The impact of wastewater treatment effluent on microbial biomasses and diversities in coastal sediment microcosms of Hangzhou Bay

Typical antibiotic resistance genes and their association with driving factors in the coastal areas of Yangtze River Estuary

The massive use of antibiotics has led to the escalation of microbial resistance in aquatic environment, resulting in an increasing concern regarding antibiotic resistance genes (ARGs), posing a serious threat to ecological safety and human health. In this study, surface water samples were collected at eight sampling sites along the Yangtze River Estuary. The seasonal and spatial distribution patterns of 10 antibiotics and target genes in two major classes (sulfonamides and tetracyclines) were analyzed. The findings indicated a high prevalence of sulfonamide and tetracycline resistance genes along the Yangtze River Estuary. Kruskal-Wallis analysis revealed significant seasonal variations in the abundance of all target genes. The accumulation of antibiotic resistance genes in the coastal area of the Yangtze River Estuary can be attributed to the influence of urban instream runoff and the discharge of effluents from wastewater treatment plants. ANISOM analysis indicated significant seasonal differences in the microbial community structure. VPA showed that environmental factors contribute the most to ARG variation. PLS-PM demonstrate that environmental factors and microbial communities pose direct effect to ARG variation. Analysis of driving factors influencing ARGs in this study may shed new insights into the mechanism of the maintenance and propagation of ARGs.

Effects of oilfield-produced water discharge on the spatial patterns of microbial communities in arid soils

Recently intensified oil exploitation has resulted in the discharge of large amounts of wastewater containing high concentrations of organic matter and nutrients into the receiving aquatic and soil environments; however, the effects of oilfield-produced water on the soil microbiota are poorly understood. In this study, we conducted a comprehensive analysis to reveal the composition and diversity of the microbial community at horizontal and vertical scales in a typical arid soil receiving oilfield-produced water in Northwest China. Oilfield-produced water caused an increase in microbial diversity at the horizontal scale, and the communities in the topsoil were more variable than those in the subsoil. Additionally, the microbial taxonomic composition differed significantly between the near- and far-producing water soils, with Proteobacteria and Halobacterota dominating the water-affected and reference soil communities, respectively. Soil property analysis revealed that pH, salt, and total organic content influenced the bacterial communities. Furthermore, the oil-produced water promoted the complexity and modularity of distance-associated microbial networks, indicating positive interactions for soil ecosystem function, but not for irrigation or livestock watering. This is the first detailed examination of the microbial communities in soil receiving oilfield-produced water, providing new insights for understanding the microbial spatial distributions in receiving arid soils.

Assessing the effects of aquaculture on tidal flat ecological status using multi-metrics interaction-based index of biotic integrity (Mt-IBI)

Given tidal flat special environmental conditions and the degree of pollution caused by human activities, there is an urgent need to quantitatively assess their ecological status. Bioindication has become an indispensable part of environmental quality monitoring on account of its sensitivity to environmental disturbance. Thus, this study used bio-indicators to establish a multi-metrics-based index of biotic integrity (Mt-IBI) to evaluate the ecological status of the tidal flats with/without aquaculture through metagenomic sequencing. Four core indexes that were significantly correlated to other indexes with redundancy (p < 0.05), including Escherichia, beta-lactam antibiotic resistance genes, cellulase and xyloglucanases and the keystone species with 21° in the network, were selected after the screening processes. By implementing Mt-IBI in the tidal flats, the ecological health of the sampling sites was categorized into three levels, with Mt-IBI values of 2.01-2.63 (severe level), 2.81-2.93 (moderate level) and 3.23-4.18 (mild level), respectively. Through SEM analysis, water chemical oxygen demand and antibiotics were determined to be the primary controlling factors of the ecological status of tidal flat regions influenced by aquaculture, followed by salinity and total nitrogen. It is worth noting that the alteration of microbial communities impacted ecological status through the mediation of antibiotics. It is hoped that the results of our study will provide a theoretical basis for coastal environment restoration and that the use of Mt-IBI to assess ecosystem status in different aquatic environments will be further popularized in the future.

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.

Impact of climate change on coastal water quality and its interaction with pollution prevention efforts

The impact of climate change on nearshore coastal water quality and its interaction with pollution prevention efforts (e.g., the development of green and gray water infrastructure) still lack systematic investigation. This study performed a holistic analysis of the impact of climate change on the salinity and concentrations of total nitrogen (TN), total phosphorus (TP) and chlorophyll a (Chl.a) in Shenzhen Bay between Shenzhen and Hong Kong, the two most developed megacities in South China, based on three-dimensional hydrodynamic and water quality modeling. The major study findings were as follows. First, Chl.a was the most sensitive parameter, and its bay-wide average concentration in 2100 was predicted to be approximately 13% and 46% higher than those in 2015 under mild and rapid climate change scenarios, respectively. Second, sea level rise was found to be a major driver of all four water quality parameters, while temperature and radiation mainly influenced Chl.a and precipitation mainly influenced nutrients. Third, water quality responses to climate change were highly heterogeneous over the bay. Even under a mild climate change scenario, the highest location-specific changes (2100 vs. 2015) in salinity and TN, TP and Chl.a concentrations were projected to be approximately 21%, 19%, 25%, and 65%, respectively. Fourth, changes in seasonal variation due to climate change may lead to an enhanced ecological risk of algal blooms. Finally, the effect of reducing TN and TP concentrations by proposed water infrastructure development was found to be significantly weakened (nearly 40% and 20% for TN and TP, respectively, under a mild climate change scenario), while the negative effect (i.e., increase in the Chl.a concentration) was notably accelerated. Regional cooperation is critical for protecting the water quality of the bay, particularly under climate change. The insights obtained in this study are applicable to other coastal water zones around the world with similar socioeconomic backgrounds and climatic conditions.

Geographic patterns and determinants of antibiotic resistomes in coastal sediments across complex ecological gradients

Coastal areas are highly influenced by terrestrial runoffs and anthropogenic disturbances, commonly leading to ecological gradients from bay, nearshore, to offshore areas. Although the occurrence and distribution of sediment antibiotic resistome are explored in various coastal environments, little information is available regarding geographic patterns and determinants of coastal sediment antibiotic resistomes across ecological gradients at the regional scale. Here, using high-throughput quantitative PCR, we investigated the geographic patterns of 285 antibiotic resistance genes (ARGs) in coastal sediments across a  ~  200  km scale in the East China Sea. Sediment bacterial communities and physicochemical properties were characterized to identify the determinants of sediments antibiotic resistome. Higher richness and abundance of ARGs were detected in the bay samples compared with those in nearshore and offshore samples, and significant negative correlations between the richness and/or abundance of ARGs and the distance to coastline (DTC) were identified, whereas different types of ARGs showed inconsistency in their relationships with DTC. The composition of antibiotic resistome showed significant correlations with nutrition-related variables (including NH4 +-N, NO3 --N, and total phosphorus) and metals/metalloid (including As, Cu, Ni, and Zn), suggesting that terrestrial disturbances largely shape the antibiotic resistome. The Bipartite network showed strong associations between ARGs and mobile genetic elements (MGEs), and Partial Least Squares Path Modeling further revealed that terrestrial disturbance strength (as indicated by DTC) directly affected abiotic environmental conditions and bacterial community composition, and indirectly affected antibiotic resistome via MGEs. These findings provide insights into regional variability of sediment antibiotic resistome and its shaping path across complex ecological gradients, highlighting terrestrial disturbances as determinative forces in shaping coastal sediment antibiotic resistomes.

Spatio-temporal variations in the physiological profiles of streambed bacterial communities: implication of wastewater treatment plant effluents

The effluents of wastewater treatment plants (WWTPs) represent a complex mixture of nutrients and toxic substances, thus, the potential exists for the effluents to significantly impact the biochemical characteristics and bacterial communities of the receiving water. We examined spatial and seasonal patterns, and the impact of effluents on microbial biomass, bacterial community structure, and metabolic diversity on a fourth-order stream. We took triplicate sediment samples at five different locations along a 5000 m transect over three sampling periods. We quantified bacterial community structure as community-level physiological profiles and microbial biomass with phospholipid phosphate analysis. Our findings highlight the worrisome impacts of effluents on microbial biomass and bacterial metabolic diversity on the receiving water. Microbial biomass was significantly higher at the WWTP outfall compared to upstream and downstream sites and correlated positively with sediment physicochemical parameters. Furthermore, our data revealed significant spatial differences in bacterial community structure in the context of WWTP impact. High nutrient availability (lower carbon/nitrogen ratios) at the outfall increased site-specific bacterial metabolic diversity in winter but decreased the same in fall. Seasonal changes in the sedimentary microbial biomass and bacterial carbon substrate utilization were evident regardless of the spatial variations or impacts of the wastewater effluents. Communities in fall showed more versatile substrate utilization patterns than the winter communities. These results suggest that WWTP effluents significantly increased microbial biomass and highlight its mixed effects on bacterial community structure and metabolic diversity. Also, our data underscore a close association between sedimentary physicochemical parameters and the associated microbial functional activities.

Nitrogen-cycling gene pool shrunk by species interactions among denser bacterial and archaeal community stimulated by excess organic matter and total nitrogen in a eutrophic bay

Microbial densities, functional genes, and their responses to environment factors have been studied for years, but still a lot remains unknown about their interactions with each other. In this study, the abundances of 7 nitrogen cycling genes in the sediments from Hangzhou Bay were analyzed along with bacterial and archaeal 16S rRNA abundances as the biomarkers of their densities. The amount of organic matter (OM) and total nitrogen (TN) strongly positively correlated with each other and microbial densities, while total phosphate (TP) and ammonia-nitrogen (NH₃-N) did not. Most studied genes were density suppressed, while nirS was density stable, and nosZ and hzo were density irrelevant. This suggests eutrophication could limit inorganic nitrogen cycle pathways and the removal of nitrogen in the sediment and emit more greenhouse gases. This study provides a new insight of microbial community structures, functions and their interactions in the sediments of eutrophic bays.

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.

Growth and nutrient uptake of Myriophyllum spicatum under different nutrient conditions and its potential ecosystem services in an enclosed sea area in the East China Sea

We investigated the growth and nutrient uptake of Myriophyllum spicatum under different nutrient conditions and evaluated its implications for ecosystem services in an enclosed area of Jinshan. The specific growth rate ranged from 1.29%-4.37%/day, and the dissolved inorganic carbon and nitrogen, and phosphorus uptake rates were 1.30-1.62, 0.040-0.453, and 0.003-0.027 mg/(g∙day), respectively, under different nutrient conditions. The O₂-production and carbon-sequestration efficiencies in the field were 154.30 and 1.25 mg/(g DW∙h), respectively. The average removal efficiencies of NH₄⁺-N, NO₃^--N, NO₂^--N, and PO₄^3--P were 43.05%, 97.03%, 64.26%, and 59.24%, respectively, in M. spicatum-cultivated areas compared with in the open sea. Harvesting of M. spicatum removed 12,936.87, 1289.97 and 114.81 kg of carbon, nitrogen, and phosphorus, respectively, from seawater in Jinshan in Nov, 2018. In conclusion, M. spicatum is a good candidate for integrated macrophyte/animal multi-trophic aquaculture in terms of nutrient extraction and economic diversification in low-salinity environments.

Sediment bacterial community structures and their predicted functions implied the impacts from natural processes and anthropogenic activities in coastal area

Coastal ecosystem structures and functions are changing under natural and anthropogenic influences. In this study, surface sediment samples were collected from disturbed zone (DZ), near estuary zone (NEZ), and far estuary zone (FEZ) of Hangzhou Bay, one of the most seriously polluted bays in China. The bacterial community structures and predicted functions varied significantly in different zones. Firmicutes were found most abundantly in DZ, highlighting the impacts of anthropogenic activities. Sediment total phosphorus was most influential on the bacterial community structures. Predicted by PICRUSt analysis, DZ significantly exceeded FEZ and NEZ in the subcategory of Xenobiotics Biodegradation and Metabolism; and DZ enriched all the nitrate reduction related genes, except nrfA gene. Seawater salinity and inorganic nitrogen, respectively as the representative natural and anthropogenic factor, performed exact-oppositely in nitrogen metabolism functions. The changes of bacterial community compositions and predicted functions provide a new insight into human-induced pollution impacts on coastal ecosystem.

Nutrient bioextraction and microalgae growth inhibition using submerged macrophyte Myriophyllum spicatum in a low salinity area of East China Sea

Myriophyllum spicatum was cultivated in a low salinity area of Hangzhou Bay (salinity 5.8-6.5), from August to October in 2016, to evaluate the abilities of its nutrient bioextraction and microalgae growth inhibition. During the 72-day cultivation period, M. spicatum had a specific growth rate (SGR) of 6.23%day^-1 and increased 20-fold in biomass (wet weight). Tissue C, N and P assimilation quantities of M. spicatum were found to be 3279.39kg, 360.61kg and 26.97kg, respectively. The concentration of NH₄-N, NO₃-N, NO₂-N and PO₄-P after M. spicatum cultivation was decreased by 47.92%, 58.28%, 36.40% and 55.57%, respectively. The phytoplankton density was decreased from 1064.60×10⁴cellsL^-1 to 12.85×10⁴cellsL^-1. These results indicated that cultivation of M. spicatum can help in nutrient bioextraction and microalgae growth inhibition in low salinity marine water bodies.