Effects of simulated nitrogen deposition on soil microbial community diversity in coastal wetland of the Yellow River Delta.

Due to the enhancement of human activities on the global scale, the total amount of atmospheric nitrogen (N) deposition and the rate keep increasing, which seriously affect the structure and function of terrestrial ecosystems. In order to study the effects of N deposition on the soil structure and function of coastal saline wetlands, we established a long-term nitrogen deposition simulation platform in 2012 in the Yellow River delta (YRD). Herein, we analyzed the composition and diversity of the soil microbial community under different N deposition treatments (LNN, MNN and HNN, which stand for 50 kg N ha-1 yr-1, 100 kg N ha-1 yr-1, and 200 kg N ha-1 yr-1) and in a water-only control (CK). The results showed that with the increasing level of N deposition, α-diversity (Shannon and Simpson indices) decreased significantly, and the composition of the microbial community changed. At the phylum level, compared with CK, the relative abundance of Chloroflexi increased significantly under the treatment of HNN (P = 0.002), but the relative abundance of Chlorobi (P = 0.013) and Verrucomicrobia (P = 0.035) decreased significantly. At the genus level, compared with CK, the relative abundance of Bacillus (P = 0.01) and Halomonas (P = 0.042) increased significantly with HNN treatment. Bacillus and Nitrococcus showed a significant correlation with soil NH4+-N. The results suggest that the response of microorganisms to N deposition treatments varied by the concentration, and the deposition of a high concentration would increase the nutrients in the soil, but reduce the diversity of soil microorganisms, causing a negative impact on the coastal wetland ecosystem of the YRD.

Recovery of the salt marsh periwinkle (Littoraria irrorata) 9 years after the Deepwater Horizon oil spill: Size matters.

Prior studies indicated salt marsh periwinkles (Littoraria irrorata) were strongly impacted in heavily oiled marshes for at least 5 years following the Deepwater Horizon oil spill. Here, we detail longer-term effects and recovery over nine years. Our analysis found that neither density nor population size structure recovered at heavily oiled sites where snails were smaller and variability in size structure and density was increased. Total aboveground live plant biomass and stem density remained lower over time in heavily oiled marshes, and we speculate that the resulting more open canopy stimulated benthic microalgal production contributing to high spring periwinkle densities or that the lower stem density reduced the ability of subadults and small adults to escape predation. Our data indicate that periwinkle population recovery may take one to two decades after the oil spill at moderately oiled and heavily oiled sites, respectively.

Shifts in soil bacterial and archaeal communities during freeze-thaw cycles in a seasonal frozen marsh, Northeast China.

Diurnal freeze-thaw cycles (FTCs) occur in the spring and autumn in boreal wetlands as soil temperatures rise above freezing during the day and fall below freezing at night. A surge in methane emissions from these systems is frequently documented during spring FTCs, accounting for a large portion of annual emissions. In boreal wetlands, methane is produced as a result of syntrophic microbial processes, mediated by a consortium of fermenting bacteria and methanogenic archaea. Further research is needed to determine whether FTCs enhance microbial metabolism related to methane production through the cryogenic decomposition of soil organic matter. Previous studies observed large methane emissions during the spring thawed period in the Sanjiang seasonal frozen marsh of Northeast China. To investigate how FTCs impact the soil microbial community and methanogen abundance and activity, we collected soil cores from the Sanjiang marsh during the FTCs of autumn 2014 and spring 2015. Methanogens were investigated based on expression level of the methyl coenzyme reductase (mcrA) gene, and soil bacterial and archaeal community structures were assessed by 16S rRNA gene sequencing. The results show that a decrease in bacteria and methanogens followed autumns FTCs, whereas an increase in bacteria and methanogens was observed following spring FTCs. The bacterial community structure, including Firmicutes and certain Deltaproteobacteria, was changed following autumn FTCs. Temperature and substrate were the primary factors regulating the abundance and composition of the microbial communities during autumn FTCs, whereas no factors significantly contributing to spring FTCs were identified. Acetoclastic methanogens from order Methanosarcinales were the dominant group at the beginning and end of both the autumn and spring FTCs. Active methanogens were significantly more abundant during the diurnal thawed period, indicating that the increasing number of FTCs predicted to occur with global climate change could potentially promote CH4 emissions in seasonal frozen marshes.

Shoreline oiling effects and recovery of salt marsh macroinvertebrates from the Deepwater Horizon Oil Spill.

Salt marshes in northern Barataria Bay, Louisiana, USA were oiled, sometimes heavily, in the aftermath of the Deepwater Horizon oil spill. Previous studies indicate that fiddler crabs (in the genus Uca) and the salt marsh periwinkle (Littoraria irrorata) were negatively impacted in the short term by the spill. Here, we detail longer-term effects and recovery from moderate and heavy oiling over a 3-year span, beginning 30 months after the spill. Although neither fiddler crab burrow density nor diameter differed between oiled and reference sites when combined across all sampling events, these traits differed among some individual sampling periods consistent with a pattern of lingering oiling impacts. Periwinkle density, however, increased in all oiling categories and shell-length groups during our sampling period, and periwinkle densities were consistently highest at moderately oiled sites where Spartina alterniflora aboveground biomass was highest. Periwinkle shell length linearly increased from a mean of 16.5 to 19.2 mm over the study period at reference sites. In contrast, shell lengths at moderately oiled and heavily oiled sites increased through month 48 after the spill, but then decreased. This decrease was associated with a decline in the relative abundance of large adults (shell length 21-26 mm) at oiled sites which was likely caused by chronic hydrocarbon toxicity or oil-induced effects on habitat quality or food resources. Overall, the recovery of S. alterniflora facilitated the recovery of fiddler crabs and periwinkles. However, our long-term record not only indicates that variation in periwinkle mean shell length and length-frequency distributions are sensitive indicators of the health and recovery of the marsh, but agrees with synoptic studies of vegetation and infaunal communities that full recovery of heavily oiled sites will take longer than 66 months.

Polychlorinated biphenyl concentrations, accumulation rates in soil from atmospheric deposition and analysis of their affecting landscape variables along an urban-rural gradient in Shanghai, China.

This study initiated an in-situ soil experimental system to quantify the annual dynamics of polychlorinated biphenyl (PCB) congener's concentrations and accumulation rates in soil from atmosphere deposition in a rural-urban fringe, and correlated them by landscape physical and demographic variables in the area. The results showed that the concentrations of all PCB congeners significantly increased with the sampling time (p < 0.05); nearly all the PCB congener concentrations decreased while moving outwards from the urban center. The moderate average concentrations along the gradient for PCB 8, 18, and 28 were 31.003, 18.825, and 19.505 ng g-1, respectively. Tetra-CBs including PCB 44, 52, 66, and 77 were 10.243, 31.214, 8.330 and 9.530 ng g-1, respectively. Penta-CBs including PCB 101, 105, 118, and 126 were 9.465, 7.896, 17.703, and 6.363 ng g-1, respectively. Hexa-CBs including PCB 128, 138, 153, 170, 180, and 187 were 6.798, 11.522, 4.969, 6.722, 6.317, and 8.243 ng g-1 respectively. PCB 195, 206, and 209 were 8.259, 9.506, and 14.169 ng g-1, respectively. Most of the PCB congeners had a higher accumulation rate approximately 28 km from the urban center. The computed variables were found to affect the soil PCB concentrations with a threshold effect (p < 0.05). Regression analysis showed that the thresholds were 10-20 km, 1 km/km2, 30%, and 20% for distance, road density, population change index, and built-up area percentage, respectively. It was concluded that factors related to industrial development, traffic, and urban sprawling (i.e. built-up areas expanding) were the sources of PCBs.

Reclamation history and development intensity determine soil and vegetation characteristics on developed coasts.

The question of where and how to carry out reclamation work in coastal areas is still not well addressed in coastal research. To answer the question, it is essential to quantify the impact of reclamation and the associated ecological and/or environmental responses. In this study, ordinary least square (OLS) analysis and geographical weighted regression (GWR) analysis were performed to identify the reclamation variables that affect soil and vegetation characteristics. Reclamation related variables, including residential population (RP), years of reclamation (YR), income per capita (IP), and land use-based human impact index (HII), were used to explain nitrate, ammonium, total phosphorous, and heavy metals in soil, and the height, density, and above-ground biomass of native hydrophytic vegetation. It was found that variables IP, RP, and HII could be used to explain the height of Scirpus and Phragmites australis as well as above-ground biomass with a R2 value of no >0.55, and almost all the variables could explain the hydrophytic vegetation characteristics with a higher R2 value. In comparison to OLS, GWR more reliably reflected the reclamation effects on soil and vegetation characteristics. By GWR analysis, total soil phosphorous, and nitrate and ammonium nitrogen could be explained by RP, YR, and HII, with the highest Ad-R2 value of 0.496, 0.631 and 0.632, respectively. Both of the GWR and OLS analysis revealed that HII and RP were the better variables for explaining the soil and vegetation characteristics. This work demonstrated that coastal reclamation was highly spatial dependent, which sheds a light on the future development of spatial explicit and process-based models to guide coastal reclamation around the world.

4 Years after the Deepwater Horizon Spill: Molecular Transformation of Macondo Well Oil in Louisiana Salt Marsh Sediments Revealed by FT-ICR Mass Spectrometry.

Gulf of Mexico saltmarsh sediments were heavily impacted by Macondo well oil (MWO) released from the 2010 Deepwater Horizon (DWH) oil spill. Detailed molecular-level characterization of sediment extracts collected over 48 months post-spill highlights the chemical complexity of highly polar, oxygen-containing compounds that remain environmentally persistent. Electrospray ionization (ESI) Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS), combined with chromatographic prefractionation, correlates bulk chemical properties to elemental compositions of oil-transformation products as a function of time. Carboxylic acid incorporation into parent MWO hydrocarbons detected in sediment extracts (corrected for mass loss relative to C30 hopane) proceeds with an increase of ∼3-fold in O2 species after 9 months to a maximum of a ∼5.5-fold increase after 36 months, compared to the parent MWO. More importantly, higher-order oxygenated compounds (O4-O6) not detected in the parent MWO increase in relative abundance with time as lower-order oxygenated species are transformed into highly polar, oxygen-containing compounds (Ox, where x > 3). Here, we present the first molecular-level characterization of temporal compositional changes that occur in Deepwater Horizon derived oil contamination deposited in a saltmarsh ecosystem from 9 to 48 months post-spill and identify highly oxidized Macondo well oil compounds that are not detectable by routine gas-chromatography-based techniques.

Response of salt marshes to oiling from the Deepwater Horizon spill: Implications for plant growth, soil surface-erosion, and shoreline stability.

We investigated the initial impacts and post spill recovery of salt marshes over a 3.5-year period along northern Barataria Bay, LA, USA exposed to varying degrees of Deepwater Horizon oiling to determine the effects on shoreline-stabilizing vegetation and soil processes. In moderately oiled marshes, surface soil total petroleum hydrocarbon concentrations were ~70mgg(-1) nine months after the spill. Though initial impacts of moderate oiling were evident, Spartina alterniflora and Juncus roemerianus aboveground biomass and total live belowground biomass were equivalent to reference marshes within 24-30months post spill. In contrast, heavily oiled marsh plants did not fully recover from oiling with surface soil total petroleum hydrocarbon concentrations that exceeded 500mgg(-1) nine months after oiling. Initially, heavy oiling resulted in near complete plant mortality, and subsequent recovery of live aboveground biomass was only 50% of reference marshes 42months after the spill. Heavy oiling also changed the vegetation structure of shoreline marshes from a mixed Spartina-Juncus community to predominantly Spartina; live Spartina aboveground biomass recovered within 2-3years, however, Juncus showed no recovery. In addition, live belowground biomass (0-12cm) in heavily oiled marshes was reduced by 76% three and a half years after the spill. Detrimental effects of heavy oiling on marsh plants also corresponded with significantly lower soil shear strength, lower sedimentation rates, and higher vertical soil-surface erosion rates, thus potentially affecting shoreline salt marsh stability.

Impacts of Macondo oil from Deepwater Horizon spill on the growth response of the common reed Phragmites australis: a mesocosm study.

We investigated impacts of Macondo MC252 oil from the Deepwater Horizon (DWH) spill on the common reed Phragmites australis (Cav.) Trin. ex Steud., a dominant species of the Mississippi River Delta. In greenhouse experiments, we simulated the most common DWH oiling scenarios by applying weathered and emulsified Macondo oil to aboveground shoots at varying degrees of coverage (0-100%) or directly to marsh soil at different dosages (0-16 Lm(-)(2)). P. australis exhibited strong resistance to negative impacts when oil was applied to shoots alone, while reductions in above- and belowground plant growth were apparent when oil was applied to the soil or with repeated shoot-oiling. Although soil-oiling compromised plant function, mortality of P. australis did not occur. Our results demonstrate that P. australis has a high tolerance to weathered and emulsified Macondo oil, and that mode of exposure (aboveground versus belowground) was a primary determinant of impact severity.

Host-Microbe Interactions in Caenorhabditis elegans.

A good understanding of how microbes interact with hosts has a direct bearing on our capability of fighting infectious microbial pathogens and making good use of beneficial ones. Among the model organisms used to study reciprocal actions among microbes and hosts, C. elegans may be the most advantageous in the context of its unique attributes such as the short life cycle, easiness of laboratory maintenance, and the availability of different genetic mutants. This review summarizes the recent advances in understanding host-microbe interactions in C. elegans. Although these investigations have greatly enhanced our understanding of C. elegans-microbe relationships, all but one of them involve only one or few microbial species. We argue here that more research is needed for exploring the evolution and establishment of a complex microbial community in the worm's intestine and its interaction with the host.

23S rRNA gene-based enterococci community signatures in Lake Pontchartrain, Louisiana, USA, following urban runoff inputs after Hurricane Katrina.

Little is known about the impacts of fecal polluted urban runoff inputs on the structure of enterococci communities in estuarine waters. This study employed a 23S rRNA gene-based polymerase chain reaction (PCR) assay with newly designed genus-specific primers, Ent127F-Ent907R, to determine the possible impacts of Hurricane Katrina floodwaters via the 17th Street Canal discharge on the community structure of enterococci in Lake Pontchartrain. A total of 94 phylotypes were identified through the restriction fragment length polymorphism (RFLP) screening of 494 clones while only 8 phylotypes occurred among 88 cultivated isolates. Sequence analyses of representative phylotypes and their temporal and spatial distribution in the lake and the canal indicated the Katrina floodwater input introduced a large portion of Enterococcus flavescens, Enterococcus casseliflavus, and Enterococcus dispar into the lake; typical fecal groups Enterococcus faecium, Enterococcus durans, Enterococcus hirae, and Enterococcus mundtii were detected primarily in the floodwater-impacted waters. This study provides a global picture of enterococci in estuarine waters impacted by Hurricane Katrina-derived urban runoff. It also demonstrates the culture-independent PCR approach using 23S rRNA gene as a molecular marker could be a good alternative in ecological studies of enterococci in natural environments to overcome the limitation of conventional cultivation methods.

Temporal and spatial variability in culturable pathogenic Vibrio spp. in Lake Pontchartrain, Louisiana, following hurricanes Katrina and Rita.

We investigated the abundance, distribution, and virulence gene content of Vibrio cholerae, V. parahaemolyticus, and V. vulnificus in the waters of southern Lake Pontchartrain in Louisiana on four occasions from October 2005 to September 2006, using selective cultivation and molecular assays. The three targeted pathogenic vibrios were generally below the detection level in January 2006, when the water was cold (13°C), and most abundant in September 2006, when the lake water was warmest (30°C). The maximum values for these species were higher than reported previously for the lake by severalfold to orders of magnitude. The only variable consistently correlated with total vibrio abundance within a single sampling was distance from shore (P = 0.000). Multiple linear regression of the entire data set revealed that distance from shore, temperature, and turbidity together explained 82.1% of the variability in total vibrio CFU. The log-transformed mean abundance of V. vulnificus CFU in the lake was significantly correlated with temperature (P = 0.014), but not salinity (P = 0.625). Virulence-associated genes of V. cholerae (ctx) and V. parahaemolyticus (trh and tdh) were not detected in any isolates of these species (n = 128 and n = 20, respectively). In contrast, 16S rRNA typing of V. vulnificus (n = 298) revealed the presence of both environmental (type A) and clinical (type B) strains. The percentage of the B-type V. vulnificus was significantly higher in the lake in October 2005 (35.8% of the total) than at other sampling times (P ≤ 0.004), consistent with the view that these strains represent distinct ecotypes.

Emergency drinking water treatment during source water pollution accidents in China: origin analysis, framework and technologies.

China has suffered frequent source water contamination accidents in the past decade, which has resulted in severe consequences to the water supply of millions of residents. The origins of typical cases of contamination are discussed in this paper as well as the emergency response to these accidents. In general, excessive pursuit of rapid industrialization and the unreasonable location of factories are responsible for the increasing frequency of accidental pollution events. Moreover, insufficient attention to environmental protection and rudimentary emergency response capability has exacerbated the consequences of such accidents. These environmental accidents triggered or accelerated the promulgation of stricter environmental protection policy and the shift from economic development mode to a more sustainable direction, which should be regarded as the turning point of environmental protection in China. To guarantee water security, China is trying to establish a rapid and effective emergency response framework, build up the capability of early accident detection, and develop efficient technologies to remove contaminants from water.

The 2007 water crisis in Wuxi, China: analysis of the origin.

An odorous tap water crisis that affected two million residents for several days occurred in Wuxi, China in the summer of 2007. Volatile sulfide chemicals including methyl thiols, dimethyl sulfide, dimethyl disulfide, and dimethyl trisulfide were the dominant odorous contaminants in Lake Taihu and in tap water during the crisis. These contaminants originated from the decomposition of a massive cyanobacterial bloom that was triggered by illegal industrial discharges and inadequately regulated domestic pollution. A specific emergency drinking water treatment process was quickly developed using a combination of potassium permanganate oxidation and powdered activated carbon adsorption. The emergency treatment process removed the odor from the tap water and solved the crisis successfully in several days. This experience underscores the suggestion that a combination of stresses associated with eutrophication and industrial and domestic wastewater discharges can push an aquatic system to the tipping point with consequences far more severe than would occur if the system were subjected to each stress separately.

Characterization of clinical and environmental types of Vibrio vulnificus isolates from Louisiana oysters.

Vibrio vulnificus, a naturally occurring estuarine bacterium frequently transmitted to humans via raw oysters, is a leading cause of seafood-related deaths in the United States. Although unique virulence markers have not been identified to date, multiple biomarkers have been used previously to associate strains with clinical or environmental types of V. vulnificus. In this study, we evaluated the usefulness of these biomarkers in characterizing 349 V. vulnificus oyster isolates by the presence/absence of a viuB-associated fragment and genotypes of three biomarkers: the virulence-correlated gene (vcg), 16S rRNA, and the capsular polysaccharide (CPS) operon. Genotyping data indicated that environmental-type V. vulnificus strains accounted for the majority of oyster isolates, and the percentages ranged from 51.6% for 16S rRNA (type A) to 72.5% for CPS (allele 2 or none). There was also a small percentage (8%) of V. vulnificus isolates possessing both environmental (type A) and clinical (type B) genotypes of 16S rRNA. Additionally, the presence of the viuB fragment (41%) was significantly associated with clinical genotypes of V. vulnificus (p < 0.0001). An interesting seasonal pattern was observed, with clinical-type V. vulnificus isolates more frequently associated with warmer months. In conclusion, the majority of V. vulnificus isolates present in Louisiana raw oysters were of environmental type. There existed a seasonal variation in the V. vulnificus genotypes identified, which may help guide future control measures to focus more specifically on seasons that tend to accumulate more clinical-type V. vulnificus. The study also highlighted the need to identify unique virulence markers in this organism, which could facilitate future screening of virulent V. vulnificus strains from oysters.

Toxic Elements in Aquatic Sediments: Distinguishing Natural Variability from Anthropogenic Effects.

Regressions of aluminum against potentially toxic elements in the sediments of freshwater aquatic systems in Louisiana were used to distinguish natural variability from anthropogenic pollution when elemental concentrations exceeded screening effects levels. The data were analyzed using geometric mean model II regression methods to minimize, insofar as possible, bias that would have resulted from the use of model I regression. Most cadmium concentrations exceeded the threshold effects level, but there was no evidence of an anthropogenic impact. In Bayou Trepagnier, high concentrations of Cr, Cu, Pb, Ni, and Zn appeared to reflect anthropogenic pollution from a petrochemical facility. In Capitol Lake, high Pb concentrations were clearly associated with anthropogenic impacts, presumably from street runoff. Concentrations of potentially toxic elements varied naturally by as much as two orders of magnitude; hence it was important to filter out natural variability in order to identify anthropogenic effects. The aluminum content of the sediment accounted for more than 50% of natural variability in most cases. Because model I regression systematically under-estimates the magnitude of the slope of the regression line when the independent variable is not under the control of the investigator, use of model II regression methods in this application is necessary to facilitate hypothesis testing and to avoid incorrectly associating naturally high elemental concentrations with human impacts.

Total Hg, methyl Hg and other toxic heavy metals in a northern Gulf of Mexico estuary: Louisiana Pontchartrain basin.

Concentration of total Hg, methyl Hg, and other heavy metals were determined in sediment collected along a salinity gradient in a Louisiana Gulf Coast estuary. Surface sediment was collected at established coordinates (n = 292) along a salinity gradient covering Lake Maurepas, Lake Pontchartrain, Lake Borgne and the Chandeleur Sound located in the 12,170 km(2) Pontchartrain basin estuary southeastern coastal Louisiana. Lake Maurepas sediment with lower salinity contained higher levels of methyl Hg (0.80 microg/kg) than Lake Pontchartrain (0.55 microg/kg). Lake Maurepas sediment also had higher levels of total Hg (98.0 microg/kg) as compared to Lake Pontchartrain (67.0 microg/kg). Average total Hg content of Lake Borgne and the Chandeleur Sound sediment was 24.0 microg/kg dry sediment and methyl Hg content averaged 0.21 microg/kg dry sediment. Methyl Hg content of sediment was positively correlated with total Hg, organic matter and clay content of sediment. Methyl Hg was inversely correlated with salinity, sediment Eh and sand content. Total Hg and methyl Hg decreased with increase in salinity in the order of Lake Maurepas > Lake Pontchartrain > Lake Borgne/ the Chandeleur Sound. Lake Maurepas containing several times higher amount of methyl Hg in sediment as compared to Lake Pontchartrain and Lake Borgne and the Chandeleur Sound is an area that could serve as potential source of mercury to the aquatic food chain. Methyl Hg content of sediment in the estuary could be predicted by the equation: Methyl Hg = 0.11670-0.0625 x Salinity + 0.05349 x O.M. + 0.00513 x Total Hg - 0.00250 x Clay. Concentrations of other toxic heavy metals (Pb, Cd, Ni, Cu and Zn) in sediment were not elevated and was statistically correlated with sediment texture and iron and aluminum content of sediment.

Pathogen indicator microbes and heavy metals in Lake Pontchartrain following Hurricane Katrina.

Storm surge and several breaches of the New Orleans, Louisiana levee system caused flooding of more than 80% of the city following Hurricane Katrina in August 2005. Most of the floodwaters pumped out of the city were discharged to Lake Pontchartrain. Lake water and sediment samples were collected during September 19 to October 9, 2005 to determine the possible impact of the dewatering operation on Lake Pontchartrain. Surface water E. coli and enterococcus counts were high at stations near the mouth of the 17th Street Canal (geometric means = 6.0 x 10(3) CFU/100 mL and 1.7 x 10(2) CFU/100 mL, respectively) but decreased by factors of 40 and 5, respectively, at stations 5 km from the mouth of the canal. Priority heavy metal concentrations were generally undetectable or below U.S. EPA criterion maximum and criterion continuous concentrations. Surface sediments near the mouth of the canal contained generally higher concentrations of enterococcus, E. coli, and Al-normalized metals than points further from the canal. The impact of the discharged floodwaters on heavy metal concentrations and indicator organism counts in the water column of Lake Pontchartrain appears to have been small and short-lived. Historically, however, the canal has been a significant contributor of pollutants to the sediments.