Heavy metal (Pb,Zn) uptake and chemical changes in rhizosphere soils of four wetland plants with different radial oxygen loss

Lead and Zn uptake and chemical changes in rhizosphere soils of four emergent-rooted wetland plants;Aneilema bracteatum,Cyperus alternifolius,Ludwigia hyssopifolia and Veronica serpyllifolia were investigated by two experiments：（1） rhizobag filled with ＂clean＂ or metal-contaminated soil for analysis of Pb and Zn in plants and rhizosphere soils;and （2） applied deoxygenated solution for analyzing their rates of radial oxygen loss （ROL）.The results showed that the wetland plants with different ROL rates had significant effects on the mobility and chemical forms of Pb and Zn in rhizosphere under flooded conditions.These effects were varied with different metal elements and metal concentrations in the soils.Lead mobility in rhizosphere of the four plants both in the ＂clean＂ and contaminated soils was decreased,while Zn mobility was increased in the rhizosphere of the ＂clean＂ soil,but decreased in the contaminated soil.Among the four plants,V.serpyllifolia,with the highest ROL,formed the highest degree of Fe plaque on the root surface,immobilized more Zn in Fe plaque,and has the highest effects on the changes of Zn form （EXC-Zn） in rhizosphere under both ＂clean＂ and contaminated soil conditions.These results suggested that ROL of wetland plants could play an important role in Fe plaque formation and mobility and chemical changes of metals in rhizosphere soil under flood conditions.

Accumulation Laws of Nitrogen and Phosphorus in Wetland Plants

To study the accumulation regularity of nitrogen and phosphorus in typical constructive plants in coastal wetland,samples of Suaeda glauca(Bunge) Bunge,Phragmites austrahs and Tamarix chinensis Lour,were taken from the Yellow River Delta National Coast Wetland Nature Reserve,nitrogen and phosphorus content in plants was measured and analyzed.The results showed that ① nitrogen and phosphorus content in different wetland plants is correlated;② different species in the same place and the same species in different spaces show different accumulation regularity of nitrogen and phosphorus;③ nitrogen and phosphorus content in plants is closely related to nitrogen and phosphorus content in the habitat;④ nitrogen content in T.chinensis Lour,is the highest,the mean is 11.63 g/kg,and phosphorus content in S glauca(Bunge) Bunge is the highest,the mean is 1.38 g/kg;⑤ nitrogen content in the 3 species:T.chinensis Lour.> S.glauca(Bunge) Bunge > P.australis;⑥ nitrogen content in aboveground parts of all plants is significantly higher than that in underground parts,and phosphorus content in aboveground parts of all plants except S.glauca(Bunge) Bunge is significantly higher than that in underground parts;⑦ nitrogen content in the 3 species in the study area is significantly higher than phosphorus content in these species.

Relationship between electrogenic performance and physiological change of four wetland plants in constructed wetland-microbial fuel cells during non-growing seasons

To find suitable wetland plants for constructed wetland-microbial fuel cells（CW-MFCs）,four commonly used wetland plants, including Canna indica, Cyperus alternifolius L., Acorus calamus, and Arundo donax, were investigated for their electrogenic performance and physiological changes during non-growing seasons. The maximum power output of12.82 mW/m^2 was achieved in the A. donax CW-MFC only when root exudates were being released. The results also showed that use of an additional carbon source could remarkably improve the performance of electricity generation in the C. indica and A. donax CW-MFCs at relatively low temperatures（2–15°C）. However, A. calamus withered before the end of the experiment, whereas the other three plants survived the winter safely, although their relative growth rate values and the maximum quantum yield of PSII（Fv/Fm） significantly declined, and free proline and malondialdehyde significantly accumulated in their leaves.On the basis of correlation analysis, temperature had a greater effect on plant physiology than voltage. The results offer a valuable reference for plant selection for CW-MFCs.

Metal accumulation and tolerance in wetland plants

This paper briefly reviews the progress in studies of wetland plants in terms of heavy metal pollution.The current research mainly includes the following areas:(1)metal uptake,translocation,and distributions in wetland plants and toxicological effects on wetland plants,(2)radial oxygen loss(ROL)of wetland plants and its effects on metal mobility in rhizosphere soils,(3)constitutional metal tolerance in wetland plants,and(4)mechanisms of metal tolerance by wetland plants.Although a number of accomplishments have been achieved,many issues still remain unanswered.The future research effort is likely to focus on the ROL of wetland plants affecting metal speciation and bioavailability in rhizosphere soils,and the development of rhizosphere management technologies to facilitate and improve practical applications of phytoremediation of metalpolluted soils.

A barrier to metal movement: Synchrotron study of iron plaque on roots of wetland plants

A wetland with attractive plants hosting birds and other wildlife is an esthetically pleasing prospect that is gaining popularity as a way of stabilizing or remediating metalcontaminated soils and sediment（Weber and Gagnon,2014;

Characteristics of Photosynthetic Fluorescence of Dominant Submerged Plants in Nanjishan Wetland of Poyang Lake in Winter

Based on the investigation of the species and frequency of submerged plants in Nanjishan Wetland of Poyang Lake in the winter of 2013,chlorophyll contents and photosynthetic fluorescence characteristics of the dominant submerged plants were studied using chlorophyll fluorescence imaging method. The results indicate that the major submerged plants of Nanjishan Wetland in Poyang Lake in winter included Hydrilla verticillata,Vallisneria natans,Najas minor,Potamogeton pectinatus,Nymphoides peltatum,Myriophyllum verticillatum and so on,and the dominant species were mainly H. verticillata and V. natans in different submerged plant communities. The chlorophyll content of H. verticillata is higher than that of V.natans,and the photosynthesis intensity of H. verticillata is stronger than that of V. natans. The value of Ca / Cb of H. verticillata is not large,which shows that the light-harvesting capacity of H. verticillata＇s chlorophyll is considerable in different sampling sites. The highest value of QY-max of V.natans is up to 0. 732,while the lowest value is only 0. 465; the highest value of QY-max of H. verticillata is 0. 677,while the lowest value is 0. 556.All values of QY-max of the submerged plants were lower than 0. 8,which shows that the submerged plants in Nanjishan Wetland of Poyang Lake may be subjected to certain external stress,which indicates that the external stress might cause some damage for the PSII reaction centers.

Influence of environment and substrate quality on the decomposition of wetland plant root in the Sanjiang Plain,Northeast China

The litterbag method was used to study the decomposition of wetland plant root in three wetlands along a water level gradient in the Sanjiang Plain,Northeast China.These wetlands are Calamagrostis angustifolia(C.aa),Carex meyeriana(C.ma)and Carex lasiocarpa (C.la).The objective of our study is to evaluate the influence of environment and substrate quality on decomposition rates in the three wetlands.Calico material was used as a standard substrate to evaluate environmental influences.Roots native to each we...

Toxic effect of perfluorooctane sulfonate on plants in vertical-flow constructed wetlands

Per-and polyfluoroalkyl substances(PFASs)can be taken up and bioaccumulated in plants,but the toxic mechanisms of PFASs on wetland plants are still unclear.In present study,the toxic influences of perfluorooctane sulfonate(PFOS)on Eichhornia crassipes(E.crassipes)and Cy perus alternifolius(C.alternifolius)in a vertical-sub surface-flow constructed wetland were evaluated.The results showed that E.crassipes was more tolerant to PFOS stress than C.alternifolius,and the growth and chlorophyll synthesis of the two plants were promoted by low concentration(<0.1 mg/L)of PFOS,and the chlorophyll synthesis was inhibited by high concentration(10 mg/L)of PFOS but the growth did not change obviously.The catalase activity and malondialdehyde content in the leaves of the two plants increased,peroxidase activity decreased under exposure to high concentrations of PFOS,and superoxide dismutase activity did not change.Under PFOS stress,the membrane of plant leaves and the cell structure of the two wetland plants were destroyed,and the mitochondrial contour of root cells became incomplete.Tanscriptomic analysis showed that the expression levels of genes related to cell wall formation,the cell apoptosis pathway,material synthesis,and metabolism in the plants were changed by PFOS.Analysis in fluorogenic quantitative real time polymerase chain reaction(RT-qPCR)also confirmed that the photosynthesis system of E.crassipes was inhibited,while that of C.alternifolius was promoted.

Removal,distribution and plant uptake of perfluorooctane sulfonate(PFOS)in a simulated constructed wetland system

A vertical-flow constructed wetland(VFCW)was used to treat simulated domestic sewage containing perfluorooctane sulfonate(PFOS).The removal rate of PFOS in the domestic sewage was 93%–98%,through soil adsorption and plant uptake,suggesting that VFCWs can remove PFOS efficiently from wastewater.The removal of PFOS in the VFCW was dependent on soil adsorption and plant uptake;moreover,the percentage of soil adsorption was 61%–89%,and was higher than that of the plants uptake(5%–31%).The absorption capacity of Eichhornia crassipes(E.crassipes)(1186.71 mg/kg)was higher than that of Cyperus alternifolius(C.alternifolius)(162.77 mg/kg)under 10 mg/L PFOS,and the transfer factor of PFOS in E.crassipes and C.alternifolius was 0.04 and 0.58,respectively,indicating that PFOS is not easily translocated to leaves from roots of wetland plants;moreover,uptake of PFOS by E.crassipes was more than that of C.alternifolius because the biomass of E.crassipes was more than that of C.alternifolius and the roots of E.crassipes can take up PFOS directly from wastewater while C.alternifolius needs to do so via its roots in the soil.The concentration of 10 mg/L PFOS had an obvious inhibitory effect on the removal rate of total nitrogen,total phosphorus,chemical oxygen demand,and ammonia nitrogen in the VFCW,which decreased by 15%,10%,10%and 12%,respectively.Dosing with PFOS in the wastewater reduced the bacterial richness but increased the diversity in soil because PFOS stimulated the growth of PFOS-tolerant strains.

Impact of photosynthesis and transpiration on nitrogen removal in constructed wetlands

To determine the impact of photosynthesis and transpiration on nitrogen removal in wetlands,an artificial wetland planted with reeds was constructed to treat highly concentrated domestic wastewater.Under different meteoro-logical and hydraulic conditions,the daily changes of photo-synthesis and transpiration of reeds,as well as nitrogen removal efficiency were measured.It was found that net pho-tosynthesis rate per unit leaf area was maintained on a high level(average 19.0μmol CO_(2)/(m^(2)·s))from 10:00 to 14:00 in July 2004 and reached a peak of 21.1μmol CO2/(m2·s)when Photon Flux Density was high during the day.Meanwhile,TN and NH_(4)^(+)-N removal efficiency rose to 79.6%and 89.6%,respectively-the maximum values observed in the test.Correlation coefficient analysis demonstrated a positive cor-relation among photon flux density,net photosynthetic rate,transpiration rate,and TN and NH_(4)^(+)-N removal efficiency.In contrast,there was a negative correlation between stomatal conductance and TN and NH_(4)^(+)-N removal efficiency.Results suggest that the photosynthesis and transpiration of wetland plants have a great impact on nitrogen removal efficiency of wetlands,which can be enhanced by an increase in the photo-synthesis and transpiration rate.In addition,the efficiency of water usage by reeds and nitrogen removal efficiency could be affected by the water level in wetlands;a higher level boosts nitrogen removal efficiency.

Contaminant removal from low-concentration polluted river water by the bio-rack wetlands

The bio-rack is a new approach for treating low-concentration polluted river water in wetland systems.A comparative study of the efficiency of contaminant removal between four plant species in bio-rack wetlands and between a bio-rack system and control system was conducted on a small-scale （500 mm length × 400 mm width × 400 mm height） to evaluate the decontamination effects of four different wetland plants.There was generally a significant difference in the removal of total nitrogen （TN）,ammonia nitrogen （NH 3-N） and total phosphorus （TP）,but no significant difference in the removal of permanganate index （COD Mn） between the bio-rack wetland and control system.Bio-rack wetland planted with Thalia dealbata had higher nutrient removal rates than wetlands planted with other species.Plant fine-root （root diameter 3 mm） biomass rather than total plant biomass was related to nutrient removal efficiency.The study suggested that the nutrient removal rates are influenced by plant species,and high fine-root biomass is an important factor in selecting highly effective wetland plants for a bio-rack system.According to the mass balance,the TN and TP removal were in the range of 61.03-73.27 g/m^2 and 4.14-5.20 g/m^2 in four bio-rack wetlands during the whole operational period.The N and P removal by plant uptake constituted 34.9%-43.81% of the mass N removal and 62.05%-74.81% of the mass P removal.The study showed that the nitrification/denitrification process and plant uptake process are major removal pathways for TN,while plant uptake is an effective removal pathway for TP.

Nitrogen mass balance in a constructed wetland treating piggery wastewater effluent

The nitrogen changes and the nitrogen mass balance in a free water surface flow constructed wetland （CW） using the four-year monitoring data from 2008 to 2012 were estimated. The CW was composed of six cells in series that include the first settling basin （Cell 1）, aeration pond （Cell 2）, deep marsh （Cell 3）, shallow marsh （Cell 4）, deep marsh （Cell 5） and final settling basin （Cell 6）. Analysis revealed that the NH4＋-N concentration decreased because of ammonification which was then followed by nitrification. The NO4＋-N and NO4＋-N were also further reduced by means of microbial activities and plant uptake during photosynthesis. The average nitrogen concentration at the influent was 37,819 kg/year and approximately 45% of that amount exited the CW in the effluent. The denitrification amounted to 34% of the net nitrogen input, whereas the accretion of sediment was only 7%. The biomass uptake of plants was able to retain only 1% of total nitrogen load. In order to improve the nutrient removal by plant uptake, plant coverage in four cells （i.e., Cells 1, 3, 4 and 5） could be increased.

Resource utilization of typical biomass wastes as biochars in removing plasticizer diethyl phthalate from water: characterization and adsorption mechanisms

Plastic pollution as a global environmental issue has become a research hotspot,among which the removal of inherent plasticizer(e.g.,phthalic acid esters,PAEs)received increasing attention.However,the effects of biochars derived from different feedstocks on the adsorption of PAEs are poorly understood.Thus,the characteristics of biochars derived from six largely produced biomass wastes in China at 400°C,as well as their performance in adsorption of diethyl phthalate(DEP),one of frequently detected PAEs in aqueous environment,were investigated.The results indicated that the variation in feedstock type showed significant changes in the properties(e.g.,porosity,specific surface area,surface functional groups)of biochars,which affected DEP adsorption and desorption.Pseudosecond order and Freundlich models fitted the adsorption data well,and adsorption mechanisms mainly included hydrophobic effect,followed by micropore filling,hydrogen bonding,andπ-πEDA interactions.Adsorption thermodynamics revealed that the adsorption was a spontaneous and exothermic the adsorption capacities of DEP on these biochars slightly decreased with the increasing pH but increased with the increasing ionic strength.Among these biochars,the giant reed biochar with relatively higher DEP adsorption and low desorption exhibited the great efficiency for DEP removal as an environment-friendly sorbent.These results highlighted the significant roles of micropore filling and hydrogen bond in determining adsorption capacity of designed biochars prepared from selecting suitable agricultural straws and wetland plant waste to typical plasticizer.The findings are useful for producing designed biochars from different biomass wastes for plasticizer pollution control.