show that UAV hyperspectral observations combined with color metrics and empirical optical proxies can effectively describe fine-scale spatial optical variations in alpine karst lakes. Rather than retrieving absolute biogeochemical or bathymetric parameters, this approach provides a reference description of relative optical variability that may assist future repeated observations and spatial monitoring of protected aquatic ecosystems. Full article

This study was made to quantify ΦCO₂ and ΦCH₄ in two crater monomictic lakes on São Miguel Island (Azores, Portugal). The studied water bodies are both within maar craters, with depths equal to 22 m and 33 m, at the Congro and Santiago lakes, respectively. ΦCO₂ values in both lakes are lower in summer, with a mean equal to 2.9 and 1.4 g m⁻² d⁻¹, respectively, in Congro and Santiago lakes, when the water column is stratified. ΦCH₄ displayed a different seasonal trend, with higher emissions during the period when the water column is stratified (mean value equal to 0.036 and 0.020 g m⁻² d⁻¹, respectively). Bacterial families commonly associated with CO₂ production, through heterotrophic respiration, fermentation, and syntrophic metabolism, were identified in both lakes, being the most abundant taxa Clostridiaceae, Enterobacteriaceae, Holophagaceae and Methylomonadaceae. The microbial community composition suggests seasonal variations, reflected by shifts in the relative abundance of specific microbial taxa. In particular, Clostridiaceae and Enterobacteriaceae exhibited higher relative abundance during winter, consistent with an increased contribution of fermentative microorganisms during this period. In contrast, Methylomonadaceae, a family commonly associated with methane oxidation and subsequent CO₂ production, reached higher relative abundance during summer in both lakes, suggesting enhanced methanotrophic activity during this period. Regarding CH₄ production, methanogens showed a slightly higher abundance during summer at Congro Lake, such as Methanosarcinaceae. In Santiago Lake, Syntrophaceae and unclassified Syntrophales were more abundant during summer, coinciding with higher CH₄ emissions compared to winter. The present research contributes to understanding volcanic gas release from lake water bodies in active volcanic framework, helping also to constrain GHG budgets in oceanic islands. Full article

Reducing external phosphorus (P) inputs is central to eutrophication control, but sediment P release can sustain internal loading and delay lake recovery. This study assessed sediment P composition, vertical distribution, and short-term release potential in Datong Lake, a shallow lake formerly affected by intensive aquaculture. Total phosphorus (TP), dissolved total phosphorus (DTP), and particulate phosphorus (PP) were measured in surface and overlying waters during the dry and wet seasons. Surface-sediment P fractions were characterized in both seasons, whereas dry-season sediments were used for adsorption and release tests, vertical profiling, and depth-specific incubations. Wet-season samples had higher TP, DTP, and PP concentrations in surface water and higher TP and PP concentrations in overlying water. Surface-sediment P was predominantly inorganic, with Ca-P as the largest inorganic fraction; bioavailable P accounted for about 32% of TP. In the 24-h batch tests, the adsorbed P amount exceeded the released amount. Total P and its NaOH-extractable and organic fractions were enriched in the upper sediment. Across the 1–5 to 21–25 cm intervals, 15-d cumulative P release decreased from 22.9 ± 1.9 to 7.2 ± 1.0 mg·kg⁻¹, and the initial 3-d release rate decreased from 1.13 ± 0.18 to 0.24 ± 0.07 mg·kg⁻¹·d⁻¹. Overall, Datong Lake sediments contained high P concentrations but exhibited limited short-term release, with the greatest release amount and rate occurring in the upper sediment. Full article

Electromagnetic underwater communications are strongly limited by water conductivity and depth, particularly at ISM frequencies above 900 MHz. Although LoRa technology has been widely adopted in low-power wireless sensor networks, experimental studies of LoRa-based underwater-to-overwater (UW2OW) links at 915 MHz in real freshwater environments remain scarce. This work presents an experimental evaluation of a 915 MHz LoRa UW2OW communication link conducted in three freshwater scenarios with different conductivity conditions: a controlled swimming pool and two natural lakes. The experimental campaign analyzes the influence of water depth and horizontal distance on key performance metrics, including received signal strength indicator (RSSI), signal-to-noise ratio (SNR), packet loss rate, and end-to-end latency. Measurements were carried out at depths between 0.25 m and 0.8 m. Multiple spreading factors were evaluated in the pool scenario, while SF12 was selected for the natural-lake experiments. The results demonstrate that short-range UW2OW communication is feasible, achieving effective distances of up to 13 m at shallow depths. However, increased depth and higher water conductivity lead to significant performance degradation, with packet loss rates exceeding 80% at longer distances. The obtained results provide empirical insights and practical design criteria for short-range freshwater underwater wireless sensor networks based on LoRa technology. Full article

Coal mining in areas with high groundwater levels often induces land subsidence and water accumulation, leading to the formation of artificial secondary wetlands. Reclaimed wetlands may provide important opportunities for regional biodiversity recovery. Taking Shuoxi Lake Wetland in Huaibei City as a case study, this research aims to reveal the characteristics of waterbird diversity in artificial wetlands after ecological reclamation in a coal mining subsidence area and to identify their key environmental drivers, thereby providing a scientific basis for optimizing the habitat service functions of such wetlands. Based on habitat identification and classification of the reclaimed wetland, waterbird diversity was surveyed, and redundancy analysis (RDA), Mantel tests, and ridge regression models were used to identify the major environmental factors influencing the distribution of different waterbird groups and to quantify their relative contributions. The results showed that after ecological reclamation, a total of 28 waterbird species belonging to 7 families and 6 orders were recorded in the artificial wetland of the coal mining subsidence area. Redundancy analysis (RDA) indicated that wader assemblages were more sensitive to vegetation cover (VC), distance to water bodies (DTW), and distance to buildings (DTB), whereas waterfowl assemblages were mainly affected by distance to buildings (DTB), area (A), and distance to water bodies (DTW), and showed no significant response to vegetation heterogeneity. Mantel tests further confirmed significant spatial correlations between waterbird assemblages and area (A), distance to major roads (DTR), distance to buildings (DTB), water depth (WD), and distance to water bodies (DTW). Ridge regression analysis showed that, under conditions in which anthropogenic disturbance was minimized, vegetation cover (VC) and water depth (WD) were the main positive drivers of wader diversity, whereas perimeter to area ratio (PAR) was the main negative driver. Waterfowl diversity was mainly negatively affected by perimeter to area ratio (PAR) and distance to water bodies (DTW). These findings suggest that appropriately regulating water depth, increasing vegetation cover, and reducing patch fragmentation and anthropogenic disturbance are key measures for enhancing the habitat service functions of artificial secondary wetlands in mining areas. These management strategies provide an important reference for wetland rehabilitation in other coal mining subsidence areas. Full article

Groundwater vulnerability refers to an aquifer’s susceptibility to contamination based on natural hydrogeological properties, including geology, soil, topography, and unsaturated zone characteristics. In low-recharge arid systems, limited recharge reduces dilution and flushing, allowing contaminants introduced through anthropogenic activities to persist over time. This study assesses groundwater vulnerability in El-Farafra, El-Kharga, and Tushka using a GIS-based DRASTIC approach, enhanced with a Land-Use DRASTIC model to incorporate human activities. Parameters, including the depth-to-water table, net recharge, aquifer media, soil media, topography, the vadose zone, and hydraulic conductivity, were spatially analyzed to generate vulnerability indices. Sentinel-2 imagery was used for land-use classification. In addition, expert elicitation from twenty hydrogeology specialists provided alternative parameter weightings, which were compared with the standard DRASTIC weights. Results show that incorporating land use and expert-based weights refines vulnerability patterns, particularly in agricultural, urban, and industrial zones. El-Farafra exhibits the highest vulnerability due to intensive land use and hydrogeological conditions, El-Kharga shows moderate vulnerability, and Tushka shows lower vulnerability, where recharge from Lake Nasser enhances dilution and reduces contaminant persistence. The study highlights the importance of integrating land-use information and expert knowledge to improve vulnerability assessment in data-scarce arid environments and supports improved groundwater management strategies. Full article

Freely meandering rivers flow through gently sloping plains composed of loess and fluvial sediments. Low-gradient alluvial plains are formed without the influence of landscape features such as rock outcrops or other features that distort the flow path. The channel configurations of such rivers, and in particular the size of meanders and oxbow lakes, depend on the average long-term water discharge. Large rivers form large meanders, while small rivers form correspondingly small ones. Morphological analysis of river channel configurations can offer a metric for estimating the average long-term water discharge of a river based solely on the sinuosity of its channel. The study examined six freely meandering rivers in Kazakhstan, with discharges ranging from 4.5 to 760 m³/s and channel slopes from 0.005 to 0.06%. The morphological analysis of river channels was based on the Relative Elevation Model, specifically its version based on the Copernicus Global Digital Elevation Model, with a spatial resolution of 30 m. River channel configurations were approximated using a set of inscribed circles, the diameters of which formed the basis for the river’s average long-term water discharge metric. The largest diameter circles, which could support the river channel with a sector of at least 135°, were expertly inscribed into river bends. The diameters of the inscribed circles within these sets varied from four times for small rivers to ten times for large rivers. These sets of circles, sorted by size, can characterize the average long-term water discharge of the analyzed rivers. For example, a sample of average median values of inscribed circle diameters has a high correlation with the average long-term water discharge, with a linear approximation reliability of R² = 0.997. The scope of the developed method for assessing the average long-term water discharge of freely meandering rivers includes retrospective analysis of changes in average long-term average long-term water discharge. This can provide significant historical depth of analysis, spanning centuries and millennia, since the analysis is based on describing the results of very slow processes of natural deformation of river channels. Thus, the method proposed in this study for assessing the average long-term water discharge of freely meandering rivers based on morphological analysis of their channel configurations expands the arsenal of tools for reconstructing certain paleoclimate elements related to the hydrology of territories. Full article

Cyanobacterial harmful algal blooms (cHABs) pose increasing ecological and public health risks in shallow lakes subject to nutrient enrichment and climate change. This research describes and evaluates a three-dimensional hydrodynamic ecological modeling framework for Fairy Lake, Ontario, using MIKE 3 FM coupled with ECO Lab to simulate lake circulation, thermal structure, nutrient dynamics, and cyanobacteria (PC3) concentrations, with model calibration using 2022 data observations and validation using 2023 data. Hydrodynamic performance showed moderate agreement for lake levels (NSE 0.47–0.52) and strong predictive capability for water temperature (NSE up to 0.96 across depths). Nutrient simulations reproduced seasonal nitrate and phosphate trends, with sediment parameter adjustments to stabilize internal loading dynamics. Cyanobacteria simulations captured seasonal bloom timing and spatial variability between inflow and central basin zones during the calibration and validation periods. The results demonstrate that integrated 3D hydrodynamic ecological modeling reproduces seasonal bloom dynamics in shallow polymictic lakes employing calibrated models and subsequent data, to predict sediment nutrient processes and periodic reassessments. As a result, this framework provides a quantitative basis for evaluating bloom behavior and the ability to predict management scenarios able to test changing climatic and nutrient conditions. Full article

Semi-arid wetlands are highly sensitive to changes in hydrological regimes, as strong evaporation often exceeds limited natural recharge. Ecological water replenishment is widely used to restore these systems, but schemes designed only to meet water-volume targets may cause excessive hydrodynamic disturbance, promote sediment resuspension, and increase the release of internal pollutants. In this study, we developed an ecological water-replenishment assessment framework for Chahannaoer Wetland that incorporates ecological water-demand thresholds, suspended-solids disturbance, and an AHP–entropy weight–TOPSIS decision model. Using hydrological and meteorological data from 2014 to 2024, six replenishment scenarios were evaluated in terms of water-balance recovery, disturbance control, and habitat suitability. The results show that Chahannaoer Wetland experienced a persistent evaporation-dominated water deficit. The mean annual natural recharge was 0.225 × 10⁸ m³, with a mean annual ecological water shortage of 1.03 × 10⁸ m³ and an evapotranspiration-to-recharge ratio of 3.42–4.56. Based on the previous comprehensive water-quality assessment using DO, COD, NH₃-N, TN, and TP, the minimum water volume required to maintain Class IV water quality was 0.86 × 10⁸ m³, whereas the suitable ecological water demand ranged from 1.27 × 10⁸ to 1.56 × 10⁸ m³. With the total replenishment volume held constant, centralized replenishment met the required water volume but substantially increased near-bed disturbance and sediment resuspension risk. By contrast, decentralized uniform replenishment performed best, with the highest relative closeness coefficient of 0.9105, a disturbance index of approximately 0.32, and water depths maintained within the suitable habitat range of 30–50 cm. These findings suggest that ecological restoration in semi-arid wetlands should move beyond volume-based water supplementation and pay greater attention to the timing, pathway, and hydrodynamic effects of replenishment. The proposed framework provides a quantitative basis for optimizing ecological water replenishment in evaporation-dominated wetlands and other inland lakes in arid and semi-arid regions. Full article