Lake Group Research Articles

Eutrophication modifies the relationships between multiple facets of macroinvertebrate beta diversity and geographic distance in freshwater lakes

AbstractAimUnderstanding the distance–decay relationship (DDR) has been considered important because it reflects a combination of several ecological processes such as dispersal limitation and environmental sorting. However, effects of human disturbances on DDR are poorly known, especially in freshwater lakes. This study is aimed to examine how anthropogenic eutrophication modified the relationships between three facets (taxonomic, functional and phylogenetic) of macroinvertebrate beta diversity and geographic and environmental distances across 30 freshwater lakes.LocationThe Yangtze River floodplain, China.MethodsWe used Mantel tests to examine the relationships between multiple facets of assemblage dissimilarities (overall beta diversity, replacement and richness difference components) and geographic and environmental distances. Distance‐based redundancy analysis (dbRDA) and associated variation partitioning procedures were applied to explore the relative contributions of environmental and spatial factors on the three facets of beta diversity.ResultsWe found that none of the three beta diversity facets was related to geographic distance, but all were significantly related to environmental distance, mainly mirroring eutrophication‐related variables. Based on the variation partitioning approach, the macroinvertebrate assemblages examined were almost exclusively structured by environmental factors associated with eutrophication, while spatial variables had a negligible effect. Nevertheless, the different facets of beta diversity did not decrease (i.e., no homogenization trend) in lake groups showing the highest eutrophication levels, implying complex influences of anthropogenic disturbances in driving homogenization or differentiation in assemblage compositional dissimilarity.Main ConclusionsOur findings suggested that the high degrees of eutrophication acted as an environmental filter to significantly modify the spatial distance–decay relationships, possibly via decreasing the importance of dispersal limitation in shaping macroinvertebrate assemblages in the studied lakes. Given the sensitivity of beta diversity patterns to eutrophication we found in this study, we recommend that the role of anthropogenic disturbances should be incorporated into research on general ecological patterns like the DDR.

Growth and reproduction of the shrimp population in a lagoon system in southern Benin (West Africa)

Abstract The aim of this work was to characterize the growth and reproduction dynamics of shrimp in the Lac Nokoué-Chenal de Cotonou complex. The results of one year’s sampling from five stations (North, South, East, Central and West) of the lagoon complex revealed that linear growth in size in Lake Nokoué is decreasing over time in Macrobrachium macrobrachion (the most representative species of the genus Macrobrachium), but positive in Penaeus notialis (the most representative species of the genus Penaeus). Size-weight relationships indicate that the lowest growth coefficient () is obtained in immature males of Macrobrachium felicinum, while the highest growth coefficient () is obtained in mature females of Macrobrachium vollenhovenii, with an average of 2.84 for all shrimp species over both sexes considered. The test indicated that only the species Macrobrachium vollenhovenii has a significant sexual imbalance in favour of females in Lake Nokoué. Fisher’s Least Significant Difference test indicated that the estimated first sexual maturity sizes in Macrobrachium vollenhovenii and M. macrobrachion are significantly different from those estimated in M. felicinum at the threshold. However, the same test indicates that there is not enough evidence to differentiate the sizes of first sexual maturation in M. vollenhovenii and M. macrobrachion. This work revealed that Penaeus monodon was the only species to show better positive growth within all its groups in Lake Nokoué while exposed to anthropogenic effects. A gradual average increase in the size of Penaeus notialis in Lake Nokoué is found between the beginning and end of the saline intrusion (which confirms the life cycle of the species presented). Species of the genus Macrobrachium showed good reproductive capacity, with the absence of sexually mature Penaeus in this lagoon.

Occurrence, bioaccumulation and trophic dynamics of per- and polyfluoroalkyl substances in two tropical freshwater lakes

We have investigated the occurrence, distribution, and biomagnification of per- and polyfluoroalkyl substances (PFAS) in two tropical lakes (Asejire and Eleyele) of Southwestern Nigeria, with contrasting urban intensities. Over an 8-month period, we sampled sediment and fish species (Clarias gariepinus: CIG; Oreochromis niloticus: ON; Coptodon guineensis: CG; Sarotherodon melanotheron: SM) across trophic levels, and analyzed various PFAS congeners, in addition to a select group of toxicological responses. While herbivores (SM) and benthic omnivores (CIG) at Asejire exhibited elevated levels of PFBS and PFOS, the pelagic omnivores (ON) showed a dominance of PFOS, PFDA, PFHxDA and EtFOSE in the muscle. At the Eleyele urban lake, PFAS patterns was dominated by PFBS, EtFOSE, PFPeS, PFOcDA and PFOS in the herbivores (SM, CG), EtFOSE, PFOS and PFBS in the pelagic omnivore (ON) and benthic omnivore (ClG). The estimated biomagnification factor (BMF) analysis for both lakes indicated trophic level increase of PFOS, PFUnA and PFDA at the suburban lake, while PFOS and EtFOSE biomagnified at the urban lake. We detected the occurrence of diSAMPAP and 9CL-PF3ONS, novel compounds not commonly reported, in PFAS studies at both lakes. The studied toxicological responses varied across trophic groups in both lakes with probable modulations by environmental conditions, trophic structure, and relative PFAS exposures in the lakes. The present study documents, for the first time in Nigeria, or any other African country, the role of urbanization on contaminant load into the environment and their implications for contaminant dynamics within the ecosystem and for aquatic food safety.

Nonlinearities in phytoplankton groups across temperate high mountain lakes

Abstract High mountain lakes are increasingly recognized as sentinel ecosystems of global change. Monitoring phytoplankton changes or reconstructing their composition from sedimentary records can help identify systemic changes in these lakes and their catchments. This study aimed to evaluate the distribution of the major phytoplankton groups in high mountain lakes across environmental gradients and identify tipping points in relative dominance. The phytoplankton groups were estimated using pigment‐based chemotaxonomy in 79 lakes in the Pyrenees selected to cover the bedrock and elevation gradients. Fifty‐four environment variables were considered, including in‐lake and catchment descriptors. Redundancy analyses showed that in‐lake descriptors override the explicative capacity of landscape variables. Generalized additive models and multivariate regression trees showed that water hardness, trophic state and food‐web descriptors were, in this order, the most influential factors determining phytoplankton group dominance. Calcium concentration of about 200 μeq L−1 defined the threshold between soft waters—with chrysophytes and chlorophytes showing a higher affinity for them—and harder waters that favour diatoms and cyanobacteria. Across the trophic gradient, there was a threshold at ~5 μg L−1 of total phosphorus (TP), chrysophytes being dominant below that TP value and cryptophytes above. The dominance of chlorophytes and cryptophytes increased with the density of macrozooplankton. Chrysophytes were significantly lower and diatoms higher in lakes with fish. Synthesis. The relative abundance of phytoplankton groups in temperate high mountain lakes responds in a nonlinear way to the hardness of the water in the range 20–1195 Ca2+ μeq L−1 and the trophic state in the range 0.94–19 TP μg L −1. The thresholds across water hardness and trophic state gradients coincide with studies based on other organisms, pointing to a robust typology for mountain lakes that should be considered when selecting global change sentinel lakes and anticipating abrupt transitions across these thresholds.

Chloride hydrogeochemistry of the finger lakes in Central and Western New York, USA

Road deicing salts have impacted the hydrogeochemistry of lakes throughout the snow-belt region of the globe. This paper advances our understanding of the historical change in salt concentrations in, and sources to, the Finger Lakes of western and central New York state, and compares the results to other lakes across the globe. Surface water samples from Honeoye, Canandaigua, Keuka, Seneca, Cayuga, Owasco, Skaneateles and Otisco lakes were analyzed for chloride (Cl) concentrations, and augmented with published and unpublished decade, and for the first time, century-scale Cl data for these lakes and Hemlock Lake. A mass-balance model estimated the Cl flux required to match the measured Cl concentrations in each lake. Cl concentration and flux trends defined two groups of lakes. Group 1: A mid-1900′s peak in Cl concentrations was detected in Seneca and Cayuga lakes, that resulted from a short but significant spike of Cl, most likely from salt mine wastes during pre-Environmental Protection Agency times. Group 2: Hemlock, Honeoye, Canandaigua, Keuka, Owasco, Skaneateles and Otisco lakes, revealed smaller yet increasing concentrations and fluxes over time that were interpreted to reflect increasing use of road deicing salts in their watersheds and supported by correlations to their state and federal road lengths, percentage of impervious surfaces, water residence times in each watershed and the production of road salt in the US, but not to their trophic status, nor their percentage of agricultural land. Estimated Cl inputs from municipal wastewater treatment facilities, individual septic systems and the atmosphere (precipitation) were also insignificant in the Finger Lakes region. These results help clarify the processes responsible for increasing Chloride concentrations in lakes globally.

Morphometric and hydrological features of the lakes of the Sergachsky municipal district (Nizhny Novgorod region, Russia)

The article presents the results of a study of the morphometric and hydrological features of the lakes of the Sergachsky municipal district (Nizhny Novgorod region, Russia), lying in the north of the Privolzhskaya upland. A bathymetric survey was carried out on the lakes of the researched territory from the board of an inflatable boat, using an echo sounder, combined with a navigator. The results of the field research were processed using the geographic information program QGIS, digital models of the relief of the six researched lakes were created, and their main morphometric and hydrological characteristics were calculated. Based on the analysis of the morphometric characteristics of the lakes and data on the landscape features of their surroundings, conclusions were drawn about the origin of the lake basins. Two genetic groups of lakes within the researched area are identified: karst and riverbed (oxbow lake).

A continuous classification of the 476,697 lakes of the conterminous US based on geographic archetypes

AbstractA variety of classification approaches are used to facilitate understanding, prediction, monitoring, and the management of lakes. However, broad‐scale applicability of current approaches is limited by either the need for in situ lake data, incompatibilities among approaches, or a lack of empirical testing of approaches based on ex situ data. We developed a new geographic classification approach for 476,697 lakes ≥ 1 ha in the conterminous U.S. based on lake archetypes representing end members along gradients of multiple geographic features. We identified seven lake archetypes with distinct combinations of climate, hydrologic, geologic, topographic, and morphometric properties. Individual lakes were assigned weights for each of the seven archetypes such that groups of lakes with similar combinations of archetype weights tended to cluster spatially (although not strictly contiguous) and to have similar limnological properties (e.g., concentrations of nutrients, chlorophyll a (Chl a), and dissolved organic carbon). Further, archetype lake classification improved commonly measured limnological relationships (e.g., between nutrients and Chl a) compared to a global model; a discrete archetype classification slightly outperformed an ecoregion classification; and considering lakes as continuous mixtures of archetypes in a more complex model further improved fit. Overall, archetype classification of US lakes as continuous mixtures of geographic features improved understanding and prediction of lake responses to limnological drivers and should help researchers and managers better characterize and forecast lake states and responses to environmental change.

Estimation of Total Phosphorus Concentration in Lakes in the Yangtze-Huaihe Region Based on Sentinel-3/OLCI Images

Total phosphorus (TP) concentration is a crucial parameter to assess eutrophication in lakes. As one of the most concentrated regions for freshwater lakes, the Yangtze-Huaihe region plays a significant role in monitoring TP concentrations for the sustainable utilisation of China’s water resources. In this study, a TP concentration estimation model suitable for large-sized lake groups was developed using a combination of measured and remote sensing data powered by advanced machine learning algorithms. Compared to traditional empirical models, the model developed in this study demonstrates significant accuracy in fitting (R2 = 0.53, RMSE = 0.08 mg/L, MAPE = 34.20%). Moreover, the application of this model to lakes in the Yangtze-Huaihe region from 2017 to 2022 has been conducted. The multi-year average TP concentration was 0.18 mg/L. Spatial distribution analyses showed that total phosphorus concentrations were higher in small lakes. In terms of temporal changes, the interannual decreases in total phosphorus concentrations were 0.02 mg/L, 0.01 mg/L, and 0.01 mg/L for small, medium, and large lakes, respectively. We also found that large lakes typically exhibited a “high in spring and summer, low in autumn and winter” pattern until 2020, but transitioned to a “high in summer and autumn, low in spring and winter” pattern after 2020 due to the removal of closed fish nets, which were having a significant impact on the lake ecosystem. Other lakes in the area consistently showed a pattern of “high in spring and summer, low in autumn and winter” during the six-year period. These findings may provide useful references and suggestions for the environmental protection and management of lakes in China.

Thermokarst lakes group accelerates permafrost degradation in the Qinghai–Tibet Plateau, China: A modeling study

Thermokarst lakes in the Qinghai–Tibet Plateau (QTP) are increasing in number and lake surface area, intensifying the lake–permafrost interaction and making it more complex, thus affecting the hydrological and ecological environment. Although the impact of the individual lake on permafrost has been studied, the effects of lakes group on permafrost and regional hydrological processes remain unexplored. Hence, in this study, modified SUTRA models considering thermal conduction and convection processes were established for five scenarios, including a current environment and four thought experiments, to determine whether and how thermokarst lakes group accelerates permafrost degradation. The models could effectively simulate the variations in the ground temperature with time and depth, with the highest RMSE and lowest R2 being 1.443 °C and 0.706, respectively. Thermal conduction and convection played a dominant role before and after the formation of through-taliks below the thermokarst lakes, respectively. Through-taliks strengthened the hydraulic connection between supra-permafrost water, sub-permafrost water, and lakes, and changed the groundwater circulation pattern. An increase in the number of thermokarst lakes led to the formation of more through-taliks and improved the heat transfer efficiency, accelerating permafrost degradation. Thermal erosion of the permafrost base was more severe in the presence of a recharge source and pathway via a talik. The results highlight the importance of thermal convection and groundwater circulation in permafrost degradation. The findings can help understand the interaction mechanism between permafrost and thermokarst lakes and the variation in environmental and eco-hydrological processes in cold regions.

Synergistic effects between global warming and water quality change on modelled macrophyte species richness

Submerged freshwater macrophytes are crucial for the functioning of lakes. Their growth and survival follow environmental conditions like light, temperature, and nutrient availability. Hence, the impending increase in water temperature as well as changes of nutrients and turbidity will lead to changes in macrophyte geographic and depth distribution: Herein, we assess these potential changes. We apply an eco‐physiological macrophyte growth model to simulate biomass growth and survival of virtual species defined by random trait combinations within expert‐derived trait ranges for oligotraphentic, mesotraphentic, and eutraphentic species groups in deep lakes in Bavaria, Germany, which cover clear, moderate, and turbid lake conditions. The emergent potential species richness is compared with empirically observed species richness to evaluate general predictions for current conditions. Thereafter, we apply the model to scenarios of temperature increase and of turbidity and nutrient change to assess potential changes in species richness and the influence of species' traits on being an environmental change ‘winner' or ‘loser'. We find a cross‐lake, hump‐shaped pattern of potential species richness along depth. This largely reflects observed patterns, although mismatches were also detected and might be explained by missing processes and environmental heterogeneity within the lake. Rising temperature leads to increased richness of potential species in all lake types, species groups, and depths. Turbidity and nutrient change effects depend on depth and lake type. ‘Loser species' under increased turbidity and nutrient level are light consumptive and sensible to disturbances, while ‘winner species' have a high biomass production. These findings show that the hump‐shaped depth distributions of submerged macrophyte diversity can emerge solely considering eco‐physiology. The differential responses to environmental changes imply that management measures must account for lake type because those responses can have opposite trends depending on lake depth and type.

Where and how to cool through blue infrastructure? Large lake groups to ameliorate urban overheating in a typical inland multi-lake megacity

Large lake groups have been recognized as important blue infrastructure to ameliorate urban overheating in inland megacities. Previous studies have evaluated climate regulation capabilities of large lakes on cities. However, how the specific location of lake groups affects thermal environments across extensive built-up areas through thermal and aerodynamic mechanisms remains unclear. Therefore, we conducted sensitivity experiments using the Weather Research and Forecasting (WRF) model to explore the intensity and spatial variation of air temperatures and wind fields influenced by lake groups—located in downtown areas, inner suburbs, and outer suburbs—under typical heatwave conditions in Wuhan. Results indicate that compared to similar-sized suburban lake groups, downtown lake groups exhibit higher and lower daytime lake-land differences in sensible and latent heat fluxes, respectively, resulting in greater lake cooling intensities (LCIs). Also, upwind lake groups cool more built-up areas since lake breeze circulations (LBCs) promote the spreading of lake cooling distances (LCDs). However, the development of LCIs, LCDs, and LBCs is asynchronous, with LCIs peaking around mid-morning before the generation of LBCs, and LCDs peaking in the afternoon once LBCs have developed vigorously. Moreover, we propose a planning framework integrating the cooling effects of lake groups to support cooler, healthier, and more sustainable cities.

Morphometric characteristics of the lakes of the Pustynsky district of the projected National Park “Nizhegorodskoe Zavolzh’e”

The paper presents the results of researching the morphometric and hydrological features of a group of lakes in the eastern part of the Pustynsky district of the projected National Park “Nizhegorodskoe Zavolzh’e” (Nizhny Novgorod Region, Russia). The lakes in question are the largest component of the hydrological system of the Serezha River basin on the territory of the Pustynsky district. The Seryozha River flows through most of the largest lakes, and its tributaries flow through some of them. Based on the conducted field studies, certain conclusions were drawn.

Accurate estimation of surface water volume in tufa lake group using UAV-captured imagery and ANNs

Quantitative acquisition of surface water volume of tufa lake group is significant for protecting the tufa landscapes. Limited by low spatial resolution, satellite remote sensing failed to extract the surface water distribution of small and scattered tufa lakes. In recent years, Unmanned Aerial Vehicle (UAV) remote sensing has been increasingly applied to survey aquatic resources and environments, posing great potential for accurately measuring surface water volume of tufa lake group. In this paper, taking the Shuzheng Lakes in Jiuzhai Valley of China as the study site, we used UAV-captured images and Artificial Neural Network (ANN) models to precisely estimate the surface water volume of the tufa lake group. Digital Surface Model (DSM) and orthomosaic were first generated using aerial triangulation. Next, the two classification networks were trained to separate water from vegetation, and then the water extents of individual tufa lakes were extracted. Subsequently, the water depth map of each tufa lake was retrieved using the transferred shallow and deep bathymetry networks. Lastly, the total surface water volume of tufa lake group was achieved by summing the products of pixel unit area and the water depth of each pixel. As results, the surface water volume of tufa lake group estimated by the optimum model combination was approximately 181,360 m3, and the corresponding R-squared was 0.92. These demonstrated the effectiveness of utilizing UAV-based remote sensing and integrated ANN models to accurately estimate surface water volume of tufa lakes.

An extinct species of Tchangmargarya (Gastropoda: Viviparidae) from quaternary lacustrine deposits of a group of vanished lakes in Yunnan, China

ABSTRACT An extinct freshwater molluscan fauna has been discovered from Quaternary lacustrine deposits of a recently vanished group of lakes and surrounding lacustrine deposits in the Luliang Basin, Yunnan Province, China. Three species of Tchangmargarya He, 2013 are dominant and distributed sympatrically here. One of them is new to science. Here we describe the three Tchangmargarya species from the Luliang Basin, including the new species, Tchangmargarya cuan n. sp., and compare the species composition of this fauna with the other extant lacustrine mollusc fauna of Yunnan. The vanished lakes group in Luliang is the first case of sympatric distribution within Tchangmargarya. It is considered to have once been a diversity hotspot of Tchangmargarya and represents a vanished Quaternary lacustrine habitat in Yunnan.

A Quantification of Heat Storage Change-Based Evaporation Behavior in Middle–Large-Sized Lakes in the Inland of the Tibetan Plateau and Their Temporal and Spatial Variations

A large number of different-sized lakes exist in the inland area of the Tibetan Plateau (TP), which are examples of the important connection between the atmosphere and hydrosphere through the analysis of lake surface convergence and evaporation processes. The evaporation level changes that occur in middle–large-sized lakes (surface area > 50 km2) in the area directly influence the regional mass and energy balance values, atmospheric boundary layer heat and humidity structures, and weather processes occurring in the lower-reach areas. The studies conducted in the literature at present, concerning lake evaporation processes, generally overlook the differences in lake heat storage behavior due to the reduced amount of data in the literature concerning lake bathymetry. According to the in situ bathymetric data obtained for 68 middle–large-sized lakes in the inner basin of the TP, in this study, we calculated their heat storage (G) change values by using the different vertical-depth water-temperature-change integral method, and we established a regression equation for the heat storage and lake surface net radiation values for 68 lakes. The evaporation rates of 134 middle–large-sized lakes larger than 50 km2 in the inland are of the TP were calculated by obtaining the G regression result and adopting it into the Penman model, as well as estimating the evaporation losses of theses 134 lakes from 2002 to 2018. The result shows that the annual average evaporation rate for these lakes is 927.39 mm/year, with an insignificant upward trend (0.10 mm/year). This method achieved good accuracy compared with the Bowen ratio method, which estimates the evaporation rate during the ice-free season, with a high correlation coefficient (R) value of 0.95 and least root mean square error (RMSE) value of 61 mm. The annual mean evaporation rate can be divided into the southern and northern lake groups along a 34°N line with a difference of 314.41 mm/year. The annual average evaporation volume of these lakes was 25.02 km3 and showed an upward trend of 0.35 km3/year. Among them, the annual average evaporation volume contribution ratio of level-1 lakes (50 km2 ≤ lake’s area < 100 km2, 61 lakes) was 14.04%, showing an upward trend, and the contribution of level-3 lakes (lake’s area ≥ 500 km2, 10 lakes) was 41.50%, showing a downward trend. There were no obvious changes in the level-2 lakes (100 km2 ≤ lake’s area < 500 km2, 63 lakes), which maintained at the same level in approximately 44.46%. Air temperature is the most important factor affecting the evaporation rate of lakes, while the lake surface area is the main factor affecting lake evaporation volume. Our study, considering the actual lake heat storage value, provides a useful reference for further improving lake water budget balance values and watershed hydrologic features in the inland closed lakes located in the TP.

Spatial pattern analysis of zooplankton and surface water of pit lakes (Raniganj coal field, India)

ABSTRACT Open pit technique is often the simplest and most cost effective mining technology. Coal mining, which began in 1774 in Raniganj, West Bengal, India, led to many abandoned pits, which led to the formation of pit lakes. Mining has a tablvariety of environmental ramifications around the world. On the other hand, the pit lakes of the Raniganj coal field (RCF) are being used for recreational purposes. Knowledge of the spatial pattern in the zooplankton population and surface water quality in pit lakes waters of the Raniganj coal field region is rather limited. Sixteen pit lakes in the RCF in West Bengal, India, were investigated from January 2019 to December 2021. In the present study, we analyzed the spatial pattern and mode of distribution of zooplankton communities based on Coefficient of dispersion methods. To perform a comprehensive analysis of the water quality condition of this study area, we apply water quality index (WQI) methods. A total of 51 taxa were identified and the density was primarily dominated by rotifers. The most dominant species were: Brachionus forficula, Paracyclops sp. and Sida sp. Clumped type of zooplankton distribution pattern was observed in the studied pit lakes. The water quality in most of the studied pit lakes was poor. All the water quality parameters showed significant spatial variations as per Kruskal-Wallis test. The clustering technique produces three groups of pit lakes that are particularly convincing as the pit lakes in these groups showed comparable characteristics.

Use of Landsat Satellite Images in the Assessment of the Variability in Ice Cover on Polish Lakes

Despite several decades of observations of ice cover in Polish lakes, researchers have not broadly applied satellite images to date. This paper presents a temporal and spatial analysis of the variability in the occurrence of ice cover on lakes in the Drawskie Lakeland in the hydrological years 1984–2022 based on satellite data from Landsat missions 4, 5, 7, 8, and 9. The range of occurrence of ice cover was determined based on the value of the Normalised Difference Snow Index (NDSI) and blue spectral band (ρλblue). The determination of ice cover extent adopted ρλblue values from 0.033 to 0.120 as the threshold values. The analysis covered 67 lakes with an area from 0.07 to 18.71 km2. A total of 53 images were analysed, 14 and 39 out of which showed full and partial ice cover, respectively. The cluster analysis permitted the designation of two groups of lakes characterised by an approximate range of ice cover. The obtained results were analysed in the context of the morphometric parameters of the lakes. It was evidenced that the range of the ice cover on lakes is determined by the surface area of the lakes; their mean and maximum depth, volume, length, and width; and the height of the location above sea level. The results of analyses of the spatial range of ice cover in subsequent scenes allowed for the preparation of maps of probability of ice cover occurrence that permit the complete determination of its variability within each of the lakes. Monitoring of the spatial variability in ice cover within individual lakes as well as in reference to lakes not subject to traditional observations offers new research possibilities in many scientific disciplines focused on these ecosystems.

Hydrologic connectivity and morphologic variation of oxbow lakes in a pristine alpine fluvial system

The lifespan of oxbow lakes in a meandering system typically exhibits considerable disparity due to the diverse evolutionary processes that lead to their terrestrialization. Although oxbow lakes generally undergo a long-term gradual shrinking trend, their hydrologic connectivity and morphologic variations under variable hydrologic conditions of the river are not well understood. Here we focus on a group of oxbow lakes in a pristine alpine fluvial system in the Qinghai-Tibet Plateau to examine the hydrogeomorphic response of oxbow lakes to a variable hydrologic regime of an active meandering channel. We find that the oxbow lakes are characterized by extensively developed compound forms and connecting “tie” channels and that the lateral migration of the main channel discernably impacts lake morphology and evolution. With increasing discharges in the main channel, the oxbow lakes generally show increases in length under relatively lower flows (RI < 10 years) and more dramatic increases in width under higher flows (RI > 10 years), which collectively lead to their expansion regardless of their hydrologic connectivity. This implies hydrogeomorphic processes other than surface water connection between oxbow lakes and the main channel in adjusting water levels of the lakes. To quantify hydrologic connectivity, we propose a probability-based index and find the overall low hydrologic connectivity of the studied oxbow lakes, owing to the unique paleogeographic setting of the study area. The infrequent but pulsed sedimentation within the lakes and the relatively slow lateral migration of the meandering channel catalyze an inactive floodplain of the study reach.

Environmental heterogeneity affecting spatial distribution of phytoplankton community structure and functional groups in a large eutrophic lake, Lake Chaohu, China

The growth and development of phytoplankton are influenced by physico-chemical parameters, which can also affect the spatial distribution of phytoplankton community structure. However, it is unclear whether environmental heterogeneity caused by multiple physico-chemical factors can affect the spatial distribution of phytoplankton and its functional groups. In this study, we investigated the seasonal variation and spatial distribution of phytoplankton community structure and its relationships with environmental factors in Lake Chaohu from August 2020 to July 2021. We recorded a total of 190 species from 8 phyla, which were divided into 30 functional groups, including 13 dominating functional groups. The average annual phytoplankton density and biomass were (5.46 ± 7.17) × 107 cells/L and 4.80 ± 4.61 mg/L, respectively. The density and biomass of phytoplankton were higher in summer ((14.64 ± 20.34) × 107 cells/L, 10.61 ± 13.16 mg/L) and autumn ((6.79 ± 3.97) × 107 cells/L, 5.57 ± 2.40 mg/L), with the M and H2 of dominant functional groups. The dominant functional groups were N, C, D, J, MP, H2, and M in spring, whereas functional groups C, N, T, and Y dominated in winter. The distribution of phytoplankton community structure and dominant functional groups exhibited significant spatial heterogeneity in the lake, which was consistent with the environmental heterogeneity of the lake and could be classified into four locations. Location I had higher phytoplankton density and biomass than the other three locations. Additionally, dominant functional groups M, C, and H2 were present throughout the lake, and all 13 dominant functional groups were observed in Location II. Our findings suggest that environmental heterogeneity is a key factor influencing the spatial distribution of phytoplankton functional groups in Lake Chaohu.

Integrating ICESat-2 altimetry and machine learning to estimate the seasonal water level and storage variations of national-scale lakes in China

Lakes comprise the largest element of terrestrial surface liquid freshwater bodies, playing an indispensable part in the Earth's water cycle and alleviating floods and droughts. The seasonal variation of lake water level (LWLsv) and storage (LWSsv) reflects the periodic hydrologic fluctuations and related driving forces of the water balances at the basin scale. China, a vastly diverse country that descends from the “Roof of the World” to monsoonal coast zones, hosts a wide distribution of lakes with diverse hydro-climatological and topographic features. Most previous studies focused on monitoring long-term changes of lakes in China, while the seasonality (mostly regarding the lake area) of lake hydrologic dynamics was only investigated for typical lakes or local basins/zones due to the limited spatial coverage and temporal resolution of various observation data. Benefiting from the finer footprints and increased beams of ICESat-2 laser altimeter, we examined the seasonal variations of LWLsv of Chinese lakes (3473 lakes historically larger than 1 km2 during the 1980s–2010s) on a national scale from 2019 to 2021. Then, the machine learning algorithm termed the extreme gradient boosting tree was employed to model the LWLsv of the lakes that were not monitored by ICESat-2. We further quantized the national-scale LWSsv by combining the LWLsv estimates and lake area data. Results show that the mean LWLsv of the 1255 lakes observed by ICESat-2 during 2019–2021 is 0.44 ± 0.07 m. Among them, 1167 lakes have the LWLsv <1 m, and 12 lakes have the LWLsv exceeding 3 m. The accuracy evaluation indicates that the XGBoost model performs well in predicting LWLsv results for unobserved lakes, with the coefficient of determination of 0.76, the mean absolute error of 0.14 m, and the root mean square error of 0.03 m. Overall, the predicted LWLsv of unobserved lakes has a similar spatial pattern to that of the observed lakes. The LWSsv is estimated at 77.29 ± 6.87 Gt in total, but exhibits obvious spatial heterogeneity in China. The Middle and Lower Reaches of Yangtze River Basin and the endorheic Qiangtang Plateau Basin rank the first two contributors of the net LWSsv, which were respectively attributed to the most significant LWLsv changes and the largest lake group area. This national-scale quantification of the LWLsv and LWSsv helps advance our scientific understanding of the seasonal hydrologic behaviors for Chinese lakes in regulating the water cycle and providing a valuable reference for regional water resource management.