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To understand the spatial differentiation characteristics and potential hazards of heavy metals in lakeside wetlands caused by low-pollution water in the agricultural runoff area of Qilu Lake, the surface sediments of 32 different types of wetlands(river wetlands n=13, constructed wetlands n=10, and lake wetlands n=9) in the lakeside agricultural runoff area were collected to detect the contents of the heavy metals Cu, Zn, Pb, Cr, Cd, Ni, and Hg. The spatial distribution characteristics of the seven heavy metals were analyzed by inverse distance weighted interpolation in ArcGIS, and the Hakanson potential ecological risk index method was used to evaluate the risks of heavy metal pollution in the Qilu Lake agricultural runoff area. The results showed that the degree of pollution of the seven heavy metals in different types of wetlands was different, and the average content was in the order of river wetlands > constructed wetlands > lake wetlands. The average content of heavy metals was in the order of Zn > Cr > Cu > Ni > Pb > Cd > Hg. Except for Pb, the heavy metals exceeded the background value of Yunnan soil, and the proportion of Cd samples exceeding backgroung value was as high as 100%. The risk index of the agricultural runoff area ranged from 112 to 1 241, with an average of 264, which indicated a moderate risk level. There were clear differences in the distribution of heavy metals, which was higher in the north than in the south and higher in the west than in the east. The areas with a high distribution were consistent with the results of the potential ecological risk assessment. The correlation analysis showed that the sources of Cu, Ni, Cr, and Zn pollution were mainly agricultural activities; the sources of Pb pollution were mainly related to road traffic, but were also affected by industrial activities; and the sources of Cd pollution were mainly agricultural activities and industrial activities. There were spatial differences in heavy metal pollution among the different types of wetlands in the Qilu Lake agricultural runoff area, among which Cd and Hg pollution were serious. High ecological risk areas appeared in the northwest and southwest, which should be given more attention.

Deteriorating urban water quality has attracted considerable attention in China. We investigated the contamination levels and distribution of heavy metals (As, Cd, Cu, Ni, Pb, and Zn) in Yuxi River water and sediments, and assessed the heavy metal accumulation capability of five species of submerged macrophytes: Vallisneria natans (Lour.) Hara, Potamogeton pectinatus L., Hydrilla verticillata (L. f.) Royle, Myriophyllum spicatum L., and Potamogeton crispus L. Samples were collected from upstream and downstream locations in different season. The results showed that the levels of heavy metals in the downstream areas were higher than in the upstream areas. Heavy metal concentrations in the river water during the dry seasons were higher than those during the rainy seasons, and the opposite results appeared in sediments and submerged macrophytes. In general, the river was slightly contaminated by heavy metals, and the concentrations of Pb and Ni in this river should serve as a warning, while Cd and Zn pollution in the sediments desperately needs to be removed. Furthermore, Potamogeton pectinatus L. showed a higher accumulation capacity for these metals among the five native submerged macrophytes and could be defined as a hyperaccumulator for Cd. Therefore, the potential use of native aquatic plants in contaminated rivers is worth further exploration.

Vertical flow constructed wetlands (VF CWs) are considered to be effective for treating organic pollutants. The rhizosphere of macrophytes such as Phragmites sp., Typha sp. serves as an active and dynamic zone for the microbial degradation of organic pollutants. However, it is still not clear how soil bacterial communities respond to macrophytes and pollutants during the process. For this purpose, the seedlings of Phragmites australis and Typha angustifolia were planted respectively in the VF CWs added with HCB at a dose of 2 mg/kg. During 96 days of cultivation, we monitored hexachlorobenzene (HCB) removal efficiency by GC/MS and the structure of the rhizosphere bacterial communities in the different VF CWs by denaturing gradient gel electrophoresis (DGGE), and constructed bacterial clone library based on PCR-amplified 16S rRNA gene. As expected, the rhizosphere bacterial communities also remained insensitive to HCB exposure in the wetland soil. The diversity of these microbes presented two stages, from the varied up and down to equilibrium in the entire experimental period. Molecular analysis revealed that the phylum Firmicutes dominated over the bacterial communities. The genera that increased under HCB stress included the well-known HCB-degrading bacteria (Pseudomonas sp. and Alcaligenes sp.) and other common bacteria found in contaminated soil but with lesser known practical functions (Burkholderia sp., Lysinibacillus fusiformis, and Bacillus cereus). Furthermore, there was a certain variance in the relative abundances of the bacterial phyla and HCB removal efficiency among different VF CW treatments. The degradation of HCB in T. angustifolia microcosms was faster than that in P. australis and unvegetated wetlands, and the highest bacterial diversity and richness was found in the VF CWs comprising T. angustifolia.

Although rhizoremediation is an effective approach to remove organic pollutants from the environment, little is known about the mechanism of hexachlorobenzene (HCB) biodegradation in water. In this study, we used Typha angustifolia (T. angustifolia) grown in sterile Hoagland nutrient solution to determine the rhizosphere effects on the ability of bacteria in water to reduce HCB levels. The results revealed that T. angustifolia could facilitate HCB degradation and that the initial HCB concentration was the major factor responsible for HCB degradation in nutrient solution. Furthermore, HCB biodegradation in low-HCB nutrient solution with T. angustifolia fitted the first-order kinetics, owing to the high concentration of total organic carbon, low HCB toxicity, and unique bacterial community in the T. angustifolia rhizosphere. Denaturing gradient gel electrophoresis indicated that the rhizosphere effects and different dosages of HCB have significant effects on the bacterial communities by repressing and favoring certain populations. The most successful bacteria to adapt to HCB contamination was Bacillus sp., while the dominant bacterial phyla in HCB-polluted water were Proteobacteria and Firmicutes.

The effect of Ipomoea aquatica floating-bed on the quantity and distribution of nitrogen cycling bacteria and nitrogen removal was investigated in plastic tanks using I.aquatica as floating-bed plant.The results showed that the number of total nitrogen cycling bacteria,ammonifying bacteria,nitrosobacteria,nitrobacteria in the I.aquatica floating-bed system was significantly higher than that in the control(P0.01).No significant difference was found for the number of denitrifying bacteria between I.aquatica floating-bed system and the control(P0.05).The number of total nitrogen cycling bacteria in I.aquatica floating-bed(7×105—3×108 MPN/g) was 2 to 5 orders of magnitude higher than that in the control(3×102—5×106MPN/g).The dominant group in the I.aquatica floating-bed system was ammonifying bacteria throughout the test period(P0.01).But the dominant group in the control had changed during the test period.The dominant bacteria group in the control was ammonifying bacteria at the sixth and twelfth day of sampling(P0.05),while ammonifying bacteria and denitrifying bacteria were dominant at the nineteenth and thirty-third day of sampling(P0.05).The dominant group in the control was denitrifying bacteria at the twenty-sixth day of sampling(P0.05).The difference in the distribution of ammonifying bacteria was not significant among endo-rhizosphere,rhizoplane and water.Nitrosobacteria was mainly distributed in the endo-rhizosphere and rhizoplane.Nitrobacteria was mainly distributed in the rhizoplane and denitrifying bacteria was mainly distributed in the water.The removal rate of NH+4-N was 91.8% in the I.aquatica floating-bed system and 88.5% in the control,respectively.NH3 volatilization could be the main way of NH+4-N removal in the control.Microbial nitrification could be the main way of NH+4-N removal in the I.aquatica floating-bed system.Since I.aquatica covered only 10% of the water surface in the floating-bed system,NH+4-N removal rates in the two systems were not significantly different.The removal rate of total nitrogen was 48.2% in the I.aquatica floating-bed system and 62.1% in the control,respectively.Due to the decay of I.aquatica induced by insects after the 19th day,the removal rate of total nitrogen in the I.aquatica floating-bed system was lower than that in the control.But the interference of insects offered a possibility to have a thorough knowledge of purification mechanism of nitrogen with ecological floating-beds.Based on the correlation analysis between the number and distribution of the nitrogen cycling bacteria and the nitrogen concentration,we found that the contribution of ammonifying bacteria and nitrosobacteria in the rhizoplane is higher than that in the endo-rhizosphere and water.The contribution of nitrobacteria and denitrifying bacteria in the water is higher than that in the endo-rhizosphere and rhizoplane.Nitrogen removal is the combined effect of plant absorption,ammoniation in the rhizoplane,nitrification and denitrification in the water in the I.aquatica floating-bed system.But the main way of nitrogen removal is microbial nitrification,denitrification and NH3 volatilization in the control.The results provide sound basis for further understanding about the purification mechanism of nitrogen with ecological floating-beds.