Dynamics in the bacterial community-level physiological profiles and hydrological characteristics of constructed wetland mesocosms during start-up

The objective of this work was to study the effect of plant presence (Phragmites australis) and inoculant origin on wetland mesocosm start-up dynamics. Eight mesocosms were studied based on a duplicated 2² factorial design tracking bacterial community and hydrological changes during an 8 month start-up period. The mesocosms were characterized in terms of their hydrological character based on evapotranspiration (ET), porosity, and a dispersion coefficient. The microbiological regime was characterized using a microbial activity measure and community-level physiological profiling (CLPP) employing BIOLOG™ ECO plates. CLPP-related indices such as substrate richness, substrate diversity, over-all community profile, and community divergence are also presented. It was found that mesocosm porosities decreased over time as a result of media-related biofilm development. This biofilm development also contributed to a substantial increase in the dispersion coefficient in the mesocosms over the start-up period. Dispersion coefficients in planted systems reached values of ∼50-55 cm²/min whereas in the unplanted systems values of ∼30-35 cm²/min were observed. Bacterial community divergence in the mesocosms was quantified using a Euclidean-based divergence metric. All mesocosms showed a sharp increase in community divergence until day 75, at which point a steady state was reached. The interstitial communities were also characterized in terms of similarity based on the experimental design treatments. Four stages of mesocosm development were identified that can be described by an initial community state based on the origins of the initial inoculum [days 0-6]; a dynamic period where adjustments and shifts in the bacterial community occurred in all mesocosms [days 7-26]; a period where all interstitial CLPPs were quite similar [days 27-73]; and finally a shift towards unplanted and planted mesocosm CLPP groupings [days 74-232].     

Estimating biogeochemical and biotic interactions between a stream channel and a created riparian wetland: A medium-scale physical model

Straightened channels and altered and drained adjacent riparian wetlands have adversely impacted streams and rivers throughout the US Midwest. This research investigated the biological connection and water quality of a 0.07 ha diversion wetland and adjacent stream at the Olentangy River Wetland Research Park in central Ohio. Before the flowthrough conditions were established, we demonstrated with mark and recapture techniques that the wetland already was a biorefuge for fish under extreme conditions; two species (Centrarchidae) captured in the stream before a total drawdown of the stream were found in the wetland a year later. In addition, water at the bottom remained at around 4 °C over the winter likely due to groundwater input, which possibly provided a warmer shelter for fish. Stream water quality of the lower section, downstream of the wetland outlet, generally improved with hydrologic pulsing in spring after flow-through reconnection due to the trapping of nutrients in the wetland. Mean removal per flood pulse for nitrate-nitrite, total nitrogen (TN), soluble reactive phosphorus (SRP), total phosphorus (TP) were 1.81 g-N m⁻² per pulse, 1.02 g-N m⁻² per pulse, 0.014 g-P m⁻² per pulse, and 0.004 g-P m⁻² per pulse, respectively. The wetland exported 2.8 g-C m⁻² per pulse of organic carbon. A greater attenuation of NO₃⁻ and TP occurred in the marshy outlet channel section of the wetland than the open water section. The diversion wetland successfully removed nitrate and phosphorus during storm pulses in spring. Similar designs should be applied to other locations to examine their function under different climatic and hydrological conditions.     

Hydraulic residence time computation for constructed wetland design

Hydraulic residence time (HRT) is one of the key design parameters controlling the removal efficiency of contaminants and nutrients in stormwater and wastewater wetlands. The paper presents a new approach to the estimation of HRT using the variable residence time (VART) model. The VART model is employed to simulate the major processes (including advection, dispersion, and transient storage of contaminants/nutrients in vegetated zones) affecting HRT and thereby to produce a hydraulic residence time distribution (HRTD) for a design wetland. The HRTD in combination with a moment-based method is then utilized to find a mean design HRT for the design wetland. Methods for estimation of parameters governing the HRTD are proposed. The new approach to HRT computation is demonstrated through a case study for the Tres Rios Demonstration (TRD) Wetlands in Arizona, USA. Modeling results show that the design HRTs for the Hayfield wetland (H1) and the Cobble wetlands (C1 and C2) are 4.04, 4.66, and 2.65 days, respectively. The computed HRTs agree well with those reported by previous studies, confirming the efficacy of the new approach to hydraulic design of constructed wetlands.     

Estimation of nitrogen dynamics in a vertical-flow constructed wetland

The vertical-flow constructed wetland (VFCW) is a promising engineering technique for removal of excess nutrients and certain pollutants from wastewater and stormwater. The aim of this study was to develop a model using the STELLA software for estimating nitrogen (N) dynamics in an artificial VFCW (i.e., a substrate column with six zones) associated with a growing Cyperus alternifolius species under a wetting (wastewater) -to-drying ratio of 1:3. The model was calibrated by our experimental data with a reasonable agreement prior to its applications. Simulations showed that rates of NH₄⁺-N and NO₃⁻-N leaching decreased with increasing zone number (or column depth), although such a decrease was much more profound for NH₄⁺-N. Our simulations further revealed that rate of NH₄⁺-N leaching decreased with time within each zone, whereas rate of NO₃⁻-N leaching increased with time within each zone. Additionally, both the rates of NH₄⁺-N and NO₃⁻-N leaching through zones followed the water flow pattern: breakthrough during wetting period and cessation during drying period. In general, the cumulative amounts of total nitrogen (TN) were in the following order: leaching > denitrification > uptake > settlement. About 54% of the TN from the wastewater flowed out of the VFCW system, 18% of TN lost due to denitrification, 6% of TN was taken up by roots of a single plant (one hill), and the rest of 22% TN from the wastewater was removed from other mechanisms, such as volatilization, adsorption, and deposition. This study suggested that to improve the overall performance of a VFCW for N removal, prevention of N leaching loss was one of the major issues.     

Low-carbon assessment for ecological wastewater treatment by a constructed wetland in Beijing

Presented in this paper is a low-carbon assessment for wastewater treatment by a constructed wetland as ecological engineering. Systems accounting by combining process and input-output analyses is applied to track both direct and indirect GHG emissions associated with the wastewater treatment. Based on the detailed assessment procedures and the embodied GHG emission intensity database for the Chinese economy in 2007, the GHG emissions embodied in both the construction and operation stages of a pilot constructed wetland in Beijing are investigated in concrete detail, with parallel calculations carried out for a cyclic activated sludge plant as a typical conventional wastewater treatment system for comparison. With the overall embodied GHG emissions taken into account, the constructed wetland is shown to be remarkably less carbon intensive than the conventional wastewater treatment system, and the contrast in GHG emission structure is also revealed and characterized. According to the results, the ecological engineering of the constructed wetland is considered to be favorable for achieving the low-carbon goal.     

Nitrogen removal from secondary effluent by using integrated constructed wetland system

The treatment capacity of an integrated constructed wetland system (CWS) that was designed to reduce nitrogen (N) from secondary effluent was explored. The integrated CWS consisted of vertical-flow constructed wetland, floating bed and sand filter. The vertical-flow wetland was filled with gravel, steel slag and peat from the bottom to the top. Vetiver zizanioides was selected to grow in the vertical-flow constructed wetland and Coix lacrymajobi L. was grown in the floating bed. The results showed that the integrated CWS displayed superior removal efficiency for nitrate nitrogen (NO₃⁻-N), ammonia nitrogen (NH₄⁺-N), nitrite nitrogen (NO₂⁻-N), and total nitrogen (TN). The average NO₃⁻-N, NO₂⁻-N, NH₄⁺-N and TN removal efficiencies of the integrated CWS were 98.83%, 95.60%, 98.05% and 92.41%, respectively, during the whole experimental operation. The integrated CWS may have a good potential for removing N from secondary effluent.     

Nitrous oxide emissions from surface flow and subsurface flow constructed wetland microcosms: Effect of feeding strategies

The effects of continuous and intermittent feeding strategies on nitrogen removal and N₂O emission from surface flow and subsurface flow constructed wetlands were evaluated in this study. Microcosm wetlands planted with Phragmites australis were constructed and operated with different feeding strategies for the 4-month experiment. Results showed the intermittent feeding strategy could enhance the removal of ammonium effectively in the subsurface flow constructed wetlands, although it had no significant effect for the surface flow wetlands. And the intermittent feeding mode could promote the emission of N₂O. The amount of N₂O-N emission from the subsurface flow constructed wetlands with intermittent feeding mode was about 5 times higher than that with continuous feeding strategy and the emission rate ranged from 0.09 ± 0.03 to 7.33 ± 1.49 mg/m²/h. Compared with the surface flow constructed wetlands, the N₂O emission in the subsurface flow constructed wetlands was affected significantly by the intermittent feeding mode.     

Enhanced denitrification in a bioaugmented horizontal subsurface flow filter

The effect of adding low concentrations of a sediment/microbial community suspension to speed up the development of the denitrification capacity in the restored HSSF of a hybrid CW was studied during a one-year period after the filling of the horizontal filter with new light weight aggregates (LWA). Two HSSF filters with the same LWA substrate but different wastewater flow regimes were used as donor systems for the bioaugmentation. NO₃-N concentrations in the outflows of all variants of studied MCs were significantly influenced by the time factor (p < 0.001, repeated measures ANOVA). Post hoc comparison indicated that MCs bioaugmented with the sediment suspension from a similar HSSF had significantly lower NO₃-N concentrations than the control MCs (p < 0.05, Fisher LSD test), whereas MCs bioaugmented with the sediment suspension from a less similar HSSF did not show significant differences compared to the control MCs. This finding emphasizes the importance of the similarity of flow regime and water parameters in choosing a donor system for bioaugmentation. High variability of the effect of bioaugmentation shows that its importance for full scale operation may be overshadowed by the effect of other factors determining denitrification intensity.     

自然湿地土壤产甲烷菌和甲烷氧化菌多样性的分子检测

自然湿地是CH4排放的重要来源之一。产甲烷菌和甲烷氧化菌是介导自然湿地甲烷循环的重要功能菌群。开展产甲烷菌和甲烷氧化菌多样性的检测研究有助于揭示微生物介导的甲烷循环以及自然湿地甲烷排放的时空异质性。传统基于培养的检测方法已被证实无法充分描述产甲烷菌和甲烷氧化菌的多样性,而分子检测方法为自然湿地土壤产甲烷菌和甲烷氧化菌的多样性检测提供了一种更准确和科学的工具。本文综述了自然湿地土壤产甲烷菌和甲烷氧化菌的定性和定量分子检测方法,包括末端限制性片段长度多态性（T-RFLP）、变性梯度凝胶电泳（DGGE）、荧光原位杂交（FISH）和实时定量PCR（real-time qPCR）,重点分析了分子检测中两类重要的标记基因,总结了不同类型自然湿地产甲烷菌和甲烷氧化菌群落多样性的最新成果,提出了我国在该领域今后应深入研究探讨的一些问题及建议。     

若尔盖高寒湿地干湿土壤条件下微生物群落结构特征

土壤水分含量的空间异质性是引起湿地生态系统结构和功能空间变异的关键因素。目前有关低纬度高寒湿地土壤水分对微生物群落结构影响的研究较少。于2007年4月(冷季)和8月(暖季)采集若尔盖高寒湿地常年淹水和无淹水两种水分条件的土壤样品,利用磷脂脂肪酸方法分析其微生物群落结构。结果表明,土壤微生物总生物量、细菌生物量、革兰氏阳性细菌及革兰氏阴性细菌生物量均表现为常年淹水土壤高于无淹水土壤,且4月份高于8月份;与土壤通气量关系密切的真菌、放线菌,其生物量表现为无淹水土壤显著高于常年淹水土壤;反映群落组成的真菌:细菌磷脂脂肪酸比值也表现为无淹水土壤显著高于常年淹水土壤。磷脂脂肪酸的主成分分析表明,水分条件不同的两种土壤中微生物群落结构显著不同,季节变化并未引起土壤微生物群落结构的改变。