Pulses outweigh cumulative effects of water diversion from river to lake on lacustrine phytoplankton communities.

Due to the allochthonous input of nutrients and species, the cumulative effects of water diversion on water-receiving lakes deserve attention. Taking the water diversion project from the Yangtze River to Lake Taihu (WDYT) as an example, we explored the temporal effects of WDYT on the phytoplankton community and physicochemical habitat of Lake Taihu in autumn and winter from 2013 to 2018. Although the short-term diversion significantly increased the risk of importing nutrients, the relatively high quality of the diversion water compared with other inflow rivers had improved the water quality of the water-receiving lake region. The seasonal water diversion significantly increased phytoplankton diversity and community network complexity and reshaped the lacustrine community to be diatom-dominated with their relative proportions of 24.1-64.9% during water diversion periods. The contributions of physicochemical habitat changes induced by water diversion to variations in phytoplankton communities were 24.0-28.0%. The differences in phytoplankton diversity, community composition and physicochemical habitat in the water-receiving lake region between the diversion and non-diversion years were more evident than those between the non-diversion years in the same season, when comparing the multivariate dispersion indices among them. However, the lacustrine phytoplankton community during non-diversion periods still has not been essentially altered after several years of diversion, so the pulse effects of short-term water diversion were more obvious than the long-term cumulative impacts. Better control of allochthonous nutrients, appropriate increase in inflow water, adhering to the long-term operation, should be effective to enhance ecological benefits of such water diversion projects.

Geographic Patterns of Bacterioplankton among Lakes of the Middle and Lower Reaches of the Yangtze River Basin, China.

The revolution of molecular techniques has revealed that the composition of natural bacterial communities normally includes a few abundant taxa and many rare taxa. Unraveling the mechanisms underlying the spatial assembly process of both abundant and rare bacterial taxa has become a central goal in microbial ecology. Here, we used high-throughput sequencing to explore geographic patterns and the relative importance of ecological processes in the assembly of abundant and rare bacterial subcommunities from 25 lakes across the middle and lower reaches of Yangtze River basin (MLYB), located in Southeast China, where most of the lakes are interconnected by river networks. We found similar biogeographic patterns of abundant and rare subcommunities which could significantly distinguish the community compositions of the two lake groups that were far from each other but which could not distinguish the community compositions of the nearby lakes. Both abundant and rare bacteria followed a strong distance-decay relationship. These findings suggest that the interconnectivity between lakes homogenizes the bacterial communities in local areas, and the abundant and rare taxa therein may be affected by the same ecological process. In addition, based on the measured environmental variables, the deterministic processes explain a small fraction of variation within both abundant and rare subcommunities, while both neutral and null models revealed a high stochasticity ratio for the spatial distribution patterns of both abundant and rare taxa. These findings indicate that the stochastic processes exhibited a greater influence on both abundant and rare bacterial subcommunity assemblies among interconnected lakes.IMPORTANCE The middle and lower Yangtze Plain is a typical floodplain in which many lakes connect with each other, especially in the wet season. More importantly, with the frequent change of regional water level in the wet season, there is a mutual hydrodynamic exchange among these lakes. The microbial biogeography among these interconnected lakes is still poorly understood. This study aims to unravel the mechanisms underlying the assembly process of abundant and rare bacteria among the interconnected lakes in the middle and lower Yangtze Plain. Our findings will provide a deeper understanding of the biogeographic patterns of rare and abundant bacterial taxa and their determined processes among interconnected aquatic habitats.

Lacustrine micro-ecosystem responses to the inflow discharge gradient of water diversion from Yangtze River to Lake Taihu.

Water diversion project is always taken as the emergency and effective engineering measure to deal with the cyanobacterial blooms in eutrophic lakes. The inflow discharge and duration are the critical parameters influencing the effects and costs of the water diversion activities. Due to the impacts of meteorological and hydrological factors such as precipitation and wind-wave currents, the environmental influence of water diversion on shallow eutrophic lakes is always unclear. To explore the quantitative relationships among inflow discharges, duration and ecological parameters in water-receiving lakes, the typical water diversion engineering-Water Diversion Project from Yangtze River to Lake Taihu was taken as an example and the mesocosm experiment modeling the micro-ecosystem of the water-receiving Meiliang Bay in Lake Taihu was conducted with five groups of inflow discharges according to the practical discharges of the main river channel-Wangyu River. Each micro-ecosystem had a volume of 15 L and was studied for a period of 30 days (25 days for the water diversion period and 5 days for the stop period). The results showed that the inflow discharges had different extents of impact on the physicochemical and biological characteristics of the micro-ecosystems. The concentrations of total dissolved solids, total nitrogen, nitrate, active silicate and bacterial abundance in the experimental groups (inflow discharges > 100 m3/s) were all decreased compared with the control group, with the lowest values in the period of 10-15 days. During the stop period, the concentrations of sensitive biotic and abiotic parameters were all recovered with different extents and different from the initial state of this experiment, which revealed that the effects of the short-term water diversion on lake ecosystems were resilient and durable. There were quantitative relationships among the inflow discharge, content interpolation and variation in water nutrients, with different relationships in different periods of the water diversion. The influence of water diversion on lake ecosystems was not only related to the direct impacts of allochthonous inputs, but also with the indirect effects of internal habitat variation in lakes.

Comparative analysis of alkaline phosphatase-encoding genes (phoX) in two contrasting zones of Lake Taihu.

Limnetic habitats that are dominated by either algae or macrophytes represent the 2 dominant ecosystems in shallow lakes. We assessed seasonal variations in the diversity and abundance of alkaline phosphate-encoding genes (phoX) in these 2 zones of Lake Taihu, which is a large, shallow, eutrophic lake in China. There was no significant difference in seasonal mean phoX diversity between the 2 zones, whereas the seasonal mean phoX abundance in the macrophyte-dominated region was higher than that in the algae-dominated region. The bulk of the genotypes in the 2 regions were most similar to the alphaproteobacterial and betaproteobacterial phoX. Genotypes most similar to phoX affiliated with Betaproteobacteria were present with greater diversity in the macrophyte-dominated zone than in the algae-dominated zone. In the algae-dominated zone, the relative proportion of genotypes most similar to cyanobacterial phoX was highest (38.8%) in summer. In addition to the different genotype structures and environmental factors between the 2 stable states, the lower gene abundances and higher alkaline phosphatase activities in Meiliang Bay in summer than those in Xukou Bay reveals different organophosphate-mineralizing modes in these 2 contrasting habitats.

Recovery of novel alkaline phosphatase-encoding genes (phoX) from eutrophic Lake Taihu.

To expand current knowledge on the molecular aspects of alkaline phosphatase PhoX in shallow eutrophic freshwaters, we investigated the genetic diversity and abundance of the PhoX-encoding gene (phoX) in 4 ecological regions in Lake Taihu, China, following a gradient in total phosphorus concentrations ranging from hypereutrophic to mesotrophic. Bacterial phoX was heterogeneously distributed with the highest diversity in the eutrophic regions and the highest abundance in the mesotrophic Xukou Bay. The concentrations of total phosphorus and enzymatically hydrolyzable phosphorus determined the distribution of bacterial phoX in Lake Taihu. Most (70.8%) of the phoX-translated proteins had <90% similarity to the PhoX proteins in the GenBank database, suggesting the presence of novel phoX genotypes in Lake Taihu. The low overlap in phoX genotypes (15.8%) between Lake Taihu and some marine ecosystems, and the dominance of the translated proteins most similar to the Alphaproteobacteria-affiliated PhoX, demonstrate the uniqueness of PhoX in eutrophic freshwaters.

An ultrasonic method for separation of epiphytic microbes from freshwater submerged macrophytes.

Epiphytic microbes are common inhabitants of freshwater submerged macrophytes, which play an important role in aquatic ecosystems. An important precondition for studying the epiphytic microbes is having an effective method of separating the attached microbes from the host macrophytes. We developed an ultrasound-based method for separating epiphytic microbes from freshwater submerged macrophytes, optimized the conditions of ultrasonic separation with an orthogonal experimental design, and compared the optimized ultrasonic method with manual separation. This method can be particularly useful for freshwater submerged macrophytes having a complex morphology.

Bacterial community changes along a salinity gradient in a Chinese wetland.

We analyzed the composition and diversity of a bacterial community to determine its response to increasing salinity in the Xiangsi Lake wetland in the arid region of northwest China. We studied 12 sites, ranging from freshwater to saltwater habitats, using polymerase chain reaction (PCR)-based terminal restriction fragment length polymorphism (T-RFLP) and sequencing of the 16S rRNA genes of 5 selected samples. Cluster analysis and phylogenetic analysis revealed that the bacterial community changed significantly in response to increased salinity within the small-scale wetland (50.8 km(2)). Detailed analysis showed that (i) Betaproteobacteria can maintain balanced growth over a salinity range (from 0.34 to 6.86 g/L) through intergenus changes in community structure, followed by a sharp decrease in relative abundance (from 62.2% to 16.0%) when salinity reaches 26.18 g/L; (ii) salt-sensitive and halophobic taxa were progressively replaced by halotolerant and halophilic taxa with increasing salinity; (iii) bacterial diversity was lowest at intermediate salinity levels (6.86 g/L); and (iv) an increasing percentage of unclassified bacterial taxa were found with increasing salinity. This study has implications to improve understanding of bacterial community response to water salinization.

The response of epiphytic microbes to habitat and growth status of Potamogeton malaianus Miq. in Lake Taihu.

To investigate the effects of different habitats and plant growth status on abundance, biomass and community structure of epiphytic microbes, Potamogeton malaianus Miq. at two different habitats (Gonghu Bay and East Taihu) in Lake Taihu were collected in June, August and November (corresponding to the period of development of submerged macrophytes). The relative abundance of major epiphytic algae groups was determined with high performance liquid chromatography (HPLC), and the structures and dynamics of epiphytic bacteria were assessed by terminal restriction fragment length polymorphism (T-RFLP) analysis. Results showed that the biomass of epiphytic microbes was not significant difference between the two sites, and the analysis of similarity found no significant intra-lake heterogeneity in community structure, but the temporal heterogeneity of epiphytic microbes was significant, which linked to the growth state of submerged macrophytes and water temperature. The difference in community structure between June and August was larger than that between August and November at each site, indicating that the growth status of submerged macrophytes has a greater impact on the community structure of epiphytic microbes than the seasonal variation of environmental conditions.

Decomposition of Microcystis blooms: implications for the structure of the sediment bacterial community, as assessed by a mesocosm experiment in Lake Taihu, China.

The effect of decomposition of Microcystis blooms on the sediment bacterial communities was investigated in a 14-day mesocosm experiments under dark and anoxic condition with three differing levels of Microcystis spp. biomass (from 20 to 2000 µg L(-1)) as measured by chlorophyll-a (Chl-a) concentration in the water column. Sediment samples were collected on days 0 and 14 for bacterial community composition (BCC) analysis, based on rapid decreases in the Chl-a concentration of water column. The BCC was determined by denaturing gradient gel electrophoresis and sequencing of predominant bands. The results showed that after Microcystis decomposition (day 14), the bacterial phylotype diversity in the sediment increased in enclosures with added Microcystis, and the relative abundance of bacteria affiliated with Bacteroidetes and Verrucomicrobia strongly increased. Canonical correspondence analysis showed that organic matter and Chl-a contributed significantly to the changes in sediment bacterial communities during Microcystis decomposition. The present results demonstrate Microcystis decomposition may directly and indirectly influence the BCC of the sediment.

Occurrence of microplastic pollution in rivers globally: Driving factors of distribution and ecological risk assessment.

Microplastics, as global emerging pollutants, have received significant attention worldwide due to their ubiquitous presence in the rivers. However, there is still a lack of clarity on the occurrence, driving factors, and ecological risks of microplastics in rivers worldwide. In this study, a global microplastic dataset based on 862 water samples and 445 sediment samples obtained from 63 articles was constructed, which revealed the temporal and spatial distribution of abundance and morphological characteristics of microplastics in rivers across the globe. In global rivers, the abundance of MPs in both water and sediment spans across 10 and 4 orders of magnitude, respectively. The MP comprehensive diversity index based on the physical morphological characteristics of MPs indicated a significant positive correlation between the pollution sources of MPs in different environmental media. Based on the data was aligned to the full-scale MPs, a novel framework was provided to evaluate the ecological risk of MPs and the interaction effects between the influencing factors driving the distribution characteristics of MPs in rivers around the world. The results obtained demonstrated a wide variation in the key driving factors affecting the distribution of microplastics in different environmental media (water and sediment) in rivers globally. The diversity indices of the morphological characteristics of MPs in densely populated areas of lower-middle income countries in Asia were significantly higher, implying that the sources of microplastics in these regions are more complex and extensive. More than half of the rivers are exposed to potential ecological risks of MPs; however, microplastics may pose only immediate risks to aquatic species in Burigang River, Bangladesh. This can provide valuable insights for formulating more effective scientific strategies for the management of MP pollution in rivers.

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.

Structural changes of the sediment bacterial community in Meiliang Bay of Lake Taihu, China, during typhoon Morakot, 2009.

We investigated changes in bacterial communities of the sediment in a large, shallow, eutrophic, freshwater Lake Taihu, China, during typhoon Morakot (August 7 to 13, 2009). Based on cluster analysis of the DGGE banding patterns, bacterial communities in different sediment samples were very similar to each other. However, samples from the middle period of the typhoon were different from those of the early and late periods of the typhoon. Two bacterial groups, Bacteroidetes and Nitrospirae, rapidly appeared or increased in the sediment samples of the middle period of the typhoon, due to the strong turbulence in the water column caused by typhoon resulted in the exchange of surface sediment with a high level of organic matter with the water column, and severe disturbance to the anaerobic layer of the sediments. Redundancy analysis showed that organic matter contributed significantly to the changes in sediment bacterial communities during the typhoon. Our study demonstrated that the response of sediment bacterial communities to the typhoon event was very rapid but of short duration.

Comparing sediment bacterial communities in the macrophyte-dominated and algae-dominated areas of eutrophic Lake Taihu, China.

Bacterial community structure and the effects of several environmental factors on bacterial community distribution were investigated in the sediment of the macrophyte-dominated and algae-dominated areas in a large, shallow, eutrophic freshwater lake (Lake Taihu, China). Surface sediment samples were collected at 6 sampling sites (3 sites from each of the 2 areas) on 15 February and 15 August 2009. Based on cluster analysis of the DGGE banding patterns, there were significant seasonal variations in the structure of the sediment bacterial community in the macrophyte- and algae-dominated areas, and site-specific variation within an area and between 2 areas. However, there were no significant between-area variations due to the large within-area variation. Analysis of DNA sequences showed that there were differences in the species composition of the sediment bacteria between the macrophyte- and algae-dominated area clone libraries. In the macrophyte-dominated area library, the bacterial community was dominated by Deltaproteobacteria, Verrucomicrobia, Acidobacteria, Bacteroidetes, Gammaproteobacteria, and Betaproteobacteria. OP10 was found in the library of this area but not in the algae-dominated area library. The algae-dominated area library was dominated by Betaproteobacteria, Deltaproteobacteria, Gammaproteobacteria, and Acidobacteria. Cyanobacteria, Alphaproteobacteria, and Planctomycetes were found in this area library but not in the macrophyte-dominated area library. Canonical correspondence analysis demonstrated that total phosphorus and water temperature were the dominant environmental factors affecting bacterial community composition in the sediment.

Lake water-level fluctuation forecasting using machine learning models: a systematic review.

Lake water-level fluctuation is a complex and dynamic process, characterized by high stochasticity and nonlinearity, and difficult to model and forecast. In recent years, applications of machine learning (ML) models have yielded substantial progress in forecasting lake water-level fluctuations. This paper presents a comprehensive review of the applications of ML models for modeling water-level dynamics in lakes. Among the many existing ML models, seven popular ML model types are reviewed: (1) artificial neural network (ANN); (2) support vector machine (SVM); (3) artificial neuro-fuzzy inference system (ANFIS); (4) hybrid models, such as hybrid wavelet-artificial neural network (WA-ANN) model, hybrid wavelet-artificial neuro-fuzzy inference system (WA-ANFIS) model, and hybrid wavelet-support vector machine (WA-SVM) model; (5) evolutionary models, such as gene expression programming (GEP) and genetic programming (GP); (6) extreme learning machine (ELM); and (7) deep learning (DL). Model inputs, data split, model performance criteria, and model inter-comparison as well as the associated issues are discussed. The advantages and limitations of the established ML models are also discussed. Some specific directions for future research are also offered. This review provides a new vision for hydrologists and water resources planners for sustainable management of lakes.

Response of the photosynthetic activity and biomass of the phytoplankton community to increasing nutrients during cyanobacterial blooms in Meiliang Bay, Lake Taihu.

Nutrient enrichment facilitates algal outbreaks in eutrophic shallow lakes. To further understand the influence of various inorganic nutrient forms on cyanobacterial blooms, a nitrate (NO3 ), ammonium (NH4 ), and orthophosphate (PO4 ) amendment experiment was conducted in a large shallow lake of China (Lake Taihu) during summer. The results showed that the photosynthetic performance of phytoplankton responded more positively to phosphorus (P) than nitrogen (N), and NH4 addition stimulated higher algal photosynthetic activities in P-enriched waters. Individual inorganic N or PO4 addition significantly activated cyanobacteria and green algae. Meanwhile, the N plus P amendment promoted higher biomass of the planktonic microbial community, and the dual addition of NH4  + PO4 yielded the highest chlorophyll a concentration. NH4 additions provisionally promoted higher green algae than cyanobacteria biomass in the beginning, while cyanobacteria dominated again with increasing NH4 :PO4 ratios. These results revealed that increasing ammonium would enhance the increase in phytoplankton biomass in advance and prolong the duration of algal blooms. Hence, based on the control of P loading, the reduction in external inorganic N focusing on ammonium sources (such as ammonia N fertilizer) at the watershed scale would help to alleviate eutrophication and cyanobacterial blooms over the long term in Lake Taihu. PRACTITIONER POINTS: Ammonium addition stimulated higher algal photosynthetic activities in P-enriched waters. Individual inorganic N or PO4 addition significantly activated cyanobacteria and green algae. The dual addition of NH4  + PO4 yielded the highest chlorophyll a concentration. Increasing NH4 would enhance the increase in phytoplankton biomass in advance and prolong the duration of cyanobacterial blooms.

Comparing artificial intelligence techniques for chlorophyll-a prediction in US lakes.

Chlorophyll-a (CHLA) is a key indicator to represent eutrophication status in lakes. In this study, CHLA, total phosphorus (TP), total nitrogen (TN), turbidity (TB), and Secchi depth (SD) collected by the United States Environmental Protection Agency for the National Lakes Assessment in the continental USA were analyzed. Statistical analysis showed that water quality variables in natural lakes have strong patterns of autocorrelations than man-made lakes, indicating the perturbation of anthropogenic stresses on man-made lake ecosystems. Meanwhile, adaptive neuro-fuzzy inference systems (ANFIS) with fuzzy c-mean-clustering algorithm (ANFIS_FC), ANFIS with grid partition method (ANFIS_GP), and ANFIS with subtractive clustering method (ANFIS_SC) were implemented to model CHLA in lakes, and modeling results were compared with the multilayer perceptron neural network models (MLPNN). Results showed that ANFIS_FC models outperformed other models for natural lakes, while for man-made lakes, MLPNN models performed the best. ANFIS_GP models have the lowest accuracies in general. The results indicated that ANFIS models can be screening tools for an overall estimation of CHLA levels of lakes in large scales, especially for natural lakes.

Characterization of bacterial and microbial eukaryotic communities associated with an ephemeral hypoxia event in Taihu Lake, a shallow eutrophic Chinese lake.

While the important roles of microbial communities in oceanic hypoxic zones were beginning to be understood, little is known about microbial community associated with this phenomenon in shallow lakes. To address this deficit, both the bacterial and microbial eukaryotic communities of an ephemeral hypoxic area of Taihu Lake were characterized. The hypoxia provided nutritional niches for various bacteria, which results in high abundance and diversity. Specific bacterial groups, such as vadinBC27 subgroup of Bacteroidetes, Burkholderiales, Rhodocyclales, Pseudomonas, and Parcubacteria, were dominated in hypoxic sites and relevant to the fermentation, denitrification, nitrification, and sulfur metabolism. Conversely, most of microbial eukaryotes disappeared along with the decline of DO. An unexpected dominance of fungi was observed during hypoxia, which partly explained by the accumulation of toxic algae. Mucor was the single dominant genus in the hypoxic zone. We proposed that this group might cooperate with bacterial communities in the anaerobic degradation of algal biomass and woody materials. Generally, the hypoxic microbiome in shallow lakes is mainly involved in fermentative metabolism depending on phytodetritus and is potentially influenced by terrestrial sources. This study provided new insights into the unique microbiome in short-term hypoxia in shallow lakes and lays the foundation for studies that will enhance our understanding of the microbial players associated with hypoxia and their adaption strategy on the global scale.

Co-occurrence Network Reveals the Higher Fragmentation of the Bacterial Community in Kaidu River Than Its Tributaries in Northwestern China.

Rivers and their tributaries sculpt the earth's surface, and play an important role in substance circulation and energy flow. Bacteria are involved in most biogeochemical processes in the fluvial ecosystem; however, their pattern distribution in a river and its tributaries has not yet been investigated in detail. In the present study, high-throughput sequencing was employed to examine bacterial communities and their co-occurrence networks between Kaidu River and its nine tributaries in northwestern China. The results obtained demonstrated that both bacterial communities shared a similar dominant sub-community, mainly consisting of Actinobacteria, Bacteroidetes, and Proteobacteria, with Limnohabitans and Variovorax as the dominant genera. In spite of these commonalities, bacterial community structures still significantly differed between these two habitats, which may be related to the distance-related dispersal limitation. Their co-occurrence networks were generally both positively structured. The structural analysis showed that OTUs from the same phyla were more likely to co-occur. Although the keystone genera were taxonomically different between Kaidu River and its tributaries, they both shared common trophic properties in exploiting niches under oligotrophic conditions. We noted that their relative abundances were less than 1%, indicating the over-proportional roles of rare genera in the bacterial community. In addition, the inferred networks showed less nodes and edges, but higher modularity in Kaidu River than its tributaries, suggesting the higher fragmentation of the bacterial community in the mainstream.

Dynamics of phosphorus and bacterial phoX genes during the decomposition of Microcystis blooms in a mesocosm.

Cyanobacterial blooms are a worldwide environmental problem and frequently occur in eutrophic lakes. Organophosphorus mineralization regulated by microbial alkaline phosphatase provides available nutrients for bloom regeneration. To uncover the dynamics of bacterial alkaline phosphatase activity and microbial backgrounds in relation to organophosphorus mineralization during the decomposition process of cyanobacterial blooms, the response of alkaline phosphatase PhoX-producing bacteria were explored using a 23-day mesocosm experiment with three varying densities of Microcystis biomass from eutrophic Lake Taihu. Our study found large amounts of soluble reactive phosphorus and dissolved organophosphorus were released into the lake water during the decomposition process. Bacterial alkaline phosphatase activity showed the peak values during days 5~7 in groups with different chlorophyll-a densities, and then all decreased dramatically to their initial experimental levels during the last stage of decomposition. Bacterial phoX abundances in the three experimental groups increased significantly along with the decomposition process, positively related to the dissolved organic carbon and organophosphorus released by the Microcystis blooms. The genotypes similar to the phoX genes of Alphaproteobacteria were dominant in all groups, whereas the genotypes most similar to the phoX genes of Betaproteobacteria and Cyanobacteria were also abundant in the low density (~15 µg L-1 chlorophyll-a) group. At the end of the decomposition process, the number of genotypes most similar to the phoX of Betaproteobacteria and Cyanobacteria increased in the medium (~150 µg L-1 chlorophyll-a) and high (~1500 µg L-1 chlorophyll-a) density groups. The released organophosphorus and increased bacterial phoX abundance after decomposition of Microcystis aggregates could potentially provide sufficient nutrients and biological conditions for algal proliferation and are probably related to the regeneration of Microcystis blooms in eutrophic lakes.

Bacterial Community Composition in Oligosaline Lake Bosten: Low Overlap of Betaproteobacteria and Bacteroidetes with Freshwater Ecosystems.

Oligosaline lakes in arid regions provide indispensable water resources for humans; however, information on the bacterial community composition (BCC) of this ecosystem is limited. In the present study, we explored seasonal and vertical variations in BCC in Lake Bosten, a unique oligosaline lake (1.2‰ salinity) in arid, northwestern China, using denaturing gradient gel electrophoresis and 16S rRNA gene sequencing. We obtained 544 clones and 98 operational taxonomic units (OTUs) from six clone libraries. The top 10 OTUs represented 59.4% of the entire bacterial community. Betaproteobacteria (22.1%), Gammaproteobacteria (19.9%), Bacteroidetes (18.8%), and Firmicutes (11.4%) dominated in Lake Bosten. Although seasonal variations were recorded in BCC, the vertical changes observed were not significant. Water temperature and salinity were the most important factors shaping the dynamics of BCC. A low degree of overlap was observed in BCC between Lake Bosten and freshwater ecosystems, especially for Betaproteobacteria and Bacteroidetes. An RDP seqmatch analysis showed that 169 sequences (31%) were novel bacterial sequences (<97% similarity to the closest sequences in GenBank), which suggested that specific indigenous bacteria inhabit this oligosaline environment. Our results support bacterial endemicity being more common than previously considered, particularly in oligosaline lakes. An analysis of these communities may reveal how bacteria respond to increases in salinity and nutrients in the early stage of salinization and eutrophication.