Sediment bacteria in an urban stream: Spatiotemporal patterns in community composition

Microplastics shaped performance, microbial ecology and community assembly in simultaneous nitrification, denitrification and phosphorus removal process

The widespread use of microplastics (MPs) has led to an increase in their discharge to wastewater treatment plants. However, the knowledge of impact of MPs on macro-performance and micro-ecology in simultaneous nitrification, denitrification, and phosphorus removal (SNDPR) systems is limited, hampering the understanding of potential risks posed by MPs. This study firstly comprehensively investigated the performance, species interactions, and community assembly under polystyrene (PS) and polyvinyl chloride (PVC) exposure in SNDPR systems. The results showed under PS (1, 10 mg/L) and PVC (1, 10 mg/L) exposure, total nitrogen removal was reduced by 3.38-10.15 %. PS and PVC restrained the specific rates of nitrite and nitrate reduction (SNIRR, SNRR), as well as the activities of nitrite and nitrate reductase enzymes (NIR, NR). The specific ammonia oxidation rate (SAOR) and activity of ammonia oxidase enzyme (AMO) were reduced only at 10 mg/L PVC. PS and PVC enhanced the size of co-occurrence networks, niche breadth, and number of key species while decreasing microbial cooperation by 5.85-13.48 %. Heterogeneous selection dominated microbial community assembly, and PS and PVC strengthened the contribution of stochastic processes. PICRUSt prediction further revealed some important pathways were blocked by PS and PVC. Together, the reduced TN removal under PS and PVC exposure can be attributed to the inhibition of SAOR, SNRR, and SNIRR, the restrained activities of NIR, NR, and AMO, the changes in species interactions and community assembly mechanisms, and the suppression of some essential metabolic pathways. This paper offers a new perspective on comprehending the effects of MPs on SNDPR systems.

Response of microbial communities to exogenous nitrate nitrogen input in black and odorous sediment

Since nitrate nitrogen (NO3--N) input has proved an effective approach for the treatment of black and odorous river waterbody, it was controversial whether the total nitrogen concentration standard should be raised when the effluent from the sewage treatment plant is discharged into the polluted river. To reveal the effect of exogenous nitrate (NO3--N) on black odorous waterbody, sediments with different features from contaminated rivers were collected, and the changes of physical and chemical characteristics and microbial community structure in sediments before and after the addition of exogenous NO3--N were investigated. The results showed that after the input of NO3--N, reducing substances such as acid volatile sulfide (AVS) in the sediment decreased by 80 % on average, ferrous (Fe2+) decreased by 50 %, yet the changing trend of ammonia nitrogen (NH4+-N) in some sediment samples increased while others decreased. High-throughput sequencing results showed that the abundance of Thiobacillus at most sites increased significantly, becoming the dominant genus in the sediment, and the abundance of functional genes in the metabolome increased, such as soxA, soxX, soxY, soxZ. Network analysis showed that sediment microorganisms evolved from a single sulfur oxidation ecological function to diverse ecological functions, such as nitrogen cycle nirB, nirD, nirK, nosZ, and aerobic decomposition. In summary, inputting an appropriate amount of exogenous NO3--N is beneficial for restoring and maintaining the oxidation states of river sediment ecosystems.

Metagenomic and Culturomics Analysis of Microbial Communities within Surface Sediments and the Prevalence of Antibiotic Resistance Genes in a Pristine River: The Zaqu River in the Lancang River Source Region, China

Microbial communities inhabiting sedimentary environments in river source regions serve as pivotal indicators of pristine river ecosystems. While the correlation between antibiotic resistome and pathogenicity with core gut bacteria in humans is well established, there exists a significant knowledge gap concerning the interaction of antibiotic resistance genes (ARGs) and human pathogenic bacteria (HPB) with specific microbes in river source basins, often referred to as "terrestrial gut". Understanding the microbial composition, including bacteria and resident genetic elements such as ARGs, HPB, Mobile Genetic Elements (MGEs), and Virulence Factors (VFs), within natural habitats against the backdrop of global change, is imperative. To address this gap, an enrichment-based culturomics complementary along with metagenomics was conducted in this study to characterize the microbial biobank and provide preliminary ecological insights into profiling the dissemination of ARGs in the Lancang River Source Basin. Based on our findings, in the main stream of the Lancang River Source Basin, 674 strains of bacteria, comprising 540 strains under anaerobic conditions and 124 under aerobic conditions, were successfully isolated. Among these, 98 species were identified as known species, while 4 were potential novel species. Of these 98 species, 30 were HPB relevant to human health. Additionally, bacA and bacitracin emerged as the most abundant ARGs and antibiotics in this river, respectively. Furthermore, the risk assessment of ARGs predominantly indicated the lowest risk rank (Rank Ⅳ) in terms of endangering human health. In summary, enrichment-based culturomics proved effective in isolating rare and unknown bacteria, particularly under anaerobic conditions. The emergence of ARGs showed limited correlation with MGEs, indicating minimal threats to human health within the main stream of the Lancang River Source Basin.

Linking ecological niches to bacterial community structure and assembly in polluted urban aquatic ecosystems

Introduction

Bacterial communities play crucial roles in the functioning and resilience of aquatic ecosystems, and their responses to water pollution may be assessed from ecological niches. However, our understanding of such response patterns and the underlying ecological mechanisms remains limited.

Methods

In this study, we comprehensively investigated the effects of water pollution on the bacterial structure and assembly within different ecological niches, including water, sediment, submerged plant leaf surfaces, and leaf surfaces, using a 16S high-throughput sequencing approach.

Results

Ecological niches had a greater impact on bacterial community diversity than pollution, with a distinct enrichment of unique dominant phyla in different niches. This disparity in diversity extends to the bacterial responses to water pollution, with a general reduction in α-diversity observed in the niches, excluding leaf surfaces. Additionally, the distinct changes in bacterial composition in response to pollution should be correlated with their predicted functions, given the enrichment of functions related to biogeochemical cycling in plant surface niches. Moreover, our study revealed diverse interaction patterns among bacterial communities in different niches, characterized by relatively simply associations in sediments and intricate or interconnected networks in water and plant surfaces. Furthermore, stochastic processes dominated bacterial community assembly in the water column, whereas selective screening of roots and pollution events increased the impact of deterministic processes.

Discussion

Overall, our study emphasizes the importance of ecological niches in shaping bacterial responses to water pollution. These findings improve our understanding of the complicated microbial response patterns to water pollution and have ecological implications for aquatic ecosystem health.

Spatial distribution of sediment bacterial communities from São Francisco River headwaters is influenced by human land-use activities and seasonal climate shifts

Riverbed sediments are dynamic freshwater environments colonized by a great diversity of microorganisms which play important roles in supporting freshwater ecosystem by performing a vast array of metabolic functions. Recent evidence generated by HTS approaches has revealed that the structure of sediment microbial communities is influenced by natural seasonal variations in water such as temperature or streamflow as well by disturbances caused by local human activities. Here, a spatiotemporal analysis of sediment microbial distribution from São Francisco River headwaters section was conducted using Illumina 16S rRNA-V4 region amplicon sequencing in order to accomplish three major goals: (i) to investigate whether the diversity and composition of bacterial communities accessed in riverbed sediments vary in response to distinct land-use activities; (ii) to estimate whether the diversity patterns vary between the dry and wet seasons; and (iii) to evaluate whether the diversity of bacterial metabolic functions, predicted by PICRUSt2 approach, varies similarly to the estimated taxonomic diversity. Our findings revealed that bacterial communities in the sediment show differences in diversity and taxonomic composition according to the anthropic activities performed in the local environment. However, the patterns in which this taxonomic diversity is spatially structured show differences between the dry and wet seasons. On the other hand, the most changes in predicted bacterial metabolic functions were verified between sediment samples accessed in portions of the river located in protected and unprotected areas. Our findings contributed with new evidence about the impact of typical land-use practices conducted in countryside landscapes from developing countries on riverbed bacterial communities, both in their taxonomic and functional structure.

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.

The ASM2d model with two-step nitrification can better simulate biological nutrient removal systems enriched with complete ammonia oxidizing bacteria (comammox Nitrospira)

The discovery of comammox Nitrospira, a complete ammonia-oxidizing microorganism belonging to the genus Nitrospira, has brought new insights into the nitrification process in wastewater treatment plants (WWTPs). The applicability of Activated Sludge Model No. 2 d with one-step nitrification (ASM2d-OSN) or two-step nitrification (ASM2d-TSN) for the simulation of the biological nutrient removal (BNR) processes of a full-scale WWTP in the presence of comammox Nitrospira was studied. Microbial analysis and kinetic parameter measurements showed comammox Nitrospira was enriched in the BNR system operated under low dissolved oxygen (DO) and long sludge retention time (SRT). The relative abundance of Nitrospira under the conditions of stage I (DO = 0.5 mg/L, SRT = 60 d) was about twice of that under stage II conditions (DO = 4.0 mg/L, SRT = 26 d), and the copy number of the comammox amoA gene for stage I was 33 times higher than that for stage II. Compared to the ASM2d-OSN model, the ASM2d-TSN model simulated the performance of the WWTP under stage I conditions better, and the Theil inequality coefficient values of all the tested water quality parameters were lower than using ASM2d-OSN. These results indicate that an ASM2d model with two-step nitrification is a better choice for the simulation of WWTPs with the presence of comammox.

Insight into the spatiotemporal distribution of antibiotic resistance genes in estuarine sediments during long-term ecological restoration

In this study, we aimed to investigate the long-term spatiotemporal changes in hydrodynamics, antibiotics, nine typical subtypes of antibiotic resistance genes (ARGs), class 1 integron gene (intI1), and microbial communities in the sediments of a semi-enclosed estuary during ecological restoration with four treatment stages (influent (#1), effluent of the biological treatment area (#2), oxic area (#3), and plant treatment area (#4)). Ecological restoration of the estuary reduced common pollutants (nitrogen and phosphorus) in the water, whereas variations in ARGs showed noticeable seasonal and spatial features. The absolute abundance of ARGs at sampling site #2 considerably increased in autumn and winter, while it significantly increased at sampling site #3 in spring and summer. The strong intervention of biological treatment (from #1 to #2) and aerators (from #2 to #3) in the estuary substantially affected the distribution of ARGs and dominant antibiotic-resistant bacteria (ARB). The dominant ARB (Thiobacillus) in estuarine sediments may have low abundance but important dissemination roles. Meanwhile, redundancy and network analysis revealed that the microbial communities and intl1 were key factors related to ARG dissemination, which was affected by spatial and seasonal ecological restoration. A positive correlation between low flow velocity and certain ARGs (tetM, tetW, tetA, sul2, and ermC) was observed, implying that flow optimization should also be considered in future ecological restoration to remediate ARGs. Furthermore, the absolute abundance of ARGs can be utilized as an index to evaluate the removal capacity of ARGs by estuarine restoration.

Keystone microbial taxa organize micropollutant-related modules shaping the microbial community structure in estuarine sediments

The fluctuation of environmental conditions drives the structure of microbial communities in estuaries, highly dynamic ecosystems. Microorganisms inhabiting estuarine sediments play a key role in ecosystem functioning. They are well adapted to the changing conditions, also threatened by the presence of pollutants. In order to determine the environmental characteristics driving the organization of the microbial assemblages, we conducted a seasonal survey along the Adour Estuary (Bay of Biscay, France) using 16S rRNA gene Illumina sequencing. Microbial diversity data were combined with a set of chemical analyses targeting metals and pharmaceuticals. Microbial communities were largely dominated by Proteobacteria (41 %) and Bacteroidota (32 %), showing a strong organization according to season, with an important shift in winter. The composition of microbial communities showed spatial distribution according to three main areas (upstream, middle, and downstream estuary) revealing the influence of the Adour River. Further analyses indicated that the microbial community was influenced by biogeochemical parameters (C_org/N_org and δ¹³C) and micropollutants, including metals (As, Cu, Mn, Sn, Ti, and Zn) and pharmaceuticals (norfloxacin, oxolinic acid and trimethoprim). Network analysis revealed specific modules, organized around keystone taxa, linked to a pollutant type, providing information of paramount importance to understand the microbial ecology in estuarine ecosystems.

Wastewater treatment plant effluent discharge decreases bacterial community diversity and network complexity in urbanized coastal sediment

The wastewater treatment plant (WWTP) effluent discharge affects the microorganisms in the receiving water bodies. Despite the ecological significance of microbial communities in pollutant degradation and element cycling, how the community diversity is affected by effluent remains obscure. Here, we compared the sediment bacterial communities exposed to different intensities of WWTP effluent discharge in Hangzhou Bay, China: i) a severely polluted area that receives effluent from an industrial WWTP, ii) a moderately polluted area that receives effluent from a municipal WWTP, and iii) less affected area that inner the bay. We found that the sediment bacterial diversity decreased dramatically with pollution levels of inorganic nutrients, heavy metals, and organic halogens. Microbial community assembly model analysis revealed increased environmental selection and decreased species migration rate in the severely polluted area, resulting in high phylogenetic clustering of the bacterial communities. The ecological networks were less complex in the two WWTP effluent receiving areas than in the inner bay area, as suggested by the smaller network size and lower modularity. Fewer negative network associations were detected in the severely (6.7%) and moderately (8.3%) polluted areas than in the less affected area (16.7%), indicating more collaborative inter-species behaviors are required under stressful environmental conditions. Overall, our results reveal the fundamental impacts of WWTP effluents on the ecological processes shaping coastal microbial communities and point to the potential adverse effects of diversity loss on ecosystem functions.

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.

Microbial community composition and function in an urban waterway with combined sewer overflows before and after implementation of a stormwater storage pipe

When the wastewater volume exceeds the sewer pipe capacity during extreme rainfall events, untreated sewage discharges directly into rivers as combined sewer overflow (CSO). To compare the impacts of CSOs and stormwater on urban waterways, we assessed physicochemical water quality, the 16S rRNA gene-based bacterial community structure, and EcoPlate-based microbial functions during rainfall periods in an urban waterway before and after a stormwater storage pipe was commissioned. A temporal variation analysis showed that CSOs have significant impacts on microbial function and bacterial community structure, while their contributions to physicochemical parameters, bacterial abundance, and chlorophyll a were not confirmed. Heat map analysis showed that the impact of CSO on the waterway bacterial community structure was temporal and the bacterial community composition in CSO is distinct from that in sewers. Hierarchical clustering analysis revealed that the waterway physicochemical water qualities, bacterial community composition, and microbial community function were distinguishable from the upper reach of the river, rather than between CSO and stormwater. Changes in the relative abundance of tetracycline resistance (tet) genes-especially tet(M)-were observed after CSOs but did not coincide with changes in the microbial community composition, suggesting that the parameters affecting the microbial community composition and relative abundance of tet genes differ. After pipe implementation, however, stormwater did not contribute to the abundance of tet genes in the waterway. These results indicate that CSO-induced acute microbial disturbances in the urban waterway were alleviated by the implementation of a stormwater storage pipe and will support the efficiency of storage pipe operation for waterway management in urban areas.

Distribution of sediment microbial communities and their relationship with surrounding environmental factors in a typical rural river, Southwest China

With rapid urbanization and industrialization, rural rivers in China are facing deterioration in water quality and ecosystem health. Microorganisms living in river sediments are involved in biogeochemical processes, mineralization, and degradation of pollutants. Understanding bacterial community distribution in rural rivers could help evaluate the response of river ecosystems to environmental pollution and understand the river self-purification mechanism. In this study, the relationship between characteristics of sediment microbial communities and the surrounding environmental factors in a typical rural river was analyzed using 16S rRNA gene sequencing technology. The results showed that the dominant bacterial groups in the river sediment were Proteobacteria, Actinobacteria, Chloroflexi, Acidobacteria, Bacteroidetes, and Firmicutes, accounting for 83.61% of the total microbial load. Different areas have different sources of pollution which give rise to specific dominant bacteria. The upstream part of the river flows through an agricultural cultivation area where the dominant bacteria were norank_f_Gemmatimonadaceae, Haliangium, and Pseudolabrys, possessing obvious nitrogen- and phosphorus-metabolizing activities. The midstream section flows through an urban area where the dominant bacteria were Marmoricola, Nocardioides, Gaiella, Sphingomonas, norank_f_67-14, Subgroup_10, Agromyces, and Lysobacter, with strong metabolizing activity for toxic pollutants. The dominant bacteria in the downstream part were Clostridium_sensu_stricto_1, norank_f__Bacteroidetes_vadinHA17, Candidatus_Competibacter, and Methylocystis. Redundancy analysis and correlation heatmap analysis showed that environmental factors: ammonia nitrogen (NH₄⁺-N) and total nitrogen (TN) in the sediment, and pH, temperature, TN, electrical conductivity (EC), and total dissolved solids (TDS) in the water, significantly affected the bacterial community in the sediment. The PICRUSt2 functional prediction analysis identified that the main function of bacteria in the sediment was metabolism (77.3%), specifically carbohydrate, amino acid, and energy metabolism. These activities are important for degrading organic matter and removing pollutants from the sediments. The study revealed the influence of organic pollutants derived from human activities on the bacterial community composition in the river sediments. It gave a new insight into the relationship between environmental factors and bacterial community distribution in rural watershed ecosystems, providing a theoretical basis for self-purification and bioremediation of rural rivers.

Geochemistry and Multiomics Data Differentiate Streams in Pennsylvania Based on Unconventional Oil and Gas Activity

Unconventional oil and gas (UOG) extraction is increasing exponentially around the world, as new technological advances have provided cost-effective methods to extract hard-to-reach hydrocarbons. While UOG has increased the energy output of some countries, past research indicates potential impacts in nearby stream ecosystems as measured by geochemical and microbial markers. Here, we utilized a robust data set that combines 16S rRNA gene amplicon sequencing (DNA), metatranscriptomics (RNA), geochemistry, and trace element analyses to establish the impact of UOG activity in 21 sites in northern Pennsylvania. These data were also used to design predictive machine learning models to determine the UOG impact on streams. We identified multiple biomarkers of UOG activity and contributors of antimicrobial resistance within the order Burkholderiales. Furthermore, we identified expressed antimicrobial resistance genes, land coverage, geochemistry, and specific microbes as strong predictors of UOG status. Of the predictive models constructed (n = 30), 15 had accuracies higher than expected by chance and area under the curve values above 0.70. The supervised random forest models with the highest accuracy were constructed with 16S rRNA gene profiles, metatranscriptomics active microbial composition, metatranscriptomics active antimicrobial resistance genes, land coverage, and geochemistry (n = 23). The models identified the most important features within those data sets for classifying UOG status. These findings identified specific shifts in gene presence and expression, as well as geochemical measures, that can be used to build robust models to identify impacts of UOG development. IMPORTANCE The environmental implications of unconventional oil and gas extraction are only recently starting to be systematically recorded. Our research shows the utility of microbial communities paired with geochemical markers to build strong predictive random forest models of unconventional oil and gas activity and the identification of key biomarkers. Microbial communities, their transcribed genes, and key biomarkers can be used as sentinels of environmental changes. Slight changes in microbial function and composition can be detected before chemical markers of contamination. Potential contamination, specifically from biocides, is especially concerning due to its potential to promote antibiotic resistance in the environment. Additionally, as microbial communities facilitate the bulk of nutrient cycling in the environment, small changes may have long-term repercussions. Supervised random forest models can be used to identify changes in those communities, greatly enhance our understanding of what such impacts entail, and inform environmental management decisions.

Distribution Pattern and Influencing Factors of Heavy Metal Resistance Genes in the Yellow River Sediments of Henan Section

The transformation of heavy metal resistance genes (MRGs) in the environment has attracted increasing attention in recent years. However, few studies have reported the MRG content in the Yellow River, one of the main irrigation water sources in the North China Plain. In this study, we quantified MRG abundance by a metagenomic approach, and assessed the influence on MRGs of both bioavailable and total heavy metal (HM) content. The results indicate that Cu-resistant genes are the most common genes, and the prevalence of arsM needs more attention. Comamonadaceae is the dominant family in the Yellow River, and the presence of organic pollutants may contribute to the prevalence of Vicinamibacteraceae, Nocardioidaceae, and Flavobacteriacea. The results of the Mantel test and Spearman analysis indicate that both the bioavailable fractions and total content of HMs could have little influence on MRGs. Network analysis results indicate that some dominant bacteria could be the potential hosts of some prevalent MRGs, which may exert an adverse impact on human health.

Enhanced microbial nitrification-denitrification processes in a subtropical metropolitan river network

Urban rivers are hotspots of regional nitrogen (N) pollution and N transformations. Previous studies have reported that the microbial community of urban rivers was different from that of natural rivers. However, how microbial community affects N transformations in the urban rivers is still unclear. In this study, we employed N nutrients-related isotope technology (includes natural-abundance isotopes survey and isotope-labeling method) and bioinformatics methods (includes 16S rRNA high-throughput sequencing and quantitative PCR analysis) to investigate the major N transformations, microbial communities as well as functional gene abundances in a metropolitan river network. Our results suggested that the bacterial community structure in the highly urbanized rivers was characterized by higher richness, less complexity and increased abundances of nitrification and denitrifying bacterium compared to those in the suburban rivers. These differences were mainly caused by high sewage discharge and N loadings. In addition, the abundances of nitrifier gene (amoA) and denitrifier genes (nirK and nirS) were significantly higher in the highly urbanized rivers (2.36 × 10³, 7.43 × 10⁷ and 2.28 × 10⁷ copies·mL^-1) than that in the suburban rivers (0.43 × 10³, 2.18 × 10⁷ and 0.99 × 10⁷ copies·mL^-1). These changes in microbes have accelerated nitrification-denitrification processes in the highly urbanized rivers as compared to those in the suburban rivers, which was evidenced by environmental isotopes and the rates of nitrification (10.52 vs. 0.03 nmol·L^-1·h^-1) and denitrification (83.31 vs. 22.49 nmol·g^-1·h^-1). Overall, this study concluded that the excess exogenous N has significantly shaped the specific aquatic bacterial communities, which had a potential for enhancing nitrification-denitrification processes in the highly urbanized river network. This study provides a further understanding of microbial N cycling in urban river ecosystems and expands the combined application of isotopic technology and bioinformatics methods in studying biogeochemical cycling.

Anthropogenic Intensity-Determined Assembly and Network Stability of Bacterioplankton Communities in the Le'an River

Bacterioplankton are essential components of riverine ecosystems. However, the mechanisms (deterministic or stochastic processes) and co-occurrence networks by which these communities respond to anthropogenic disturbances are not well understood. Here, we integrated niche-neutrality dynamic balancing and co-occurrence network analysis to investigate the dispersal dynamics of bacterioplankton communities along human activity intensity gradients. Results showed that the lower reaches (where intensity of human activity is high) had an increased composition of bacterioplankton communities which induced strong increases in bacterioplankton diversity. Human activity intensity changes influenced bacterioplankton community assembly via regulation of the deterministic-stochastic balance, with deterministic processes more important as human activity increases. Bacterioplankton molecular ecological network stability and robustness were higher on average in the upper reaches (where there is lower intensity of human activity), but a human activity intensity increase of about 10%/10% can reduce co-occurrence network stability of bacterioplankton communities by an average of 0.62%/0.42% in the dry and wet season, respectively. In addition, water chemistry (especially NO₃^–-N and Cl^–) contributed more to explaining community assembly (especially the composition) than geographic distance and land use in the dry season, while the bacterioplankton community (especially the bacterioplankton network) was more influenced by distance (especially the length of rivers and dendritic streams) and land use (especially forest regions) in the wet season. Our research provides a new perspective of community assembly in rivers and important insights into future research on environmental monitoring and classified management of aquatic ecosystems under the influence of human activity.

Bacterial communities in peat swamps reflect changes associated with catchment urbanisation

Like many peat wetlands around the world, Temperate Highland Peat Swamps on Sandstone (THPSS), located in the Sydney Basin, Australia, have been impacted by urban development. In this paper, we used Illumina 16S rRNA DNA amplicon sequencing to characterise and compare the bacterial communities of surface (top 0–2 cm) and deep (50 cm) sediments in peat swamps that occur in both urbanised and non-urbanised catchments. Proteobacteria (32.2% of reads), Acidobacteria (23.6%) and Chloroflexi (10.7%) were the most common phyla of the dataset. There were significant differences in the bacterial community structure between catchment types and depths apparent at the phyla level. Proteobacteria, Bacteroidetes, Actinobacteria and Verrucomicrobia made up a greater proportion of the reads in the surface sediments than the deeper sediments, while Chloroflexi and Nitrospirae were relatively more common in the deeper than the surface sediment. By catchment type, Acidobacteria were more common in swamps occurring in non-urbanised catchments, while Nitrospirae, Bacteroidetes and Actinobacteria were more common in those in urbanised catchments. Microbial community structure was significantly correlated with sediment pH, as was the relative abundance of several phyla, including Acidobacteria (negative correlation) and Bacteroidetes (positive correlation). As an indicator of trophic shift from oligotrophic to copiotrophic conditions associated with urbanised catchment, we found significant differences ratios of β-Proteobacteria to Acidobacteria and Bacteriodetes to Acidobacteria between the catchment types. Based on SIMPER results we suggest the relative abundance of Nitrosomonadaceae family as a potential indicator of urban degradation. As the first study to analyse the bacterial community structure of THPSS using sequencing of 16S rDNA, we reveal the utility of such analyses and show that urbanisation in the Blue Mountains is impacting the microbial ecology of these important peatland ecosystems.

The response of sediment microbial communities to temporal and site-specific variations of pollution in interconnected aquaculture pond and ditch systems

Sediment microbial communities play critical roles in the health of fish and the biogeochemical cycling of elements in aquaculture ecosystems. However, the response of microbial communities to temporal and spatial variations in interconnected aquaculture pond and ditch systems remains unclear. In this study, 61 sediment bacterial samples were collected over one year from 11 sites (including five ponds and six ditches) in a 30-year-old fish aquaculture farm. The 16S rRNA approach was used to determine the relative abundances of microbial communities in the sediment samples. The relationships among nutrients, heavy metals, and abundant microorganisms were analyzed. Our results showed that Proteobacteria, Bacteroides and Chloroflexi were the predominant phyla in the sediments of aquaculture pond, with average abundances of 36.33%, 18.60%, and 14.58%, respectively. The microbial diversity in aquaculture sediments was negatively correlated (P < 0.05) with the concentrations of total nitrogen and total phosphorus in sediments, indicating that the microbial diversity is highly associated with the remediation of nutrients in sediments. The sediment samples with high similarities were discovered by the t-distributed stochastic neighbor embedding (t-SNE) method. The site-specific correlations between specific microorganisms and heavy metals were explored. The network analysis revealed that the microbial diversities in aquaculture ponds were more stable than that in aquaculture ditches. The network analysis also illustrated that the microbial genera with low relative abundances may become key groups of microbial communities in sediment ecosystems. Our work deepens the understanding of the relationships between microbial communities and the spatiotemporal characteristics of surface water and sediments in aquaculture farms.

Effects of heavy metals and hyporheic exchange on microbial community structure and functions in hyporheic zone

The responses of microbial communities in hyporheic zone to the eco-hydrological process have been a hotspot in river ecological health research. However, the impact of different metal pollution levels and hyporheic exchange on the microbial communities are still unclear. In this study, we further explored the effects of different degrees of heavy metals pollution and the strength of hyporheic exchange on the structures and functions of microbial community in hyporheic zone sediment ecosystem. Sediments were collected from the Weihe River to determine the concentrations of heavy metals, grain size distribution, and hydraulic conductivity, and the microbial information were obtained by eDNA technology. The comprehensive pollution status of the study area was at the slight and moderate level. The hydraulic conductivity (K_v) varied between 0.20 and 3.65 (m/d). The microbial community structures had complex temporal and spatial heterogeneity. The microbial molecular ecological network had modular characteristics and significant differences in different periods (p < 0.05). Metabolic functional genes in microbial communities had the highest relative abundance. In particular, there is a significant negative correlation between heavy metals and microorganisms (p < 0.05), with Cu and Zn contributing the most to microbial community changes (p < 0.05). Moreover, grain size had a significant impact on microorganisms, heavy metals and grain size significantly affect the predictive functions of microbial communities. Our in-depth research on microorganisms in the hyporheic zone provides references for monitoring and bioremediation of aquatic ecosystems.

Ecological insights into the disturbances in bacterioplankton communities due to emerging organic pollutants from different anthropogenic activities along an urban river

Emerging organic pollutants (EOPs) in urban rivers have raised concerns regarding their eco-toxicological effects. However, the bacterioplankton community disturbances caused by EOPs in urban rivers and the associated ecological mechanisms remain unclear. This study provided profiles of the spatial distribution of a bacterioplankton community disturbed by human activity along an urban river. The results showed that EOP concentration and composition were differently distributed in residential and industrial areas, which significantly influenced bacterioplankton community structure. Based on redundancy analysis, parabens (methylparaben and propylparaben) were the major factors driving bacterioplankton community changes. Parabens inhibited gram-positive bacteria and promoted oxidative stress-tolerant bacteria in the river ecosystem. Parabens also disturbed ecological processes of bacterioplankton community assembly, shifting from a homogeneous selection (consistent selection pressure under similar environmental condition) to stochastic processes (random changes due to birth, death, immigration, and emigration) with changing in paraben concentrations. Heterogeneous selection was predicted to dominate microbial community assembly with paraben concentration changes exceeding 61.6 ng/L, which could deteriorate the river ecosystem. Furthermore, specific bacterial genera were identified as potential bioindicators to assess the condition of EOP contaminants in the river. Overall, this study highlights significant disturbances in bacterioplankton communities by EOPs at environmental concentrations, and our results could facilitate generation of appropriate management strategies aimed at EOPs in urban rivers.

Assembly Processes and Co-occurrence Patterns of Abundant and Rare Bacterial Community in the Eastern Indian Ocean

Microbial communities are composed of many rare species and a few abundant species. Considering the disproportionate importance of rare species for ecosystem functioning, it is important to understand the mechanisms structuring the rare and abundant components of a diverse community in response to environmental changes. Here, we used a 16S ribosomal RNA gene sequencing approach to investigate the bacterial community diversity in the Eastern Indian Ocean (EIO) during the monsoon and intermonsoon. We employed a phylogenetic null model and network analysis to evaluate the assembly processes and co-occurrence pattern of the microbial community. We found that higher bacterial diversity was detected in the intermonsoon with high temperature and low Chlorophyll a concentrations and N/P ratios. The balance between ecological deterministic processes and stochastic processes varied with seasons in the EIO. Meanwhile, conditionally rare taxa (CRT) were more likely modulated by variable selection processes than always rare taxa (ART) and abundant taxa (AT) (CRT > ART > AT). By linking assembly process and species co-occurrence, we demonstrated that the microbial co-occurrence associations tended to be higher when deterministic processes (mainly variable selection) were weaker. This negative trend was observed in rare species rather than abundant species. The linkage could enhance our understanding of the underlying mechanisms underpinning the generation and maintenance of microbial community diversity.

How sediment bacterial community shifts along the urban river located in mining city

Bacterial communities play critical roles in biogeochemical cycles and serve as sensitive indicators of environmental fluctuation. However, the influence of mineral resource exploitation on shaping the bacterial communities in the urban river is still ambiguous. In this study, high-throughput sequencing was used to determine the spatial distribution of the sediment bacterial communities along an urban river in the famous mining city Panzhihua of China. The results showed that mineral resource exploitation had a significant impact on the urban river bacterial community structure but not on the bacterial ecological functions. Distinct families of bacteria often associated with nutrients (i.e., Comamonadaceae and Sphingomonadaceae) and metal contaminants (i.e., Rhodobacteraceae) were more predominant in the residential and mining area, respectively. Relative to dispersal dynamics, environmentally induced species sorting may primarily influence bacterial community structure. Heavy metals and sediment physicochemical properties had both similar and significant influence on shaping bacterial community structure. Among heavy metals, essential metal elements explained more rates of bacterial variation than toxic metals at moderate contaminant levels. Moreover, the bacteria with multiple metal resistances identified in culture-dependent experiments were probably not suitable for indicating heavy metal contamination in field research. Thus, several sensitive bacterial genera such as Rhodobacter, Hylemonella, and Dechloromonas were identified as potential bioindicators to monitor metals (iron and titanium) and nutrients (phosphorus and organic carbon) in the river ecosystem of the Panzhihua region. Together, these results profiled the coupling effect of urbanization and mineral resource utilization on shaping sediment bacterial communities in urban rivers.

Assessments of Bacterial Community Shifts in Sediments along the Headwaters of São Francisco River, Brazil

Sustainable use of freshwater resources for human civilization needs requires the assessment and monitoring of freshwater health, and bacterial communities from riverbed sediments have been shown to be susceptible to chronic anthropogenic disturbances in freshwater ecosystems. Here, we took advantage of the occurrence of well-recognized adjacent sections from the Upper São Francisco River basin with well-recognized levels of anthropogenic activity intensity to test the applicability of sediment bacterial communities as bioindicators of impacts on freshwater ecosystems. We applied 16S amplicon sequencing to estimate the diversity and composition of bacterial communities from 12 sampling sites across the Upper São Francisco River basin, classified as being of no, low, or high intensity of anthropogenic activities, and used diversity metrics and LEfSe to compare the patterns of community structure. Our results revealed that accessed sediment environments associated with land areas with a high intensity of anthropogenic activities presented the lowest levels of community diversity, and the bacterial community compositions of these environments were significantly different from the other sampled areas. Our findings can be considered a source of evidence for the usefulness of bacterial community-based approaches as a tool for diagnosis and monitoring of ecosystem health in areas of vulnerable freshwater environments, and can even be incorporated into regular water quality programs.

Land use intensification destabilizes stream microbial biodiversity and decreases metabolic efficiency

Urbanization and agricultural intensification can transform landscapes. Changes in land-use can lead to increases in storm runoff and nutrient loadings which can impair the health and function of stream ecosystems. Microorganisms are an integral component of stream ecosystems. Due to the sensitivity of microorganisms to perturbations, changes in hydrology and water chemistry may alter microbial activity and structure. These shifts in microbial community dynamics may alter stream metabolism and water quality, potentially impacting higher trophic levels. Here we examine the effects of land-use and associated changes in water chemistry on sediment microbial communities by studying the West Run Watershed (WRW) a mixed-land-use system in West Virginia, USA. Streams were sampled throughout the growing season at six sites within the WRW spanning different levels of land use intensification. The proportion of land impacted by agricultural and urban development was positively correlated with temporal variation in stream sediment microbial community composition (adj R² = 0.65), suggesting development can destabilize microbial communities. Moreover, streams in developed watersheds had an increased metabolic quotient (20-50% higher), this indicates that microorganisms have greater respiration per unit biomass and signifies reduced metabolic efficiency. Further, our results suggest that land use associated changes in water chemistry alter microbial function both directly and indirectly via changes in microbial community composition and biomass. Taken together our results suggest that highly developed watersheds with elevated conductivity, metal ion concentration, and pH impose stress on microbial communities resulting in reduced microbial efficiency and elevated respiration.

Seasonal and spatial distribution and assembly processes of bacterioplankton communities in a subtropical urban river

The ecological functions of core and non-core bacteria are gradually being identified, yet little is known about their responses to environmental changes and assembly processes, especially in urban river ecosystems. Here, we investigated bacterioplankton communities over 1 year in an urban section of the Ganjiang River, China. The results revealed that the alpha- and beta-diversity of bacterioplankton communities had no significant spatial differences along the urbanization gradient, but they presented distinct seasonal variations. The bacterioplankton communities were comprised of a few core taxa (11.8%) and a large number of non-core taxa (88.2%), of which the non-core taxa were the most active component responsible for community dynamics. Most non-core taxa (76.84%) belonged to non-typical freshwater bacteria, implying that they are more likely to derive from allochthonous inputs than the core taxa. Variance partitioning analyses showed that air temperature, flow rate and water chemistry together explained 58.2 and 38.9% of the variations of the core taxa and non-core taxa, respectively. In addition, the relative importance of temperature and water chemistry on the bacterioplankton communities prevailed over that of flow rate alone. This means that deterministic processes and stochastic processes simultaneously control the bacterioplankton community assembly, with deterministic processes contributing more than stochastic processes.

Long-term agricultural contamination shaped diversity response of sediment microbiome

The pollution caused by agricultural production poses a threat to the ecological integrity of river ecosystems, altering the structure and function of river ecosystems. Differences in microbial community structure provide useful information about the impact of agricultural pollution on the biological integrity of ecosystems, but generally convey little information regarding ecosystem functions. In this study, using Illumina MiSeq sequencing technology based on the 16S rRNA gene, river sediment samples associated with four different types of agricultural pollution were comprehensively analyzed. The results show that the total organic carbon (TOC) content was highest at the YZS site (animal husbandry sewage) among the assayed sites, but the species richness and uniformity were lowest at this site, which may have been caused by the high nutrient source of the sewage. Furthermore, in the three YZS samples affected by the long-term discharge of aquaculture tail-water, the unique genus Dechloromonas and the genus Candidatus-Competitor were observed, which are strongly correlated with phosphorus conversion. The formation of network modules may correspond to the coexistence of functional bacteria accustomed to multiple niche combinations under different agricultural pollution conditions in river sediments. According to the PICRUSt functional prediction, the bacterial community in the agricultural polluted river sediment primarily harbored 46 subfunctions, exhibiting richness of functions. Overall, our results provide a more comprehensive understanding of the structure and ecological processes associated with the aggregation of bacterial communities, which is beneficial for the management of river environments.

Nutrients and Pharmaceuticals Structure Bacterial Core Communities in Urban and Montane Stream Biofilms

Bacteria in stream biofilms contribute to stream biogeochemical processes and are potentially sensitive to the substantial levels of pollution entering urban streams. To examine the effects of contaminants on stream biofilm bacteria in situ, we exposed growing biofilms to experimental additions of nutrients [nitrogen (N), phosphorus (P), and iron (Fe)], pharmaceuticals (caffeine and diphenhydramine), nutrients plus pharmaceuticals, or no contaminants using contaminant exposure substrates (CES) in three catchments in northern Utah. We performed our study at montane and urban sites to examine the influence of existing pollution on biofilm response. We identified bacterial core communities (core) for each contaminant treatment at each land-use type (e.g., nutrient addition montane bacterial core, nutrient addition urban bacterial core, pharmaceutical addition montane bacterial core) by selecting all taxa found in at least 75% of the samples belonging to each specific grouping. Montane and urban land-use distinguished bacterial cores, while nutrients and pharmaceuticals had subtle, but nonetheless distinct effects. Nutrients enhanced the dominance of already abundant copiotrophs [i.e., Pseudomonadaceae (Gammaproteobacteria) and Comamonadaceae (Betaproteobacteria)] within bacterial cores at montane and urban sites. In contrast, pharmaceuticals fostered species-rich bacterial cores containing unique contaminant-degrading taxa within Pseudomonadaceae and Anaerolineaceae (Chloroflexi). Surprisingly, even at urban sites containing ambient pharmaceutical pollution, pharmaceutical additions increased bacterial core richness, specifically within DR-16 (Betaproteobacteria), WCHB1-32 (Bacteroidetes), and Leptotrichiaceae (Fusobacteria). Nutrients exerted greater selective force than pharmaceuticals in nutrient plus pharmaceutical addition treatments, creating bacterial cores more closely resembling those under nutrient rather than pharmaceutical addition, and promoting unique Oscillatoriales (Cyanobacteria) taxa in urban streams. Our results show that additions of N, P, and Fe intensified the dominance of already abundant copiotrophs, while additions of caffeine and diphenhydramine enabled unique taxa associated with contaminant degradation to participate in bacterial cores. Further, biofilm bacteria at urban sites remained sensitive to pharmaceuticals commonly present in waters, suggesting a dynamic interplay among pharmaceutical pollution, bacterial diversity, and contaminant degradation.

Connectivity of bacterial assemblages along the Loa River in the Atacama Desert, Chile

The Loa River is the only perennial artery that crosses the Atacama Desert in northern Chile. It plays an important role in the ecological and economic development of the most water-stressed region, revealing the impact of the mining industry, which exacerbate regional water shortages for many organisms and ecological processes. Despite this, the river system has remained understudied. To our knowledge, this study provides the first effort to attempt to compare the microbial communities at spatial scale along the Loa River, as well as investigate the physicochemical factors that could modulate this important biological component that still remains largely unexplored. The analysis of the spatial bacterial distribution and their interconnections in the water column and sediment samples from eight sites located in three sections along the river catchment (upper, middle and lower) was conducted using 16S rRNA gene-based Illumina MiSeq sequencing. Among a total of 543 ASVs identified at the family level, over 40.5% were cosmopolitan in the river and distributed within a preference pattern by the sediment substrate with 162 unique ASVs, while only 87 were specific to the column water. Bacterial diversity gradually decreased from the headwaters, where the upper section had the largest number of unique families. Distinct groupings of bacterial communities often associated with anthropogenic disturbance, including Burkholderiaceae and Flavobacteriaceae families were predominant in the less-impacted upstream section. Members of the Arcobacteraceae and Marinomonadaceae were prominent in the agriculturally and mining-impacted middle sector while Rhodobacteraceae and Coxiellaceae were most abundant families in downstream sites. Such shifts in the community structure were also related to the influence of salinity, chlorophyll, dissolved oxygen and redox potential. Network analyses corroborated the strong connectivity and modular structure of bacterial communities across this desert river, shedding light on taxonomic relatedness of co-occurring species and highlighting the need for planning the integral conservation of this basin.

Strong linkages between dissolved organic matter and the aquatic bacterial community in an urban river

Aquatic bacterial communities play an important role in biogeochemical cycling in river ecosystems; however, knowledge of the linkages between bacterial communities and dissolved organic matter (DOM) in urban rivers is limited. Here, 16S rRNA amplicon sequencing and parallel factor (PARAFAC) modeling of excitation-emission fluorescence spectroscopy were used to analyze the compositions, co-occurrence patterns, and interactions with chromophoric DOM (CDOM) of bacterial communities in urban river water samples influenced by different human activities. The results revealed that two protein-like components accounted for 65.2 ± 9.56% of the total variability in all three fluorescence components, which suggests that CDOM in urban rivers is mainly a microbial source. In addition to pH and DO, CDOM is also an important factor affecting bacterial community structure, and the main classes (Gammaproteobacteria and Clostridia) and genera (Limnohabitans and Alpinimonas) showed strong positive correlations with terrestrial humic-like C1 and tryptophan-like C2, respectively. When autotrophic and heterotrophic bacteria coexist in urban rivers, the production and degradation of CDOM will occur simultaneously. Furthermore, the riverine bacterial co-occurrence network had a nonrandom modular structure, which was mainly driven by classification correlation and bacterial function. The high abundance of genes related to xenobiotic metabolism, carbon metabolism and nitrogen metabolism in the urban river indicated that anthropogenic activity may be the dominant selective force altering the bacterial communities. Overall, our results provide a novel view for the assembly of bacterial communities in urban river ecosystems under the influence of different human activities.

17α-ethynylestradiol (EE2) limits the impact of ibuprofen upon respiration by streambed biofilms in a sub-urban stream

Pharmaceutical compounds such as the non-steroidal anti-inflammatory drug ibuprofen and the artificial estrogen 17α-ethynylestradiol (EE2) are contaminants of emerging concern in freshwater systems. Globally, human pharmaceutical use is growing by around ~ 3% per year; yet, we know little about how interactions between different pharmaceuticals may affect aquatic ecosystems. Here, we test how interactions between ibuprofen and EE2 affect the growth and respiration of streambed biofilms. We used contaminant exposure experiments to quantify how these compounds affected biofilm growth (biomass), respiration, net primary production (NPP) and gross primary production (GPP), both individually and in combination. We found no effects of either ibuprofen or EE2 on biofilm biomass (using ash-free dry mass as a proxy) or gross primary production. Ibuprofen significantly reduced biofilm respiration and altered NPP. Concomitant exposure to EE2, however, counteracted the inhibitory effects of ibuprofen upon biofilm respiration. Our study, thus, demonstrates that interactions between pharmaceuticals in the environment may have complex effects upon microbial contributions to aquatic ecosystem functioning.

Sediment Bacterial Community Structure Under the Influence of Different Domestic Sewage Types

Sediment bacterial communities are critical to the biogeochemical cycle in river ecosystems, but our understanding of the relationship between sediment bacterial communities and their specific input streams in rivers remains insufficient. In this study, we analyzed the sediment bacterial community structure in a local river receiving discharge of urban domestic sewage by applying Illumina MiSeq high-throughput sequencing. The results showed that the bacterial communities of sediments samples of different pollution types had similar dominant phyla, mainly Proteobacteria, Actinobacteria, Chloroflexi and Firmicutes, but their relative abundances were different. Moreover, there were great differences at the genus level. For example, the genus Bacillus showed statistically significant differences in the hotel site. The clustering of bacterial communities at various sites and the dominant families (i.e., Nocardioidaceae, and Sphingomonadaceae) observed in the residential quarter differed from other sites. This result suggested that environmentally induced species sorting greatly influenced the sediment bacterial community composition. The bacterial cooccurrence patterns showed that the river bacteria had a nonrandom modular structure. Microbial taxonomy from the same module had strong ecological links (such as the nitrogenium cycle and degradation of organic pollutants). Additionally, PICRUSt metabolic inference analysis showed the most important function of river bacterial communities under the influence of different types of domestic sewage was metabolism (e.g., genes related to xenobiotic degradation predominated in residential quarter samples). In general, our results emphasize that the adaptive changes and interactions in the bacterial community structure of river sediment represent responses to different exogenous pollution sources.

Impact of long-term industrial contamination on the bacterial communities in urban river sediments

BACKGROUND

The contamination of the aquatic environment of urban rivers with industrial wastewater has affected the abiotic conditions and biological activities of the trophic levels of the ecosystem, particularly sediments. However, most current research about microorganism in urban aquatic environments has focused on indicator bacteria related to feces and organic pollution. Meanwhile, they ignored the interactions among microorganisms. To deeply understand the impact of industrial contamination on microbial community, we study the bacterial community structure and diversity in river sediments under the influence of different types of industrial pollution by Illumina MiSeq high-throughput sequencing technology and conduct a more detailed analysis of microbial community structure through co-occurrence networks.

RESULTS

The overall community composition and abundance of individual bacterial groups differed between samples. In addition, redundancy analysis indicated that the structure of the bacterial community in river sediments was influenced by a variety of environmental factors. TN, TP, TOC and metals (Cu, Zn and Cd) were the most important driving factors that determined the bacterial community in urban river sediments (P < 0.01). According to PICRUSt analysis, the bacterial communities in different locations had similar overall functional profiles. It is worth noting that the 15 functional genes related to xenobiotics biodegradation and metabolism were the most abundant in the same location. The non-random assembly patterns of bacterial composition in different types of industrially polluted sediments were determined by a co-occurrence network. Environmental conditions resulting from different industrial pollutants may play an important role in determining their co-occurrence patterns of these bacterial taxa. Among them, the bacterial taxa involved in carbon and nitrogen cycles in module I were relatively abundant, and the bacterial taxa in module II were involved in the repair of metal pollution.

CONCLUSIONS

Our data indicate that long-term potential interactions between different types of industrial pollution and taxa collectively affect the structure of the bacterial community in urban river sediments.

Bacterial community responses to tourism development in the Xixi National Wetland Park, China

A large number of urban wetland parks have been established, but knowledge about the effects of tourism development on the microbial diversity and ecosystem functioning remains limited. This study aimed to clarify the responses of bacterial communities to tourism development targeted the Xixi National Wetland Park, China. By analyzing the diversity, composition, assembly pattern, and environmental drivers of bacterial communities, we found that tourism development considerably affected the water quality, which further decreased the α-diversity but increased the β-diversity in open areas for landscaping and recreation. Specifically, there was higher Simpson dissimilarity across functional wetland areas, indicating that species replacement mainly explained β-diversity patterns of bacterial communities. RDA analysis and ecological processes quantification further suggested that TOC and TC were the major factors in the open areas driving bacterial communities in water and sediment, respectively. Also, typical anti-disturbance taxa (Gammaproteobacteria) and potential pathogens (Bacillus) were enriched in the wetlands under more anthropogenic disturbances. Findings of the present study highlighted the effects of tourism development on bacterial communities resulted in obvious spatial variation in the Xixi National Wetland Park. This study gives us useful information for ecological assessments of urban wetlands, and further can provide references in making appropriate strategies to manage wetland ecosystems.

Linking bacterial community shifts with changes in the dissolved organic matter pool in a eutrophic lake

Aquatic bacterial communities play crucial roles in the circulation of nutrients in watershed ecosystems. However, the interaction between bacterial communities and chromophoric dissolved organic matter (CDOM) in freshwater ecosystems has not been studied in depth. In our study, we examined the constitution and interactions of CDOM with the bacterial community in Lake Chaohu and its inflow rivers under the influence of different exogenous pollutants. The results revealed that the bacterial community diversity in the inflow rivers was significantly lower than that in the lake sites. Clustering of different types of polluted inflow rivers integrated with the most abundant genera observed in specific areas indicated that environmentally guided species selection had a large impact on the composition of aquatic bacterial communities. Moreover, our study suggests that communities in lake environments may be more susceptible to interference through a variety of physiologies or via functional redundancy, allowing them to preserve their community structure. Through linear discriminant analysis effect size (Lefse) methods, we revealed that some taxa (from phylum to genus) were consistently enriched in the lake sites. Based on correlation network analysis results, the supersession niches of bacterial community members related to different CDOM in the biogeochemical process was determined. This study provides an ecological basis for the control of external pollution and the protection of the water environment in watershed ecosystems.

Sediment Microbial Diversity in Urban Piedmont North Carolina Watersheds Receiving Wastewater Input

Urban streams are heavily influenced by human activity. One way that this occurs is through the reintroduction of treated effluent from wastewater treatment plants. We measured the microbial community composition of water, sediment, and soil at sites upstream and downstream from two Charlotte treatment facilities. We performed 16S rRNA gene sequencing to assay the microbial community composition at each site at four time points between the late winter and mid-summer of 2016. Despite the location of these streams in an urban area with many influences and disruptions, the streams maintain distinct water, sediment, and soil microbial profiles. While there is an overlap of microbial species in upstream and downstream sites, there are several taxa that differentiate these sites. Some taxa characteristics of human-associated microbial communities appear elevated in the downstream sediment communities. In the wastewater treatment plant and to a lesser extent in the downstream community, there are high abundance amplicon sequence variants (ASVs) which are less than 97% similar to any sequence in reference databases, suggesting that these environments contain an unexplored biological novelty. Taken together, these results suggest a need to more fully characterize the microbial communities associated with urban streams, and to integrate information about microbial community composition with mechanistic models.

Headwater Stream Microbial Diversity and Function across Agricultural and Urban Land Use Gradients

Anthropogenic activity impacts stream ecosystems, resulting in a loss of diversity and ecosystem function; however, little is known about the response of aquatic microbial communities to changes in land use. Here, microbial communities were characterized in 82 headwater streams across a gradient of urban and agricultural land uses using 16S rRNA gene amplicon sequencing and compared to a rich data set of physicochemical variables and traditional benthic invertebrate indicators. Microbial diversity and community structures differed among watersheds with high agricultural, urban, and forested land uses, and community structure differed in streams classified as being in good, fair, poor, and very poor condition using benthic invertebrate indicators. Microbial community similarity decayed with geodesic distance across the study region but not with environmental distance. Stream community respiration rates ranged from 21.7 to 1,570 mg O₂ m^-2 day^-1 and 31.9 to 3,670 mg O₂ m^-2 day^-1 for water column and sediments, respectively, and correlated with nutrients associated with anthropogenic influence and microbial community structure. Nitrous oxide (N₂O) concentrations ranged from 0.22 to 4.41 μg N₂O liter^-1; N₂O concentration was negatively correlated with forested land use and was positively correlated with dissolved inorganic nitrogen concentrations. Our findings suggest that stream microbial communities are impacted by watershed land use and can potentially be used to assess ecosystem health.IMPORTANCE Stream ecosystems are frequently impacted by changes in watershed land use, resulting in altered hydrology, increased pollutant and nutrient loads, and habitat degradation. Macroinvertebrates and fish are strongly affected by changes in stream conditions and are commonly used in biotic indices to assess ecosystem health. Similarly, microbes respond to environmental stressors, and changes in community composition alter key ecosystem processes. The response of microbes to habitat degradation and their role in global biogeochemical cycles provide an opportunity to use microbes as a monitoring tool. Here, we identify stream microbes that respond to watershed urbanization and agricultural development and demonstrate that microbial diversity and community structure can be used to assess stream conditions and ecosystem functioning.

Dynamics of coastal bacterial community average ribosomal RNA operon copy number reflect its response and sensitivity to ammonium and phosphate

The nutrient-rich effluent from wastewater treatment plants (WWTPs) constitutes a significant disturbance to coastal microbial communities, which in turn affect ecosystem functioning. However, little is known about how such disturbance could affect the community's stability, an important knowledge gap for predicting community response to future disturbances. Here, we examined dynamics of coastal sediment microbial communities with and without a history of WWTP's disturbances (named H1 and H0 hereafter) after simulated nutrient input loading at the low level (5 mg L^-1 NH₄⁺-N and 0.5 mg L^-1 PO₄^3--P) or high level (50 mg L^-1 NH₄⁺-N and 5.0 mg L^-1 PO₄^3--P) for 28 days. H0 community was highly sensitive to both low and high nutrient loading, showing a faster community turnover than H1 community. In contrast, H1 community was more efficient in nutrient removal. To explain it, we found that H1 community constituted more abundant and diversified r-strategists, known to be copiotrophic and fast in growth and reproduction, than H0 community. As nutrient was gradually consumed, both communities showed a succession of decreasing r-strategists. Accordingly, there was a decrease in community average ribosomal RNA operon (rrn) copy number, a recently established functional trait of r-strategists. Remarkably, the average rrn copy number of H0 communities was strongly correlated with NH₄⁺-N (R² = 0.515, P = 0.009 for low nutrient loading; R² = 0.749, P = 0.001 for high nutrient loading) and PO₄^3--P (R² = 0.378, P = 0.034 for low nutrient loading; R² = 0.772, P = 0.001 for high nutrient loading) concentrations, while that of H1 communities was only correlated with NH₄⁺-N at high nutrient loading (R² = 0.864, P = 0.001). Our results reveal the potential of using rrn copy number to evaluate the community sensitivity to nutrient disturbances, but community's historical contingency need to be taken in account.

Identifying ecological processes driving vertical and horizontal archaeal community assemblages in a contaminated urban river

Understanding environmental factors driving ecological processes of archaeal communities in heavily contaminated rivers is crucial for improvements in river ecological monitoring and indication. However, succession mechanisms underlying vertical and horizontal archaeal community assemblages in contaminated rivers remains largely unstudied. Here, to investigate ecological processes controlling archaeal community succession in a contaminated urban river, multivariate statistics approaches were applied to fields samples collected from locations representing vertical and horizontal assemblages of archaeal community. Our results revealed that archaeal community in the river showed distinct vertical and horizontal distribution patterns and the differences between water and sediment samples were most significant. Beta-diversity patterns in the vertical and horizontal assemblages are both almost completely caused by species replacement between sampling points (horizontal β_SIM = 0.60 ± 0.09, β_NES = 0.09 ± 0.05; vertical β_SIM = 0.40 ± 0.07, β_NES = 0.10 ± 0.06). Considering phylogenetic turnover deviation, homogenizing dispersal was the most crucial process dominating archaeal community assemblages in water samples while main ecological process in sediment samples was variable selection. Euryarchaeota and Thaumarchaeota were found to prefer high-nutrients and low-nutrients environments, respectively. Analysis of environmental drivers of archaeal phyla distribution and community assemblages indicated that nutrients played a decisive role in driving the sediment archaeal community. Dissolved oxygen (DO) explained the most variation in phylogenetic turnover deviation within all water archaeal community while oxidation reduction potential (ORP) contributed most for horizontal sediment archaeal community assemblages. These findings help to indicate the pollution situation of the river and provide information to predict how archaeal communities would respond to different environmental variations.

Rare Species Shift the Structure of Bacterial Communities Across Sphagnum Compartments in a Subalpine Peatland

Sphagnum-associated microbiomes are crucial to Sphagnum growth and peatland ecological functions. However, roles of rare species in bacterial communities across Sphagnum compartments are poorly understood. Here the structures of rare taxa (RT) and conditionally abundant and rare taxa (CART) from Sphagnum palustre peat (SP), S. palustre ectosphere (Ecto) and S. palustre endosphere (Endo) were investigated in the Dajiuhu Peatland, central China. Our results showed that plant compartment effects significantly altered the diversities and structures of bacterial communities. The Observed species and Simpson indices of RT and CART in alpha diversity significantly increased from Endo to SP, with those of Ecto in-between. The variations of community dissimilarities of RT and CART among compartments were consistent with those of whole bacterial communities (WBC). Network analysis indicated a non-random co-occurrence pattern of WBC and all keystone species are affiliated with RT and CART, indicating their important role in sustaining the WBC. Furthermore, the community structures of RT and CART in SP were significantly shaped by water table and total nitrogen content, which coincided with the correlations between WBC and environmental factors. Collectively, our results for the first time confirm the importance of rare species to bacterial communities through structural and predicted functional analyses, which expands our understanding of rare species in Sphagnum-associated microbial communities in subalpine peatlands.

Spatial variation of sediment bacterial community in an acid mine drainage contaminated area and surrounding river basin

Microbial community is sensitive to the variations of environment, and it plays an important role in biogeochemical cycling in acid mine drainage (AMD). In this study, an integrated high-throughput absolute abundance quantification (iHAAQ) method was applied to study the dynamics of microbial community and the characteristics of microorganism. The results showed a significant difference in bacterial community with diversity being higher in watershed area. The main influential factors for bacterial communities in watershed were physicochemical properties (e.g., pH and potassium), while in mining areas the main driving factors were metals/metalloids (e.g., As, Zn, and Pb). Notably, the major functions of microbial community were transporter and ABC transporter in mining area, while two-component system was more abundant in watershed by the Kyoto Encyclopedia of Genes and Genomes (KEGG) annotation analysis (level 3). In particular, Phyllobacterium, Bacteroides, and Sulfurovum were demonstrated to be potentially useful bacterial species for bioremediation, which should be a good choice for future studies. These results could facilitate our understanding of microbial diversity in different sediments of mining areas and identify microbial communities for bioremediation projects.

The responses of bacterial community and N2O emission to nitrogen input in lake sediment: Estrogen as a co-pollutant

Excessive nitrogen (N) input is one of the most important causative factors of lake eutrophication, which has aroused increasing public attention in past decades. Estrogen contamination is also an increasing environmental problem in aquatic systems around the world. Although both substances usually co-exist in aquatic ecosystems, many researches have only investigated the influences of either N or estrogen individually on sediment bacterial community and nitrous oxide (N₂O) emission. Knowledge regarding the combined effects of N and estrogen is still very limited. In this study, a 30-day laboratory incubation experiment was performed to examine the impacts of different N sources (ammonium and nitrate) combined with 17β-estradiol (E2) on sediment bacterial community. High-throughput 16S rRNA gene sequencing technique was used and N₂O emission was measured. The results revealed that the relative abundances of Proteobacteria and Bacteroidetes were higher in nitrate treatment than ammonium treatment. Compared to N treatments, N and E2 combined treatments showed higher relative abundances of Proteobacteria, Bacteroidetes, and Firmicutes, but lower relative abundances of Chloroflexi, Acidobacteria, and Actinobacteria over entire incubation period. At the genus level, the relative abundances of genera Flavobacterium, Pseudomonas, Arenimonas, Novosphingobium, Massilia, Aquabacterium, and Bacillus were enhanced by N treatments and especially N and E2 combined treatments, compared to sediment without addition of N and E2. However, the relative abundances of Sporacetigenium, Gaiella, Desulfatiglans, Nitrospira, and Haliangium were decreased in N treatments. Apart from the changes in bacterial community structure, N₂O emission was also influenced by different treatments. Nitrate exerted a more significant positive effect on N₂O emission than ammonium, and the cumulative emission of N₂O was highest in nitrate and E2 combined treatment. Very low abundances of ammonia monooxygenase (amoA) gene and hydroxylamine oxidase (hao) gene were observed in sediments compared to other genes involved in N cycles (such as nitrate reductase (narG and napA) genes, nitrite reductase (nirB, nirK, and nrfA) genes, and nitric oxide reductase (norB) gene), implying that denitrification rather than nitrification played an important role in sediments. The abundances of napA, nirK, and norB were higher in N and E2 combined treatments, indicating that E2 might provide a carbon source for denitrifiers. Moreover, decrease in the abundance of nitrous oxide reductase (nosZ) gene during the denitrifying process in N and E2 combined treatment might be an important reason for increases of N₂O emission. These results indicated that alterations of the bacterial community structure due to the co-existence of N and E2 could also change the abundances of genes involved in N cycle.

Combined use of calcium nitrate addition and anion exchange resin capping to control sedimentary phosphorus release and its nitrate‑nitrogen releasing risk

Calcium nitrate (Ca(NO₃)₂) addition can be used to control the release of phosphorus from sediments, however it can also cause an increase in the concentration of nitrate‑nitrogen (NO₃^--N) in the water column. The risk of NO₃^--N release from the Ca(NO₃)₂-injected sediments may be reduced by the placement of the anion exchange resin (AER) capping layer. In this study, the effectiveness of the combined use of Ca(NO₃)₂ addition and AER capping to prevent the liberation of phosphorus from sediments was investigated, and the reduction of the risk of NO₃^--N released from the Ca(NO₃)₂-injected sediment by the AER capping was also evaluated. The combined application of Ca(NO₃)₂ addition and AER capping could tremendously reduce the amount of soluble reactive phosphorus (SR-P) in the overlying water, with SR-P reduction rates of 75.9-98.7%. Furthermore, it could cut down the contents of high-resolution diffusive gradients in thin films (DGT)-labile phosphorus in the sediments, resulting in the formation of phosphorus static layer in the upper sediments. The combined treatment using Ca(NO₃)₂ and AER had a relatively small effect on the contents of mobile phosphorus in the sediments, but it could greatly increase the amount of residual phosphorus in the top 30mm sediments (increased by 27.7-42.9%). The amount of NO₃^--N in the overlying water under the action of the combined treatment method using Ca(NO₃)₂ and AER was much lower than that under the action of the single Ca(NO₃)₂ treatment during the early stage of sediment remediation. In conclusion, the combined use of Ca(NO₃)₂ addition and AER capping is a more promising strategy for the control of sedimentary phosphorus release than the single use of Ca(NO₃)₂ addition from the point of view of both the control efficiency of P release from sediments and the releasing risk of the added nitrate.

Distribution and co-occurrence of antibiotic and metal resistance genes in biofilms of an anthropogenically impacted stream

Urban stream biofilms are potential hotspots for resistomes and antibiotic resistance genes (ARGs). Biofilm communities that harbor resistance genes may be influenced by contaminant input (e.g., metals and antibiotics) from urban drainage (i.e., Wastewater Treatment Plant effluent and stormwater runoff); understanding the ecology of these communities and their resistome is needed. Given the potential importance of the co-occurrence of ARGs and metal resistance genes (MRGs), we investigated the spatial and temporal distribution of three ARGs (tetracycline [tetW] and sulfonamides [sulI and sulII]), four MRGs (lead [pbrT], copper [copA], and cadmium/cobalt/zinc [czcA and czcC]) via quantitative PCR and biofilm bacterial community composition via MiSeq 16S sequencing at four time points along an urbanization gradient (i.e., developed, agriculture, and forested sites) in a stream's watershed. Our results revealed that ARG and MRG abundances were significantly affected by land use-time interaction, with greater resistance abundances occurring in more urban locations during particular times of the year. It was also observed that changes in ARG and MRG profiles were influenced by differences in community composition among land use types, and that these differences were in response to changes in stream physicochemical parameters (pH, redox, temperature, nutrient availability, and metal concentration) that were driven by sub-watershed land use. Moreover, the dynamics between ARGs and MRGs within these communities correlated strongly and positively with one another. Taken altogether, our results demonstrate that changes in environmental properties due to human activity may drive the ARG-MRG profiles of biofilm communities by modulating community structure over time and space.

Determination of vertical and horizontal assemblage drivers of bacterial community in a heavily polluted urban river

Identifying vertical and horizontal assemblage drivers of bacterial community is important for improving the efficacies of ecological evaluation and remediation for a huge contaminated river (e.g. black-odor urban river). However, little is known about the effect of stochastic vs. deterministic processes on the reliability of the identification processes. Here, a comprehensive analysis was performed to reveal vertical and horizontal assemblage drivers of bacterial community in a heavily polluted urban river (total area of 4.23 km² and total length of 9.3 km), considering the relative importance of stochastic and deterministic processes. Heterogeneous bacterial community assemblages were observed in both vertical and horizontal profiles and the differences in the bacterial community between depths were relatively significant at genus level. The higher values for the Simpson dissimilarity index (horizontal β_SIM = 0.59 ± 0.02; vertical β_SIM = 0.48 ± 0.03) compared to the nestedness-resultant dissimilarity index (horizontal β_NES = 0.05 ± 0.02; vertical β_NES = 0.05 ± 0.05) showed that species replacement explained both the vertical and horizontal beta-diversity patterns. Comparison of horizontal and vertical Sørensen dissimilarity indices further indicated that the biodiversity of vertical community deserved more attention due to the shorter geographical distance with similar beta-diversity patterns compared to horizontal assemblages. Various traditional analysis without consideration for phylogenetic turnover revealed that TN, TP, NH₄⁺-N, DO, ORP, Conductivity and COD_Mn were all the related environmental factors that influenced bacterial community. However, after taking stochastic vs. deterministic processes into account, only NH₄⁺-N and ORP were identified as the main driving forces of trends in the vertical and in the horizontal assembly of bacterial community in the polluted urban river, respectively. This study is helpful for improving ecological assessment methodology and remediation strategy for contaminated urban rivers.

Distinct responses of planktonic and sedimentary bacterial communities to anthropogenic activities: Case study of a tributary of the Three Gorges Reservoir, China

Anthropogenic activities can cause serious negative effects on ecosystems. Despite the ecological significance of bacterial communities, the integrated biogeography of planktonic and sedimentary bacterial communities in response to anthropogenic activities is not adequately understood. Here, we examined environmental parameters and the composition of planktonic and sedimentary bacteria in the Yulin River, a tributary of Three Gorges Reservoir, in response to changes in land use and dam construction. The results revealed that human-induced land use changes enhanced the nutrient concentrations in surface water and dam construction reduced the content of carbon and nitrogen in immediately downstream sediments. Intensified human-dominated land use showed a slight impact on sedimentary bacterial communities but largely reduced the diversity of planktonic bacterial communities. Moreover, human-induced land use changes increased the abundance of genes associated with denitrification, nitrification, and anammox in planktonic bacterial communities by 19.04%, 32.40% and 30.45%, respectively. In dam construction regions, the diversity and nutrient-related metabolic activity of sedimentary bacterial communities immediately downstream of the dam were decreased, whereas these changes were not observed in planktonic bacterial communities. Additionally, bacterial community composition was significantly related to nutrient concentrations variability and followed a distance-decay pattern. Furthermore, environmental effects explained more of the variation in planktonic bacterial community composition as compared with spatial effects did, whereas, sedimentary bacterial communities were more closely related to spatial effects. Our results demonstrated the distinct responses of planktonic and sedimentary bacterial communities to anthropogenic activities, and offered new insight for understanding their potential ecological influence on rivers.

In search of microbial indicator taxa: shifts in stream bacterial communities along an urbanization gradient

A majority of environmental studies describe microbiomes at coarse scales of taxonomic resolution (bacterial community, phylum), ignoring key ecological knowledge gained from finer-scales and microbial indicator taxa. Here, we characterized the distribution of 940 bacterial taxa from 41 streams along an urbanization gradient (0%-83% developed watershed area) in the Raleigh-Durham area of North Carolina (USA). Using statistical approaches derived from macro-organismal ecology, we found that more bacterial taxa were classified as intolerant than as tolerant to increasing watershed urbanization (143 vs 48 OTUs), and we identified a threshold of 12.1% developed watershed area beyond which the majority of intolerant taxa were lost from streams. Two bacterial families strongly decreased with urbanization: Acidobacteriaceae (Acidobacteria) and Xanthobacteraceae (Alphaproteobacteria). Tolerant taxa were broadly distributed throughout the bacterial phylogeny, with members of the Comamonadaceae family (Betaproteobacteria) presenting the highest number of tolerant taxa. Shifts in microbial community structure were strongly correlated with a stream biotic index, based on macroinvertebrate composition, suggesting that microbial assemblages could be used to establish biotic criteria for monitoring aquatic ecosystems. In addition, our study shows that classic methods in community ecology can be applied to microbiome datasets to identify reliable microbial indicator taxa and determine the environmental constraints on individual taxa distributions along environmental gradients.

Profiling microbial communities in a watershed undergoing intensive anthropogenic activities

In lotic ecosystems highly susceptible to anthropogenic activities, the influences of environmental variables on microbial communities and their functions remain poorly understood, despite our rapidly increasing sequencing ability. In this study, we profiled the microbial communities in the hyporheic sediments of a watershed undergoing intensive anthropogenic activities via next-generation sequencing of 16S rRNA V4-V5 hypervariable regions on Illumina MiSeq platform. Tidal impacts on microbial communities were investigated via co-occurrence networks. In addition, the influences of physicochemical variables including salinity, and the concentrations of nutrients, organic matter and heavy metals on the microbial communities were explored via canonical correspondence analyses. The sediment samples were collected from 19 sites covering the whole main river stem of the target watershed (n = 19; Maozhou river watershed, Shenzhen, China). The samples were sub-divided in the field for microbiological analyses and measurements of physicochemical variables. The results indicated that core microbiome was associated with archaea methanogens and bacteria members from Proteobacteria, Chloroflexi, Bacteroidetes, Acidobacteria, Synergistetes and Firmicutes, among which, gram-negative and anaerobic bacteria genera contributing to the cycling of carbon, nitrogen and sulfur were predominant. Site-specific microbiomes were revealed that may serve as indicators of local environmental conditions (e.g., members affiliated to Oceanospirillales were abundant at sites with salt intrusion). Distinct microbial co-occurrence networks were identified for non-tidal, inter-tidal and tidal sites. Major environmental factors influencing microbial community composition included the concentrations of nitrate and bicarbonate in river water, pore water concentrations of sulfate, dissolved organic carbon and electrical conductivity, as well as manganese concentrations associated with the solid sediment. Collectively, the results of this study provide fundamental insights into the influence of environmental perturbations on microbial community composition in a lotic system, which may aid in the design of effective remediation and/or restoration strategies in the target watershed and beyond.

Water Quality and Microbial Community Changes in an Urban River after Micro-Nano Bubble Technology in Situ Treatment

Currently, black-odor river has received great attention in China. In this study, the micro-nano bubble technology (MBT) was used to mitigate the water pollution rapidly and continuously by increasing the concentration of dissolved oxygen (DO) in water. During treatment, the concentration of DO increased from 0.60 mg/L to over 5.00 mg/L, and the oxidation reduction potential (ORP) also changed from a negative value to over 100.00 mV after only five days aeration. High throughput pyrosequencing technology was employed to identify the microbial community structure. At genus level, the dominant bacteria were anaerobic and nutrient-loving microbes (e.g., Arcobacter sp., Azonexus sp., and Citrobacter sp.) before, and the relative abundances of aerobic and functional microbes (e.g., Perlucidibaca sp., Pseudarcicella sp., Rhodoluna sp., and Sediminibacterium sp.) were increased after treatment. Meanwhile, the water quality was significantly improved with about 50% removal ratios of chemical oxygen demand (CODCr) and ammonia nitrogen (NH4+-N). Canonical correspondence analysis (CCA) results showed that microbial community structure shaped by COD, DO, NH4+-N, and TP, CCA1 and CCA2 explained 41.94% and 24.56% of total variances, respectively. Overall, the MBT could improve the water quality of urban black-odor river by raising the DO and activate the aerobic microbes.