Efficiency of three halophyte species in removing nutrients from saline water: a pilot study

Saline wetlands may be well suited for purifying contaminated water from saline agriculture and aquaculture or from freshwater-based agriculture in areas subject to increased salinity. However, case studies on the nutrient removal efficiency of halophyte species are scarce, especially for temperate regions. Here we tested the nutrient removal efficiency and ability to store nutrients in aboveground and belowground biomass of three halophyte species, Aster tripolium, Bolboschoenus maritimus subsp. compactus, and Spartina anglica, in a greenhouse microcosm experiment at two salinity levels. Nutrient removal from water differed among the species: Spartina had the highest nitrogen removal, Bolboschoenus and Spartina had the highest phosphorus removal. The species also differed in the allocation of the nutrient uptake. Bolboschoenus had the highest absolute uptake of nitrogen and phosphorus in shoots, whereas Spartina had the highest uptake of nitrogen and phosphorus in roots. The applicability of these three species in constructed saline wetlands depends on the local salinity and water regime.     

Effects of variable hydroperiods and water level fluctuations on denitrification capacity, nitrate removal, and benthic-microbial community structure in constructed wetlands

The hydrologic character of wetlands is one of the attributes by which they are defined. There are, however, conflicting reports about the detrimental versus beneficial responses of wetland systems to water level fluctuations and variable hydroperiods. We conducted water level and hydroperiod fluctuation studies in full-scale experimental wetlands in order to determine the effects of hydraulic operation on wetland performance (in terms of nutrient removal), and benthic-bacterial community function (in terms of denitrification potential, DNP) and structure (via terminal restriction fragment length polymorphisms, T-RFLP). In our comparison, detention time was the controlling factor for nitrate removal at the system level. However, widely fluctuating water levels and variable hydroperiods did not diminish either the nitrate removal capacity of the experimental wetlands, or the size or composition of benthic-bacterial communities relative to the more stable water level systems. Rather, significant differences in denitrification potential rates, bacterial cell densities, and benthic community structure were a function of sampling location within the experimental wetlands regardless of hydraulic operation. The results of this study support the need for reconsidering the hydraulic criteria for wetland delineation.     

Nutrient removal in constructed microcosm wetlands for treating polluted river water in northern China

River water pollution is increasingly widespread in northern China and can lead to problems with the drinking water for the residents if not properly treated. Constructed wetlands are a promising solution and have become increasingly popular in China. In this study the nutrient removal and plant uptake in constructed microcosm wetlands vegetated with Typha orientalis, Phragmites australis, Scirpus validus and Iris pseudacorus for treating simulated polluted river water in northern China were investigated. The performance of the treatment systems from April to November was assessed. The maximum TN, NH₄-N and TP removal efficiencies were 68%, 93% and 67%, respectively. And the maximum nutrient uptake by plants constituted 51.89% of the N removal and 34.17% of the P removal throughout the trial. S. validus and I. pseudacorus have a higher nutrient uptake capacity and are preferred species from a treatment perspective in constructed wetland in northern China.     

Fluxes and retention of sediment and nutrients in valley bottom fish and rice farms and wetlands: impacts on surface water

This study compares nutrient and sediment retention among rice and fish farms and wetlands in valley bottoms in southern Rwanda. Small-scale wetland, rice and fishpond experimental systems were established to measure sediment, nitrogen (N) and phosphorus (P) fluxes during a 9-month period. There were significant differences in the processes contributing to sediment, N and P retention in the three systems related to system characteristics, management practices, and seasons. Overall nutrient retention was higher in the rice and fish systems, but these systems had higher inputs and outputs of sediment and nutrients. In rice plots, resuspension and discharge of sediment and nutrients to the outflow were caused by ploughing and weeding during the first 3 months of the culture period. In fishponds, nutrients and sediment discharge were associated with water renewal and sediment removal during the last 5 months of the farming period. The undisturbed wetland plots had the lowest outflows of sediment and nutrients. Nutrient uptake and accumulation in biomass was much higher in rice and wetland vegetation than in fish biomass. In fishponds and wetlands, nutrients accumulated in soil, whereas rice plots showed a decrease or depletion in nutrient storage. To increase nutrient utilization at the plot level, sediment and nutrient discharge from land preparation and rice transplanting should be reduced by better farm practices. Within a catchment, nutrient flows can be integrated by using fishpond sediments for crop farming, by incorporating natural wetlands in crop rotations or using them as buffer zones.

     

Water source utilization and foliar nutrient status differs between upland and flooded plant communities in wetland tree islands

Tree islands in the Everglades wetlands are centers of biodiversity and targets of restoration, yet little is known about the pattern of water source utilization by the constituent woody plant communities: upland hammocks and flooded swamp forests. Two potential water sources exist: (1) entrapped rainwater in the vadose zone of the organic soil (referred to as upland soil water), that becomes enriched in phosphorus, and (2) phosphorus-poor groundwater/surface water (referred to as regional water). Using natural stable isotope abundance as a tracer, we observed that hammock plants used upland soil water in the wet season and shifted to regional water uptake in the dry season, while swamp forest plants used regional water throughout the year. Consistent with the previously observed phosphorus concentrations of the two water sources, hammock plants had a greater annual mean foliar phosphorus concentration over swamp forest plants, thereby supporting the idea that tree island hammocks are islands of high phosphorus concentrations in the oligotrophic Everglades. Foliar nitrogen levels in swamp forest plants were higher than those of hammock plants. Linking water sources with foliar nutrient concentrations can indicate nutrient sources and periods of nutrient uptake, thereby linking hydrology with the nutrient regimes of different plant communities in wetland ecosystems. Our results are consistent with the hypotheses that (1) over long periods, upland tree island communities incrementally increase their nutrient concentration by incorporating marsh nutrients through transpiration seasonally, and (2) small differences in micro-topography in a wetland ecosystem can lead to large differences in water and nutrient cycles.     

Plant growth and nutrient removal in constructed monoculture and mixed wetlands related to stubble attributes

The aim of this study is to test the hypothesis that it depends on plant species used in the wetlands and their stubble growth attributes, as to whether monoculture or mixed wetland is superior in plant growth and nutrient removal. Monoculture and mixed wetland microcosms of five wetland plant species were studied. Significant differences in growth and aboveground biomass were found in the monoculture wetlands. Species that showed faster growth and larger biomass in monoculture wetland were also dominant in the mixed wetland. The mixed wetland exhibited similar biomass and root growth to the averages of five monocultures. ANOVA showed that there were very significant differences among the wetlands in removal rates of all the nutrients studied except nitrate nitrogen (NO₃-N) and chemical oxygen demand (COD). The removal rates from the mixed wetland were generally comparable to the highest removal rates from the monocultures. The species exhibited different stubble growth attributes, with some species showing increasing stubble growth and removal rates, while other species showing decreasing stubble growth and removal rates. The results indicated that in both monocultures and mixed constructed wetlands, growth and nutrient removal rates depended on plant species, and attributes of plant stubble growth affected overall growth and nutrient removal capabilities.     

‘HALOPHYTE FILTERS’: THE POTENTIAL OF CONSTRUCTED WETLANDS FOR APPLICATION IN SALINE AQUACULTURE

World consumption of seafood continues to rise, but the seas and oceans are already overexploited. Land-based (saline) aquaculture may offer a sustainable way to meet the growing demand for fish and shellfish. A major problem of aquaculture is nutrient waste, as most of the nutrients added through feed are released into the environment in dissolved form. Wetlands are nature's water purifiers. Constructed wetlands are commonly used to treat contaminated freshwater effluent. Experience with saline systems is more limited. This paper explores the potential of constructed saline wetlands for treating the nutrient-rich discharge from land-based saline aquaculture systems. The primary function of constructed wetlands is water purification, but other ancillary benefits can also be incorporated into treatment wetland designs. Marsh vegetation enhances landscape beauty and plant diversity, and wetlands may offer habitat for fauna and recreational areas. Various approaches can be taken in utilizing plants (halophytes, macro-algae, micro-algae) in the treatment of saline aquaculture effluent. Their strengths and weaknesses are reviewed here, and a conceptual framework is presented that takes into account economic and ecological benefits as well as spatial constraints. Use of the framework is demonstrated for assessing various saline aquaculture systems in the southwestern delta region of the Netherlands.     

Heavy metal pollution in aquatic ecosystems and its phytoremediation using wetland plants: an ecosustainable approach

This review addresses the global problem of heavymetal pollution originating from increased industrialization and urbanization and its amelioration by using wetland plants both in a microcosm as well as natural/field condition. Heavymetal contamination in aquatic ecosystems due to discharge of industrial effluents may pose a serious threat to human health. Alkaline precipitation, ion exchange columns, electrochemical removal, filtration, and membrane technologies are the currently available technologies for heavy metal removal. These conventional technologies are not economical and may produce adverse impacts on aquatic ecosystems. Phytoremediation of metals is a cost-effective "green" technology based on the use of specially selected metal-accumulating plants to remove toxic metals from soils and water. Wetland plants are important tools for heavy metal removal. The Ramsar convention, one of the earlier modern global conservation treaties, was adopted at Ramsar, Iran, in 1971 and became effective in 1975. This convention emphasized the wise use of wetlands and their resources. This review mentions salient features of wetland ecosystems, their vegetation component, and the pros and cons involved in heavy metal removal. Wetland plants are preferred over other bio-agents due to their low cost, frequent abundance in aquatic ecosystems, and easy handling. The extensive rhizosphere of wetland plants provides an enriched culture zone for the microbes involved in degradation. The wetland sediment zone provides reducing conditions that are conducive to the metal removal pathway. Constructed wetlands proved to be effective for the abatement of heavymetal pollution from acid mine drainage; landfill leachate; thermal power; and municipal, agricultural, refinery, and chlor-alkali effluent. the physicochemical properties of wetlands provide many positive attributes for remediating heavy metals. Typha, Phragmites, Eichhornia, Azolla, Lemna, and other aquatic macrophytes are some of the potent wetland plants for heavy metal removal. Biomass disposal problem and seasonal growth of aquatic macrophytes are some limitations in the transfer of phytoremediation technology from the laboratory to the field. However, the disposed biomass of macrophytes may be used for various fruitful applications. An ecosustainable model has been developed through the author's various works, which may ameliorate some of the limitations. The creation of more areas for phytoremediation may also aid in wetlands conservation. Genetic engineering and biodiversity prospecting of endangered wetland plants are important future prospects in this regard.     

Rejuvenating the largest municipal treatment wetland in Florida

The Orlando Easterly Wetland (OEW), one of the largest constructed wetlands for the treatment of wastewater in Florida, started operation in 1987 for the reduction of nutrient loads in tertiary treated domestic wastewater produced by the City of Orlando. The wetland has performed better than design expectations, but phosphorus removal effectiveness experienced some seasonal declines beginning with the winter of 1999. Subsequent studies indicated that the OEW treatment capacity was hindered by inefficient phosphorus removal in the upstream cells of one of three flow trains. Therefore, rejuvenating management activities were initiated on these cells in 2002. The management included the removal of plants and organic top sediments, site grading in the interior of the cells, construction of baffles and islands, and re-vegetation. This study evaluates the improvement in hydraulic and phosphorus removal performance realized from the wetland modifications. Improvement of hydraulic performance was evaluated based on tracer tests, and improvement of phosphorus removal performance was evaluated based on episodic spatially distributed water samples as well as model prediction. The results showed that both the hydraulic efficiency and the phosphorus removal effectiveness of the rejuvenated wetland were significantly increased. However, the wetland has likely re-entered a start-up phase and long-term observation will be necessary to determine eventual steady-state conditions.     

Functioning and dynamics of wetland vegetation of Lake Victoria: an overview

The aquatic macrophytic vegetation constituting the wetlands situated along the coast of Lake Victoria provides valuable services to both local and regional communities as well as an important ecological function through the transition between terrestrial and aquatic ecosystems. The wetland vegetation is typically rooted in the substrate on the landward side of the lake, but forms a floating mat towards the middle of the wetland and at the wetland/lake interface. Cyperus papyrus and Miscanthidium violaceum vegetation typically dominate the permanently inundated wetland areas along most of the shores of Lake Victoria. Due to the prevailing climatic and hydrological catchment conditions, these macrophytic plants (papyrus in particular) tend to exhibit high net productivity and nutrient uptake which strongly influences both wetland status and lake water quality. In addition, these wetlands provide important economic livelihoods for the local populations. The integrity and physical structure of these wetlands strongly influences their associated mass transport mechanisms (water, nutrients and carbon) and ecosystem processes. Wetland degradation in Africa is an increasing problem, as these ecosystems are relied upon to attenuate industrial, urban and agricultural pollution and supply numerous services and resources. In an integrated project focused on the wetlands of Lake Victoria, the ecological and economic aspects of littoral wetlands were examined and new instruments developed for their sustainable management.     

Potential of constructed wetlands in treating the eutrophic water: evidence from Taihu Lake of China

Three parallel units of pilot-scale constructed wetlands (CWs), i.e., vertical subsurface flow (VSF), horizontal subsurface flow (HSF) and free water surface flow (FWS) wetland were experimented to assess their capabilities in purifying eutrophic water of Taihu Lake, China. Lake water was continuously pumped into the CWs at a hydraulic loading rate of 0.64 m d(-1) for each treatment. One year's performance displayed that average removal rates of chemical oxygen demand (COD), ammonia nitrogen (NH(4)(+)-N), nitrate nitrogen (NO(3)(-)-N), total nitrogen (TN) and total phosphorous (TP) were 17-40%, 23-46%, 34-65%, 20-52% and 35-66%, respectively. The VSF and HSF showed statistically similar high potential for nutrients removal except NH(4)(+)-N, with the former being 14% higher than that of the latter. However, the FWS wetland showed the least effect compared to the VSF and HSF at the high hydraulic loading rate. Mean effluent TP concentrations in VSF (0.056 mg L(-1)) and HSF (0.052 mg L(-1)) nearly reached Grade III (0.05 mg L(-1) for lakes and reserviors) water quality standard of China. Wetland plants (Typha angustifolia) grew well in the three CWs. We noted that plant uptake and storage were both important factors responsible for nitrogen and phosphorous removal in the three CWs. However, harvesting of the above ground biomass contributed 20% N and 57% P of the total N and P removed in FWS wetland, whereas it accounted for only 5% and 7% N, and 14% and 17% P of the total N and P removed in VSF and HSF CWs, respectively. Our findings suggest that the constructed wetlands could well treat the eutrophic lake waters in Taihu. If land limiting is considered, VSF and HSF are more appropriate than FWS under higher hydraulic loading rate.     

人工湿地除磷研究进展

从人工湿地除磷机理着手,综述了国内外有关湿地基质、湿地植物及微生物强化除磷的研究机理以及进展。深入研究多种基质组合对磷素的吸附与解析机理,可以从理论上推进诸多高效除磷基质的实际应用进程;植物间接净化作用及其与湿地水力停留时间的关系,是影响湿地植物选种和种植的重要依据;植物根际微环境以及植物与微生物的耦合作用可能是人工湿地除磷的主要途径之一;强调湿地的污水净化功能而忽视其生态服务功能,是湿地运行中普遍存在的认识错误。最后指出：湿地运行应采取高水力负荷、低污染负荷的方式,强调强化一级处理的重要性。     

Effects of Eichhornia crassipes and Ceratophyllum demersum on Soil and Water Environments and Nutrient Removal in Wetland Microcosms

Wetland plants are important components that influence the biogeochemistry of wetland ecosystems. Therefore, remediation performance in wetlands can differ depending on the growth forms of plants. In this study, the effects of Eichhornia crassipes (floating plant) and Ceratophyllum demersum (submerged plant) on the wetland soil and water environments were investigated using a microcosm study with simulated hydrology of retention-type wetlands between rainfall events. The C. demersum microcosm (SP) showed the fastest recovery with a diel fluctuation pattern of dissolved oxygen, pH, and oxidation-reduction potential (ORP) from the impacts of nutrient inflow. Moreover, SP exhibited the lowest decrease in sediment ORP, the highest dehydrogenase activity, and more organic forms of nitrogen and phosphorus. E. crassipes microcosms exhibited the lowest water temperature, and efficiently controlled algae. In the presence of plants, the total nitrogen and phosphorus concentrations in water rapidly decreased, and the composition of organic and inorganic nutrient forms was altered along with a decrease in concentration. The results indicate that wetland plants help retain nutrients in the system, but the effects varied based on the wetland plant growth forms.     

Effects of vegetation on flow through free water surface wetlands

The one-dimensional Saint-Venant equations are modified to account for stem drag and volumetric displacement effects of dense emergent plants on free surface flow. The modified equations are solved with an implicit finite difference method to give velocities and depths for shallow flows through a vegetated wetland channel. Estimated flow profiles are used to investigate how vegetation density, downstream boundaries and aspect ratio affect detention time, an important parameter in determining nutrient and pollutant removal efficiencies of wetlands constructed to treat wastewater. Results show that free water surface wetlands may exhibit static, neutral or dynamic behavior. Under static conditions, the wetland behaves like a pond in which displacement effects caused by submerged plant mass invariably decrease detention times. Under dynamic conditions, stem drag induced by aquatic plants predominates and wetland detention times increase with vegetation density. These opposing responses are separated by a narrow neutral condition where the presence of vegetation has virtually no net effect on detention time. For a given flow rate and surface area, detention times and hence treatment efficiencies in vegetated free water surface wetlands can be managed to some degree by adjusting the downstream control or by changing the aspect ratio.     

九段沙芦苇湿地生态系统N、P、K的循环特征

对九段沙(上沙、中沙、下沙)芦苇湿地土壤、植物中N、P、K含量进行了测定,研究其分布规律.结果表明:水平分布上,湿地土壤全量养分与速效性养分含量均是中沙最低,并以中沙为中心向两端递增,速效性养分的这种变化尤为显著.垂直分布上,土壤全N和全K含量的分布规律一致,为上层＞下层＞中层;全P含量分布为中层＞上层＞下层.速效N含量分布为上层＞中层＞下层;速效P含量上层土壤最高,中、下层土壤含量因湿地类型而异;速效K含量多以中层土壤最低,上、下层土壤含量变化不稳定,以不同湿地而异.不同芦苇湿地的土壤速效性养分含量差异显著大于全量养分的差异,0～60 cm深度土壤的全量养分和速效性养分含量排序均为K＞N＞P.中沙湿地植物中养分含量最低,与土壤中营养元素总体水平分布一致;多数芦苇湿地植物中营养元素含量排序为N＞K＞P,与土壤养分含量排序不一致.不同芦苇湿地的吸收系数排序均为N＞P＞K;芦苇湿地利用系数排序为P＞K＞N;循环系数排序为N＞K＞P.     

大型人工湿地生态可持续性评价

大型人工湿地现已广泛应用于湖滨带、河滨带水质净化及湿地生态修复,这些人工湿地的生态可持续性评价对于其科学管理调控及长期可持续运行具有重要意义。运用综合指标评价及层次分析法,根据人工湿地生态系统的特点,提出并建立了适合评价人工湿地可持续性运行的指标体系,建立的评价指标包括生态特征与功能、水质净化功能及经济社会功能三项一级指标,及对应的14个二级指标。运用建立的评价指标体系对南四湖湖滨带新薛河大型人工湿地示范工程的生态可持续性运行了评价,评价结果显示:植物多样性、氨氮去除能力、生物入侵抵抗力、野生动物栖息地、COD去除能力是影响大型人工湿地运行效果的主要制约因素;新薛河人工湿地生态可持续性综合指数为0.6862,处于"良"级,其中生态特征功能可持续性指数最高,为0.7732;水质净化功能和社会经济功能指数分别为0.6190,0.6492。由结果可知,南四湖新薛河大型人工湿地具有重要的生态修复功能,水质净化功能方面应加强植物定期收割及植被管理,同时经济社会功能还有待加强,植物经济效益及旅游娱乐效益还有待深入开发。建立的人工湿地可持续性运行的评价指标体系具有较强的针对性,可用于其他大型人工湿地的生态可持续性评价。     

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.     

Constructed wetlands in Queensland: Performance efficiency and nutrient bioaccumulation

Nine pilot wetlands (eight free water surface and one subsurface flow) have been constructed in Queensland as joint projects between the State and Local Governments, to treat municipal wastewater. The wetlands are in several geographical locations which include tropical, subtropical and arid climates. Each wetland is a different configuration and contains a variety of macrophyte types and species. Most species are native and were collected in the locality or self colonised. This paper examines the performance efficiency of the wetlands and nutrient bioaccumulation in wetland plants. Biochemical oxygen demand concentrations were reduced by 17–89% and suspended solids concentrations by 14–77% to produce wetland effluent with BOD less than 12 mg l⁻¹ and suspended solids less than 22 mg l⁻¹. Reduction in total nitrogen concentrations ranged from 18 to 86%, ammonia nitrogen from 8 to 95% and oxidised nitrogen from 55 to 98%, producing effluent with total nitrogen between 1.6 and 18 mg l⁻¹. Reduction in reactive phosphorus concentration was less than 13% in the free water surface systems with concentration in the effluent exceeding the influent in many of the systems over long term operation. In contrast reduction through the single household subsurface system was 65%. Nutrient bioaccumulation was investigated in 60 species. Submerged (Ceratophyllum) and free floating species (duckweed) had the highest tissue nutrient concentrations, followed by the waterlily (Nymphoides indica), aquatic vines (Ipomoea spp., Ludwigia peploides), and waterferns (Ceratopteris, Marsilea). All these species remove nutrients from the water column. Emergent species had lower nutrient concentrations with the highest nutrients occurring in the exotic sedge Cyperus involucratus. Aquatic grasses including Phragmites had higher nutrient content than the sedges. Nitrogen concentrations were higher in leaf/stem tissue compared to the root/rhizome, whereas phosphorus was higher in root/rhizome tissue. Emergent species had a greater biomass than submerged or free floating species and were therefore able to store more nutrients per unit area of wetland. Cropping the shoots of emergent species increased nutrient content in new shoot growth.     

Laboratory experiment to determine the potential of two macroalgae from the Russian Far-East as biofilters for integrated multi-trophic aquaculture (IMTA)

Two local macroalgal species (Undaria pinnatifida and Gracilaria vermiculophylla) were tested in laboratory experiments to determine their nutrient uptake potential and their physiological response to waste water effluents from a mariculture project on bivalve mollusks (mussels). No negative effects on the growth and photosynthesis rates of the algae were detected. High nutrient uptake rates and high nutrient removal efficiency were measured in both tested species. We propose that U. pinnatifida be introduced into IMTA systems during the cold-water season to remove nutrients from cultured animals. The culture of this species can be alternated with that of G. vermiculophylla during warm-water season in order to provide a longer biofiltration period.