Systematically quantifying the dynamic characteristics of PM2.5 in multiple indoor environments in a plateau city: Implication for internal contribution.

People generally spend most of their time indoors, making a comprehensive evaluation of air pollution characteristics in various indoor microenvironments of great significance for accurate exposure estimation. In this study, field measurements were conducted in Kunming City, Southwest China, using real-time PM2.5 sensors to characterize indoor PM2.5 in ten different microenvironments including three restaurants, four public places, and three household settings. Results showed that the daily average PM2.5 concentrations in restaurants, public spaces, and households were 78.4 ± 24.3, 20.1 ± 6.6, and 18.0 ± 4.3 µg/m3, respectively. The highest levels of indoor PM2.5 in restaurants were owing to strong internal emissions from cooking activities. Dynamic changes showed that indoor PM2.5 levels increased during business time in restaurants and public places, and cooking time in residential kitchens. Compared with public places, restaurants generally exhibit more rapid increases in indoor PM2.5 due to cooking activities, which can elevate indoor PM2.5 to high levels (5.1 times higher than the baseline) in a short time. Furthermore, indoor PM2.5 in restaurants were dominated by internal emissions, while outdoor penetration contributed mostly to indoor PM2.5 in public places and household settings. Results from this study revealed large variations in indoor PM2.5 in different microenvironments, and suggested site-specific measures for indoor PM2.5 pollution alleviation.

Invasive Spartina alterniflora accelerates the increase in microbial nitrogen fixation over nitrogen removal in coastal wetlands of China.

Salt marsh plants play a vital role in mediating nitrogen (N) biogeochemical cycle in estuarine and coastal ecosystems. However, the effects of invasive Spartina alterniflora on N fixation and removal, as well as how these two processes balance to determine the N budget, remain unclear. Here, simultaneous quantifications of N fixation and removal via 15N tracing experiment with native Phragmites australis, invasive S. alterniflora, and bare flats as well as corresponding functional gene abundance by qPCR were carried out to explore the response of N dynamics to S. alterniflora invasion. Our results showed that N fixation and removal rates ranged from 0.77 ± 0.08 to 16.12 ± 1.13 nmol/(g·h) and from 1.42 ± 0.14 to 16.35 ± 1.10 nmol/(g·h), respectively, and invasive S. alterniflora generally facilitated the two processes rates. Based on the difference between N removal and fixation rates, net N2 fluxes were estimated in the range of -0.39 ± 0.14 to 8.24 ± 2.23 nmol/(g·h). Estimated net N2 fluxes in S. alterniflora stands were lower than those in bare flats and P. australis stands, indicating that the increase in N removal caused by S. alterniflora invasion may be more than offset by N fixation process. Random forest analysis revealed that functional microorganisms were the most important factor associated with the corresponding N transformation process. Overall, our results highlight the importance of N fixation in evaluating N budget of estuarine and coastal wetlands, providing valuable insights into the ecological effect of S. alterniflora invasion.

Dynamics of Benthic Nitrate Reduction Pathways and Associated Microbial Communities Responding to the Development of Seasonal Deoxygenation in a Coastal Mariculture Zone.

Intensive mariculture activities result in eutrophication and enhance coastal deoxygenation. Deoxygenation profoundly influences nitrate reduction processes and further the fate of nitrogen (N) in coastal systems. Herein, 15N isotope labeling, real-time PCR, and high-throughput sequencing techniques were jointly used to investigate the participation and seasonal dynamics of sediment nitrate reduction pathways and the succession of functional microbial communities during the development of seasonal deoxygenation in a coastal aquaculture zone. Denitrification dominated benthic nitrate reduction (46.26-80.91%). Both denitrification and dissimilatory nitrate reduction to ammonium were significantly enhanced by summer deoxygenation (dissolved oxygen levels fell to 2.94 ± 0.28 mg L-1), while anammox remained unchanged. The abundance of the nitrous oxide reductase gene nosZ increased during deoxygenation. The community of the nosZ gene was sensitive to deoxygenation, with Azospirillum and Ruegeria accounting for the majority. Pelobacter was overwhelming in the nrfA gene (encoding dissimilatory nitrite reductase) community, which was less affected by deoxygenation. The variations of benthic nitrate reduction processes were driven by bottom water oxygen combined with temperature, chlorophyll a, and microbial gene abundances and community compositions. Our results implicated that seasonal oxygen-deficient zones could be substantial N sinks of coastal ecosystems and important for N balance. Effective management measures need to be developed to avoid further exacerbation of coastal deoxygenation and maintain the sustainable development of mariculture.

Metagenomic Views of Microbial Communities in Sand Sediments Associated with Coral Reefs.

Reef sediments, the home for microbes with high abundances, provide an important source of carbonates and nutrients for the growth and maintenance of coral reefs. However, there is a lack of systematic research on the composition of microbial community in sediments of different geographic sites and their potential effect on nutrient recycling and health of the coral reef ecosystem. In combination of biogeochemical measurements with gene- and genome-centric metagenomics, we assessed microbial community compositions and functional diversity, as well as profiles of antibiotic resistance genes in surface sediments of 16 coral reef sites at different depths from the Xisha islands in the South China Sea. Reef sediment microbiomes are diverse and novel at lower taxonomic ranks, dominated by Proteobacteria and Planctomycetota. Most reef sediment bacteria potentially participate in biogeochemical cycling via oxidizing various organic and inorganic compounds as energy sources. High abundances of Proteobacteria (mostly Rhizobiales and Woeseiales) are metabolically flexible and contain rhodopsin genes. Various classes of antibiotic resistance genes, hosted by diverse bacterial lineages, were identified to confer resistance to multidrug, aminoglycoside, and other antibiotics. Overall, our findings expanded the understanding of reef sediment microbial ecology and provided insights for their link to the coral reef ecosystem health.

Bait input altered microbial community structure and increased greenhouse gases production in coastal wetland sediment.

Coastal wetland reclamation contributed to development of aquaculture industry, and the residual bait accumulation in aquaculture processes could influence biogeochemical elements cycling, which threaten ecological functions and services in aquaculture and adjacent ecosystems. However, systematic studies for changes in sediment microbial community structure and greenhouse gasses (GHGs) production, as well as environmental parameters following bait input at time scale are still rare. A 90-day incubation experiment was conducted using sediment collected from coastal wetland in Qi'ao Island in southern China, followed by the observations of temporal variations of physicochemical properties, sediment microbial community, and GHGs production in response to different amounts of bait input (0, 20, and 40 mg bait g-1 wet sediment). The results showed that dissolved oxygen of overlying water was profoundly decreased owing to bait input, while dissolved organic carbon of overlying water and several sediment properties (e.g., organic matter, sulfide, and ammonium) varied in reverse patterns. Meanwhile, bait input led to significant loss of microbial community richness and diversity, and strongly altered microbial compositions from aerobic, slow-growing, and oligotrophic (Actinobacteriota, Chloroflexi, and Acidobacteriota) to anaerobic, fast-growing, and copiotrophic (Firmicutes and Bacteroidota). Moreover, both GHGs production and global warming potential were significantly enhanced by bait input, implying that aquaculture ecosystem is an important hotspot for global GHGs emission. Overall, bait input triggered quick responses of physicochemical properties, sediment microbial community, and GHGs production, followed by long-term resilience of the ecosystem. This study could provide new insight into temporal interactive effects of bait input on physicochemical properties, microbial community, and GHGs production, which can enhance the understanding of the temporal dynamics and ecological impacts of coastal aquaculture activities and emphasize the necessity of sustainable assessment and management in aquaculture ecosystems.

Bacterial, archaeal, and fungal community structure and interrelationships of deep-sea shrimp intestine and the surrounding sediment.

Invertebrate shrimp are one of the dominant benthic macrofaunae in the deep-sea environment. The microbiota of shrimp intestine can contribute to the adaptation of their host. The impact of surrounding sediment on intestinal microbiota has been observed in cultured shrimp species, but needs to be further investigated in deep-sea shrimp. The characterization of bacterial, archaeal, and fungal community structure and their interrelationships is also limited. In this study, wild-type deep-sea shrimp and the surrounding sediment were sampled. Shrimp individuals incubated in a sediment-absent environment were also used in this study. Microbial community structure of the shrimp intestine and sediment was investigated through amplicon sequencing targeting bacterial 16S rRNA genes, archaeal 16S rRNA genes, and fungal ITS genes. The results demonstrate distinct differences in community structure between shrimp intestine and the surrounding sediment and between surface and deep (5 mbsf) sediment. The composition of the intestinal microbiota in shrimp living without sediment was different from that of wild-type shrimp, indicating that the presence or absence of sediment could influence the shrimp intestinal microbiota. Carbohydrate metabolism, energy metabolism (carbon fixation, methane metabolism, nitrogen metabolism, and sulfur metabolism), amino acid metabolism, and xenobiotic biodegradation were the most commonly predicted microbial functionalities and they interacted closely with one another. Overall, this study provided comprehensive insights into bacterial, archaeal, and fungal community structure of deep-sea shrimp intestine as well as potential ecological interactions with the surrounding sediment. This study could update our understanding of the microbiota characteristics in shrimp and sediment in deep-sea ecosystems.

Effects of marine produced organic matter on the potential estuarine capacity of NOx- removal.

Dissolved inorganic nitrogen (DIN) is very high in the Pearl River Estuary (PRE) and nitrate (NOx-) removal processes such as denitrification, anaerobic ammonium oxidation (anammox) and dissimilatory nitrate reduction to ammonium (DNRA) are important for determining export of DIN to coastal waters. However, fluxes of NOx- removal and influencing factors in the PRE are still unclear. We conducted 4 cruises at 11 sites in the PRE to investigate potential NOx- removal rates, their contributions, and corresponding gene abundances, and controlling factors in surface sediments (0-5 cm). The results showed that the potential rates of denitrification, anammox, and DNRA as well as their contributions varied spatially and seasonally. Denitrification (1.98 ± 1.7 µg N g-1 d-1) was the major NOx- removal processes (68.43 ± 14.61%) while DNRA (0.45 ± 0.28 µg N g-1 d-1) contributed 22.61 ± 14.89% in NOx- removal. The NOx- removal processes and corresponding gene abundances were correlated with the chlorophyll concentrations in both overlying water and sediment, indicating that marine-produced organic matter was the major driver for benthic NOx- removal processes. In addition, water column turbidity had important effects on primary production, which affects benthic N processes. Our study provides evidences for that the turbidity-regulated primary production in overlying water is the primary driver for benthic NOx- removal processes. The contribution of sediment NOx- removal fluxes to water column NOx- concentration was low in the upper estuary and increased in the lower estuary where marine produced chlorophyll a was higher. However, daily fluxes of NOx- removal were estimated to account for only 0.18-7.22% (mean 1.85 ± 1.62%) of NOx- in the whole overlying water column. This suggests that most riverine NOx- was exported out into the adjacent coastal waters.

Shifts in the relative abundance and potential rates of sediment ammonia-oxidizing archaea and bacteria along environmental gradients of an urban river-estuary-adjacent sea continuum.

Ammonia-oxidizing archaea (AOA) and bacteria (AOB) play important roles in N cycling in sediments globally. However, little is known about their ammonia oxidation rates along a river-estuary-sea continuum. In this study, we investigated how the potential ammonia oxidation rates (PARs) of AOA and AOB changed spatially along a continuum comprising three habitats: the Shanghai urban river network, the Yangtze Estuary, and the adjacent East China Sea, in summer and winter. The AOA and AOB PARs (0.53 ± 0.49 and 0.72 ± 0.69 µg N g-1 d-1, mean ± SD, respectively) and their amoA gene abundance (0.47 ± 0.85 × 106 and 2.4 ± 3.54 × 106 copies g-1, respectively) decreased along the continuum, particularly from the urban river to the estuary, driven by decreasing sediment total organic C and N and other correlated inorganic nutrients (e.g., NH4+) along the gradient of anthropogenic influences. These spatial patterns were consistent between the seasons. The urban river network, where the anthropogenic influences were strongest, saw the largest seasonal differences, as both AOA and AOB had higher PARs and abundance in summer than in winter. The ratios between AOA and AOB PARs (~0.87 ± 0.51) and gene abundances (~0.25 ± 0.24), however, were predominantly <1, indicating an AOB-dominated community. Comparing the different NH4+ consumption pathways, total aerobic oxidation accounted for 12-26% of the total consumption, with the largest proportion in the estuary, where the system was well oxygenated, and the lowest in the adjacent sea, where inorganic N was highly depleted. This study revealed the spatiotemporal patterns of AOA and AOB potential rates and gene abundance along gradients of human influences and identified organic matter and nutrients as key environmental factors that shaped the variation of AOA and AOB along the continuum.

Sediment nitrate reduction processes in response to environmental gradients along an urban river-estuary-sea continuum.

Sediment denitrification (DEN), anaerobic ammonium oxidation (Anammox), and dissimilatory nitrate reduction to ammonium (DNRA) are three important nitrate (NO3-) reduction pathways in aquatic ecosystems. These processes modify nitrogen (N) loadings from land to the ocean, with important implications on the management of coastal eutrophication. While NO3- reduction has been studied intensively for various types of habitats, studies on its distributions along river-estuary-sea continua remain scarce. In this study, we examined these three pathways along a N-laden urban river-estuary-sea continuum comprised of three types of habitats (urban river, estuary, and adjacent sea) in the densely populated Shanghai-East China Sea area. The potential DEN, Anammox, and DNRA rates decreased seaward both in summer and winter in response to decreasing sediment organic matter (OM, 20 to 7 to 7 mg C g-1), ferrous oxide (9 to 2.7 to 2.8 mg Fe g-1), and bottom water dissolved inorganic nitrogen (543 to 112 to 21 µM). Among these pathways, DEN remained a major component (~69.6%) across habitats, while Anammox (47.9%) rivaled DEN (48.3%) in the urban river in winter. N retention index (NIRI), the ratio between retained and removed NO3-, ranged from 0 to 0.5 and increased downstream. Together, these results suggest that the decreasing gradients of OM and inorganic matter shape the distribution of NO3- reduction along the continuum, reflecting the diminishing impact of the river and human inputs from the urban river to the ocean. Our results highlight the importance of taking a continuum perspective in N cycling studies and emphasize the role of urban rivers as N removal hotspots, which should be a focus of research and management.

Bacterial Community Shifts Driven by Nitrogen Pollution in River Sediments of a Highly Urbanized City.

Effects of nitrogen pollution on bacterial community shifts in river sediments remain barely understood. Here, we investigated the bacterial communities in sediments of urban and suburban rivers in a highly urbanized city, Shanghai. Sediment nitrate (NO3-) and ammonia (NH4+) were highly accumulated in urban river. Operation Taxonomic Units (OTUs), Abundance-based Coverage Estimators (ACEs) and Chao 1 estimator in urban rivers were slightly lower than those in suburban rivers, while Shannon and Simpson indices were higher in urban rivers than those in suburban rivers. Proteobacteria, Firmicutes, and Bacteroidetes were the dominant bacterial phylum communities, accounting for 68.5-84.9% of all communities. In particular, the relative abundances of Firmicutes and Nitrospirae were significantly higher in suburban rivers than in urban rivers, while relative abundances of Bacteroidetes, Verrucomicrobia, and Spirochaetes were significantly lower in suburban rivers than in urban rivers. NH4+ was significantly and negatively correlated with abundances of Firmicutes, Nitrospirae, and Actinobacteria. Importantly, the significant and negative effects of sediment NH4+ on bacterial richness and diversity suggested that nitrogen pollution likely contribute to the decrease in the bacterial richness and diversity. The results highlight that nitrogen enrichment could drive the shifts of bacterial abundance and diversity in the urban river sediments where are strongly influenced by human activities under the rapid urbanization stress.

Effects of multiple antibiotics exposure on denitrification process in the Yangtze Estuary sediments.

Denitrification is a dominant reactive nitrogen removal pathway in most estuarine and coastal ecosystems, and plays a significant role in regulating N2O release. Although multiple antibiotics residues are widely detected in aquatic environment, combined effects of antibiotics on denitrification remain indistinct. In this work, 5 classes of antibiotics (sulfonamides, chloramphenicols, tetracyclines, macrolides, and fluoroquinolones) were selected to conduct orthogonal experiments in order to explore their combined effects on denitrification. 15N-based denitrification and N2O release rates were determined in the orthogonal experiments, while denitrifying functional genes were examined to illustrate the microbial mechanism of the combined antibiotics effect. Denitrification rates were inhibited by antibiotics treatments, and synergistic inhibition effect was observed for multiple antibiotics exposure. Different classes of antibiotics had different influence on N2O release rates, but multiple antibiotics exposure mostly led to stimulatory effect. Abundances of denitrifying functional genes were inhibited by multiple antibiotics exposure due to the antimicrobial properties, and different inhibition on denitrifiers may be the major mechanism for the variations of N2O release rates. Combined effects of antibiotics on denitrification may lead to nitrate retention and N2O release in estuarine and coastal ecosystems, and consequently cause cascading environmental problems, such as greenhouse effects and hyper-eutrophication.

PAHs uptake and translocation in Cinnamomum camphora leaves from Shanghai, China.

Foliage uptake and inner-leaf translocation of polycyclic aromatic hydrocarbons (PAHs) by Cinnamomum camphora from different urbanized areas were comparatively investigated in this study. Spatial and seasonal variations of ∑16PAHs in leaves were observed, likely due to the diversity of leaf wax contents sampled in different seasons and locations. A negative correlation between the wax contents and ∑16PAHs concentrations in the cuticular wax was observed. The low values of TFf-m (translocation factor from foliar dust to mesophyll) indicated a poor translocation ability of PAHs from the foliar dust to the mesophyll. However, the transportation of PAHs from the foliar dust to the cuticular wax was the primary pathway of leaf accumulation, and TFf-w (translocation factor from foliar dust to cuticular wax) values showed an increasing tendency of low molecular weight (LMW) PAHs and a decreasing tendency of high molecular weight (HMW) PAHs. This result indicated a rapid diffusion of gas-phase PAHs with LMW and a slow desorption of the particle-bound PAHs with HMW in the foliar dust. The concentrations of PAHs pollutants followed an obvious order of Rural area>Suburb area>Urban area in winter, and the higher contaminated locations were associated with some pollution sources nearby. Furthermore, the results of principal component analysis with multiple linear regression analysis analysis indicated that PAHs in leaves derived mainly from vehicle emissions. Overall, the accumulation and transformation of PAHs in leaves suggests the extensive amount of atmospheric pollutant release in high urbanization area.

Dissimilatory nitrate reduction processes in sediments of urban river networks: Spatiotemporal variations and environmental implications.

Urbanizations have increased the loadings of reactive nitrogen in urban riverine environments. However, limited information about dissimilatory nitrate reduction processes and associated contributions to nitrogen removal is available for urban riverine environments. In this study, sediment slurry experiments were conducted with nitrogen isotope-tracing technique to investigate the potential rates of denitrification, anaerobic ammonium oxidation (anammox) and dissimilatory nitrate reduction to ammonium (DNRA) and their contributions to nitrate reduction in sediments of urban river networks, Shanghai. The potential rates of denitrification, anammox and DNRA measured in the study area ranged from 0.193 to 98.7 nmol N g-1 h-1 dry weight (dw), 0.0387-23.7 nmol N g-1 h-1 dw and 0-10.3 nmol N g-1 h-1 dw, respectively. Denitrification and DNRA rates were higher in summer than in winter, while anammox rates were greater in winter than in summer for most sites. Dissolved oxygen, total organic carbon, nitrate, ammonium, sulfide, Fe(II) and Fe(III) were found to have significant influence on these nitrate reduction processes. Denitrification contributed 11.5-99.5%% to total nitrate reduction, as compared to 0.343-81.6% for anammox and 0-52.3% for DNRA. It is estimated that nitrogen loss of approximately 1.33 × 105 t N year-1 was linked to both denitrification and anammox processes, which accounted for about 20.1% of total inorganic nitrogen transported annually into the urban river networks of Shanghai. Overall, these results show the potential importance of denitrification and anammox in nitrogen removal and provide new insight into the mechanisms of nitrogen cycles in urban riverine environments.

Polycyclic aromatic hydrocarbons and black carbon in intertidal sediments of China coastal zones: Concentration, ecological risk, source and their relationship.

Polycyclic aromatic hydrocarbons (PAHs) and black carbon (BC) have attracted many attentions, especially in the coastal environments. In this study, spatiotemporal distributions of PAHs and BC, and the correlations between BC and PAHs were investigated in the intertidal sediments of China coastal zones. BC in sediments was measured through dichromate oxidation (BCCr) and thermal oxidation (BCCTO). The concentrations of BCCr in the intertidal sediments ranged between 0.61 and 6.32mgg(-1), while BCCTO ranged between 0.57 and 4.76mgg(-1). Spatial variations of δ(13)C signatures in TOC and BC were observed, varying from -21.13‰ to -24.87‰ and from -23.53‰ to -16.78‰, respectively. PAH contents of sediments ranged from 195.9 to 4610.2ngg(-1) in winter and 98.2 to 2796.5ngg(-1) in summer, and significantly seasonal variations were observed at most sampling sites. However, the results of potential toxicity assessment indicated low ecological risk in the intertidal sediments of China coastal zones. Greater concentrations of PAHs measured in the sediments of estuarine environments indicated that rivers runoff may have been responsible for the higher PAH pollution levels in the intertidal sediments of China coastal zones. Pearson's correlation analysis suggested that pyrogenic compounds of PAH were significantly related to BC, due to that both BC and these compounds derived mainly from the combustion process of fossil fuels and biomass. Overall, increasing energy consumptions caused by anthropogenic activities can contribute more emissions of BC as well as PAHs and thus improve the importance of BC in indicating pyrogenic compounds of PAHs in the intertidal sediments of China coastal zones.

nirS-Encoding denitrifier community composition, distribution, and abundance along the coastal wetlands of China.

For the past few decades, human activities have intensively increased the reactive nitrogen enrichment in China's coastal wetlands. Although denitrification is a critical pathway of nitrogen removal, the understanding of denitrifier community dynamics driving denitrification remains limited in the coastal wetlands. In this study, the diversity, abundance, and community composition of nirS-encoding denitrifiers were analyzed to reveal their variations in China's coastal wetlands. Diverse nirS sequences were obtained and more than 98 % of them shared considerable phylogenetic similarity with sequences obtained from aquatic systems (marine/estuarine/coastal sediments and hypoxia sea water). Clone library analysis revealed that the distribution and composition of nirS-harboring denitrifiers had a significant latitudinal differentiation, but without a seasonal shift. Canonical correspondence analysis showed that the community structure of nirS-encoding denitrifiers was significantly related to temperature and ammonium concentration. The nirS gene abundance ranged from 4.3 × 10(5) to 3.7 × 10(7) copies g(-1) dry sediment, with a significant spatial heterogeneity. Among all detected environmental factors, temperature was a key factor affecting not only the nirS gene abundance but also the community structure of nirS-type denitrifiers. Overall, this study significantly enhances our understanding of the structure and dynamics of denitrifying communities in the coastal wetlands of China.

Investigation into atmospheric PM2.5-borne PAHs in Eastern cities of China: concentration, source diagnosis and health risk assessment.

This study investigated PM2.5-PAHs associations collected in Beijing, Jinan, and Shanghai in Eastern China. The results indicated that PM2.5 concentrations in Beijing, Jinan, and Shanghai were 125.7 µg m(-3) (18.6-355.5 µg m(-3)), 115.9 µg m(-3) (44.2-345.4 µg m(-3)), and 85.1 µg m(-3) (24.3-232.8 µg m(-3)), respectively. The PAH concentrations in terms of PM2.5 in Beijing, Jinan, and Shanghai ranged from 23.2 to 819.8 ng m(-3), 25.7 to 727.1 ng m(-3), and 8.5 to 133.9 ng m(-3), respectively. PAH concentrations were found to be positively correlated with PM2.5 concentration in Beijing and Shanghai. The compositions of PAHs in PM2.5 in Beijing and Jinan were almost the same: 11% low ring, 80-82% middle ring, and 7-9% high ring. However, Shanghai had a different composition. Source apportionment indicated that the incomplete combustion of coal and diesel and gasoline emissions were the main sources of PAHs in PM2.5 in all three cities, whereas Shanghai had a greater contribution from liquid fossil fuels. The values for the health risk assessment estimated by the benzo[a]pyrene equivalent concentration in Beijing and Jinan were 2.39 × 10(-6) and 2.57 × 10(-6), respectively, thus both exceeding the 1 × 10(-6) limit (USEPA) considered likely to pose an inhalation cancer risk to people. Shanghai, however, had a risk estimate of 5.05 × 10(-7), which is still in a safe range. This study is the first to simultaneously monitor the PAHs in PM2.5 in three cities in Eastern China and may point to a long-range transportation of PM2.5-PAHs from Beijing to Jinan and partially to Shanghai.

Community composition and activity of anaerobic ammonium oxidation bacteria in the rhizosphere of salt-marsh grass Spartina alterniflora.

Anaerobic ammonium oxidation (anammox) as an important nitrogen removal pathway has been investigated in intertidal marshes. However, the rhizosphere-driven anammox process in these ecosystems is largely overlooked so far. In this study, the community dynamics and activities of anammox bacteria in the rhizosphere and non-rhizosphere sediments of salt-marsh grass Spartina alterniflora (a widely distributed plant in estuaries and intertidal ecosystems) were investigated using clone library analysis, quantitative PCR assay, and isotope-tracing technique. Phylogenetic analysis showed that anammox bacterial diversity was higher in the non-rhizosphere sediments (Scalindua and Kuenenia) compared with the rhizosphere zone (only Scalindua genus). Higher abundance of anammox bacteria was detected in the rhizosphere (6.46 × 10(6)-1.56 × 10(7) copies g(-1)), which was about 1.5-fold higher in comparison with that in the non-rhizosphere zone (4.22 × 10(6)-1.12 × 10(7) copies g(-1)). Nitrogen isotope-tracing experiments indicated that the anammox process in the rhizosphere contributed to 12-14 % N2 generation with rates of 0.43-1.58 nmol N g(-1) h(-1), while anammox activity in the non-rhizosphere zone contributed to only 4-7 % N2 production with significantly lower activities (0.28-0.83 nmol N g(-1) h(-1)). Overall, we propose that the rhizosphere microenvironment in intertidal marshes might provide a favorable niche for anammox bacteria and thus plays an important role in nitrogen cycling.

Effects of thiamphenicol on nitrate reduction and N2O release in estuarine and coastal sediments.

Nitrate overload is an important driver of water pollution in most estuarine and coastal ecosystems, and thus nitrate reduction processes have attracted considerable attention. Antibiotics contamination is also an emerging environmental problem in estuarine and coastal regions as a result of growing production and usage of antibiotics. However, the effects of antibiotics on nitrate reduction remain unclear in these aquatic ecosystems. In this study, continuous-flow experiments were conducted to examine the effects of thiamphenicol (TAP, a common chloramphenicol antibiotic) on nitrate reduction and greenhouse gas N2O release. Functional genes involved in nitrogen transformation were also quantified to explore the microbial mechanisms of the TAP influence. Production of N2 were observed to be inhibited by TAP treatment, which implied the inhibition effect of TAP on nitrate reduction processes. As intermediate products of nitrogen transformation processes, nitrite and N2O were observed to accumulate during the incubation. Different TAP inhibition effects on related functional genes may be the microbial mechanism for the changes of nutrient fluxes, N2 fluxes and N2O release rates. These results indicate that the antibiotics residues in estuarine and coastal ecosystems may contribute to nitrate retention and N2O release, which could be a major factor responsible for eutrophication and greenhouse effects.

Gross Nitrogen Mineralization in Surface Sediments of the Yangtze Estuary.

Nitrogen mineralization is a key biogeochemical process transforming organic nitrogen to inorganic nitrogen in estuarine and coastal sediments. Although sedimentary nitrogen mineralization is an important internal driver for aquatic eutrophication, few studies have investigated sedimentary nitrogen mineralization in these environments. Sediment-slurry incubation experiments combined with 15N isotope dilution technique were conducted to quantify the potential rates of nitrogen mineralization in surface sediments of the Yangtze Estuary. The gross nitrogen mineralization (GNM) rates ranged from 0.02 to 5.13 mg N kg(-1) d(-1) in surface sediments of the study area. The GNM rates were generally higher in summer than in winter, and the relative high rates were detected mainly at sites near the north branch and frontal edge of this estuary. The spatial and temporal distributions of GNM rates were observed to depend largely on temperature, salinity, sedimentary organic carbon and nitrogen contents, and extracellular enzyme (urease and L-glutaminase) activities. The total mineralized nitrogen in the sediments of the Yangtze Estuary was estimated to be about 6.17 × 10(5) t N yr(-1), and approximately 37% of it was retained in the estuary. Assuming the retained mineralized nitrogen is totally released from the sediments into the water column, which contributed 12-15% of total dissolved inorganic nitrogen (DIN) sources in this study area. This result indicated that the mineralization process is a significant internal nitrogen source for the overlying water of the Yangtze Estuary, and thus may contribute to the estuarine and coastal eutrophication.