Search Results (789)

Coastal lakes require monitoring approaches that capture spatial and temporal variability beyond the limits of conventional in situ measurements. In this study, a SIGMaL framework (Satellite–In situ–GIS-multicriteria decision analysis (MCDA)–Machine Learning (ML)) was developed, a unified methodology that integrates in situ monitoring, GIS MCDA-derived water quality index (WQI), satellite imagery, and ML models for comprehensive coastal lake water quality assessment. A WQI, derived from a 12-month series of in situ measurements and environmental parameters, was used alongside four physicochemical parameters measured by a multiparameter probe. First, satellite reflectance from each sensor was used to train a set of nine regression models for modelling electrical conductivity (EC), turbidity, water temperature (WT), and dissolved oxygen (DO). Second, convolutional neural networks (CNNs) with spectral and temporal inputs were trained to classify WQI classes, enabling a cross-sensor evaluation of their suitability for lake water quality monitoring. Third, the trained CNNs were applied to generate WQI maps for a subsequent 12-month period without in situ data. Across all analyses, WQI-based models provided more stable and accurate models than those trained on raw parameters. Sentinel-2 achieved the most consistent WQI performance (AUC ≈ 1.00, R² ≈ 0.84), PlanetScope captured fine-scale spatial detail (R² ≈ 0.77), while Landsat 8–9 was most effective for WT but less reliable for multi-class WQI discrimination. Sentinel-2 is recommended as the primary satellite sensor for WQI mapping within the SIGMaL framework. These findings demonstrate the advantages of WQI-based modelling and highlight the potential of ML–remote sensing integration to support coastal lake water quality monitoring. Full article

Thermal stability is a key factor in determining the phenomena of deep chlorophyll maxima (DCM) in stratified lakes, as it mediates the vertical balance between light and nutrients required by phytoplankton. While it is well established that lake stratification is sensitive to latitude gradients, the ways in which thermal stability modulates DCM characteristics (i.e., depth, thickness, and concentration) and nutrient–chlorophyll relationships across different latitude classifications remain unclear. In this study, data on thermocline depth, DCM feature, and water quality parameters were collected from 88 globally distributed stratified lakes. Our findings indicate that (1) higher-latitude lakes exhibit strong thermoclines, with light and nitrogen serving as the primary drivers of thermal stratification; (2) in high-latitude lakes, surface chlorophyll a concentrations are more tightly linked to total phosphorus than that at DCM depth in low-latitude lakes; and (3) structural equation modeling (SEM) results demonstrate that higher-latitude lakes form shallower and thinner DCM structures, where low light levels contribute to reduced peaks in algal biomass. These findings provide valuable insights for the management of stratified lakes facing the dual pressures of climate change and eutrophication. Full article

Over the past several centuries, many lakes in the Yunnan Plateau disappeared or are disappearing due to climate change and human activities; the developments of these lakes are thus crucial for understanding their evolutions and underlying causes. Here we present a near 260-year history of water area changes in Lake Zhehai, a disappearing lake in northeastern Yunnan of Southwest China, based on historical documents such as local and regional annals and gazetteers, water conservancy records, and old maps using GIS and remote sensing techniques, to identify the dominant drivers of the lake disappearing. Results show that the reconstructed water area of Lake Zhehai was ca. 1500, 710, 370, 340, and 110 ha in 1761, 1912, 1935, 1950, and 1975 AD; this indicates that Lake Zhehai experienced three-phase lake evolution over the past 260 years, i.e., large lake in 1761–1920 AD, shrinking lake in 1921–1980 AD, and disappearing lake since 1981. Significant changes in the water area of Lake Zhehai were mainly attributed to both climate change and human activities, especially human activities as dominant drivers during the last two phases of lake evolution. Our findings provide a reference for both understanding the driving mechanisms of large shallow lake evolution during historical times in Yunnan, as well as assessing strategies of lake environmental protection under global warming and increasing human activities. Full article

Water diversion projects are a crucial measure for addressing eutrophication in shallow lakes worldwide. However, the impacts of different water diversion operation schemes on lake hydrodynamics and water quality can vary significantly, necessitating targeted, refined simulation assessments. This study focuses on Chaohu Lake, one of China’s most eutrophic lakes, and uses a mesoscale meteorological model coupled with a three-dimensional hydrodynamic and water quality model to conduct detailed numerical simulations. The study evaluates the effects of three water diversion operation scenarios and three subsurface flow guide dam scenarios during the ecological water replenishment period in Chaohu Lake from September to November. The simulation results indicate that all three water diversion operation scenarios improve the hydrodynamic conditions of Chaohu Lake, but there are significant differences in their effects on pollutant reduction in the lake. The retention of chemical oxygen demand (COD) in the water ranges from −36,812.1 to 472.8 tons, total nitrogen (TN) retention ranges from −22,637.2 to 3 tons, total phosphorus (TP) retention ranges from −4974 to 10.7 tons, and chlorophyll-a (Chl-a) retention ranges from −310.8 to −3.3 tons. Among the three subsurface flow guide dam schemes, all can promote the outflow of pollutants from Chaohu Lake. The combined subsurface flow guide dam scheme is the most effective, enabling an approximately 7.4% increase in pollutant export. The study demonstrates that diverting Huaihe River water through Paihe into Chaohu Lake, along with adding a combined subsurface flow guide dam in the West Lake area, can significantly improve the hydrodynamics and water quality in the West Lake area. This research provides essential technical support for the future operation of the Yangtze-to-Huaihe River Water Diversion Project and the layout of subsurface flow guide dams in Chaohu Lake, offering valuable insights for the ecological management of other shallow lakes. Full article

To overcome the limitations in maneuverability and adaptability of traditional underwater vehicles, a novel hybrid-actuated, multimodal cephalopod-inspired robot is proposed. This robot innovatively integrates a hybrid drive system wherein sinusoidal undulating fins provide primary propulsion and steering, water-flapping tentacles offer auxiliary burst propulsion, and a gear-and-rack center-of-gravity (CoG) adjustment module modulates the pitch angle to enable depth control through hydrodynamic lift during forward motion. The effectiveness of the design was validated through a series of experiments. Thrust tests demonstrated that the undulating fin thrust scales quadratically with oscillation frequency, aligning with hydrodynamic theory. Mobility experiments confirmed the multi-degree-of-freedom control of the robot, demonstrating effective diving and surfacing via the CoG module and high maneuverability, achieving a turning radius of approximately 15 cm through differential fin control. Furthermore, field trials in an outdoor artificial lake with a depth of less than 1 m validated its environmental robustness. These results confirm the versatile maneuvering capabilities of the robot and its robust adaptability to confined and shallow-water environments, presenting a novel platform for complex underwater observation tasks. Full article

The small freshwater lakes of Spitsbergen remain poorly studied compared to surrounding marine ecosystems despite their sensitivity to rapid environmental changes. During the short ablation season, these shallow lakes exhibit physicochemical variability influenced by the harsh Arctic climate, local geology, and hydrology. This study analyzed six lakes located on marine terraces, moraine areas, and outwash plains in the Bellsund region to assess how physicochemical variability in their waters affects phytoplankton development. The lakes exhibited local and temporal variations in temperature, conductivity, ion composition, and nutrient levels, with generally low nutrient availability limiting biological productivity. Phytoplankton communities were quantitatively and qualitatively poor, dominated by green algae, either flagellates or mixed communities, including cyanobacteria. Green algae clearly dominated in lakes closest to the fjord shoreline, while dinoflagellates and cryptophytes dominated in inland lakes. Phytoplankton abundance and biomass were extremely low in one of the lakes situated on the raised marine terraces within the tundra vegetation zone (3 × 10³ ind L⁻¹ and 0.004 mg L⁻¹, respectively). In contrast, the much larger lake situated within the tundra zone nearer the fjord shoreline had values that were comparable to fertile lakes in the temperate zone (~30 thousand × 10³ ind L⁻¹ and ~28 mg L⁻¹, respectively). It should be noted that Monoraphidium contortum and Rhodomonas minuta dominated some of the lakes almost entirely. Phytoplankton abundance was related to physicochemical conditions: green algae increased with increasing ion concentrations (Cl⁻, Na⁺, K⁺, SO₄²⁻), P_min, Fe, and Mn; flagellates preferred colder waters with higher N_min and low TOC; cyanobacteria occurred in waters with lower COND, TOC, Ca²⁺, Si, Cu, and Zn. Phytoplankton biomass increased in July with increasing water temperature. Bird activity likely facilitated phytoplankton dispersal, increasing taxonomic diversity in frequently visited lakes. Full article

Lakes in the Amur River Basin (ARB) are increasingly influenced by climate variability and human activities, yet long-term basin-scale patterns of colored dissolved organic matter (CDOM) remain unclear. In this study, we developed a support vector regression (SVR) model to retrieve lake CDOM from Landsat 5/7/8 imagery and generated a 40-year (1984–2023) CDOM dataset for 69 large lakes. The model provides a reliable tool for multi-decadal, large-area water quality monitoring considering its robust performance (R² = 0.88, rRMSE = 22.4%, MAE = 2.63 m⁻¹). Trend analysis revealed a significant rise in CDOM since 1999, particularly across the Mongolian Plateau and Northeast China Plain. Among the 69 lakes, 27 exhibited increasing CDOM, while 4 showed declines, highlighting pronounced regional variability. Variance partitioning indicated that human activities, especially irrigation and grazing, account for ~30% of CDOM variation, exceeding the contribution of any single climatic driver, whereas temperature represents the dominant climate driver (12.8%). Shallow systems were more sensitive to external disturbances, while deep lakes responded more strongly to thermal conditions. This study delivers the first long-term satellite-based CDOM assessment in the ARB and underscores the combined impacts of climate change and land-use pressures on lake optical dynamics. Full article

Submerged macrophytes play a pivotal role in the restoration of shallow lakes. Compared to meadow-forming Vallisneria, canopy-forming Myriophyllum spicatum exhibits characteristics that may render it the dominant species. However, M. spicatum may hamper recreational and commercial activities. Herbivorous fish may potentially regulate the biomass and interspecific competition between the two plant species. We conducted an enclosure experiment to elucidate the effects of grass carp (Ctenopharyngodon idella) and Wuchang bream (Megalobrama amblycephala) on the biomass ratio and morphological traits of M. spicatum and V. denseserrulata. Grass carp significantly reduced the biomass, density, and relative growth rate of both plant species, while Wuchang bream had no significant effect on any of these variables. Accordingly, the biomass ratio of M. spicatum to V. denseserrulata was significantly lower in the grass carp treatment than in both the fish-free controls and the Wuchang bream treatment. Wuchang bream significantly decreased the individual height of V. denseserrulata, whereas grass carp substantially reduced the height of both plant species. Our findings suggest that Wuchang bream may be more appropriate for maintaining meadow-forming species such as Vallisneria than grass carp, though it faces challenges in controlling both the biomass and height of canopy-forming species like M. spicatum. Full article

The seasonal freeze–thaw cycle induces a fundamental regime shift in lake ecosystems, primarily through the restructuring of microbial communities. This study investigated the dynamics and mechanisms of species diversity maintenance in protistan communities in Gonghai Lake, a shallow subalpine lake in China, across both ice-covered and ice-free periods. During ice cover, the protistan community exhibited a vertically stratified structure dominated by cryotolerant diatoms such as Stephanodiscus. Following thaw, the community transitioned to a more homogeneous, resource-driven assembly. Concurrently, the key environmental controls shifted from physical stratification (proxied by depth) to resource availability (notably NO₃⁻ and TOC), a change reflected in the taxonomic succession from Ochrophyta to Chlorophyta. Nevertheless, depth retained ecological relevance mediated by benthic–pelagic coupling, which supported a distinct near-sediment community. Our findings demonstrate that freeze–thaw-mediated terrestrial nutrient inputs directly modified protistan diversity and community structure. These alterations have fundamental implications for ecosystem functions in subalpine lakes, including nutrient cycling rates and energy flow through the microbial loop. Full article

Water replenishment projects (WRP) are widely regarded by lake managers as an effective method for ecological restoration. But studies on multiple water receiving lakes indicate that multi-source water supplementation may exacerbate spatial heterogeneity in water quality. The primary causes are the uneven quality of external water sources and the morphology of the lakes themselves. Hangzhou’s West Lake, which relies on a single water source, also exhibits ecological differences between its lake areas. To explain this phenomenon from a hydrodynamic perspective, this study employs Delft3D model simulations to determine the spatiotemporal heterogeneity in the impact of artificial water replenishment on local water renewal times (LWRT) across different lake areas. The results indicate that, compared to natural conditions, WRP shortens the typical LWRT at most sites in West Lake and reduces the seasonal variation amplitude of LWRT. The WRP impedes local water exchange capacity in certain lake areas during specific months, potentially creating stagnant zones. Moreover, the spatiotemporal heterogeneity of its impact on West Lake’s hydrodynamic conditions amplifies differences in flow rhythms between lake regions, leading to fragmented water movement. This may ultimately compromise the integrity of the lake’s overall ecological environment. Managers of receiving lakes should consider increasing monitoring frequency and the number of monitoring stations to address more complex water quality conditions. Future designers of WRPs should incorporate the prevention of fragmented hydrodynamic conditions as an evaluation criterion in diversion scheme planning. This study provides references and evidence for lake ecological management and research on the impact mechanisms of WRPs on shallow lakes. Full article

Climate-driven hydrological changes are transforming river valleys, particularly floodplain lakes (FLs). Increasingly prolonged droughts and reduced flooding are causing the desiccation of oxbow and floodplain lakes, leading to the conversion of aquatic sediments into soils. This study investigates both the quantity and quality of carbon in these environments by analysing submerged sediments and sediments transformed into soils in small FLs of the Middle Vistula Valley (central Poland). Samples from eight FLs, representing both submerged and desiccated zones, were analysed for total organic carbon (TOC), humic substances (HSs), fulvic acids (FAs), humic acids (HAs), and carbonates (CaCO₃). The TOC content averaged about 40 g kg⁻¹ in both sediments and soils, indicating considerable carbon storage. However, the proportion of FA and HA was low (3–4 g kg⁻¹, or 12–15% of TOC), suggesting a low degree of humification and a predominance of labile, easily degradable organic compounds susceptible to microbial mineralization and CO₂ emission. CaCO₃ content was also low (<1%), implying minimal potential for carbonate-derived CO₂ release. These findings confirm that drying FLs represent transitional systems and may shift from carbon sinks to carbon sources under ongoing climatic change. They also emphasize the need for more focused research on these, until now, underestimated ecosystems. Full article

Shallow lakes are highly sensitive to hydrological changes and human activities; however, the effect of hydrological extremes on water quality dynamics remains unclear. In this study, we investigated hydroclimatic and water quality changes in Datong Lake (a typical shallow lake within the Yangtze River Basin) over the period 2021–2024, with the objective of detecting the dynamic response of lake water quality to its driving factors during extreme hydrological years. Our analysis suggested that precipitation, water level, and temperature of Datong Lake all fluctuated during the study period. Total nitrogen (TN) concentrations increased to 1.25 mg/L, 1.42 mg/L, and 1.05 mg/L in the lake, inlets, and outlet, respectively, driven largely by external nutrient inputs from agricultural and aquacultural activities. Precipitation and water level were significantly higher in the wet year (1051.15 mm and 27.26 m, respectively) than in the dry year (805.05 mm and 27.05 m, respectively). TN and total phosphorus (TP) concentrations at the river inlet were higher in wet years than in dry years, whereas TN and TP in the lake showed the opposite trend. Notably, both TN and TP were positively correlated with temperature, water level, and turbidity, and negatively correlated with dissolved oxygen and electrical conductivity. Among these drivers, turbidity emerged as key influential variable (R² ranging from 0.18 to 0.41) in modulating lake water quality during extreme hydrological years, followed by temperature (R² ranging from 0.11 to 0.17) and water level (R² ranging from 0.12 to 0.13). These findings reveal that extreme hydrological shifts drive changes in lake water quality, underscoring the necessity of integrated management strategies to alleviate climate change impacts on shallow lake ecosystems. Full article

Rain-on-snow (ROS) events significantly impact hydrological processes in snowy regions, yet their seasonal drivers remain poorly understood, particularly in low-elevation and low-gradient catchments. This study uses an XGBoost-SHAP explainable artificial intelligence (XAI) model to analyze meteorological and watershed controls on ROS runoff in the Laurentian Great Lakes region. We used daily discharge, precipitation, temperature, and snow depth data from 2000 to 2023, available from HYSETS, to identify ROS runoff. The XGBoost model’s performance for predicting ROS runoff was higher in winter (R² = 0.65, Nash–Sutcliffe = 0.59) than in spring (R² = 0.56, Nash–Sutcliffe = 0.49), indicating greater predictability in colder months. The results reveal that rainfall and temperature dominated ROS runoff generation, jointly explaining more than 60% of total model importance, while snow depth accounted for 8–12% depending on season. Winter runoff is predominantly governed by climatic factors—rainfall, air temperature, and their interactions—with soil permeability and slope orientation playing secondary roles. In contrast, spring runoff shows increased sensitivity to land cover characteristics, particularly agricultural and shrub cover, as vegetation-driven processes become more influential. Snow depth effects shift from predominantly negative in winter, where snow acts as storage, to positive contributions in spring at shallow to moderate depths. ROS runoff responded positively to air temperatures exceeding approximately 2.5 °C in both winter and spring. Land cover influences on ROS runoff differ by vegetation type and season. Agricultural areas consistently increase runoff in both seasons, likely due to limited infiltration, whereas shrub-dominated regions exhibit stronger runoff enhancement in spring. The seasonal shift in dominant controls underscores the importance of accounting for land–climate interactions in predicting ROS runoff under future climate scenarios. These insights are essential for improving flood forecasting, managing water resources, and developing adaptive strategies. Full article

Kumamoto is a city in Japan that relies completely on groundwater for drinking water. Groundwater in the Kumamoto region divided into shallow and deep aquifers. Around Lake Ezu, where one of Kumamoto City’s largest tap-water source wells are located, groundwater from both aquifers mixes, resulting in numerous springs. The aim of this study was to identify and quantify the relative contributions of the groundwater sources that discharge into Ezu Lake. River, lake, spring, and artesian well samples were collected every month between April 2021 and March 2022, and groundwater chemistry data for the shallow and deep aquifers were obtained from previous studies. The NO₃⁻ and SO₄²⁻ concentrations indicated three end-members: (A) high NO₃⁻ from anthropogenic sources, (B) high SO₄²⁻ from Shirakawa River water, and (C) low NO₃⁻ and SO₄²⁻ from denitrification or dilution. Mixing analysis show 60–70% from A, 17–22% from B, and 7–25% from C for the lake waters. Also, the result showed that springs in the Kami-Ezu area were dominated by shallow aquifer water, whereas artesian wells in the Shimo-Ezu area reflected deep aquifer water. This is the first time that the contributions of groundwater sources in this area have been quantified using a three-component mixing approach. Furthermore, it was estimated that Shirakawa River infiltration, including the artificial recharge project from rice paddy, contributed approximately 57% to groundwater discharge into Ezu Lake in 2020. These results provide new insights into the contribution of artificial recharge from agricultural land to groundwater. Full article

Groundwater in the Nansi Lake Basin, a key reservoir of the South-to-North Water Diversion Project, supports domestic, agricultural, and ecological needs but faces pressure from overexploitation and pollution. This study clarifies the hydrochemical characteristics, controlling processes, environmental quality, and source contributions of shallow groundwater in the basin. Hydrochemical data from 67 wells were interpreted using Piper and Schukalev diagrams, Gibbs and ion-ratio plots, the entropy-weight water quality index (EWQI), and an absolute principal component scores–multiple linear regression (APCS-MLR) model. Groundwater shows high mineralization and hardness, with 35.82% and 55.22% of samples exceeding standard limits for total dissolved solids and total hardness, respectively. The dominant facies are HCO₃-Ca, HCO₃-Ca·Mg, and HCO₃·Cl-Na·Ca, indicating dissolution and ion exchange involving carbonate and silicate rocks. Gibbs and ion-ratio analyses demonstrate that rock–water interaction is the main control, with secondary influence from evaporation. EWQI results indicate generally good groundwater quality (68.66% Class I, 20.90% Class II). APCS-MLR identifies natural, agricultural, ion-exchange, and anthropogenic sources, contributing 53.34%, 22.71%, 4.79% and 19.14%, respectively. These findings show that protection should focus on pollution control in northern agricultural and mining zones while conserving high-quality groundwater elsewhere in the basin. Full article