Summer heatwaves promote harmful algal blooms in the Fuchunjiang Reservoir, an important drinking water source.

Extensive outbreaks of harmful algal blooms (HABs) occurred in the Fuchunjiang Reservoir in 2022, a crucial urban drinking water source, coinciding with extreme summer heatwaves. We hypothesize that these heatwaves contributed to HABs formation and expansion. Leveraging Landsat 8 and Sentinel-2 data, we employed clustering and machine learning methods to quantify the HABs distribution and area. Concurrent meteorological and water quality data aided in uncovering the effects of heatwave on HABs. When applying different methods to extract HABs from remote sensing images, random forest (RF) analyses indicated accuracies of 99.3% and 99.8% for Landsat 8 and Sentinel-2 data, respectively, while classification and regression tree (CART) analyses indicated 99.1% and 99.7% accuracies, respectively. Support vector machine (SVM) exhibited lower accuracies (83.5% and 97.4%). Thus RF, given its smaller differences between satellites and high accuracy, was selected for further analysis. Both satellites detected extensive HABs in 2022, with Sentinel-2 recording a peak area of 24.13 km2 (44.6% of cloud-free water area) on August 11, 2022. Increasing trends with amplified durations were observed for summer heatwaves in Jiande and Tonglu around the Fuchunjiang Reservoir. Notably, these areas experienced extreme heatwaves for 63 and 58 days in 2022, respectively, more than double the 1980-2022 average. From June 1 to October 8, 2022, water temperature peaks significantly coincided with expansive HABs and elevated chlorophyll a (Chl-a) concentration from 4.8 µg/L to 119.2 µg/L during the summer heatwaves. Our findings indicated that the reservoir became more HAB-prone during heatwave events, escalating the drinking water safety risk. These results emphasize the challenges faced by reservoir managers in dealing with climate-induced extreme heatwaves and underscore the urgency for heightened attention from water source management departments.

Sediment DNA Records the Critical Transition of Bacterial Communities in the Arid Lake.

It is necessary to predict the critical transition of lake ecosystems due to their abrupt, non-linear effects on social-economic systems. Given the promising application of paleolimnological archives to tracking the historical changes of lake ecosystems, it is speculated that they can also record the lake's critical transition. We studied Lake Dali-Nor in the arid region of Inner Mongolia because of the profound shrinking the lake experienced between the 1300 s and the 1600 s. We reconstructed the succession of bacterial communities from a 140-cm-long sediment core at 4-cm intervals and detected the critical transition. Our results showed that the historical trajectory of bacterial communities from the 1200 s to the 2010s was divided into two alternative states: state1 from 1200 to 1300 s and state2 from 1400 to 2010s. Furthermore, in the late 1300 s, the appearance of a tipping point and critical slowing down implied the existence of a critical transition. By using a multi-decadal time series from the sedimentary core, with general Lotka-Volterra model simulations, local stability analysis found that bacterial communities were the most unstable as they approached the critical transition, suggesting that the collapse of stability triggers the community shift from an equilibrium state to another state. Furthermore, the most unstable community harbored the strongest antagonistic and mutualistic interactions, which may imply the detrimental role of interaction strength on community stability. Collectively, our study showed that sediment DNA can be used to detect the critical transition of lake ecosystems.

Unraveling the impact of climatic warming and wetting on eukaryotic microbial diversity and assembly mechanisms: A 10-year case study in Lake Bosten, NW China.

Over the last six decades, northwest China has undergone a significant climatic shift from "warm-dry" to "warm-wet", profoundly impacting the structures and functions of lake ecosystem across the region. However, the influences of this climatic transition on the diversity patterns, co-occurrence network, and assembly processes of eukaryotic microbial communities in lake ecosystem, along with the underlying mechanisms, remain largely unexplored. To bridge this knowledge gap, our study focused on Lake Bosten, the largest inland freshwater body in China, conducting a comprehensive analysis. Firstly, we examined the dynamics of key water quality parameters in the lake based on long-term monitoring data (1992-2022). Subsequently, we collected 93 water samples spanning two distinctive periods: low water level (WL) and high total dissolved solids (TDS) (PerWLTDS; 2010-2011; attributed to "warm-dry" climate), and high WL and low TDS (PerTDSWL; 2021-2022; associated with "warm-wet" climate). Eukaryotic microorganisms were further investigated using 18S rRNA gene sequencing and various statistical methods. Our findings revealed that climatic warming and wetting significantly increased eukaryotic microbial α-diversity (all Wilcox. test: P<0.05), while simultaneously reducing ß-diversity (all Wilcox. test: P<0.001) and network complexity. Through the two sampling periods, assembly mechanisms of eukaryotic microorganisms were predominantly influenced by dispersal limitation (DL) and drift (DR) within stochastic processes, alongside homogeneous selection (HoS) within deterministic processes. WL played a mediating role in eukaryotic microbial DL and HoS processes in the PerTDSWL, whereas water quality and α-diversity influenced the DL process in the PerWLTDS. Collectively, these results underscore the direct and indirect impacts of "warm-wet" conditions on the eukaryotic microorganisms within Lake Bosten. This study provides valuable insights into the evolutionary dynamics of lake ecosystems under such climatic conditions and aids in predicting the ecological ramifications of global climatic changes.

Eutrophication diminishes bacterioplankton functional dissimilarity and network complexity while enhancing stability: Implications for the management of eutrophic lakes.

Eutrophication is a growing environmental concern in lake ecosystems globally, significantly impacting the structures and ecological functions of bacterioplankton communities and posing a substantial threat to the stability of lake ecosystems. However, the patterns of functional dissimilarity, network complexity, and stability within bacterioplankton communities across different trophic states, along with the underlying mechanisms through which eutrophication influences these aspects, are not well-understood. To bridge this knowledge gap, we collected 88 samples from 34 lakes spanning trophic gradients and investigated bacterioplankton communities using network analysis and multiple statistical methods. Our results reveal that eutrophication, progressing from mesotrophic to hyper-eutrophic states, reduces the putative functional dissimilarity of bacterioplankton, particularly affecting the relative proportions of functional groups such as oxygenic photoautotrophy, phototrophy, and photoautotrophy. Network complexity exhibited a unimodal pattern across increasing trophic states, peaking at mesotrophic states and then decreasing towards hyper-eutrophic conditions, while stability exhibited the opposite pattern (U-shaped), indicating a variation in response to trophic state changes. In essence, eutrophication diminishes network complexity but enhances network stability. Collectively, these findings shed light on the ecological impact of eutrophication on bacterioplankton communities and elucidate the potential mechanisms by which eutrophication drives functional dissimilarity, network complexity and stability within bacterioplankton communities. These insights carry significant implications for the ecological management of eutrophic lakes.

Bacterioplankton diversity and potential health risks in volcanic lakes: A study from Arxan Geopark, China.

Bacterioplankton play a vital role in maintaining the functions and services of lake ecosystems. Understanding the diversity and distribution patterns of bacterioplankton, particularly the presence of potential pathogenic bacterial communities, is crucial for safeguarding human health. In this study, we employed 16S rRNA gene amplicon sequencing to investigate the diversity and geographic patterns of bacterioplankton communities, as well as potential pathogens, in eight volcanic lakes located in the Arxan UNESCO Global Geopark (in the Greater Khingan Mountains of China). Our results revealed that the bacterial communities primarily comprised Bacteroidota (45.3%), Proteobacteria (33.1%), and Actinobacteria (9.0%) at the phylum level. At the genus level, prominent taxa included Flavobacterium (31.5%), Acinetobacter (11.0%), Chryseobacterium (7.9%), and CL500-29 marine group (5.6%). Among the bacterioplankton, we identified 34 pathogen genera (165 amplicon sequence variants [ASVs]), with Acinetobacter (59.8%), Rahnella (18.3%), Brevundimonas (9.6%), and Pseudomonas (5.8%) being the most dominant. Our findings demonstrated distinct biogeographic patterns in the bacterial communities at the local scale, driven by a combination of dispersal limitation and environmental factors influenced by human activities. Notably, approximately 15.3% of the bacterioplankton reads in the Arxan lakes were identified as potential pathogens, underscoring the potential risks to public health in these popular tourist destinations. This study provides the first comprehensive insight into the diversity of bacterioplankton in mountain lake ecosystems affected by high tourist activity, laying the groundwork for effective control measures against bacterial pathogens.

Sediment Bacteria in the Alpine Lake Sayram: Vertical Patterns in Community Composition.

Bacterial communities inhabiting alpine lakes are essential to our understanding of ecosystem processes in a changing climate, but little has been reported about the vertical patterns of sediment bacterial communities in alpine lakes. To address this knowledge gap, we collected the 100 cm long sediment core from the center of Lake Sayram, the largest alpine lake in Xinjiang Uygur autonomous area, China, and used 16S rRNA gene-targeted amplicon sequencing to examine the bacterial populations. The results showed that bacterial diversity, as estimated by the Shannon index, was highest at the surface (6.9849 at 0-4 cm) and gradually decreased with depth up to 3.9983 at 68-72 cm, and then increased to 5.0927 at 96-100 cm. A total of 56 different phyla and 1204 distinct genera were observed in the sediment core of Lake Sayram. The bacterial community structure in the sediment samples from the various layers was dissimilar. The most abundant phyla in alpine Lake Sayram were Proteobacteria, Firmicutes, and Planctomycetes, accounting for 73%, 6%, and 4% of the total reads, respectively; the most abundant genera were Acinetobacter, Hydrogenophaga, and Pseudomonas, accounting for 18%, 12%, and 8% of the total reads, respectively. Furthermore, the relative abundance of Acinetobacter increased with sediment depth, while the relative abundance of Hydrogenophaga and Pseudomonas decreased with sediment depth. Our findings indicated that the nitrate-reducing bacteria (Acinetobacter, Hydrogenophaga, and Pseudomonas) may be prevalent in the sediment core of Lake Sayram. Canonical correspondence analysis showed that carbonate and total organic carbon (TOC) may be the main environmental factors affecting the vertical patterns of bacterial community composition (BCC) in the sediment of Lake Sayram. This work significantly contributes to our understanding of the BCC of sediments from alpine lakes in arid and semiarid regions.

Bacterial community assembly driven by temporal succession rather than spatial heterogeneity in Lake Bosten: a large lake suffering from eutrophication and salinization.

Oligosaline lakes in arid and semi-arid regions play a crucial role in providing essential water resources for local populations. However, limited research exists on the impact of the environment on bacterial community structure in these lakes, co-occurrence patterns and the mechanisms governing bacterial community assembly. This study aims to address this knowledge gap by examining samples collected from five areas of Lake Bosten over four seasons. Using the 16S rRNA gene sequencing method, we identified a total of 510 to 1,005 operational taxonomic units (OTUs) belonging to 37 phyla and 359 genera in Lake Bosten. The major bacterial phyla were Proteobacteria (46.5%), Actinobacteria (25.9%), Bacteroidetes (13.2%), and Cyanobacteria (5.7%), while the major genera were hgcI_clade (12.9%), Limnohabitans (6.2%), and Polynucleobacter (4.7%). Water temperature emerged as the primary driver of these community structure variations on global level. However, when considering only seasonal variations, pH and nitrate were identified as key factors influencing bacterial community structures. Summer differed from other seasons in aspects of seasonal symbiotic patterns of bacterial communities, community assembly and function are different from other seasons. There were notable variations in bacterial community structures between winter and summer. Deterministic processes dominated community assembly, but there was an increase in the proportion of stochastic processes during summer. In summer, the functions related to photosynthesis, nitrogen fixation, and decomposition of organic matter showed higher abundance. Our findings shed light on the response of bacterial communities to environmental changes and the underlying mechanisms of community assembly in oligosaline lakes in arid regions.

Warming reduces microeukaryotic diversity, network complexity and stability.

Unraveling how climate warming affects microorganisms and the underlying mechanisms has been a hot topic in climate change and microbial ecology. To date, many studies have reported microbial responses to climate warming, especially in soil ecosystems, however, knowledge of how warming influences microeukaryotic diversity, network complexity and stability in lake ecosystems, in particular the possible underlying mechanisms, is largely unknown. To address this gap, we conducted 20 mesocosms spanning five temperature scenarios (26 °C, 27.5 °C, 29 °C, 30.5 °C, and 32 °C) in Lake Bosten, a hotspot for studying climate change, and investigated microeukaryotic communities using 18S rRNA gene sequencing. Our results demonstrated that warming, time, and their interactions significantly reduced microeukaryotic α-diversity (two-way ANOVA: P＜0.01). Although warming did not significantly affect microeukaryotic community structure (ANOSIM: P＞0.05), it enhanced species turnover. Microeukaryotic networks exhibited distinct co-occurrence patterns and topological properties across temperature scenarios. Warming reduced network complexity and stability, as well as altered species interactions. Collectively, these findings are likely to have implications for ecological management of lake ecosystems, in particular semi-arid and arid regions, and for predicting ecological consequences of climate change.

Relationships between environmental factors and N-cycling microbes reveal the indirect effect of further eutrophication on denitrification and DNRA in shallow lakes.

Traditional views indicate that eutrophication and subsequent algal blooms favor denitrification and dissimilatory nitrate reduction to ammonium (DNRA) in lake ecosystems. However, lakes tend to show an increasing propensity for inorganic nitrogen (N) limitation as they become more eutrophic. Thus, the influence of further eutrophication on denitrification and DNRA in eutrophic lakes are unclear due to the uncertainty of N availability. To fill this gap, we investigated the genes abundance (AOA, AOB, nirS, nirK and nrfA) and the composition of N-cycling microbes through quantitative PCR and 16S rRNA sequencing analysis, respectively, in 15 shallow eutrophic lakes of the Yangtze-Huaihe River basin, China. The results indicated that denitrification and DNRA rates could be modulated mainly by their functional gene abundances (nirS, nirK and nrfA), followed by the environmental factors (sediment total organic carbon and nitrogen). Denitrification rates significantly increased from slightly to highly eutrophic lakes, but DNRA rates were not. An explanation is that nitrification provided ample nitrate for denitrification, and this cooperative interaction was indicated by the positive correlation of their gene abundances. In addition, Pseudomonas and Anaeromyxobacter was the dominant genus mediated denitrification and DNRA, showing the potential to perform facultative anaerobic and strict anaerobic nitrate reduction, respectively. High level of dissolved oxygen might favor the facultatively aerobic denitrifiers over the obligately anaerobic fermentative DNRA bacteria in these shallow lakes. Chlorophyll a had a weak but positive effect on the gene abundances for nitrification (AOA and AOB). Further eutrophication had an indirect effect on denitrification and DNRA rates through modulating the genes abundances of N-cycling microbes.

The collapse and re-establishment of stability regulate the gradual transition of bacterial communities from macrophytes- to phytoplankton-dominated types in a large eutrophic lake.

Eutrophic lakes often exhibit two alternative types: macrophytes-dominated (MD) and phytoplankton-dominated (PD). However, the nature of bacterial community types that whether the transition from the MD to the PD types occurs in a gradual or abrupt manner remains hotly debated. Further, the theoretical recognition that stability regulates the transition of bacterial community types remains qualitative. To address these issues, we divided the transition of bacterial communities along a trophic gradient into 12 successional stages, ranging from the MD to the PD types. Results showed that 12 states were clustered into three distinct regimes: MD type, intermediate transitional type and PD type. Bacterial communities were not different between consecutive stages, suggesting that the transition of alternative types occurs in a continuous gradient. At the same time, the stability of bacterial communities was significantly lower in the intermediate type than in the MD or PD types, highlighting that the collapse and re-establishment of community stability regulate the transition. Further, our results showed that the high complexity of taxon interactions and strong stochastic processes disrupt the stability. Ultimately, this study enables deeper insights into understanding the alternative types of microbial communities in the view of community stability.

Climate Change Causes Salinity To Become Determinant in Shaping the Microeukaryotic Spatial Distribution among the Lakes of the Inner Mongolia-Xinjiang Plateau.

Climate change greatly affects lake microorganisms in arid and semiarid zones, which alters ecosystem functions and the ecological security of lakes. However, the responses of lake microorganisms, especially microeukaryotes, to climate change are poorly understood. Here, using 18S ribosomal RNA (rRNA) high-throughput sequencing, we investigated the distribution patterns of microeukaryotic communities and whether and how climate change directly or indirectly affected the microeukaryotic communities on the Inner Mongolia-Xinjiang Plateau. Our results showed that climate change, as the main driving force of lake change, drives salinity to become a determinant of the microeukaryotic community among the lakes of the Inner Mongolia-Xinjiang Plateau. Salinity shapes the diversity and trophic level of the microeukaryotic community and further affects lake carbon cycling. Co-occurrence network analysis further revealed that increasing salinity reduced the complexity but improved the stability of microeukaryotic communities and changed ecological relationships. Meanwhile, increasing salinity enhanced the importance of deterministic processes in microeukaryotic community assembly, and the dominance of stochastic processes in freshwater lakes transformed into deterministic processes in salt lakes. Furthermore, we established lake biomonitoring and climate sentinel models by integrating microeukaryotic information, which would provide substantial improvements to our predictive ability of lake responses to climate change. IMPORTANCE Our findings have important implications for understanding the distribution patterns and the driving mechanisms of microeukaryotic communities among the lakes of the Inner Mongolia-Xinjiang Plateau and whether and how climate change directly or indirectly affects microeukaryotic communities. Our study also establishes the groundwork to use the lake microbiome for the assessment of aquatic ecological health and climate change, which is critical for ecosystem management and for projecting the ecological consequences of future climate warming.

Bacterial community composition of the sediment in Sayram Lake, an alpine lake in the arid northwest of China.

Sediment bacterial communities play a critical role in biogeochemical cycling in alpine lake ecosystems. However, little is known about the sediment microbial communities in these lakes. In this study, the bacterial community composition (BCC) and their relationships with environmental factors of the sediment in Sayram Lake, the largest alpine and cold-water inland lake, China was analyzed using Illumina MiSeq sequencing. In total, we obtained 618,271 high quality sequences. The results showed that the bacterial communities with 30 phyla and 546 genera, were spread out among the 5 furface sediment samples, respectively. The communities were dominated by Proteobacteria, Acidobacteria, Planctomycetes, Gemmatimonadetes, Chloroflexi, Actinobacteria, Verrucomicrobia and Bacteroidetes, accounting for 48.15 ± 8.10%, 11.23 ± 3.10%, 8.42 ± 2.15%, 8.37 ± 2.26%, 7.40 ± 3.05%, 5.62 ± 1.25%, 4.18 ± 2.12% and 2.24 ± 1.10% of the total reads, respectively. At the genus level, the communities were dominated by Aquabacterium, Pseudomonas, Woeseia, MND1, Ignavibacterium and Truepera, accounting for 7.89% ± 8.24%, 2.32% ± 1.05%, 2.14% ± 0.94%, 2% ± 1.22%, 0.94% ± 0.14% and 0.80% ± 0.14% of the total reads, respectively. Statistical analyses showed the similarity of the sediment bacterial communities at our field sites was considerably low, far below 35%, and total organic carbon (TOC) was the dominant environmental factor affecting the spatial changes of BCC in the sediment. Thus, this study greatly improving our understanding of the microbial ecology of alpine lake in the arid and semi-arid ecosystems today so seriously threatened.

Climate-induced salinization may lead to increased lake nitrogen retention.

Salinization caused by climate change and nitrogen (N) pollution are both important environmental threats for inland lakes. However, evaluating their interactive effects continues to be challenging. Here, field observation and microcosmic experiments were conducted in six lakes of East Asia with the different salinity and climate characteristics, to explore the response of the key N cycle processes related to N fate to the climate-induced change in salinity. The results indicated that increased salinity inhibited denitrification, which was the outcome of two cumulative effects: the long-term microbial adaptation effect and the direct salinity stress. Whereas increased salinity had unsignificant or positive effects on dissimilatory nitrate reduction to ammonium. It had caused that N retention capacity is relatively stronger in saline than freshwater lakes. Inland lakes are long-term basin-wide integrators of climatic conditions that drying (salinization) and wetting (desalination) with climate change. In semi-arid regions of East Asia, lake shrinkage, salinization and increasing temperature driven by climate warming and drying may exert a negative impact on N pollution through concentrating, decreasing denitrification and increasing ammonium release from sediment. The threat of climate change on these lakes is not just the quantity of water, but its quality.

Effects of wind-wave disturbance and nutrient addition on aquatic bacterial diversity, community composition, and co-occurrence patterns: A mesocosm study.

Wind-wave disturbance and nutrient input are the major environmental factors that shape bacterial diversity and community composition in lakes. However, knowledge of bacteria as bio-indicators' synergistic response to disturbance patterns and nutrient addition is still poor. To address this knowledge gap, we conducted a mesocosm experiment over 21 days, and collected 90 water samples from tanks under six different patterns of disturbance and nutrient addition; we explored the bacterial communities using high-throughput 16S rRNA gene sequencing. We found significantly increased bacterial diversity in continuously disturbed conditions and in intermittently disturbed conditions, and significantly decreased bacterial diversity under the synergistic effect of disturbances and nutrients. Bacterial community composition (BCC) under conditions of disturbance and nutrient addition exhibited different variations. However, there were no significant differences in BCC between continuously and intermittently disturbed mesocosms. Co-occurrence networks analysis showed that the proportion of positive correlations among edges in nutrient addition conditions were significantly higher than that in disturbed condition, indicating that nutrient input may increase the proportion of niche overlap, and enhance positive interactions among bacteria. Meanwhile, the co-occurrence patterns between algal and bacterial communities suggested shared environmental preferences or potential interactions among these two groups. Our study provides a new insight into the restoration of shallow eutrophic lake ecosystems. Moreover, the different distribution patterns of bacterial community act as ecological indicators of response to disturbances and nutrient input.

Contrasting diversity patterns and community assembly mechanisms of bacterioplankton among different aquatic habitats in Lake Taihu, a large eutrophic shallow lake in China.

Eutrophication leads to the degradation of lake habitat types from macrophyte-dominated habitats (MDH) to algae-dominated habitats (ADH), which is a common environmental problem faced by many lakes. However, the variations in diversities and community assembly processes of bacterioplankton in the process of lake eutrophication have not been thoroughly elucidated. Here, we contrasted bacterial diversity patterns and processes of community assembly among ADH, MDH, and other habitats (OH) of Lake Taihu, a large shallow eutrophic lake in China with strong wind-induced disturbances. We found that the bacterial diversity patterns and potential functions between ADH and MDH were significantly different. Moreover, the contributions of purely environmental variables to the bacterial diversity patterns of all habitat types were much higher than those of spatial variables. However, the relative importance of stochasticity in the bacterial community assembly of each habitat type was much higher than that of determinism. Intriguingly, 'undominated' stochastic processes shape the diversity patterns of bacterioplankton in ADH, MDH, and OH of Lake Taihu. These findings demonstrate that the degradation of lake habitats caused by eutrophication can profoundly change the diversity and potential function patterns of the bacterioplankton community in lake ecosystems. Although the distinct diversity patterns of the bacterioplankton among the different aquatic habitats in Lake Taihu can be affected by deterministic processes (local environmental variables), they were dominated by stochastic processes (drift). Our study confirms that strong, disordered, wind-induced disturbances in shallow lakes could lead to strong hydrologic mixing, thus increasing the randomness of bacterial community assembly in each habitat.

Similar assembly mechanisms but distinct co-occurrence patterns of free-living vs. particle-attached bacterial communities across different habitats and seasons in shallow, eutrophic Lake Taihu.

Eutrophication due to nitrogen and phosphorus input is an increasing problem in lake ecosystems. Free-living (FL) and particle-attached (PA) bacterial communities play a primary role in mediating biogeochemical processes in these lakes and in responding to eutrophication. However, knowledge of factors governing function, assembly mechanisms, and co-occurrence patterns of these communities remain poorly understood and are key challenges in microbial ecology. To address this knowledge gap, we collected 96 samples from Lake Taihu across four seasons and investigated the bacterial community using 16S rRNA gene sequencing. Our results demonstrate that the α-diversity, ß-diversity, community composition, and functional composition of FL and PA bacterial communities exhibited differing spatiotemporal dynamics. FL and PA bacterial communities displayed similar distance-decay relationships across seasons. Deterministic processes (i.e., environmental filtering and species interaction) were the primary factors shaping community assembly in both FL and PA bacteria. Similar environmental factors shaped bacterial community structure while different environmental factors drove bacterial functional composition. Habitat filtering influenced enrichment of bacteria within specific functional groups. Among them, the FL bacterial community appeared to play a critical role in methane-utilization, whereas the PA bacteria contributed more to biogeochemical cycling of carbon. FL and PA bacterial communities exhibited distinct co-occurrence pattern across different seasons. In the FL network, Methylotenera and Methylophilaceae were identified as keystone taxa, while Burkholderiaceae and the hgcI clade were keystone taxa in the PA network. The PA bacterial community appeared to possess greater stability in the face of environmental change than did FL counterparts. These results broaden our knowledge of the driving factors, co-occurrence patterns, and assembly processes in FL and PA bacterial communities in eutrophic ecosystems and provide improved insight into the underlying mechanisms responsible for these results.

Salinity-Linked Denitrification Potential in Endorheic Lake Bosten (China) and Its Sensitivity to Climate Change.

Endorheic lakes in arid regions of Northwest China are generally vulnerable and sensitive to accelerated climate change and extensive human activities. Therefore, a better understanding of the self-purification capacity of ecosystems, such as denitrification, is necessary to effectively protect these water resources. In the present study, we measured unamended and amended denitrification rates of Lake Bosten by adding the ambient and extra nitrate isotopes in slurry incubations. Meanwhile, we investigated the abundances and community structure of nitrous oxide-reducing microorganisms using qPCR and high-throughput sequencing, respectively, in the surface sediments of Lake Bosten to study denitrification potential in endorheic lakes of arid regions as well as the response of those denitrifiers to climatically induced changes in lake environments. Amended denitrification rates increased by one order of magnitude compared to unamended rates in Lake Bosten. The great discrepancy between unamended and amended rates was attributed to low nitrate availability, indicating that Lake Bosten is not operating at maximum capacity of denitrification. Salinity shaped the spatial heterogeneity of denitrification potential through changes in the abundances and species diversity of denitrifiers. Climate change had a positive effect on the water quality of Lake Bosten so far, through increased runoff, decreased salinity, and enhanced denitrification. But the long-term trajectories of water quality are difficult to predict alongside future glacier shrinkage and decreased snow cover.

Effects of climate change and anthropogenic activities on lake environmental dynamics: A case study in Lake Bosten Catchment, NW China.

Arid and semiarid regions account for âˆ¼ 40% of the world's land area. Rivers and lakes in these regions provide sparse, but valuable, water resources for the fragile environments, and play a vital role in the development and sustainability of local societies. During the late 1980s, the climate of arid and semiarid northwest China dramatically changed from "warm-dry" to "warm-wet". Understanding how these environmental changes and anthropogenic activities affect water quantity and quality is critically important for protecting aquatic ecosystems and determining the best use of freshwater resources. Lake Bosten is the largest inland freshwater lake in NW China and has experienced inter-conversion between freshwater and brackish status. Herein, we explored the long-term water level and salinity trends in Lake Bosten from 1958 to 2019. During the past 62 years, the water level and salinity of Lake Bosten exhibited inverse "W-shaped" and "M-shaped" patterns, respectively. Partial least squares path modeling (PLS-PM) suggested that the decreasing water level and salinization during 1958-1986 were mainly caused by anthropogenic activities, while the variations in water level and salinity during 1987-2019 were mainly affected by climate change. The transformation of anthropogenic activities and climate change is beneficial for sustainable freshwater management in the Lake Bosten Catchment. Our findings highlight the benefit of monitoring aquatic environmental changes in arid and semi-arid regions over the long-term for the purpose of fostering a balance between socioeconomic development and ecological protection of the lake environment.

Regional-scale investigation of the molecular weight distribution and metal-binding behavior of dissolved organic matter from a shallow macrophytic lake using multispectral techniques.

In this work, based on excitation-emission matrix spectroscopy combined with parallel factor analysis (EEM-FARAFAC) and two-dimensional correlation analysis of synchronous fluorescence spectroscopy, Fourier transform infrared spectroscopy, and combination of two spectra (2D-SF-COS, 2D-FTIR-COS, and Hetero-2D-COS), the characteristics and metal-binding behaviors of DOM in Dongping Lake were explored for molecular weight (MW), fluorescence components, and functional groups. The results showed that the entire lake was governed by protein-like materials with low MW(< 1 kDa). The complexation occurred preferentially in protein-like materials for bulk DOM after adding copper (Cu2+) and lead (Pb2+), which were changed by fractionation for MW. The active points were aliphatic C－OH for DOM-Cu and phenol －OH or polysaccharide for DOM-Pb from 2D-FTIR-COS. The protein-like components possessed higher LogK than humic-like component during binding to Cu2+ or Pb2+. Moreover, the complexing affinities of DOM-Cu (LogKCu: 3.26 ± 0.87-4.04 ± 0.49) were higher than those of DOM-Pb (LogKPb: 2.66 ± 0.52-3.78 ± 0.36). On a spatial scale, high LogKCu and LogKPb were found in the center and entrance of the lake, respectively. Humic-like component C2 in the LMW fraction possessed a stronger binding capacity with Cu2+. This study affords new insights into the migration and conversion of HMs in lakes.

Salinity Is a Key Determinant for the Microeukaryotic Community in Lake Ecosystems of the Inner Mongolia Plateau, China.

The arid and semiarid areas experienced remarkable lake shrinkage during recent decades due to intensive human activities and climate change, which would result in unprecedented changes of microeukaryotic communities. However, little is known about how climate change affects the structure and ecological mechanisms of microeukaryotic communities in this area. Here, we used an 18S rRNA gene-based high-throughput sequencing approach to explore the structure, interspecies interaction, and assembly processes of the microeukaryotic community in lake ecosystems of the Inner Mongolia Plateau. As a direct result of climate change, salinity has become the key determinant of the lacustrine microeukaryotic community in this region. The microeukaryotic community in this ecosystem can be divided into three groups: salt (Lake Daihai), brackish (Lake Dalinuoer) and freshwater lakes. Co-occurrence network analysis revealed that salinity shapes the interspecies interactions of the microeukaryotic community. This causes interspecies interactions to change from antagonistic to cooperative with an increase in salinity. Phylogenetic-based ß-nearest taxon distance analyses revealed that stochastic processes mainly dominated the microeukaryotic community assembly in lake ecosystems of the Inner Mongolia Plateau, and salinity stress drove the assembly processes of the microeukaryotic community from stochastic to deterministic. Overall, these findings expand the current understanding of interspecies interactions and assembly processes of microeukaryotic communities during climate change in lake ecosystems of the Inner Mongolia Plateau.