Lake Research Articles

Bioresources of lake Mostovoye and ways of their rational use

The ichthyofauna of most water bodies in the Altai Krai is represented by low-value and slow-growing fish. Fish productivity is largely determined by the degree of exploitation of the reservoir and the form of organization of the fishery. Rational fishery in natural reservoirs should ensure the exploitation of the ecosystem of the reservoir as a single whole. Mostovoe Lake is located in the Zavyalovsky and Baevsky districts of the Altai Krai, is one of the largest freshwater lakes in the Altai Territory, belonging to the floodplain of the Kulunda River. The water in the reservoir is of the sulfate-chloride class of the first type, fully meets all fish farming requirements. The collection of ichthyological material was carried out by the method of control catches. The species composition and spatial distribution of fish were studied by setting a set of fixed gill nets in the reservoirs. Information on the size and age structure of populations, catches of the main commercial fish and crayfish in Mostovoe Lake is provided. The magnitude of the fishing effort and the assessment of the state of aquatic bioresources (ichthyofauna) in the reservoir were carried out using one of the expert assessment options — the point systems method. The ichthyofauna of Mostovoe Lake includes six species that are subject to commercial fishing: common pike, roach, silver carp, river perch, common carp (carp), and common pike perch. Of the commercial invertebrates, crayfish is caught. The indicators of the commercial stock and the recommended catch of bioresources in the reservoir were calculated. Recommendations for regulating fisheries based on ichthyological monitoring are proposed. A certain effect for stabilizing the structure of the ichthyocenosis of the reservoir can be made by fishery melioration: the introduction of herbivorous fish — white amur (Ctenopharyngodon idella) and silver carp (Hypophthalmichthys molitrix) for a more complete use of the food base of the lake — phytoplankton and macrophytes. It is necessary to continue monitoring studies of the lake’s winter oxygen regime.

Ubiquitous genome streamlined Acidobacteriota in freshwater environments

Abstract Acidobacteriota are abundant in soil, peatlands and sediments, but their ecology in freshwater environments remains understudied. UBA12189, an Acidobacteriota genus, is an uncultivated, genome-streamlined lineage with small genome size found in aquatic environments, in which detailed genomic analyses are lacking. Here, we analyzed 66 MAGs of UBA12189 (including 1 complete genome) from freshwater lakes and rivers in Europe, North America and Asia. UBA12189 have small genome sizes (< 1.4Mbp), low GC content and a highly diverse pangenome. In freshwater lakes, this bacterial lineage is abundant from the surface waters (epilimnion) down to 300 meters depth (hypolimnion). UBA12189 appears to be free-living from CARD-FISH analysis. When compared to other genome-streamlined bacteria such as Nanopelagicales and Methylopumilus, genome reduction has caused UBA12189 to have a more limited metabolic repertoire in carbon, sulfur and nitrogen metabolisms, limited numbers of membrane transporters, as well as a higher degree of auxotrophy for various amino acids, vitamins and reduced sulfur. Despite having reduced genomes, UBA12189 encodes proteorhodopsin, complete biosynthesis pathways for heme and vitamin K2, cbb3-type cytochrome c oxidases and heme-requiring enzymes. These genes may give a selective advantage during the genome streamlining process. We propose the new genus Acidiparvus, with two new species named “A. lacustris” and “A. fluvialis”. Acidiparvus is the first described genome streamlined lineage under the phylum Acidobacteriota, which is a free-living, slow-growing scavenger in freshwater environments.

Cyanobacteria can benefit from freshwater salinization following the collapse of dominant phytoplankton competitors and zooplankton herbivores

Abstract Freshwater salinization is an increasing threat to lakes worldwide, but despite being a widespread issue, little is known about its impact on biological communities at the base of the food chain. Here we used a mesocosm set‐up coupled with modern high‐frequency sensor technology to identify short‐ and longer‐term responses of phytoplankton to salinization in an oligotrophic lake. We tested the effects of salinization over a gradient of increasing salt concentrations that can be found in natural lakes exposed to road salt contamination (added salt range: from 0 to 1500 mg Cl− L−1). The high‐frequency chlorophyll‐a (chl‐a) fluorescence measurements showed an increasing divergence of chl‐a concentrations along the salinization gradient over time, with substantially lower concentrations at higher salt levels. At the sub‐daily scale, we found a profound suppression of day–night signal cycles with increasing salinity, which could be related to physiological stress due to the impairment of photosynthesis via effects on the photosystem II or potential changes in the active migration of phytoplankton. Community analyses revealed a similar decline pattern for the total phytoplankton biomass and a collapse of the total zooplankton biomass. Interestingly, we found a loss of phytoplankton diversity coupled with a compositional re‐organization involving the loss of dominant green algae but increased biomass of salt‐tolerant cyanobacteria. Altogether, these results suggest that specific cyanobacterial taxa can benefit from freshwater salinization following the collapse of dominant phytoplankton competitors and zooplankton herbivores. The results also highlight the value of autonomous sensor technology to capture novel, small‐scale ecological responses to freshwater salinization, and thereby to track fast changes in primary producer communities.

Detection of Complex Formations in an Inland Lake from Sentinel-2 Images Using Atmospheric Corrections and a Fully Connected Deep Neural Network

The detection of complex formations, initially suspected to be oil spills, is investigated using atmospherically corrected multispectral satellite images and deep learning techniques. Several formations have been detected in an inland lake in Northern Greece. Four atmospheric corrections (ACOLITE, iCOR, Polymer, and C2RCC) that are specifically designed for water applications are examined and implemented on Sentinel-2 multispectral satellite images to eliminate the influence of the atmosphere. Out of the four algorithms, iCOR and ACOLITE are able to depict the formations sufficiently; however, the latter is chosen for further processing due to fewer uncertainties in the depiction of these formations as anomalies across the multispectral range. Furthermore, a number of formations are annotated at the pixel level for the 10 m bands (red, green, blue, and NIR), and a deep neural network (DNN) is trained and validated. Our results show that the four-band configuration provides the best model for the detection of these complex formations. Despite not being necessarily related to oil spills, studying these formations is crucial for environmental monitoring, pollution detection, and the advancement of remote sensing techniques.

Tire wear particles enhance horizontal gene transfer of antibiotic resistance genes in aquatic ecosystems

Microplastics (MPs) have introduced new surfaces for biofilm development and gene exchange among bacteria. We investigated Tire Wear Particles (TWPs) for their involvement in horizontal gene transfer (HGT), particularly in relation to associated metals in the matrices of TWPs. We employed red-fluorescently tagged E. coli strain as a donor with green-fluorescently tagged, broad-host-range plasmid pKJK5, resistant to trimethoprim. As a recipient, we utilized Pseudomonas sp. and a natural lake microbial community. HGT activity on TWPs was determined and compared with that on polystyrene (PS) (with and without metals), and chitosan, which was used as a natural surface. Exposure to TWPs significantly enhanced HGT frequency of antibiotic resistance gene (ARG) from donor to recipient compared to PS and chitosan, and metals of TWPs further promoted HGT. HGT frequency on TWPs with Pseudomonas sp. was found to be 10−3 at 30 °C. in the lake community, it was similarly high already at 25 °C suggesting a higher permissiveness of the natural microbial community towards ARG at lower temperatures. This study sheds light on the potential impact of TWPs in promoting HGT, forming the basis for health risk assessments of TWPs and more generally of MP pollution in various aquatic ecosystems.

What drives the distinct evolution of the Aral Sea and Lake Balkhash? Insights from a novel CD-RF-FA method

Study RegionThe Aral Sea and Lake Balkhash. Study FocusThis study explores the impacts of climate change and human activities on the inflow of the Aral Sea and Lake Balkhash, revealing the different driving factors behind the evolution of inland lakes in arid environments. To achieve this, we propose a novel approach that combines classical seasonal decomposition with Random Forest and Factor Analysis (CD-RF-FA) to quantitatively assess the influences of climate change and human activities on lake inflow. New Hydrological Insights for the RegionDuring the period from 1960 to 1990, anthropogenic factors predominantly influenced the inflow to the lakes, contributing 89.9 %, 91.8 %, and 91.6 % to the Lake Balkhash Basin (BAK), the Syr Darya Basin (SYR), and the Amu Darya Basin (AMU), respectively. However, from 1991 to 2020, the influence of human activities diminished, and climate variables gradually dominated the changes in inflow, contributing 52.2 % and 47.2 % to BAK and SYR, respectively, with upstream inflow being the main driving factor. Additionally, reservoir construction and political factors also played significant roles in the variation of inflow, exerting direct or indirect effects. This study provides crucial insights into the complex interplay of factors affecting inland lakes in arid regions and informs strategies to mitigate the Aral Sea Syndrome.

Are you filtering enough? Unveiling the impact of water sample volumes on eukaryotic microbial community in freshwater lakes

The appropriate volume of filtered water samples is crucial for accurately reflecting microbial community characteristics. Previous research has shown that changes in water sample volumes significantly affect bacterial diversity and the relative abundance of dominant taxa in marine environments. However, the specific impact on freshwater microbial diversity and community structure, particularly for eukaryotic microorganisms, remains unclear. To address this gap, we collected water samples from eutrophic Lake Taihu and mesotrophic Lake Bosten. We filtered the samples through 0.2 μm filters using volumes ranging from 0.1 to 2 L for Lake Taihu and 0.1 to 3.2 L for Lake Bosten. Analysis of 18S rRNA gene amplicons revealed that variations in filtered water sample volume significantly affected the diversity, community structure, and composition of eukaryotic microorganisms. In light of these findings, we recommend using a filtered water sample volume of approximately 0.2 L for eutrophic aquatic ecosystems and 0.8 L for mesotrophic aquatic ecosystems in microbial analyses. These recommendations underscore the importance of selecting the appropriate filtered water sample volume to ensure representative and reliable results in the study of eukaryotic microorganisms in freshwater ecosystems.

Pollution of organophosphorus pesticides in the Dongting Lake, China and its relationship with dissolved organic matter: Occurrence, source identification and risk assessment

The escalating global demand for food and industrialization has placed significant pressure on the integrity and management of inland lake ecosystems. Herein, the organophosphorus pesticides (OPPs) pollution status and their relationship with dissolved organic matter (DOM) in Dongting Lake were investigated to identify the ecological risks and potential sources of OPPs. The total concentrations of 18 detected OPPs were in the range of 13.49–375.24 ng/L, with higher concentration observed in east and west lake regions. Among these, fenthion was the dominant contributor, accounting for 64% of total OPPs, posing significant ecological risk to aquatic organisms. Nearly all of sites showed high combined risk of total OPPs. Parallel factor analysis (PARAFAC) and fluorescence regional integration (FRI) technique showed that DOM was mainly composed of terrestrial humic-like and tryptophan-like substances. Moreover, correlation analysis revealed a close association between DOM optical parameters and OPP concentrations. Specifically, OPPs exhibited a significantly positive correlation with tyrosine-like substances, while displaying a negative correlation with fulvic acid-like substances. These results indicated that OPP concentrations may decrease with increasing humification levels and declining tyrosine-like substance contents. This study underscores the critical role of DOM in assessing the occurrence and sources of OPPs in aquatic environments, providing valuable insights for effective environmental management strategies.

A novel framework reveals anthropogenic stressors of phosphorus polluted river-lake connection water system in Poyang lake basin of China

Poyang lake (PYL), as China's largest freshwater lake, has been suffering from increasing total phosphorus (TP) pollution associated with rapid basinal socio-economic development. However, anthropogenic phosphorus stressors were rarely examined in PYL basin due to its large-scale and complex river-lake connection water system, hampering phosphorus pollution control efforts. In this study, water pollution stress from multiple anthropogenic activities is quantitatively examined in PYL basin based on a newly developed framework coupling grey water footprint (GWF) analysis with the SPARROW model. Results show that the phosphorus source-sink process in PYL basin has been well simulated by SPARROW model quantifying an overall TP delivery rate of 0.39, with catchments closer to PYL showing higher delivery rate of phosphorus (up to over 0.8). The GWF analysis demonstrates that anthropogenic phosphorus sources have imposed much higher pollution stress on PYL than its inflowing rivers, with twelve catchments nearby PYL identified as critical source areas of TP contamination. Agricultural farming, livestock & poultry production, and urban household are recognized as the dominant anthropogenic stressors burdening water environment of PYL. Based on these, policy recommendations are provided for advancing control of the phosphorus pollution stressors. The methodology is effective in refined examination of water pollution sources, which is expected to be applied in other watersheds providing informative diagnosis of water issues especially in lakes.

Reconstructing Tibetan Plateau lake bathymetry using ICESat-2 photon-counting laser altimetry

Lake bathymetry is important for quantifying and characterizing underwater morphology and its geophysical state, which is critical for hydrological and ecological studies. Due primarily to the harsh environment of the Tibetan Plateau, there is a severe lack of lake bathymetry measurements, limiting the accurate estimation of total lake volumes and their evolutions. Here, we propose a novel lake bathymetry reconstruction by combining ICESat-2/ATLAS (Advanced Topography Laser Altimetry System) data with a numerical model. An improved grid-based photon noise removal method is used to address the photon signal buried in the background noise during the local daytime. The developed model was validated for seven lakes on the Tibetan Plateau and showed good agreement between simulated and measured lake volumes, with an average absolute percentage error of 8.0 % for maximum water depth and 19.7 % for lake volume simulations. The model was then utilized to estimate the water volume of other lakes by combining it with the self-affine theory. The lake depths obtained from ICESat-2/ATLAS show good agreement (RMSE = 0.69 m; rRMSE = 10.3 %) with available in-situ measurements for lakes with depths <16.5 m, demonstrating the potential of ICESat-2/ATLAS for improved reconstruction of the bathymetry of clear water inland lakes. Our study reveals for the first time, that the Tibetan Plateau has an estimated total lake water volume of 1043.69 ± 341.31 km3 for 33,477 lakes (>0.01 km2) in 2022. Over 70 % (∼734.8 km3) of the lake water storage is concentrated in the Inner Plateau, with the Yellow River basin accounting for 10.9 % (∼113.9 km3), followed by the Indus River basin with 7.2 % (∼75.1 km3). Our study provides a robust method for estimating total lake volumes where in-situ measurements are scarce and can be extended to other clear water lakes, thus contributing to more accurate global assessments and towards comprehensive quantification of Earth's surface water resources distribution.

Sedimentary processes and patterns in deposits corresponding to freshwater lake-facies of hyperpycnal flow – An experimental study based on flume depositional simulations

Abstract The article establishes a depositional model for lacustrine hyperpycnal flow by examining dynamics, transport factors, and laminae formation. The results show that several typical experimental phenomena such as fluid front mixing, double flow division, underwater leap, water skiing, and “new head” can be observed in the flume experiment. Based on the experimental observation of the flow process, three modes of transport of hyperpycnal flow in freshwater lake basins are summarized: bottom-bed loading, suspended loading, and uplift loading. Further, the change of fluid properties in hyperpycnal flow is summarized in three stages: a high-concentration stage, a low-concentration stage, and an uplifting stage. There are two main factors affecting the long-range transport of hyperpycnal flow: (1) the concentration difference between the head deposits and the ambient water body and (2) shear force of turbulence in the upper part of hyperpycnal flow. The simulation experiments of hyperpycnites laminae show that the laminae change from continuous to intermittent with the increase of the transportation distance. It is clear that the mode of transport of the hyperpycnal flow has a controlling effect on the degree of development of the laminae. Eventually, a depositional model of lake-facies hyperpycnal flow under experimental conditions was constructed.

Simulating lake ice phenology using a coupled atmosphere–lake model at Nam Co, a typical deep alpine lake on the Tibetan Plateau

Abstract. Simulating the ice phenology of deep alpine lakes is important and challenging in coupled atmosphere–lake models. In this study, the Weather Research and Forecasting (WRF) model, coupled with two lake models, the freshwater lake (WRF–FLake) model and the default lake (WRF–CLake) model, was applied to Nam Co, a typical deep alpine lake located in the centre of the Tibetan Plateau, to simulate its lake ice phenology. Due to the large errors in simulating lake ice phenology, related key parameters and parameterizations were improved in the coupled model based on observations and physics-based schemes. By improving the momentum, hydraulic, and thermal roughness length parameterizations, both the WRF–FLake model and the WRF–CLake model reasonably simulated the lake freeze-up date. By improving the key parameters associated with shortwave radiation transfer processes when lake ice exists, both models generally simulated the lake break-up date well. Compared with WRF–CLake without improvements, the coupled model with both revised lake models significantly improved the simulation of lake ice phenology. However, there were still considerable errors in simulating the spatial patterns of freeze-up and break-up dates, implying that significant challenges in simulating the lake ice phenology still exist in representing some important model physics, including lake physics such as grid-scale water circulation and atmospheric processes such as snowfall and surface snow dynamics. Therefore, this work can provide valuable new implications for advancing lake ice phenology simulations in coupled models, and the improved model also has practical application prospects in weather and climate forecasts.

Response of Water Quality to Land Use and Landscape Pattern in the Ganjiang River Watershed.

Analysing the impact of landscape composition and structure on water quality at different scales is of great significance to water quality protection. The aim of this study was to determine scale-dependent impacts of land use/landscape patterns on water quality. The Ganjiang River, the largest water system in the Poyang Lake watershed, the largest freshwater lake in China. The response of water quality to land use and landscape patterns in the Ganjiang River watershed was explored based on land use and water quality data using redundancy and Spearman correlation analyses. Considering upstream monitoring of the entire Ganjiang River watershed; watersheds at the county level administrative region; and 1, 2, 5, 10, 15, 20, and 30 km-radius circular buffer zones, a total of nine scales of land use/landscape patterns that influence water quality in the Ganjiang River watershed were analysed. Results indicated that the county-level scale and the land use type of the 20 km-radius buffer zone upstream of the monitoring site were closely linked to water quality (96.28% and 93.23%, respectively). Among the land use types, construction land and cultivated land were the main output sources of pollutants. Regarding landscape pattern index, the greater the fragmentation of the landscape, the heavier was the water pollution load; the more the patches per unit area, the more stable was the ecosystem and the lower was the pollutant concentration. In addition, the eco-hydrological system of the Ganjiang River watershed was revealed to some extent through multi-angle analysis. These conclusions can serve as a reference for government departments to formulate land management and water quality protection measures.

Isotopic signature of N2O produced during sulfur‐ and thiosulfate‐driven chemoautotrophic denitrification in freshwaters

AbstractChemoautotrophic denitrification plays an important role in nitrogen removal and the formation of a greenhouse gas (N2O) in aquatic environments. Natural stable isotopes support the tracing of nitrogen sources and the identification of biogeochemical processes in field research. However, the isotopic characteristics of N2O produced during chemoautotrophic denitrification have not been investigated so far. In this study, we analyzed isotopic signatures of nitrate and N2O in sulfur‐ and thiosulfate‐dependent denitrifying enrichments obtained from freshwater lakes. Chemoautotrophic denitrification exhibited a nitrate isotope pattern similar to heterotrophic denitrification: the 18ε/15ε‐nitrate followed a ratio close to 1. However, chemoautotrophic denitrification produced N2O with lower δ15N, δ18O, and higher site preference (SP = δ15Nα‐δ15Nβ) values, compared to heterotrophic denitrification. The SP value, approximately 5.1‰, was characteristic in detecting chemoautotrophic denitrification driven by different sulfur forms. δ18O varied with specific electron donors, around 20‰ and 40‰ during sulfur‐ and thiosulfate‐dependent denitrification, respectively. The unique N2O isotope characteristics were likely regulated by nitric oxide reductases of Burkholderiaceae populations during sulfur‐dependent denitrification and Sulfurovum during thiosulfate‐dependent denitrification. These findings improve our understanding of N2O production processes and have important implications for predicting N2O emissions at a greater spatial and temporal resolution.

Sedimentary record of primary productivity changes in a crater lake in Northeast China since the Last Glacial Maximum

High-resolution primary productivity records are valuable for identifying lacustrine ecosystem degradation in the context of long-term climatic variability. In this paper, we analyse primary productivity changes in a seasonally ice-covered crater lake (Lake Tuofengling) in northeast China since the Last Glacial Maximum using biogenic silica content and the carbon preference index of short-chain n-alkanes as proxies. Results show that primary productivity was lower during the cold and dry glacial period, whereas it was higher during the warm and humid Holocene. During the last deglaciation, primary productivity experienced a ∼ 1.5-kyr lagged response to Bølling-Allerød warming, and multiple oscillations during the Younger Dryas. Additionally, the peak productivity of the entire profile also occurred during this period. These fluctuations and the highest primary productivity are suggested to be the result of the combined influences of increased summer temperatures and regional permafrost melting. The current state of primary productivity in Lake Tuofengling is moderate but has been increasing since the abrupt increase in diatom productivity after ∼3 ka B.P. This stage is associated with increased dust deposition and longer ice-free periods under winter-warming conditions. We suggest that longer seasonal stratification under the current warmer winters and increased nutrient concentrations caused by decreased lake level will increase the risk of lake ecosystem degradation in the future.

Terrestrial generalist predators have larger isotopic niches but rely less on aquatic prey at a natural compared to a post-mining lakeshore

The flooded pits from former opencast mining (post-mining lakes) are young aquatic ecosystems often with low primary productivity due to the high acidity. The limited availability of nutrients and simplified aquatic food webs in these artificial lakes may affect the matter fluxes towards food webs in adjacent terrestrial habitats. To understand the impact of emerging prey from a post-mining lake on terrestrial food webs and associated arthropod communities, we compared the emergence and activity of arthropods as well as the isotopic niches of generalist predators and their potential prey between lakeshores of a post-mining and a natural lake. We used aquatic and terrestrial emergence tents to sample potential prey that emerged locally (Collembola and Diptera) and pitfall traps to sample terrestrial arthropod predators (Carabidae and Araneae) from lakeshores. Community and stable isotope (δ13C and δ15N) analyses were performed to compare diversity and isotopic niches of generalist arthropod predators between the natural and post-mining lakeshores. The number of emerging aquatic and terrestrial prey did not differ significantly between lakes, but the δ15N values of aquatic emerging dipterans differed between the two lakes. Predator community diversity did not differ significantly between lakeshores, but generalist predator species from the natural lakeshore generally had larger isotopic niche sizes than the same species at the post-mining lakeshore indicating a more diverse diet. Additional estimates of diet composition suggest that predators at the natural lakeshore utilized aquatic prey to a lesser degree than at the post-mining lake, but still had a more diverse diet.

Assessment of the correlation between environmental variables and the spatial distribution and species structure of testate amoebae (Arcellinida and Euglyphida) in a stratified freshwater lake

Assessment of the correlation between environmental variables and the spatial distribution and species structure of testate amoebae (Arcellinida and Euglyphida) in a stratified freshwater lake

Hydrodynamic driven microplastics in Dongting Lake, China: Quantification of the flux and transportation

Hydrodynamic conditions have a significant effect on the fate of microplastics (MPs). Moreover, research on the relation between hydrodynamic conditions and MPs in freshwater environments is critical and unquantified. In this regard, herein, a methodological framework integrating system monitoring with numerical simulation has been developed and successfully implemented for Dongting Lake, a large freshwater lake fed by multiple rivers. According to time-series monitoring and hydrological data, 199.29/128.50 trillion MP items entered or exited Dongting Lake in 2021. In addition, a coupled numerical model identified four key areas of MP accumulation, which overlap with nature reserves and agricultural zones, posing considerable risks to the ecological gene pool and food security. The quantitative results obtained using the developed framework enable calculation of MP inflow and outflow fluxes and facilitate analysis of MP transportation. Overall, this study provides a scientific basis for preventing and controlling MP pollution in Dongting Lake and offers valuable insights for future research on related issues in freshwater ecosystems.

Satellite algorithms for retrieving dissolved organic carbon concentrations in Chinese lakes

Water quality and the carbon cycle in lakes are strongly related to the concentration of dissolved organic carbon (DOC). Several regional algorithms have been proposed to remotely retrieve lake DOC concentration at a regional scale, but further efforts are needed to reliably retrieve DOC concentration over a large area. Based on bio-optical measurements from 55 lakes across China, this study investigates feasible satellite algorithms for retrieving DOC concentrations from OLCI/Sentinel-3 imagery. The results revealed that the bio-optical characteristics of DOC were different in freshwater and saline lakes. Compared to saline lakes, freshwater lakes had lower DOC concentrations (9.89 ± 3.97 mg/L vs. 32.97 ± 42.07 mg/L) but similar levels of colored dissolved organic matter as indicated by its absorption coefficient at 280 nm (aCDOM(280), 12.8 ± 6.94 1/m vs. 17.15 ± 22.97 1/m). Moreover, DOC concentrations in freshwater lakes were exponentially related to aCDOM(280) (r = 0.74) and linearly correlated with red-to-green reflectance ratios. However, DOC concentration in saline lakes was linearly related to aCDOM(280) (r = 0.93) and exponentially correlated with red-to-blue reflectance ratios. Then, although we discriminated freshwater and saline lakes with a conductivity threshold of 2000 μs/cm, the three commonly used linear regression methods for estimating DOC concentrations still obtained mean absolute percent difference (MAPD) of 55.68–66.44 %. Alternatively, we developed a hybrid machine learning algorithm (MAPD = 18.16 %), that used water reflectance and lake/basin properties to model DOC concentrations in freshwater and saline lakes, respectively. Satellite monitoring of 370 large lakes (> 20 km2) showed that DOC concentration was high in the northwest and low in the southeast of China. This study has implications for dynamic monitoring of DOC concentrations in lakes using satellite imagery.

Different patterns of bacterioplankton in response to inorganic and organic phosphorus inputs in freshwater lakes - a microcosmic study

Phosphorus (P) is a limiting factor in fresh waters and is also the main cause of water eutrophication and deterioration, However, the practical effect of elevated P level on bacterioplankton is less evaluated. In this study, we investigated the bacterioplankton in a 96 hours microcosm experiment with P additions in two forms (organic/inorganic P, OP/IP) and three levels (final conc., 0.040, 0.065 and 0.125 g/L), aiming to find out the response pattern of bacterioplankton in coping with the increasing P levels. Results showed a more dramatic change of water properties and bacterioplankton between P forms (OP and IP) than among the addition levels, and a more remarkable effect of OP addition than the IP. Both OP and IP treatments significantly decreased the water pH, dissolved oxygen (DO), Electrical Conductivity (EC), Nitrate Nitrogen (NO3--N) and Total Organic Carbon (TOC), and reduced the α-diversity of bacterioplankton and relative abundance of Cyanobacteria, but increased the abundance of Proteobacteria. The IP addition decreased Actinobacteria abundance (especially for HgcI) and showed higher denitrification potentials, while the OP addition depressed the Bateroidota and exhibited lowed methylotrophic functions, but such trends decreased with increasing addition concentrations. The network analysis showed that both IP and OP additions increased the proportion of positively correlated edges and reduced the network complexity and stability, but the OP network was more stable than the IP network. The study clarifies the response pattern of bacterioplankton to the P input with different forms and levels, and deepens our understanding of the eutrophication process, which provides a scientific basis for the management and control of freshwater lakes facing eutrophication.