Ecological risk of polycyclic aromatic hydrocarbons (PAHs) and organochlorine pesticides (OCPs) in the sediment of a protected karst plateau lake (Caohai) wetland in China.

Understanding PAH and OCP distributions and sources in lakes is necessary for developing pollutant control policies. Here, we assessed the occurrence, risk, and sources of PAHs and OCPs in the sediment of Caohai Lake. The PAHs were predominantly high-molecular-weight compounds (mean 57.5 %), and the diagnostic ratios revealed that coal, biomass burning, and traffic were the sources of PAHs. HCHs (6.53 ± 7.22 ng g-1) and DDTs (10.86 ± 12.16 ng g-1) were the dominant OCPs and were primarily sourced from fresh exogenous inputs. RDA showed that sediment properties explained 74.12 % and 65.44 % of the variation in PAH and OCP concentrations, respectively. Incremental lifetime cancer risk (ILCR) assessment indicated that hazardous PAHs in Caohai Lake sediment posed moderate risks to children and adults (ILCR>1.0 × 10-4), while the risk from OCPs was low; however, the recent influx of HCHs and DDTs requires additional attention.

Cascade dams altered taxonomic and functional composition of bacterioplankton community at the regional scale.

Dams are increasingly disrupting natural river systems, yet studies investigating their impact on microbial communities at regional scale are limited. Given the indispensable role of bacterioplankton in aquatic ecosystems, 16S rRNA gene sequencing was performed to explore how these communities respond to dam-influenced environmental changes at the regional scale in the Shaying River Basin. Our findings revealed that cascade dams create distinct environments, shaping bacterioplankton communities near the dams differently from those in natural rivers. In the upstream of the cascade dams, water quality was superior, while bacterioplankton community structure was simple with weak community interactions. In the midstream, nutrient and heavy metal content were increased, making bacterioplankton structures more susceptible to environmental changes. In the downstream of the cascade dams, water quality had a significant impact on the community and the bacterioplankton structures were highly complex. Additionally, environmental variables significantly influenced bacterioplankton functional groups. However, the response to these factors, as well as the interplay between functional and taxonomic diversity, varied markedly depending on the specific region of the cascade dams. We here delved into the effects of cascade dams on the taxonomic diversity and functional groups of bacterioplankton to provide a theoretical basis for segmentally regulating these dams.

Effect of Tubifex tubifex on the purification function of saturated vertical flow constructed wetlands for effluents with varying C/N ratios.

The improvement effect of Tubifex tubifex on the pollutant removal efficiencies (REs) of vertical flow constructed wetlands (VF-CWs) treating wastewater with various C/N ratios was explored. The experiment was conducted in pilot-scale saturated VF-CWs, being added different densities of T. tubifex and fed synthetic wastewater with successive C/N ratios of 0.5, 1.5, 3.0 and 6.0. The results suggest that T. tubifex addition and the influent C/N ratio had an interactive effect, i.e., T. tubifex addition improved NOx--N, NH4+-N, TN and COD REs by 36.7%, 56.5%, 22.6%, and 10.0%, respectively, under low C/N ratios, while high C/N ratios inhibited this improvement. Low-density T. tubifex addition significantly increased substrate dissolved oxygen (DO) by retarding excessive soil organic matter (OM) accumulation. With T. tubifex addition, an improvement in bacterial diversity, the relative abundance of N-cycle and fermentative bacteria, and N-cycle functional genes was only observed in substrates under low C/N ratios. T. tubifex can improve the purification function of saturated VF-CWs, but this strategy strongly depends on both the influent C/N ratio and density of T. tubifex addition.

Abundance trade-offs and dominant taxa maintain the stability of the bacterioplankton community underlying Microcystis blooms.

Microcystis blooms are an intractable global environmental problem that pollute water and compromise ecosystem functioning. Closed-lake management practices keep lakes free of sewage and harmful algae invasions and have succeeded in controlling local Microcystis blooms; however, there is little understanding of how the bacterioplankton communities associated with Microcystis have changed. Here, based on metagenomic sequencing, the phyla, genera, functional genes and metabolic functions of the bacterioplankton communities were compared between open lakes (underlying Microcystis blooms) and closed lakes (no Microcystis blooms). Water properties and zooplankton density were investigated and measured as factors influencing blooms. The results showed that (1) the water quality of closed lakes was improved, and the nitrogen and phosphorus concentrations were significantly reduced. (2) The stability of open vs. closed-managed lakes differed notably at the species and genus levels (p < 0.01), but no significant variations were identified at the phylum and functional genes levels (p > 0.05). (3) The relative abundance of Microcystis (Cyanobacteria) increased dramatically in the open lakes (proportions from 1.44 to 41.76%), whereas the relative abundance of several other dominant genera of Cyanobacteria experienced a trade-off and decreased with increasing Microcystis relative abundance. (4) The main functions of the bacterioplankton communities were primarily related to dominant genera of Proteobacteria and had no significant relationship with Microcystis. Overall, the closed-lake management practices significantly reduced nutrients and prevented Microcystis blooms, but the taxonomic and functional structures of bacterioplankton communities remained stable overall.

Assessment and sources of heavy metals in the suspended particulate matter, sediments and water of a karst lake in Guizhou Province, China.

An integrated assessment of heavy metal (HM) contamination in dissolved matter, suspended particular matter (SPM) and sediments in lakes is essential. This study assessed the risks of HMs in the water, SPM and sediment of Caohai, China, and analyzed the changes in sediment HM contamination in conjunction with historical data. The HM transport was dominated by the SPM load, and the concentrations of Zn (179.07-1821.24 mg kg-1), Pb (53.63-181.46 mg kg-1), and Cd (3.68-21.31 mg kg-1) in SPM and sediment were 5.34-149.11 times higher than the upper continental crust (UCC) values. SPM and sediments were lightly to extremely polluted and had moderate to very high toxicity risks with Cd, Pb and Zn, and these three HMs originated from industrial and agricultural sources. The concentrations of Zn, Pb, and Cd in Caohai sediments increased by 36.7-187.9 % in 2022 compared to pre-2020. This research provides valuable reference data for the remediation of polluted karst lakes.

Intensive human land uses cause the biotic homogenization of algae and change their assembly process in a major watershed of China.

Human land uses are a crucial driver of biodiversity loss in freshwater ecosystems, and most studies have focused on how cities or croplands influence alpha diversity while neglecting the changes in community composition (beta diversity), especially in algae. Here, we examined the taxonomic and functional composition of algae communities and their underlying drivers along the human land-use intensity gradient in the Huai River basin, the third largest basin in China. Our results indicated that the increased intensity of human land use caused biotic homogenization (decreasing compositional dissimilarity between sites) of algae communities in terms of both taxonomic and functional traits. Functional beta diversity was more sensitive to human land uses than taxonomic beta diversity. Furthermore, we found that the increased intensity of human land use altered algae assemblage processes. As opposed to the low- or moderate-intensity human land uses, in high-intensity groups, species sorting rather than dispersal limitations dominated algae community assembly. NO2-N, HCO3, and Fe were the major factors explaining the variance in the taxonomic and functional beta diversities of algae. Human land use reshaped the taxonomic and functional structures of algae, raising concerns about the ecological processes altered by human activity.

Elemental composition and microbial community differences between wastewater treatment plant effluent and local natural surface water: A Zhengzhou city study.

Wastewater treatment plant (WWTP) effluent is discharged into rivers as supplemental water, which may result in ecological risk. This study compares the element composition and microbial community of WWTP effluent and natural surface water (NSW) and reveals the potential ecological risk of WWTP effluent discharge. Twenty recently upgraded WWTPs and three relatively large reservoirs in Zhengzhou city, China, were selected. The contents of N, P, S, K, Ca, Mg, B, Si, Na, Fe, Mn, Co, Ni and Sn were significantly higher in WWTP effluent than in NSW, while those of Mo, V, Pb and Cd were significantly lower. There was no significant difference between WWTP effluent and NSW in terms of the element imbalance index (IMI) (representing the extent of imbalance of element proportions) relative to the class IV surface water quality standard (the control standard for most Chinese rivers). The macronutrient IMI relative to the Hoagland formula was significantly lower in WWTP effluent than in NSW, and WWTP effluent discharge could significantly lower this index in NSW; this may be an important cause of primary productivity explosion. The microbial diversity was significantly higher in WWTP effluent than in NSW. The predicted relative abundances of mobile genetic elements and oxidative-stress-tolerant phenotypes were significantly higher in WWTP effluent than in NSW, whereas the abundance of gram-negative phenotypes was significantly lower, and that of potential pathogenic phenotypes was slightly lower. The effluent from upgraded WWTPs exhibited a low risk of pathogen diffusion but a high risk of antibiotic resistance gene diffusion. The element composition and microbial community should be considered when evaluating the ecological risk of WWTP effluent discharge.

Damming has changed the migration process of microplastics and increased the pollution risk in the reservoirs in the Shaying River Basin.

The impact of damming on river ecosystems has received increasing attention, but a comprehensive understanding of the occurrence, drivers and exposure risks of microplastic (MP) pollution in multigate dam-type rivers is lacking. We investigated the characteristics and abundance of MPs in water, sediment and biological tissues from samples collected in the vicinity of ten dams in the Shaying River basin and analyzed the effect of environmental and food web structural changes on MP accumulation in freshwater animals under the influence of dams. Dam construction affects the transportation, suspension, and deposition of MPs at different dam locations (upstream, reservoir, and downstream) by altering hydrodynamihas changed the migration process of MPs. The dams intercepted a large amount of MPs from upstream sediments in the reservoir but had no significant capturing effect on MPs in water. The structure of the food web in the reservoir was simplified and the animals in the reservoir had the highest risk of MP contamination. A high MP abundance (or high microplastic diversity integrated index (MDII) values) in the environment or simplification of the food web may have led to higher MP accumulation in animals. More effort is needed to monitor MP pollution in reservoirs and control it sources.

Comparison and interpretation of freshwater bacterial structure and interactions with organic to nutrient imbalances in restored wetlands.

Chemical oxygen demand to nitrogen (COD/N) and nitrogen to phosphorus (N/P) ratios have distinct effects on bacterial community structure and interactions. However, how organic to nutrient imbalances affect the structure of freshwater bacterial assemblages in restored wetlands remains poorly understood. Here, the composition and dominant taxa of bacterial assemblages in four wetlands [low COD/N and high N/P (LH), low COD/N and low N/P (LL), high COD/N and high N/P (HH), and high COD/N and low N/P (HL)] were investigated. A total of 7,709 operational taxonomic units were identified by high throughput sequencing, and Actinobacteria, Proteobacteria, and Cyanobacteria were the most abundant phyla in the restored wetlands. High COD/N significantly increased bacterial diversity and was negatively correlated with N/P (R 2 = 0.128; p = 0.039), and the observed richness (Sobs) indices ranged from 860.77 to 1314.66. The corresponding Chao1 and phylogenetic diversity (PD) values ranged from 1533.42 to 2524.56 and 127.95 to 184.63. Bacterial beta diversity was negatively related to COD/N (R 2 = 0.258; p < 0.001). The distribution of bacterial assemblages was mostly driven by variations in ammonia nitrogen (NH4 +-N, p < 0.01) and electrical conductivity (EC, p < 0.01), which collectively explained more than 80% of the variation in bacterial assemblages. However, the dominant taxa Proteobacteria, Firmicutes, Cyanobacteria, Bacteroidetes, Verrucomicrobia, Planctomycetes, Chloroflexi, and Deinococcus-Thermus were obviously affected by variation in COD/N and N/P (p < 0.05). The highest node and edge numbers and average degree were observed in the LH group. The co-occurrence networkindicated that LH promoted bacterial network compactness and bacterial interaction consolidation. The relationships between organic to nutrient imbalances and bacterial assemblages may provide a theoretical basis for the empirical management of wetland ecosystems.

Responses of soil fungal communities and functional guilds to ~160 years of natural revegetation in the Loess Plateau of China.

Natural revegetation has been widely confirmed to be an effective strategy for the restoration of degraded lands, particularly in terms of rehabilitating ecosystem productivity and soil nutrients. Yet the mechanisms of how natural revegetation influences the variabilities and drivers of soil residing fungal communities, and its downstream effects on ecosystem nutrient cycling are not well understood. For this study, we investigated changes in soil fungal communities along with ~160 years of natural revegetation in the Loess Plateau of China, employing Illumina MiSeq DNA sequencing analyses. Our results revealed that the soil fungal abundance was greatly enhanced during the later stages of revegetation. As revegetation progresses, soil fungal richness appeared first to rise and then decline at the climax Quercus liaotungensis forest stage. The fungal Shannon and Simpson diversity indexes were the lowest and highest at the climax forest stage among revegetation stages, respectively. Principal component analysis, Bray-Curtis similarity indices, and FUNGuild function prediction suggested that the composition, trophic modes, and functional groups for soil fungal communities gradually shifted along with natural revegetation. Specifically, the relative abundances of Basidiomycota, Agaricomycetes, Eurotiomycetes, and ectomycorrhizal fungi progressively increased, while that of Ascomycota, Sordariomycetes, Dothideomycetes, Tremellomycetes, saprotrophic, pathotrophic, arbuscular mycorrhizal fungi, and endophyte fungi gradually decreased along with natural revegetation, respectively. The most enriched members of Basidiomycota (e.g., Agaricomycetes, Agaricales, Cortinariaceae, Cortinarius, Sebacinales, Sebacinaceae, Tricholomataceae, Tricholoma, Russulales, and Russulaceae) were found at the climax forest stage. As important carbon (C) sources, the most enriched symbiotic fungi (particularly ectomycorrhizal fungi containing more recalcitrant compounds) can promote organic C and nitrogen (N) accumulation in soils of climax forest. However, the most abundant of saprotrophic fungi in the early stages of revegetation decreased soil organic C and N accumulation by expediting the decomposition of soil organic matter. Our results suggest that natural revegetation can effectively restore soil fungal abundance, and modify soil fungal diversity, community composition, trophic modes, and functional groups by altering plant properties (e.g., plant species richness, diversity, evenness, litter quantity and quality), quantity and quality of soil nutrient substrates, soil moisture and pH. These changes in soil fungal communities, particularly their trophic modes and functional groups along with natural revegetation, impact the accumulation and decomposition of soil C and N and potentially affect ecosystem C and N cycling in the Loess Plateau of China.

Gradual Enhancement of the Assemblage Stability of the Reed Rhizosphere Microbiome with Recovery Time.

Rhizoplane microbes are considered proxies for evaluating the assemblage stability of the rhizosphere in wetland ecosystems due to their roles in plant growth and ecosystem health. However, our knowledge of how microbial assemblage stability is promoted in the reed rhizosphere of wetlands undergoing recovery is limited. We investigated the assemblage stability, diversity, abundance, co-occurrence patterns, and functional characteristics of reed rhizosphere microbes in restored wetlands. The results indicated that assemblage stability significantly increased with recovery time and that the microbial assemblages were capable of resisting seasonal fluctuations after more than 20 years of restoration. The number of bacterial indicators was greater in the restoration groups with longer restoration periods. Most bacterial indicators appeared in the 30-year restoration group. However, the core taxa and keystone species of module 2 exhibited greater abundance within longer recovery periods and were well organized, with rich and diverse functions that enhanced microbial assemblage stability. Our study provides insight into the connection between the rhizosphere microbiome and recovery period and presents a useful theoretical basis for the empirical management of wetland ecosystems.

Influent salinity affects substrate selection in surface flow constructed wetlands.

To identify the effect of influent salinity on substrate selection, a study was conducted in pilot-scale surface flow constructed wetlands (SFCWs). Compared with gravel and sand SFCWs, soil SFCWs performed similarly or worse at low salinities, while at high salinities, soil SFCWs performed similarly or better in removal efficiency (RE) of salt, total nitrogen (TN), total phosphorous (TP), and chemical oxygen demand (COD). Soil generally increased macrophyte growth (especially at high salinity) in terms of biomass, leaf chlorophyll concentration, root activity, and root catalase and superoxide dismutase activities. A general decrease in bacterial α-diversity in the rhizosphere was observed at high salinity, while compared with gravel or sand, soil improved rhizosphere bacterial community stability at varying salinities. At high salinity, compared with that of gravel or sand, the soil support of macrophytes and rhizosphere microorganisms increased pollutant RE in SFCWs. This finding highlights the necessity of varying substrate selection in SFCWs with influent salinities for both increasing pollutant RE and reducing input cost, with soil recommended at high influent salinity.

The Dynamic Response of Nitrogen Transformation to the Dissolved Oxygen Variations in the Simulated Biofilm Reactor.

Lab-scale simulated biofilm reactors, including aerated reactors disturbed by short-term aeration interruption (AE-D) and non-aerated reactors disturbed by short-term aeration (AN-D), were established to study the stable-state (SS) formation and recovery after disturbance for nitrogen transformation in terms of dissolved oxygen (DO), removal efficiency (RE) of NH4+-N and NO3--N and activity of key nitrogen-cycle functional genes amoA and nirS (RNA level abundance, per ball). SS formation and recovery of DO were completed in 0.56-7.75 h after transition between aeration (Ae) and aeration stop (As). In terms of pollutant REs, new temporary SS formation required 30.7-52.3 h after Ae and As interruptions, and seven-day Ae/As interruptions required 5.0% to 115.5% longer recovery times compared to one-day interruptions in AE-D and AN-D systems. According to amoA activity, 60.8 h were required in AE-D systems to establish new temporary SS after As interruptions, and RNA amoA copies (copy number/microliter) decreased 88.5%, while 287.2 h were required in AN-D systems, and RNA amoA copies (copy number/microliter) increased 36.4 times. For nirS activity, 75.2-85.8 h were required to establish new SSs after Ae and As interruptions. The results suggested that new temporary SS formation and recovery in terms of DO, pollutant REs and amoA and nirS gene activities could be modelled by logistic functions. It is concluded that temporary SS formation and recovery after Ae and As interruptions occurred at asynchronous rates in terms of DO, pollutant REs and amoA and nirS gene activities. Because of DO fluctuations, the quantitative relationship between gene activity and pollutant RE remains a challenge.

Coastal reclamation alters soil microbial communities following different land use patterns in the Eastern coastal zone of China.

Coastal reclamation seriously disturbs coastal wetland ecosystems, while its influences on soil microbial communities remain unclear. In this study, we examined the impacts of coastal reclamation on soil microbial communities based on phospholipid fatty acids (PLFA) analysis following the conversion of Phragmites australis wetlands to different land use types. Coastal reclamation enhanced total soil microbial biomass and various species (i.e., gram-positive bacterial, actinomycete, saturated straight-chain, and branched PLFA) following the conversion of P. australis wetland to aquaculture pond, wheat, and oilseed rape fields. In contrast, it greatly decreased total soil microbial biomass and various species following the conversion of P. australis wetland to town construction land. Coastal reclamation reduced fungal:bacterial PLFA, monounsaturated:branched PLFA ratios, whereas increasing gram-positive:gram-negative PLFA ratio following the conversion of P. australis wetland to other land use types. Our study suggested that coastal reclamation shifted soil microbial communities by altering microbial biomass and community composition. These changes were driven primarily by variations in soil nutrient substrates and physiochemical properties. Changes in soil microbial communities following coastal reclamation impacted the decomposition and accumulation of soil carbon and nitrogen, with potential modification of carbon and nitrogen sinks in the ecosystems, with potential feedbacks in response to climate change.

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.

Effect of influent salinity on the selection of macrophyte species in floating constructed wetlands.

Pilot-scale floating constructed wetlands (FCWs) under varying influent salinities were implemented, and the effects of influent salinity on pollutant removal efficiency (RE) and macrophyte species selection were identified. The results suggest that a salinity increase generally decreased pollutant REs, while some macrophytes, such as Iris pseudacorus, could effectively resist this decrease. The average coefficients of variation between macrophyte species in REs of chemical oxygen demand, ammonium nitrogen, nitrate nitrogen and total phosphorus increased from 28.6% at low salinity to 91.3% at high salinity, which suggests the greater importance of macrophyte selection under high salinity. With an increase in salinity, the rhizosphere bacterial community showed convergent evolution or convergence followed by slight divergent evolution between macrophyte species, while the importance of macrophyte parameter selection in characterizing pollutant REs decreased. Therefore, influent salinity is a key factor to consider in macrophyte selection and application, especially in FCWs without soil.

Accelerated nitrogen consumption in sediment by Tubifex tubifex and its significance in eutrophic sediment remediation.

Sediment remediation in eutrophic aquatic ecosystems is imperative, but effective ecological measures are scarce. A pilot-scale trial investigated sediment remediation by the addition of Tubifex tubifex. The results showed that the addition of T. tubifex accelerated sediment organic matter (OM) and nitrogen (N) loss, with averages of 7.7% and 75.1% increased loss (IL) compared to treatments without T. tubifex in the 60-day experiment, respectively. The percentages of the increased in water to the IL in sediment were only 0.6%, 0.21%, 2.1% and 6.3% for NH4+-N, NOx--N, TN and COD, respectively, at the end of the experiment. The absolute abundances of the nitrifying genes AOA and AOB; the denitrifying genes napA, nirS, nirK, cnorB and nosZ; and the anaerobic ammonia oxidation gene anammox increased 2.3- to 11.0-fold with the addition of T. tubifex. Therefore, the addition of T. tubifex is an effective strategy for sediment remediation by accelerating OM and N loss in sediment without substantially increasing the water N concentration.

Metagenomic Analysis Revealed that the Terrestrial Pollutants Override the Effects of Seasonal Variation on Microbiome in River Sediments.

Researching the structure and function of sediment microbiome contribute to understanding the response of microbiome to external disturbances. However, seasonal changes in sediment microbiome with different terrestrial pollutants input have not yet been clearly understood. Metagenomic sequencing was used to evaluate the effects of seasonal variations and different land use types on sediment microbiome. Results showed that the differences in structure and functions of sediment microbiome among different land use types were obviously greater than different seasons. This indicated that the terrestrial pollutants weakened the effects of seasonal variations on shaping the sediment microbiome. The significant differences in sediment properties under the input of different terrestrial pollutants was observed, but no obvious differences between seasons, which may be the reason why terrestrial pollutants override the effects of seasonal variation on the sediment microbiome. Overall, the results extended our understanding of the impacts of seasonal variation and terrestrial pollutants on river sediment microbiome.

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.

Operation strategy for constructed wetlands in dry seasons with insufficient influent wastewater.

Using vertical flow constructed wetlands (VFCWs) with different influent wastewater volumes and feeding modes, this study aimed to identify the optimal operation strategy for dry seasons under wastewater deficiency. Using half the influent wastewater volume (HIWV) did not necessarily improve the removal efficiency (RE) of the chemical oxygen demand (COD), NH4+-N, NO3--N and total nitrogen. In the HIWV treatments, intermittent resting did not result in significantly different pollutant REs, whereas strategies involving partial saturation and prolongation of the hydraulic retention time (HRT) slightly decreased the pollutant REs compared with those obtained in the constant feeding mode. Of the three HIWV strategies, the intermittent resting mode achieved the highest anaerobic ammoxidation, the dominant pathway for nitrogen removal in the systems, and thus stimulated nitrogen transformation. The intermittent resting mode forms part of the recommended operation strategy for VFCWs in dry seasons with wastewater deficiency.