Xin Leng

A Hardy Plant Facilitates Nitrogen Removal via Microbial Communities in Subsurface Flow Constructed Wetlands in Winter.

The plants effect in subsurface flow constructed wetlands (SSF-CWs) is controversial, especially at low temperatures. Consequently, several SSF-CWs planted with Iris pseudacorus (CWI) or Typha orientalis Presl. (CWT) and several unplanted ones (CWC) were set up and fed with secondary effluent of sewage treatment plant during the winter in Eastern China. The 16S rDNA Illumina Miseq sequencing analysis indicated the positive effects of I. pseudacorus on the bacterial community richness and diversity in the substrate. Moreover, the community compositions of the bacteria involved with denitrification presented a significant difference in the three systems. Additionally, higher relative abundances of nitrifying bacteria (0.4140%, 0.2402% and 0.4318% for Nitrosomonas, Nitrosospira and Nitrospira, respectively) were recorded in CWI compared with CWT (0.2074%, 0.0648% and 0.0181%, respectively) and CWC (0.3013%, 0.1107% and 0.1185%, respectively). Meanwhile, the average removal rates of NH4+-N and TN in CWI showed a prominent advantage compared to CWC, but no distinct advantage was found in CWT. The hardy plant I. pseudacorus, which still had active root oxygen release in cold temperatures, positively affected the abundance of nitrifying bacteria in the substrate, and accordingly was supposed to contribute to a comparatively high nitrogen removal efficiency of the system during the winter.

Spartina alterniflora invasion alters soil microbial community composition and microbial respiration following invasion chronosequence in a coastal wetland of China

The role of exotic plants in regulating soil microbial community structure and activity following invasion chronosequence remains unclear. We investigated soil microbial community structure and microbial respiration following Spartina alterniflora invasion in a chronosequence of 6-, 10-, 17-, and 20-year-old by comparing with bare flat in a coastal wetland of China. S. alterniflora invasion significantly increased soil moisture and salinity, the concentrations of soil water-soluble organic carbon and microbial biomass carbon (MBC), the quantities of total and various types of phospholipid fatty acids (PLFAs), the fungal:bacterial PLFAs ratio and cumulative microbial respiration compared with bare flat. The highest MBC, gram-negative bacterial and saturated straight-chain PLFAs were found in 10-year-old S. alterniflora soil, while the greatest total PLFAs, bacterial and gram-positive bacterial PLFAs were found in 10- and 17-year-old S. alterniflora soils. The monounsaturated:branched PLFAs ratio declined, and cumulative microbial respiration on a per-unit-PLFAs increased following S. alterniflora invasion in the chronosequence. Our results suggest that S. alterniflora invasion significantly increased the biomass of soil various microbial groups and microbial respiration compared to bare flat soil by increasing soil available substrate, and modifying soil physiochemical properties. Soil microbial community reached the most enriched condition in the 10-year-old S. alterniflora community.

Phytoremediation potential of Acorus calamus in soils co-contaminated with cadmium and polycyclic aromatic hydrocarbons

Phytoremediation is a promising technology for the remediation of sites co-contaminated with inorganic (heavy metal) and organic pollutants. A greenhouse experiment was conducted to investigate the independent and interactive effects of cadmium (Cd) and polycyclic aromatic hydrocarbons (PAHs) on the growth of the wetland plant Acorus calamus and its ability to uptake, accumulate, and remove pollutants from soils. Our results showed that growth and biomass of A. calamus were significantly influenced by the interaction of Cd and PAHs after 60 days of growth. The combined treatment of low Cd and low PAHs increased plant biomass and Cd accumulation in plant tissues, thus enhancing Cd removal. Dissipation of PAHs from soils was not significantly influenced by Cd addition or by the presence of plants. Correlation analysis also indicated a positive relationship between residual concentrations of phenantherene and pyrene (PAHs), whereas enzyme activities (dehydrogenase and polyphenol oxidase) were negatively correlated with each other. Cluster analysis was used to evaluate the similarity between different treatments during phytoremediation of Cd and PAHs. Our results suggest that A. calamus might be useful for phytoremediation of co-contaminated soil.

Effects of reclamation on heavy metal pollution in a coastal wetland reserve

Owing to accelerating reclamation activities in the coastal wetland reserves, it is of great importance to analyze the effects of wetland reclamation on heavy metal pollution in these areas. Soil samples were collected from reclamation and natural habitats in Yancheng National Nature Reserve for Coastal Rare Birds in Jiangsu, China to investigate the effects of reclamation on the total amounts, availability, and vertical distribution of seven elemental heavy-metal pollutants. In general, the total amount and availability each element were relatively low in the two habitats and were classified as “no pollution”. Reclamation was found to significantly increase the total amount of As, Cu, and Zn as well as the pollution degrees of As, Cr, and Zn. The availability of Cu, Pb, Cd, and Cr can also be significantly affected by reclamation. Furthermore, surface-accumulation patterns of the total amounts of these heavy metals could be observed in both habitats, and the availabilities of these elements were higher in deeper soils. Reclamation also had significant impacts on the vertical distribution of Cu, Pb, Cd, and Zn. It is essential to properly monitor nearby aquacultural activities, freshwater irrigation, and traffic pollution during plant harvest to alleviate the negative effects of these human activities.

Combined effects of light reduction and ammonia nitrogen enrichment on the submerged macrophyte Vallisneria natans

The decline of submerged plants resulting from low light and high ammonia nitrogen (ammonia-N) has become a serious problem worldwide. In the present study, three levels of ammonia-N concentrations (0, 3 and 6mgL–1) and four levels of light intensity (control, 15, 2.5 and 0.75% underwater light) were designed to investigate the combined effects of low light and high ammonia-N stress on the submerged plant Vallisneria natans. The effects of low light and ammonia-N were examined by measuring the relative growth rate (RGR), chlorophyll content and superoxide dismutase (SOD) and peroxidase (POD) activity in response to the stressors. The decline in RGR and increase in SOD and POD activity in high ammonia-N water were more significant than under low light conditions, indicating that the stress imposed on submerged plants due to ammonia-N enrichment is stronger. Moreover, the combination of ammonia-N enrichment and low light had a greater effect on submerged plants. This study indicates that V. natans were tolerant to ammonia-N concentrations <6mgL–1. Moreover, low light intensity (0.75% underwater light) amplified the toxic effects of ammonia-N, reducing ammonia-N tolerance from <6 to <3mgL–1.

Performance of a large-scale wetland treatment system in treating tailwater from a sewage treatment plant

Water quality standards pertaining to effluent from sewage treatment plants (STPs) in China have become more stringent, requiring upgrading of STPs and entailing huge capital expenditure. Wetland treatment systems (WTSs) are a low-cost and highly efficient approach for deep purification of tailwater from STPs. The Hongze WTS (HZ-WTS), a large-scale surface-flow constructed wetland, with a total area of 55.58ha and a treatment capacity of 4×104m3day–1, was built for the disposal of tailwater from STPs. The aim of the present study was to evaluate the performance of HZ-WTP with regard to seasonal variations and to compare treatment costs with those of other STPs. The performance of the HZ-WTS was evaluated in 2013 using online monitoring. HZ-WTS exhibited significant removal efficiency of ammonia nitrogen (NH4+-N), chemical oxygen demand and total phosphorus (mean±s.d., percentage removal efficiency 56.33±70.44, 55.64±18.58 and 88.44±22.71% respectively), whereas there was significant seasonal variation in the efficiency of NH4+-N removal. In addition, the average treatment cost was ¥0.17m–3, significantly lower than the corresponding value for other STPs. Therefore, WTSs are recommended for use with STPs in order to improve waste water quality in a cost-effective manner.

Elevated salinity inhibits nitrogen removal by changing the microbial community composition in constructed wetlands during the cold season

In the present study we investigated whether subsurface flow constructed wetlands (SSF-CWs) can remove nitrogen from saline waste water and whether salinity affects nitrogen removal during the cold season (mean water temperature <10°C). Eight Iris pseudacorus-planted SSF-CWs were fed with normal (salinity 1.3–1.5‰; CWP) or saline (salinity 6.3–6.5‰; CWP+) waste water; similarly, eight unplanted SSF-CWs were fed with normal (CWU) or saline waste water (CWU+). The systems were run continuously at a hydraulic loading rate of 187.5mmday–1 and a hydraulic retention time of 4 days. Nitrogen removal efficiency, plant parameters and bacterial abundance and community composition were measured. In CWP, 80% of NH4+-N and 52% of total nitrogen (TN) were removed. In contrast, the removal rates of NH4+-N and TN in CWP+ were reduced by 27 and 37% respectively. In the presence of higher salinity, not only were there decreases in plant biomass (32.1%) and nitrogen uptake (50.1%), but the growth, activity and oxygen release of roots were also reduced (by 37.8, 68.0 and 62.9% respectively). Bacterial community composition also differed under conditions of elevated salinity. Elevated salinity is associated with lower nitrogen removal in SSF-CWs, which we speculate is a result of suppressed wetland macrophyte growth and activity, as well as changes in microbial community composition.

How Spartina alterniflora adapts to a new environment created by embankment reclamation through C-N-P stoichiometry in the coastal wetlands of eastern China

Although embankment reclamation is a recurring activity in the coastal wetlands of China, the effect of embankment construction on plant growth has attracted little attention. Leaf carbon, nitrogen and phosphorus stoichiometry (C-N-P stoichiometry) of a plant can be used to reflect plant adaptation to new environments created by reclamation. In the present study we investigated the biomass and leaf C-N-P stoichiometry of Spartina alterniflora Loisel., soil C-N-P stoichiometry and soil moisture, salinity, bulk density and pH in both embankment-reclaimed and natural S. alterniflora salt marshes in eastern China. Plant biomass, leaf P content, soil salinity and soil moisture were significantly lower in the reclaimed compared with natural marsh. The decrease in leaf P content is possibly attributed to changes in soil salinity, soil moisture and soil organic C and N content in the reclaimed marsh. The results of the present study indicate that the decreased aboveground biomass in the reclaimed marsh is likely to be correlated with an increase in the leaf N:P ratio, in accordance with the ‘growth rate hypothesis’. However, previously published threshold values of the N:P ratio as indicators of N or P limitation of plant growth may not be applicable to S. alterniflora at our study site.

Individual and combined effects of cadmium and polycyclic aromatic hydrocarbons on the phytoremediation potential of Xanthium sibiricum in co-contaminated soil

ABSTRACT Soil contamination with heavy metals and organic pollutants continues to cause major ecological damage and human health problems. Phytoremediation offers a highly promising technology for the recovery of sites contaminated with mixed pollutants. In this study, we performed a greenhouse experiment to investigate the individual and combined effects of cadmium (Cd) and polycyclic aromatic hydrocarbon (PAH) contamination on the growth of Xanthium sibiricum, and also the ability of this species to accumulate and remove Cd and to reduce PAHs over a period of 75 days. Our results demonstrated that individual or combined contamination by Cd and PAHs showed no significant differences to the control treatment except in the high Cd treatment. The reduction of PAH concentration in the soil with the passage of time was similar in the presence or absence of plants. At higher levels of Cd, the removal of pyrene decreased in both planted and non-planted soils; however, this effect might be due to the higher Cd content. Soil dehydrogenase and polyphenol oxidase activities showed that soil contamination did not have a significant effect on the removal of PAHs. Overall, our results suggest that X. sibiricum might be a suitable species for use in the phytoremediation of contaminated soils.

Nitrogen removal during the cold season by constructed floating wetlands planted with Oenanthe javanica

Constructed floating wetlands (CFWs) are used to treat waste waters of various origins either alone or as part of waste water treatment trains. The aim of the present study was to determine the extent of nitrogen removal by CFWs planted with Oenanthe javanica (Blume) DC. at low temperatures (<10°C) and whether CFWs with vesuvianite as a substrate perform better than those without substrate. A batch model was used, with CFWs planted with O. javanica (Tc), CFWs without O. javanica (Ts), CFWs without substrate (Tp) and floating mats only (To) as a control. The average removal rates of NH4+-N, NO3–-N and total nitrogen were 78.3, 44.4 and 49.7% respectively in Tc; 72.0, 40.0 and 39.5% respectively in Ts; and 73.1, 33.7 and 44.0% respectively in Tp. In addition to a gradual increase in chemical oxygen demand during the experimental period, Tc had higher microbial richness and diversity, as well as a higher abundance of bacteria, archaea, anaerobic ammonium oxidation (Anammox) bacteria and key genes (ammonia mono-oxygenase, amoA, nitrous oxide reductase, nosZ, dissimilatory cd1-containing nitrite reductase, nirS, and dissimilatory copper-containing nitrite reductase, nirK) involved in nitrogen metabolism in the substrate than Ts. Further analysis of microbial community composition revealed a difference at multiple taxonomic levels among different systems. These results demonstrate the positive roles of O. javanica and vesuvianite in CFWs in nitrogen removal from waste water during the cold season (mean water temperature <10°C).