Dissipation characteristics of pyrene and ecological contribution of submerged macrophytes and their biofilms-leaves in constructed wetland

Submerged macrophyte promoted nitrogen removal function of biofilms in constructed wetland

Biofilm is one of the important factors affecting nitrogen removal in constructed wetlands (CWs). However, the impact of submerged macrophyte on nitrogen conversion of biofilms on leaf of submerged macrophyte and matrix remains poorly understood. In this study, the CWs with Vallisneria natans and with artificial plant were established to investigate the effects of submerged macrophyte on nitrogen conversion and the composition of nitrogen-converting bacteria in leaf and matrix biofilms under high ammonium nitrogen (NH4+-N) loading. The 16S rRNA sequencing method was employed to explore the changes in bacterial communities in biofilms in CWs. The results showed that average removal rates of total nitrogen and NH4+-N in CW with V. natans reached 71.38% and 82.08%, respectively, representing increases of 24.19% and 28.79% compared with the control with artificial plant. Scanning electron microscope images indicated that high NH4+-N damaged the leaf cells of V. natans, leading to the cellular content release and subsequent increases of aqueous total organic carbon. However, the specific surface area and carrier function of V. natans were unaffected within 25 days. As a natural source of organic matters, submerged macrophyte provided organic matters for bacterial growth in biofilms. Bacterial composition analysis revealed the predominance of phylum Proteobacteria in CW with V. natans. The numbers of nitrifiers and denitrifiers in leaf biofilms reached 1.66 × 105 cells/g and 1.05 × 107 cells/g, as well as 2.79 × 105 cells/g and 7.41 × 107 cells/g in matrix biofilms, respectively. Submerged macrophyte significantly increased the population of nitrogen-converting bacteria and enhanced the expressions of nitrification genes (amoA and hao) and denitrification genes (napA, nirS and nosZ) in both leaf and matrix biofilms. Therefore, our study emphasized the influence of submerged macrophyte on biofilm functions and provided a scientific basis for nitrogen removal of biofilms in CWs.

The effect of polyvinyl chloride (PVC) color on biofilm development and biofilm-heavy metal chemodynamics in the aquatic environment

Plastic surfaces are colonized by microorganisms and biofilms are formed in the natural aquatic environment. As the biofilm develops, it changes the density and buoyancy of the plastic-biofilm complex, results in plastic sinking, and increases the heavy metals accumulated by biofilm's mobility and availability in aquatic ecosystems. In this experiment, biofilms were cultured on five colors of polyvinyl chloride (PVC; transparent, green, blue, red, black) in an aquatic environment to investigate the effects of plastic color on biofilm formation and development (Phase 1) and to study the effects of being sunk below the photic zone on biofilm (Phase 2). The PVC color significantly affected the biofilm formation rate but had no impact on the final biofilm biomass. After sinking the biofilm-PVC below the photic zone in Phase 2, the layer of diatoms on the biofilm surface began to disintegrate, and the biomass and Chlorophyll-a (Chla) content of the biofilm decreased, except on the red PVC. Below the photic zone, the microbial community of the biofilm changed from primarily autotrophic microbes to mostly heterotrophic microbes. Microbial diversity increased and extracellular polymeric substances (EPS) content decreased. The primary factor leading to microbial diversity and community structure changes was water depth rather than PVC color. The changes induced in the biofilm led to an increase in the concentration of all heavy metals in the biofilm, related to the increase in microbial diversity. This study provides new insights into the biofilm formation process and the effects on a biofilm when it sinks below the photic zone.

Purification of aquaculture wastewater by macrophytes and biofilm systems: Efficient removal of trace antibiotics and enrichment of antibiotic resistance genes

The purification performance of aquaculture wastewater and the risk of antibiotic resistance genes (ARGs) dissemination in wetlands dominated by macrophytes remain unclear. Here, the purification effects of different macrophytes and biofilm systems on real aquaculture wastewater were investigated, as well as the distribution and abundance of ARGs. Compared to the submerged macrophytes, artificial macrophytes exhibited higher removal rates of TOC (58.80 ± 5.04 %), TN (74.50 ± 2.50 %), and TP (77.33 ± 11.66 %), and achieved approximately 79.92 % removal of accumulated trace antibiotics in the surrounding water. Additionally, the biofilm microbial communities on the surface of artificial macrophytes exhibited higher microbial diversity with fewer antibiotic-resistant bacteria (ARB) enrichment from the surrounding water. The absolute abundance of ARGs (sul1, sul2, and intI1) in the mature biofilm to be one to two orders of magnitude higher than that in the water. Although biofilms could decrease ARGs in the surrounding water by enriching ARB, the intricate network structure of biofilms further facilitated the proliferation of ARB and the dissemination of ARGs in water. Network analysis suggested that Proteobacteria and Firmicutes phyla were dominant and potential carriers of ARGs, contributing 69.00 % and 16.70 %, respectively. Our findings highlight that macrophytes and biofilm systems have great performance on aquaculture wastewater purification, but with high risk of ARGs.

Potamogeton crispus restoration increased the epiphytic microbial diversity and improved water quality in a micro-polluted urban river

Special characterization and assembly of epiphytic microbial communities remain unclear in micro-polluted water column during submersed macrophytes restoration. In this study, an in-situ enclosure area sowing with turions of Potamogeton crispus (P. crispus) was conducted in a micro-polluted urban river to investigate the characterization of P. crispus and epiphytic microbial communities and their response to water environment under different water depths. Turions completely germinated in water column with <90 cm water depth and the germination speed decreased with increasing water depth within 18 days. There were obvious differences in morphological characteristics of P. crispus between deep and shallow water layers. P. crispus restoration decreased by 12-32%, 13-36%, 9-43% and 5-36% of COD, NH₄⁺-N, TN and TP concentration, respectively, in enclosed overlying water compared to the river (P < 0.05) during 5 months of experiment. Illumina sequencing was employed to explore the epiphytic bacterial and microeukayotic communities at water depth 25-35 cm (shallow area) and 80-90 cm (deep area). A total of 9 bacterial and 12 microeukayotic dominant phyla were obtained in eight samples. It should be noted that the algae abundances were higher in shallow area than deep area but a reverse trend was observed for methanotrophs. Null model analysis revealed that dispersal limitation and undominated process was the most important assembly process, whereas stochastic processes gained more importance in shallow area than deep one. According to cooccurrence analysis (|r| > 0.6, P < 0.05), there were more strongly correlated edges in shallow area (456 edges) than deep area (340 edges). These results highlight that submerged macrophytes restoration can increase microbial diversity and improve water quality, and provide a "summer disease cured in winter" way by using could-resistant P. crispus for water purification in micro-polluted rivers in low-temperature season.

Response of submerged macrophytes and leaf biofilms to different concentrations of oxytetracycline and sulfadiazine

Oxytetracycline and sulfadiazine were widely used and they entered the environment through various channels such as domestic sewage, medical wastewater and agricultural wastewater, causing significant ecological risk. To determine the effects of different antibiotic concentrations on submerged macrophytes, Vallisneria natans was exposed to solutions containing different concentrations of oxytetracycline and sulfadiazine (0.1 mg/L、1 mg/L、10 mg/L、50 mg/L). After 20-days exposure, we found that 10 mg/L groups had a significant effect on Vallisneria natans. Under high antibiotic concentrations, the growth of Vallisneria natans was inhibited, chloroplasts were deformed, the chlorophyll content was reduced, and antioxidant enzyme activities, such as superoxide dismutase and glutathione, were increased. There was no significant difference between the control group and groups with low antibiotic concentrations (≤1 mg/L). The N-acyl-l-homoserine lactone concentration tended to increase with increasing antibiotic concentrations. The presence of antibiotics also affected the microbial community structure of biofilms on the submerged macrophytes. For example, the higher the concentration of antibiotics, the higher the proportion of Proteobacteria. These results suggest that high concentrations of oxytetracycline and sulfadiazine can disrupt homeostasis, induce effective Vallisneria natans defense mechanisms and alter biofilms in aquatic ecosystems.

Unraveling the ecological mechanisms of bacterial succession in epiphytic biofilms on Vallisneria natans and Hydrilla verticillata during bioremediation of phenanthrene and pyrene polluted wetland

In wetland ecosystem, the microbial succession in epiphytic biofilms of submerged macrophytes remains to be fully elucidated, especially submerged macrophytes used to remediate organic pollutants contaminated sediment. Herein, 16 S rRNA gene sequencing was used to investigate the bacterial dynamics and ecological processes in the biofilms of two typical submerged macrophytes (Vallisneria natans and Hydrilla verticillata) settled in sediment polluted by polycyclic aromatic hydrocarbons (PAHs) at two growth periods. The results presented that the variations of bacterial community in the biofilms were influenced by attached surfaces (explanation ratio: 17.30%), incubation time (32.30%) and environmental factors (39.10%). Bacterial community assembly was mainly driven by dispersal limitation which triggered more positive co-occurrence associations in microbial networks, maintaining ecological stability in the process of bioremediation of PAHs. Additionally, the functional redundancy strength of bacterial community was more affected by attached surface than incubation time. The structural equation model illustrated that community assembly drove β-diversity and explained a part of ecological functions. Environmental factors, community assembly, and β-diversity jointly affected microbial networks. Overall, our study offers new insights into the microbial ecology in biofilms attached on the submerged macrophytes settled in PAH-polluted sediment, providing important information for deeply understanding submerged macrophyte-biofilm complex and promoting sustainable phytoremediation in shallow lacustrine and marshy ecosystems.

The Growth of Vallisneria natans and Its Epiphytic Biofilm in Simulated Nutrient-Rich Flowing Water

This paper investigates the effects of water flow on the growth and physiological indicators of the submerged macrophyte, Vallisneria natans, and the bacteria and algae community composition on its epiphytic biofilm-covered leaves. The authors set up a simulated flowing water laboratory experiment testing high nitrogen (N) and phosphorus (P) concentrations. Total chlorophyll and dissolved oxygen (DO) was significantly enhanced, and turbidity was reduced, thereby accelerating the growth of V. natans. These experiments were compared to another set of observations on a static group. The accumulation of malonaldehyde (MDA) in the dynamic groups was significantly higher than that in the static group. As an antioxidant stress response, the total superoxide dismutase (T-SOD) was also induced in plants exposed to nutrient-rich flowing water. The results of 16S rRNA high-throughput sequencing analyses showed that the water flow increased the bacteria community diversity of biofilm-producing bacteria with N and P removing bacteria, carbon cycle bacteria, and plant growth-promoting rhizobacteria on the epiphytic biofilm. This research determined that water flow alleviates the adverse effects of eutrophication when V. natans grows in water containing high N and P concentrations. Water flow also inhibits the growth of cyanobacteria (also referred to as blue-green algae) in epiphytic biofilm. The ecological factor of water flow, such as water disturbance and aeration measures, could alleviate the adverse effect of eutrophic water by providing a new way to restore submerged macrophytes, such as V. natans, in eutrophic water.

Nitrogen addition facilitates phytoremediation of PAH-Cd cocontaminated dumpsite soil by altering alfalfa growth and rhizosphere communities

Thousands of unlined landfills and open dumpsites seriously threatened the safety of soil and groundwater due to leachate leakage with a mass of pollutants, particularly heavy metals, organic contaminants and ammonia. Phytoremediation is widely used in the treatment of cocontaminated soils because it is cost-effective and environmentally friendly. However, the extent to which phytoremediation efficiency and plant physiological responses are affected by the high nitrogen (N) content in such cocontaminated soil is still uncertain. Here, pot experiments were conducted to investigate the effects of N addition on the applicability of legume alfalfa remediation for polycyclic aromatic hydrocarbon‑cadmium (PAHCd) co-/contaminated soil and the corresponding microbial regulation mechanism. The results showed that the PAH dissipation rates and Cd removal rates in the high-contamination groups increased with the external N supply, among which the pyrene dissipation rates in the cocontaminated soil was elevated most significantly, from 78.10% to 87.25%. However, the phytoremediation efficiency weakened in low cocontaminated soil, possibly because the excessive N content had inhibitory effects on the rhizobium Ensifer and restrained alfalfa growth. Furthermore, the relative abundance of PAH-degrading bacteria in the rhizosphere dominated PAH dissipation. As reflected by principal coordinate analysis (PCoA) analysis and hierarchical dendrograms, the microbial community composition changed with N addition, and a more pronounced shift was found in the rhizosphere relative to the endosphere or shoots of alfalfa. This study will provide a theoretical basis for legume plant remediation of dumpsites as well as soil contaminated with multiple pollutants.

Presence of polycyclic aromatic hydrocarbons among multi-media in a typical constructed wetland located in the coastal industrial zone, Tianjin, China: Occurrence characteristics, source apportionment and model simulation

In-depth understanding and accurately predicting the occurrence and fate of polycyclic aromatic hydrocarbons (PAHs) in constructed wetlands (CWs) is extremely crucial for optimizing the CWs construction and strengthening the risk control. However, few studies have focused on the PAHs among sediment-water-plant and model simulation in CWs. In this study, sediment, surface water and reed samples were gathered and analyzed from a typical CW. The concentrations of 16 PAHs (Σ₁₆PAHs) in sediments, surface water and reeds ranged from 620 to 4277 μg/kg, 114 to 443 ng/L and 74.5 to 362 μg/kg, respectively. The coefficients of variation (CV) were calculated as 0.796, 0.431 and 0.473 for the above three media respectively, indicating that the spatial distribution variation was medium intensity. The fugacity fraction (ff) suggested that sediments might act as the secondary release source of most PAHs. According to the diagnostic ratios and principal component analysis-multiple linear regression (PCA-MLR), PAHs in this CW mainly come from fossil fuels combustion and petroleum leakage. PAHs in sediments showed high ecological risk at water inlet and moderate risk at the other functional zones, while low risks for surface water at all functional zones. Although the human health risk assessment indicated relatively low cancer risk, the health risk still cannot be ignored with the continuous input and accumulation of exogenous PAHs. A mathematical model covering the hydraulics parameters and composition characteristics of the wetland was established, and its reliability was verified. The simulated results obtained by the established model were basically consistent with the measured values. In addition, the total remove efficiency of PAHs in surface water was 40.2%, which calculated by the simulated model. This work provides helpful insight into the comprehension of occurrence and fate of PAHs among multi-media in CWs.

Application of constructed wetlands in the PAH remediation of surface water: A review

Polycyclic aromatic hydrocarbons (PAHs) pose adverse risks to ecosystems and public health because of their carcinogenicity and mutagenicity. As such, the extensive occurrence of PAHs represents a worldwide concern that requires urgent solutions. Wastewater treatment plants are not, however, designed for PAH removal and often become sources of the PAHs entering surface waters. Among the technologies applied in PAH remediation, constructed wetlands (CWs) exhibit several cost-effective and eco-friendly advantages, yet a systematic examination of the application and success of CWs for PAH remediation is missing. This review discusses PAH occurrence, distribution, and seasonal patterns in surface waters during the last decade to provide baseline information for risk control and further treatment. Furthermore, based on the application of CWs in PAH remediation, progress in understanding and optimising PAH-removal mechanisms is discussed focussing on sediments, plants, and microorganisms. Wetland plant traits are key factors affecting the mechanisms of PAH removal in CWs, including adsorption, uptake, phytovolatilization, and biodegradation. The physico-chemical characteristics of PAHs, environmental conditions, wetland configuration, and operation parameters are also reviewed as important factors affecting PAH removal efficiency. Whilst significant progress has been made, several key problems need to be addressed to ensure the success of large-scale CW projects. These include improving performance in cold climates and addressing the toxic threshold effects of PAHs on wetland plants. Overall, this review provides future direction for research on PAH removal using CWs and their large-scale operation for the treatment of PAH-contaminated surface waters.

Mutual promotion of submerged macrophytes and biofilms on artificial macrophytes for nitrogen and COD removal improvement in eutrophic water

Both submerged macrophytes (SMs) and artificial macrophytes (AMs) have been widely used to improve water quality in eutrophic water. However, in heavily eutrophic aquatic ecosystems, the purification function of SMs is often restricted by the poor growth state due to competition from algae, while the purification function of AMs is often restricted by the limited carbon source supply for biofilm microbes attached to the AM surface. The objective of this study was to develop a new strategy to increase pollutant removal efficiency (RE) by combining the use of SMs and AMs. Pilot-scale microcosms, including treatments with both SMs and AMs (S&A), only SMs (SO) and only AMs (AO), were established to identify the performance of the new strategy. The results suggest that treatment S&A obtained REs of 88.9% for total nitrogen (TN) and 48.1% for chemical oxygen demand (COD); as comparison, treatments SO and AO obtained REs of 77.4% and 81.2% for TN and REs of -13.7% and 39.0% for COD, respectively. Compared with SO, the S&A treatment benefited SM growth in biomass, leaf chlorophyll concentration and root activity by inhibiting algae growth. In addition, compared with treatment AO, S&A increased the biofilm microbial biomass and the relative abundance of nitrifiers of families Nitrosomonadaceae and Nitrospira attached to AM surfaces. Therefore, by the mutual promotion of SMs and biofilms on AMs, the synergic application of SMs and AMs is a useful strategy for improving TN and COD REs in eutrophic water bodies such as rivers and constructed wetlands. A strategy was developed to increase nitrogen and COD removal in eutrophic water by the mutual promotion of submerged macrophytes and biofilms on artificial macrophytes.

Impacts of water flow on epiphytic microbes and nutrients removal in constructed wetlands dominated by Vallisneria natans with decreasing temperature

The mechanisms behind water flow on contaminant removal by a submerged macrophyte-biofilm complex in surface flow wetlands remain to be fully elucidated. In this study, water flow (2.02 ~ 2.12 or 4.06 ~ 4.5 L s^-1; hydraulic retention time, 7d) significantly enhanced NH₄⁺-N and COD but inhibited TN and TP removal compared to the static ones. No more than 30% of TN and TP were assimilated by V. natans-biofilm complex in wetland system. Water flow remarkably affected alpha-diversity of microbial community in epiphytic biofilm. As revealed by beta-diversity analysis, turnover played greater contribution to the total dissimilarity than nestedness. Network analyses revealed that the microbial interactions including predation, symbiosis and competition in epiphytic biofilms were much more intensive in the Sept.- Oct. than the Nov.-Dec group. Redundancy and Mantel correlation analyses revealed that temperature played a key role in determining microbial community structure, especially for bacteria.

The improvement of pollutant removal efficiency in saturated vertical flow constructed wetlands by tubifex tubifex

Pilot-scale saturated vertical flow constructed wetlands (VF-CWs) were established to identify whether T. tubifex has the similar performance in saturated VF-CWs to that in surface flow CWs in improving pollutant removal efficiency (RE). The saturated VF-CWs with T. tubifex achieved REs of 67.3% total nitrogen (TN) and 39.8% chemical oxygen demand (COD), which were significantly higher than treatments without T. tubifex (42.2% TN and 31.4% COD). There existed significant interactions between macrophytes and T. tubifex. T. tubifex greatly improved the dissolved oxygen by increasing the connectivity between layers, and enhanced dehydrogenase activity and fluorescein diacetate. Adding T. tubifex improved the bacterial diversity and relative abundance of both N-cycle bacteria and fermentation bacteria in the biofilms. The improvements of ammonia oxidation and anammox were the main pathways for the increased nitrogen removal by T. tubifex. Therefore, T. tubifex is a useful tool for improving pollutant REs in saturated VF-CWs.

Spatial Changes in Microbial Communities along Different Functional Zones of a Free-Water Surface Wetland

Constructed wetlands (CWs) are complicated ecosystems that include vegetation, sediments, and the associated microbiome mediating numerous processes in wastewater treatment. CWs have various functional zones where contrasting biochemical processes occur. Since these zones are characterized by different particle-size composition, physicochemical conditions, and vegetation, one can expect the presence of distinct microbiomes across different CW zones. Here, we investigated spatial changes in microbiomes along different functional zones of a free-water surface wetland located in Moscow, Russia. The microbiome structure was analyzed using Illumina MiSeq amplicon sequencing. We also determined particle diameter and surface area of sediments, as well as chemical composition of organic pollutants in different CW zones. Specific organic particle aggregates similar to activated sludge flocs were identified in the sediments. The highest accumulation of hydrocarbons was found in the zones with predominant sedimentation of fine fractions. Phytofilters had the highest rate of organic pollutants decomposition and predominance of Smithella, Ignavibacterium, and Methanothrix. The sedimentation tank had lower microbial diversity, and higher relative abundances of Parcubacteria, Proteiniclasticum, and Macellibacteroides, as well as higher predicted abundances of genes related to methanogenesis and methanotrophy. Thus, spatial changes in microbiomes of constructed wetlands can be associated with different types of wastewater treatment processes.

Pilot-scale study on the effects of cyanobacterial blooms on Vallisneria natans and biofilms at different phosphorus concentrations

Cyanobacterial blooms cause potential risk to submerged macrophytes and biofilms in eutrophic environments. This pilot-scale study investigated the growth, oxidative responses, and detoxification activity of aquatic plants in response to cyanobacterial blooms under different phosphorus concentrations. Variations of extracellular polymeric substances (EPSs) and microbial community composition were also assessed. Results showed that the biomass of Vallisneria natans increased with exposure to cyanobacterial blooms at higher phosphorous concentrations (P > 0.2 mg L^-1). The amount of microcystin compounds (MC-LR) released into the water and the accumulation of MC-LR into both plant tissue and biofilms changed according to the phosphorus concentration. Furthermore, a certain degree of oxidative stress was induced in the plants, as evidenced by increased activity of superoxide dismutase, catalase, and peroxidase, as well as increased malondialdehyde concentrations; significant differences were also seen in acid phosphatase and glutathione S-transferase activities, as well as in glutathione concentrations. Together, these responses indicate potential mechanisms of MC-LR detoxification. Broader α-D-glucopyranose polysaccharides (PS) increased with increasing phosphorous and aggregated into clusters in biofilm EPS in response to the cyanobacterial blooms. In addition, alterations were seen in the abundance and structure of the microbial communities present in exposed biofilms. These results demonstrate that cyanobacterial blooms under different concentrations of phosphorus can induce differential responses, which can have a significant impact on aquatic ecosystems.

Removal pathways of benzofluoranthene in a constructed wetland amended with metallic ions embedded carbon

The limited adsorption capacity of the substrate and the concentration of dissolved oxygen in constructed wetlands (CWs) have inhibited their ability to efficiently remove polycyclic aromatic hydrocarbons (PAHs) from wastewater. Presently, biochar and activated carbon modified with Fe³⁺ and Mn⁴⁺ were used as effective sorbents in the removal of benzofluoranthene (BbFA), a typical PAH, in CW microcosms. The addition of metallic ions embedded carbon increased NO₃-N accumulation by the reduction of Fe³⁺ and Mn⁴⁺, which led to improved BbFA degradation. Additionally, plant adsorption in root and stem sections were observed separately. The abundance of PAH-degrading microbes in the rhizosphere substrate was higher with the metallic ions embedded carbon than control group. The Fe³⁺, Mn⁴⁺ and NO₃-N served as electron acceptors increased BbFA microbial degradation. The removal pathways of BbFA in the modified CWs were proposed which involved settlement in the substrate, plant absorption, and microbial degradation.

Response of the submerged macrophytes Vallisneria natans to snails at different densities

The study investigated the responses of the submerged macrophyte Vallisneria natans (V. natans) to snails (Bellamya aeruginosa) at different densities, with changes in physiological parameters, morphology, leaf-epiphytic bacteria community and water quality parameters examined. The changes of water quality parameters (pH, total nitrogen (TN), total phosphorus (TP) and total organic carbon (TOC)) indicated that snails secreted nutrients into water. Changes in morphological and physiological parameters (fresh weight, root length, shoot height, chlorophyll, malondialdehyde (MDA), activities of superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD)) demonstrated that the presence of snails were beneficial to the growth of submerged macrophytes. Microbial diversity analyses indicated that snails could decrease microbial community richness and diversity. At medium densities (340 ind. m^-2), an increase in snail density was beneficial to the growth of submerged macrophytes. The results of this study provide theoretical guidance and technical support for the maintenance and restoration of submerged macrophytes.

Coupled photocatalytic-bacterial degradation of pyrene: Removal enhancement and bacterial community responses

Polycyclic aromatic hydrocarbons (PAHs) are a class of pollutants that ubiquitously present in environment and hard to be degraded by microorganisms. Herein, we reported a novel photocatalytic-bacterial coupled removal system to treat PAH-polluted water. Using pyrene as the model pollutant, we demonstrated that the removal percentage of different groups was in order: 63.89% ± 1.03% (Vis-Biological) > 61.27% ± 1.08% (UV-Biological) > 59.58% ± 1.15% (UV) > 57.41% ± 1.13% (Vis) > 6.65% ± 0.72% (Biological) > 1.70% ± 0.34% (Control), showing the coupled system significantly improved the removal percentage of pyrene. Additionally, we observed that the coupled system driven by visible light showed higher removal percentage than UV light, exhibiting a good potential for future application. Sequencing analysis of 16S rRNA genes showed that alpha diversity (richness, evenness and diversity) got promoted and data of the relative abundance showed that Pseudomonadaceae was substituted as the dominant bacteria for Planococcaceae, with some other functional bacteria quickly acclimatizing in the bacterial community. Difference analysis indicated that over half of top fifteen genera were generally different significantly (p < 0.001) among two different samples, and UV light altered structure and composition of bacterial community more than visible light. Functional features' change suggested that the bacterial community not only protected itself but also participated in degrading pyrene. Overall, our study offered a new method for PAH degradation and contributed to further understanding of coupled catalytic-bacterial degradation processes.

Can Constructed Wetlands be Wildlife Refuges? A Review of Their Potential Biodiversity Conservation Value

The degradation of wetland ecosystems is currently recognized as one of the main threats to global biodiversity. As a means of compensation, constructed wetlands (CWs), which are built to treat agricultural runoff and municipal wastewater, have become important for maintaining biodiversity. Here, we review studies on the relationships between CWs and their associated biodiversity published over the past three decades. In doing so, we provide an overview of how wildlife utilizes CWs, and the effects of biodiversity on pollutant transformation and removal. Beyond their primary aim (to purify various kinds of wastewater), CWs provide sub-optimal habitat for many species and, in turn, their purification function can be strongly influenced by the biodiversity that they support. However, there are some difficulties when using CWs to conserve biodiversity because some key characteristics of these engineered ecosystems vary from natural wetlands, including some fundamental ecological processes. Without proper management intervention, these features of CWs can promote biological invasion, as well as form an ‘ecological trap’ for native species. Management options, such as basin-wide integrative management and building in more natural wetland components, can partially offset these adverse impacts. Overall, the awareness of managers and the public regarding the potential value of CWs in biodiversity conservation remains superficial. More in-depth research, especially on how to balance different stakeholder values between wastewater managers and conservationists, is now required.

Response of submerged macrophytes and leaf biofilms to the decline phase of Microcystis aeruginosa: Antioxidant response, ultrastructure, microbial properties, and potential mechanism

Decaying cyanobacterial blooms carry a potential risk for submerged macrophyte and periphyton biofilms in aquatic environments. This study comprehensively studied the responses in growth, oxidative response, detoxification pathway, and ultrastructure characteristics of aquatic plants to Microcystis aeruginosa (M. aeruginosa) exudates and extracts released during the decline phase. Particular emphasis was placed on the variation of extracellular polymeric substances (EPS) and quorum-sensing signaling molecules. The results showed that superoxide dismutase, peroxidase, and glutathione S-transferase were significantly induced as antioxidant response, and the malondialdehyde content increased. Increased content of MC-LR (1.129 μg L^-1) and NH₄⁺-N (1.35 mg L^-1) were found in the decline phase of M. aeruginosa, which played a vital role in the damage to submerged plants. In addition, a change in the amount of osmiophilic granules and a variation of organelles and membranes was observed. A broad distribution of α-d-glucopyranose polysaccharides was dominant and aggregated into clusters in biofilm EPS in response to exposure to decaying M. aeruginosa. Furthermore, exposure to exudates and extracts changed the abundance and structure of the microbial biofilm community. Increased contents of N-acylated-L-homoserine lactone signal molecule might result in a variation of biofilm EPS production in response to decaying M. aeruginosa. These results expand the understanding of how submerged macrophyte and periphyton biofilms respond to environmental stress caused by exudates and extracts of decaying M. aeruginosa.

The dissipation and risk alleviation mechanism of PAHs and nitrogen in constructed wetlands: The role of submerged macrophytes and their biofilms-leaves

The role of submerged macrophytes (Vallisneria natans, Hydrilla verticillata and artificial plant) and their biofilms-leaves for the dissipation and risk alleviation mechanism of PAHs (phenanthrene and pyrene) and nitrogen in constructed wetland systems with PAH-polluted sediments were investigated. Biofilms-leaves/surface might contribute to PAHs degradation, which was positively correlated with PAHs degrading bacteria. Nitrogen-fixing bacteria in biofilms on surface might cause total nitrogen in sediment (TNs) increasing by 4% from 14th d to 28th d indirectly when suffering PAHs pollution. The relative abundance of nitrogen-fixing bacteria significantly increased with the increase of PAHs concentrations in early period (p < 0.01), which might lead to risk of nitrogen accumulation further. Heat maps showed that the relative abundance of functional bacteria were influenced in order of attached surface > incubation time > spiking concentration of PAHs. Interestingly, differences of deduced bacterial functions were affected in order of incubation time > attached surface > spiking concentration. Thus, submerged macrophytes and their biofilms on leaves not only played an important role in PAHs degradation, but also regulated the nitrogen cycling in constructed wetland systems, which could reduce these pollutants risk for natural environment, organisms and human health.