Surface Flow Constructed Wetlands Research Articles

Nitrogen Removal from Agricultural Subsurface Drainage by Surface-Flow Wetlands: Variability

Agriculture has long been considered a great source of nitrogen (N) to surface waters and a major cause of eutrophication. Thus, management practices at the farm-scale have since attempted to mitigate the N losses, although often limited in tile-drained agricultural catchments, which speed up the N transport, while minimizing natural removal in the landscape. In this context, surface-flow constructed wetlands (SFWs) have been particularly implemented as an edge-of-field strategy to intercept tile drains and reduce the N loads by re-establishing ecosystems services of previously drained water ponded areas. These systems collect the incoming water volumes in basins sufficiently large to prolong the hydraulic residence time to a degree where biogeochemical processes between the water, soil, sediments, plants, macro and microorganisms can mediate the removal of N. Despite their documented suitability, great intra and inter-variability in N treatment is still observed to date. Therefore, it is essential to thoroughly investigate the driving factors behind performance of SFWs, in order to support their successful implementation according to local catchment characteristics, and ensure compliance with N removal goals. This review contextualizes the aforementioned issue, and critically evaluates the influence of hydrochemistry, hydrology and biogeochemistry in the treatment of N by SFWs.

Improved denitrification in surface flow constructed wetland planted with calamus

The calamus type surface-flow constructed wetland (SFCW) is widely used for treating low-polluted water bodies, such as effluents from wastewater treatment plants. The calamus biomass is considered a potential carbon source for denitrification, integrating plant biomass into the carbon cycle in SFCWs. This study conducted experiments on the calamus biomass decomposition and evaluated its potential application for denitrification in an SFCW system. We showed that decomposition of the biomass could release a high ratio of total organic carbon (TOC) to total nitrogen (TN), reaching 26.9, 27.7, and 23.6 at biomass doses of 0.1, 0.5, and 1.0 g L −1 . A continuous-flow experiment on the SFCW system revealed that higher TN removal efficiency and load were obtained after the addition of biomass, approximately three times before the biomass addition. Microbial community analysis revealed an increase in heterotrophic denitrifying bacteria (i.e., Flavobacterium , Dechloromonas , and Bacillus ) content throughout the period of biomass addition. This study demonstrated an excellent enhancement of the denitrification efficiency in the SFCW caused by the addition of calamus biomass, suggesting its potential application as an excellent plant carbon source for biological denitrification. • A high C/N ratio (26.9) was released from decomposing 0.1 g L −1 of calamus biomass. • Calamus biomass can be used as carbon source in denitrification processes. • Denitrification efficiency was enhanced by about 200% with the addition of biomass. • Content of denitrifying bacteria was increased by 8 times via adding the biomass.

Cold temperature increases nitrate accumulation in pilot-scale surface flow constructed wetlands with high rates of nitrogen removal

Nitrogen dynamics were studied over 3 years in pilot-scale surface flow constructed wetlands (SFCWs) treating three strengths of ammonium-rich swine wastewater. A high removal rate of ammonium (1.2–2.9 g m−2 d−1) and total nitrogen (1.5–3.5 g m−2 d−1) was achieved from highstrength wastewater in the SFCWs. Nitrate concentration was significantly higher (p < 0.01) in the effluent than in the influent, and the increased nitrate concentration did not significantly affect ammonium removal in the SFCWs. The effluent nitrate concentration showed annual cyclical changes and could be described using a harmonic regression equation over time (y = a + b sin (2π/365.25 t + c); R2 = 0.152–0.566). The multiple regression equation (R2 = 0.200–0.551) indicated that water temperature and oxidation reduction potential were the primary factors affecting nitrate accumulation in the SFCWs. The abundance of nitrification functional genes (amoA in ammonia-oxidizing archaea and bacteria) was higher in spring and winter than in summer. The abundance of denitrification functional genes (narG, nirK, nirS, and nosZ) was higher in summer than in spring and winter. At cold temperatures (5–10 °C), nitrate accumulated significantly in the water column rather than in the sediments and the potential nitrification rates increased slightly, suggesting the importance of nitrogen transformation in the water column during nitrogen removal. These results are helpful for selecting targeted seasonal intensification strategies to improve the SFCWs performance.

Bacterial community response to different nitrogen gradients of swine wastewater in surface flow constructed wetlands

How sediment bacterial community structure and diversity responds to different gradients of nitrogen (N) in swine wastewater is poorly understood. Here, the effects of different total nitrogen (TN) concentrations in swine wastewater on the microbial diversity and community composition in surface flow constructed wetlands (SFCWs) were investigated. The five concentration gradients included 2, 250, 300, 350, and 400 mg L−1. Under high N concentrations (>300 mg L−1), the Ace and Chao1 indexes increased, however, the Shannon index declined with increasing N concentration. The relative abundance of Chloroflexi, Acidobacteria and Actinobacteria showed an increasing trend. In contrast, under relatively low N concentrations (≤300 mg L−1), Shannon index increased with increasing N concentration. The relative abundance of Bacteroidetes and Verrucomicrobia exhibited an increasing trend with increasing N concentration. TN, NH4+ and NO3− significantly influenced on the microbial community distribution and composition (P < 0.05). These findings provide evidence that N concentration of swine wastewater is powerful predictor of bacterial diversity and community composition in SFCWs.

Differences in bacterial N, P, and COD removal in pilot-scale constructed wetlands with varying flow types

The mechanisms of bacterial nitrogen (N), phosphorus (P), and chemical oxygen demand (COD) removal in pilot-scale constructed wetlands (CWs) were investigated in the present work. Three types of CWs were assessed: vertical flow (VF), horizontal flow (HF), and surface flow (SF), each with three planting conditions, with either Thalia, Canna or without plants. The results show that construction types affected microbes more than planting conditions. VF CWs promoted the aerobic processing of total N, total P, COD, and NH3-N, increasing the respective removal efficiencies by 4–19%, 13–32%, 19–29%, and 75–80%, respectively, compared with SF CWs. The relative abundance of nitrifying, denitrifying, methanotrophic and dephosphorized bacteria, and functional genes such as nxrA, nirK, nosZ, mmoX, and phoD were higher in VF CWs. Positive and simple gene networks in VF CWs can effectively reduce the redundancy in functional genes, enhance bacterial function and gene interactions, thus promoting nutrient removal.

Treatment of Agricultural Drainage Water by Surface-Flow Wetlands Paired with Woodchip Bioreactors

Nutrient losses from agricultural fields have long been a matter of concern worldwide due to the ecological disturbance this can cause to surface waters downstream. In this paper a new design concept, which pairs a surface-flow constructed wetland (SFW) with a woodchip bioreactor (WB), was tested in relation to its capacity to reduce both nitrogen (N) and phosphorus (P) loads from agricultural tile drainage water. A nutrient mass balance and a comparative analysis were carried out together with statistical regressions in order to evaluate the performance of four SFW+WBs under different catchment conditions. We found marked variations between the systems in regard to hydraulic loading rate (0.0 to 5.0 m/day) and hydraulic retention time (1 to 87 days). The paired system worked as nutrient sinks throughout the study period. Total N and total P removal efficiencies varied from 8% to 51% and from 0% to 80%, respectively. The results support the use of the new design concept for nutrient removal from tile-drained agricultural catchments in Denmark as part of national management plans, with the added advantage that smaller areas are needed for construction (0.1% to 0.2% of the catchment area) in comparison to standalone and currently used SCWs (~1%).

Performance of a full scale constructed wetland as ecological practice for agricultural drainage water treatment in Northern Italy

Non-point sources of pollution, primarily agricultural drainage waters, can cause eutrophication and deterioration of water bodies. Surface flow constructed wetlands (SFCWs) are an ecological solution that can represent an efficient barrier and prevent agricultural pollutants from reaching other ecosystems. However, to better manage them and to understand removal processes occurring, it is important to study SFCWs that are functioning for longer periods of time and assess their efficiencies. This study concentrates on a full-scale SFCW in the Northern Italy that is used for agricultural drainage water treatment since the year 2000. An in-deep monitoring done for two years (2018 and 2019) showed that the system achieved satisfactory retention of up to 82% for TSS and up to 78% for TN and NO3--N. TP retention seemed to be poor (-27%), but further analysis showed that the SFCW performed well in this aspect as well, and that it is important to include precipitation loads in the overall balance. Soil content of nutrients and different trace elements did not show considerable differences in respect to the beginning of the monitoring period, and the uptake rates of TN and TP by above-ground vegetation were in the range 19.0-26.3 and 1.6-2.1 g m-2, respectively.

Influence of Phragmites communis and Zizania aquatica on rhizosphere soil enzyme activity and bacterial community structure in a surface flow constructed wetland treating secondary domestic effluent in China.

The present study aims to investigate the effects of Phragmites communis and Zizania aquatica on rhizosphere soil enzyme activity and bacterial community structure in a surface flow constructed wetland (SFCW) for the treatment of domestic sewage from the Shanxi province of China. The basic physical and chemical properties of the soil, the contents of soil urease (UE), alkaline phosphatase (ALP), soil microbial biomass carbon and nitrogen (SMBC, SMBN), and bacterial community structure were measured in the Phragmites communis group (PG), Zizania aquatica group (ZG), and control group (CG), respectively. The results showed that (1) the contents of UE, ALP, SMBC, and SMBN in rhizosphere soil of PG were more than those of ZG; (2) the highest bacterial abundance and α-diversity appeared in PG, in which Gp6 was the most abundant bacterial genus in PG; (3) the main functions of the dominant bacteria Gp6 and Longilinea in PG were involved in metabolizing multiple carbohydrates and participating in the carbon cycle in the soil based on the clusters of orthologous groups pathway analysis data; (4) the bacterial community of PG was mainly affected by the positive correlation with arsenic, nickel, or SMBC via the redundancy analysis. Collectively, Phragmites communis is a recommended species for wastewater wetland treatment system in Shanxi province, and the special enzymes and dominant bacteria in plant rhizosphere soil had obvious functions of removing organic pollutants. Besides, the influences of environmental factors on rhizosphere bacteria and the combined effects of Phragmites communis and dominant bacteria in wetland wastewater treatment system should be taken seriously.

Purification Effect of Sequential Constructed Wetland for the Polluted Water in Urban River

Constructed wetlands can play an active role in improving the water quality of urban rivers. In this study, a sequential series system of the floating-bed constructed wetland (FBCW), horizontal subsurface flow constructed wetland (HSFCW), and surface flow constructed wetland (SFCW) were constructed for the urban river treatment in the cold regions of North China, which gave full play to the combined advantages. In the Yitong River, the designed capacity and the hydraulic loading of the system was 100 m3/d and 0.10 m3/m2d, respectively. The hydraulic retention time was approximately 72 h. The monitoring results, from April to October in 2016, showed the multiple wetland ecosystem could effectively remove chemical oxygen demand (COD), ammonia nitrogen (NH4+-N), total nitrogen (TN), total phosphate (TP), and suspended solids (SS) at average removal rates of 74.79%, 80.90%, 71.12%, 78.44%, and 91.90%, respectively. The removal rate of SS in floating-bed wetland was the largest among all the indicators (80.24%), which could prevent the block of sub-surface flow wetland effectively. The sub-surface flow wetland could remove the NH4-N, TN, and TP effectively, and the contribution rates were 79.20%, 64.64%, and 81.71%, respectively. The surface flow wetland could further purify the TN and the removal rate of TN could reach 23%. The total investment of this ecological engineering was $12,000. The construction cost and the operation cost were $120 and $0.02 per ton of polluted water, which was about 1/3 to 1/5 and 1/6 to 1/3 of the conventional sewage treatment, respectively. The results of this study provide a technical demonstration of the restoration of polluted water in urban rivers in northern China.

Dynamic variations of microbial community structure in Myriophyllum aquaticum constructed wetlands in response to different NH4+-N concentrations

Constructed wetlands (CWs) have received increasing attentions for their N removal performances, especially regarding NH4+-N. Different influent NH4+-N concentration may influence N removal efficiency in practice, while the effects of different NH4+-N concentrations on microorganisms removing N in CWs are poorly understood. In this study, surface flow CWs planted with Myriophyllum (M). aquaticum were established to investigate the influences of different NH4+-N concentrations on the composition, structure, and interactions of microbial community. Our findings suggested 105 mg/L NH4+-N CWs achieved highest N removal rate, removing 89.30 % NH4+-N and 92.34 % TN from the influent. The results of real-time quantitative polymerase chain reactions (qPCR) indicated abundances of nitrifying genes (nxrA) and denitrifying genes (narG, nirS, nirK, and nosZ) were increased by increasing NH4+-N concentrations, and the strongest effects were observed in narG (8-fold) and nosZ genes (11-fold). Different NH4+-N concentrations was proved to alter composition and structure of microbial communities via high-throughput sequencing, e.g. denitrifiers including Brevendomonas.sp, Dokdonella.sp and Rhodococcus.sp were enriched obviously with increasing NH4+-N concentrations. In addition, network showed interactions among microbial populations and positive interactions were dramatically shifted and enhanced by increasing NH4+-N concentrations.

Internal hydraulics and wind effect in a surface flow constructed wetland receiving agricultural drainage water

Variations of internal water velocities in surface flow constructed wetlands (SF-CWs) affect the hydraulic efficiency and are responsible for heterogeneous distribution of the biogeochemical processes. Internal obstructions, short circuiting due to the presence of immobile zones, and incomplete mixing are among the main culprits. In this study, a high resolution spatial analysis of solute transport is presented aiming at identifying internal flow preferentiality of the system and the influence of wind effects. Dye (Uranine) and salt (Bromide) tracer tests were performed in a compartment-designed SF-CW constituted of alternated deep and shallow zones. Water samples were collected from the outflow and a number of internal stations located according to a 3-transect system at two different depths. Bromide outflow and internal breakthrough curves (BTCs) were fitted using the tank-in-series (TIS) model. The results showed that the hydraulic efficiencies at internal stations (0.08–1.63) generally decreased with increasing distances from the tracer injection point. Both spline interpolation and dye tracer results showed preferential flow alongside the southern side of the SF-CW. Analysis further showed that the shallow zones and the wind blowing in opposite direction to the flow facilitate water mixing and recirculation. The method is a valuable exploiting tool for already operating SF-CWs.

Myriophyllum elatinoides growth and rhizosphere bacterial community structure under different nitrogen concentrations in swine wastewater

In this study, Myriophyllum elatinoides growth under different nitrogen (N) concentrations (2, 250, 300, 350 and 400 mg L−1) and changes in rhizosphere bacterial community structure were investigated. High N (>300 mg L−1) concentrations caused reduction in M. elatinoides biomass. Growth tended to stabilize at 49 days. N concentration in roots were higher than that in stems and leaves under high N conditions. TN and NH4+ removal efficiencies reached 84.0% and 87.2%, respectively, in M. elatinoides surface flow constructed wetlands (SFCWs). Rhizosphere bacterial diversity increased over time. Proteobacteria, Firmicutes, Cyanobacteria, and Bacteroidetes dominated at the phylum level. Genera Turicibacter, Allochromatium, and Methylocystis increased at low N (<300 mg L−1) concentrations, while Pseudomonas increased at high N concentrations over the experimental period. Redundancy analysis showed that pH was strongly correlated with changes in rhizosphere bacterial community structure. These findings helped to insight into N removal mechanism in M. elatinoides.

Nitrogen and phosphorus removal performance and bacterial communities in a multi-stage surface flow constructed wetland treating rural domestic sewage

A multi-stage surface flow constructed wetland (SFCW) is used to treat decentralized rural domestic sewage. The performance of a multi-stage SFCW located in Hunan, China, and the associated microbial community structures were investigated. The average removal rates of the multi-stage SFCW planted with Myriophyllum elatinoides were 1.0 g m−2 d−1, 0.84 g m−2 d−1, 61.3 mg m−2 d−1, and 85.3 mg m−2 d−1 for total nitrogen (TN), ammonia (NH4+), nitrate (NO3−), and total phosphorus (TP), respectively. Furthermore, the sediment and presence of plants were found to be important for the removal N and P. The average removal rates by sediment and plants were 196.6 mg N m−2 d−1 and 49.9 mg P m−2 d−1, 17.6 mg N m−2 d−1 and 8.1 mg P m−2 d−1, respectively. The microbial community profiles demonstrated that Proteobacteria, Chloroflexi, Bacteroidetes, Firmicutes and Euryarchaeota were the predominant phyla in each stage and at different sampling times. The concentrations of NO3−, TP, TN, and NH4+, and the pH of the sediment and water had a significant effect on the presence of denitrifying bacteria in the anaerobic environment. Whereas, dissolved oxygen (DO) and redox potential (Eh) had a significant effect on the presence of nitrifying bacteria in the aerobic environment. This research strongly supports that the use of the multi-stage SFCW promotes bacterial diversity and changes bacterial community in the sediment.

Nitrogen removal performance and needed area estimation of surface-flow constructed wetlands using a probabilistic approach

Pollutant concentrations in influents into constructed wetlands (CWs) are highly fluctuating and may vary over several orders of magnitude, leading to large uncertainties in removal performance assessment when using pollutant concentrations in the influent and effluent directly. Incorporating a probabilistic approach into removal performance assessment and needed area estimation of CWs could advantage decision making regarding wastewater treatment and engineering applications. A series of three-stage surface-flow CWs (SFCWs) were constructed for treating ammonium-rich swine wastewater. The surface removal rate and removal efficiency of ammonium nitrogen in the SFCWs using the probabilistic approach were 0.27–3.23 g m−2 d−1 and 43.0–99.9% (95% confidence interval (CI)), which were consistent with the deterministic approach (95% CI: 0.24–3.18 g m−2 d−1 and 70.4–99.9%). The needed SFCW area was estimated as 6.6 (95% CI: 1.4–17.8) to 29.7 (95% CI: 6.4–80.1) m2 for required removal efficiency from 40% to 90% for 0.18 m3 d−1 swine wastewater with different strengthens. For specific removal efficiency of 90%, the needed CW areas was 13.9 (95%CI: 4.9–42.7), 25.1 (95%CI: 5.9–66.0), 33.5 (95%CI: 13.5–87.1), and 40.8 (95%CI: 16.2–89.4) m2 for influent ammonium loading rate of 0.18–2.7, 2.7–14.4, 14.4–36, and 36–60 g d−1, respectively. The first-order removal constant of ammonium nitrogen decreased logarithmically with increasing influent and effluent concentration/loading rate in the SFCW units (p < 0.001), which was responsible for the needed SFCW areas covering a wide range. The reliability analysis confirmed the results from the probabilistic approach were appropriate. The present study shed new lights on the performance evaluation and design of CWs for treating wastewater with highly-fluctuating concentrations using a probabilistic approach.

An exploration of plant characteristics for plant species selection in wetlands

Plants are a major component of constructed wetlands (CWs) but arriving at a reasonable choice of plants is a challenge. In this study, surface flow CWs planted with eight different species of plants were investigated to explore the relationship between plant characteristics, including density, height, leaf area index, evapotranspiration (ET) and plant coefficient (the ratio of the actual plant ET to a reference ET), and the treatment performance of these plants in purifying water. Of the five plant characteristics, only the plant coefficient was found to be negatively correlated with kv (first-order removal rate) for nitrogen and phosphorus. The interpretation of this relationship requires caution, as the negative relationship may be caused by the water consumed by ET in the long term. The relationship between ETc (actual ET of a plant), plant coefficient and the removal load explain the two contradictory effects of ET on the removal load. Considering treatment performance and plant coefficient, the plant most recommended for use in CWs is Iris sibirica and that which is the least recommended is Nelumbo nucifera Gaertn. The combination of treatment performance and plant coefficient provides a robust approach to the selection of plants for areas with a high ET.

Aromatic Compounds and Organic Matter Behavior in Pilot Constructed Wetlands Treating Pinus Radiata and Eucalyptus Globulus Sawmill Industry Leachate

The objective of this research was to evaluate the fate of aromatic compounds and organic matter in pilot constructed wetlands (CW) treating Pinus radiata and Eucalyptus globulus sawmill industry leachate. Six lab-scale surface flow CW were built and fed in batches. Three CW were fed with P. radiata leachate, while the other three CW were fed with E. globulus leachate. Each group of three CW included two CW planted with Phragmites australis and one unplanted CW as control unit. A stable hydraulic retention time of seven days was maintained in each CW. The organic loading rate was gradually increased in three phases in the CW fed with P. radiata leachate (i.e., from 12 to 19 g COD/m2/day) and with E. globulus leachate (i.e., from 14 to 40 g COD/m2/day). The operation of the six CWs lasted 98 days. The CW treating P. radiata and E. globulus leachate had a similar performance. The highest performance was obtained by the unplanted CW (approximately 10–20% higher than the planted CW), without significant differences observed between the P. radiata and E. globulus leachate treatment, regarding the removal efficiencies of organic matter and total phenolic compounds. The planted systems were probably affected by the high concentrations of these compounds applied, which probably created a toxic environment hindering the microbial community growth.

Hydrological and hydraulic behaviour of a surface flow constructed wetland treating agricultural drainage water in northern Italy

A surface flow constructed wetland (SFCW) treating agricultural drainage water was investigated with the aim to detect modifications in hydrological and hydraulic characteristics after more than a decade of operation. Ponded infiltration tests were conducted to estimate the saturated hydraulic conductivity, Ks, of the surface soil layer at the point scale. At the global scale, infiltration rate, i, was computed from the water balance to detect leakages from the pervious wetland surface. Tracer tests were conducted to analyse the existence of preferential flow inside the system and to estimate its hydraulic retention time (HRT). Clogging phenomena occurred given a mean Ks value of 30 mm h−1 was measured near the SFCW inlet, that was 9.61 times lower than the value at the outlet zone. The estimated infiltration losses were two orders of magnitude lower than infiltration measured at the point scale. The results also confirmed the existence of a moderate amount of preferential flow paths and dead zones in the SFCW as the actual HRT (6.7 days) was shorter than the nominal one (8.1 days). Despite this, it can be concluded that the system performance is still good after 17 years of operation.

Stimulation of optimized influent C:N ratios on nitrogen removal in surface flow constructed wetlands: Performance and microbial mechanisms

Exploring optimal C:N ratio is necessary to ensure balanced microbial nitrification and denitrification in constructed wetlands (CWs), which has become an important management practice for more efficient nitrogen removal and sustainability of CWs. Surface flow constructed wetlands (SFCWs) vegetated with Myriophyllum aquaticum were designed to investigate the effects of five different influent C:N ratios (0:1, 2.5:1, 5:1, 10:1, and 15:1) on nitrogen removal performance and microbial communities over a 175-day experimental period. Compared to the influent C:N ratios of 0:1, higher NH4+-N, NO3−-N, and total nitrogen (TN) removal efficiencies and lower NO3−-N accumulation were observed at influent C:N ratios higher than 5:1. In addition, the highest TN removal efficiency (70.4%) and the lowest nitrous oxide emission flux (4.12 mg m−2 d−1) were obtained at the influent C:N ratio of 5:1. High-throughput sequencing revealed that influent C:N ratios altered the distribution and composition of microbial communities in the sediment, which resulted in a dynamic interplay between N-transforming functional microbes and NH4+-N and NO3−-N removal. In particular, the dominant denitrifiers, including Desulfovibrio, Zoogloea, and Dechloromonas, were more abundant in the sediment with an influent C:N ratio of 5:1, which contributed to the high N removal rate. These findings may be used to screen for an optimum influent C:N ratio to maintain the sustainability of SFCWs with higher N removal efficiency.

Nitrous oxide emissions from pilot scale three-stage constructed wetlands with variable nitrogen loading

Pilot scale three-stage surface flow constructed wetlands (SFCWs) were constructed to study nitrous oxide (N2O) emissions from swine wastewater with different nitrogen levels. The SFCWs had mean total nitrogen (TN) removal efficiencies and removal rates of 84.6–97.1% and 0.6–2.4 g N m−2 d−1 respectively. The N2O emissions and nitrate nitrogen (NO3–-N) concentration both peaked at a TN value of approximately 100 mg N L−1. N2O emissions had a positive correlation with NO3–-N concentration (p < 0.001). This correlation suggests that the effect of TN loading on N2O emissions may be related to NO3–-N in aquatic environment. Significant correlation was observed between N2O emission and the gene abundance of N2O reductase (nosZ; p < 0.05). The general linear model revealed that TN loading affected nosZ gene abundance. These results suggest that pollution loading should be considered to balance nitrogen removal and N2O emissions when designing constructed wetlands.

Comparative study on nitrogen removal and functional genes response between surface flow constructed wetland and floating treatment wetland planted with Iris pseudacorus.

Excessive nitrogen accumulated from wastewater with low C/N ratio is a new threat to water ecosystem. In this study, surface flow constructed wetland (SFCW) and floating treatment wetland (FTW) planted with Iris pseudacorus were set in parallel for nitrogen removal. The nitrogen removal efficiencies and pathways, as well as the abundance and functional diversities of the microbial community, were investigated. The results demonstrated that SFCW generally had better nitrogen removal performance than FTW did over four seasons. The average total nitrogen removal efficiency was 66.0% and 43.8% in SFCW and FTW, respectively. The plant uptake played a vital role in nitrogen reduction, which accounted for 29.3% and 7.7% of the total removed nitrogen in SFCW and FTW, respectively. A combination of high-throughput sequencing and quantitative polymerase chain reaction analysis revealed that the two wetland systems had complete nitrogen cycling, and the narG gene was the dominant nitrogen-transformation functional gene in both systems. More abundant denitrifying genes in SFCW than in FTW were also responsible for higher removal capacity of nitrogen. The results suggest that the planting pattern of wetland vegetation has an important impact on nitrogen removal efficiency by influencing the plant absorption and the development of microbial communities.