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.     

Adaptation of wastewater surface flow wetland formulae for application in constructed stormwater wetlands

Over the past 30 years, the use of constructed wetlands for wastewater treatment has been a topic of significant research culminating in a good data base from which simplistic equations have been derived to aid in the design of these facilities to meet long term water quality treatment performance criteria. Over the past decade, the use of treatment wetlands has extended to stormwater and combined sewer overflow (CSO) management applications. Designing constructed wetlands for stormwater and CSO applications have unique challenges stemming from the highly stochastic nature of the hydraulic and pollutant loading on a stormwater wetland compared with wastewater treatment systems. This paper explores the possibility of adapting the simplistic models for wastewater wetlands for interim use in developing design guidelines for stormwater wetland systems. A procedure that takes into account the unsteady intermittent nature of stormwater inflows to these wetlands has been incorporated into one of these simplistic models and a case study presented to demonstrate the application of the procedure.     

Nitrogen removal in constructed wetland systems

Since the mid 1990s, constructed wetlands have been increasingly used as a low‐energy ‘green’ technique, in the treatment of wastewater and stormwater, driven by the rising cost of fossil fuels and increasing concern about climate change. Among various applications of these wetlands, a significant area is the removal of nitrogenous pollutants to protect the water environment and to enable effective reclamation and reuse of the wastewater. This paper provides a review of the current state of nitrogen removal technology, focusing on existing types of wetlands, the mechanisms of nitrogen removal, major environmental factors relative to nitrogen removal, and the operation and management of the wetlands.     

Opportunities and challenges for managing nitrogen in urban stormwater: A review and synthesis

Although nitrogen (N) is prevalent in urban stormwater, regulation of this pollutant has occurred only more recently. This paper reviews the concerns over N in urban stormwater, mechanisms and design enhancements for N uptake and denitrification through various stormwater control measures (SCMs), and presents opportunities to integrate this current knowledge into the regulatory framework. A survey of personnel directly involved in various aspects of US state and territory NPDES programs revealed that the top three pollutants of concern were total suspended solids (TSS), pathogens and bacteria, and total phosphorus (TP). Surprisingly, nitrate (NO₃^?) was of little concern among the survey respondents, with 3.9% giving it the highest level of concern, 2.0% ranking it second, and 6.0% ranking it third. When asked which strategies were currently used in their geographic area for stormwater management, the most common results were wet ponds and dry ponds. At the same time, wet ponds and dry ponds were recognized as less effective practices to manage stormwater.A review of current literature reveals that several alternative SCMs, such as bioretention, filters, and wetlands, show greater promise in their ability to remove N from stormwater than more conventional practices such as dry ponds and wet ponds. Enhanced N removal via denitrification and plant uptake is often observed under the combination of aerobic followed by sustained anoxic conditions, the presence of a carbon source (organic material), and the presence of mature, dense vegetation.Given the lack of concern or awareness of local officials related to N loading from urban stormwater, and variation in the efficacy of various SCMs, it is not surprising that regulators remain focused on conventional dry pond and wet pond control measures. More needs to be done to quantify the impact of urban sources of N on water quality and aquatic ecosystems. In addition, greater focus needs to be placed on the development of design criteria for SCMs, such as bioretention, filters, and constructed wetlands, which show more promise for N removal.     

A water quality analysis system to evaluate the impact of agricultural activities on N outflow in river basins in Japan

We have developed a personal-computer-based water quality analysis system for river basins. The system estimates potential N outflow by model and calculates actual N outflow from monitoring data. For the former it uses the potential load factor method to estimate annual nitrogen load from various sources and runoff potential from each area of land in a basin. For the latter it analyzes water quality monitoring data in relation to meteorological data. We used the system to analyze N outflow in basins around Lake Kasumigaura and the Yahagi River in central Honshu, Japan. The land around Lake Kasumigaura is rather flat, and about 25% is periodically flooded for rice and lotus cultivation. The land around the Yahagi River is mountainous, and much less land is flooded. In the Yahagi River basin the actual N outflow agreed closely with the potential. However, the actual N outflow in the basin around Lake Kasumigaura was much less than the potential, suggesting that a large part of the N load is denitrified in flooded soils. This further indicates that a sequence of different land uses including flooded rice fields is an important factor determining N outflow in basins in Japan. On the basis of the above analyses, we incorporated a denitrification model into the system that enables us to estimate N balance in a designated basin;this system may be helpful in the formulation of scenarios of land use andsoil management for improving water quality.     

A water quality analysis system to evaluate the impact of agricultural activities on N outflow in river basins in Japan

We have developed a personal-computer-based water quality analysis system for river basins. The system estimates potential N outflow by model and calculates actual N outflow from monitoring data. For the former it uses the potential load factor method to estimate annual nitrogen load from various sources and runoff potential from each area of land in a basin. For the latter it analyzes water quality monitoring data in relation to meteorological data. We used the system to analyze N outflow in basins around Lake Kasumigaura and the Yahagi River in central Honshu, Japan. The land around Lake Kasumigaura is rather flat, and about 25% is periodically flooded for rice and lotus cultivation. The land around the Yahagi River is mountainous, and much less land is flooded. In the Yahagi River basin the actual N outflow agreed closely with the potential. However, the actual N outflow in the basin around Lake Kasumigaura was much less than the potential, suggesting that a large part of the N load is denitrified in flooded soils. This further indicates that a sequence of different land uses including flooded rice fields is an important factor determining N outflow in basins in Japan. On the basis of the above analyses, we incorporated a denitrification model into the system that enables us to estimate N balance in a designated basin; this system may be helpful in the formulation of scenarios of land use and soil management for improving water quality.     

Phosphorus release and sedimentation in three contiguous shallow brackish lakes, as estimated from changes in phosphorus stock and loading from catchment

In situ phosphorus release rates in three contiguous shallow brackish lakes were calculated by considering the amount of water inflow, changes in salinity and phosphorus stock, and loading from phosphorus inflow based on monthly data. The annual amount of sedimental phosphorus relative to that of phosphorus inflow was different for each of the three water bodies: 16% for Lake Shinji, 3% for the Honjo area, and −8% for Lake Nakaumi, as estimated in a 10-year period from January 1993 to December 2002. During the warm season, the quantity of phosphorus released surpassed sedimentation in these three water bodies. The low annual sedimentation ratio in Lake Nakaumi is related to a large seawater backflow resulting in phosphorus removal, in addition to a stable stratified structure promoting phosphorus release from sediment due to oxygen depletion in the lower layer. In Lake Nakaumi, field data shows that if dissolved oxygen at the sediment surface falls below 2.54 mg L⁻¹, phosphorus release from the sediment begins to be accelerated.     

Synergism of natural and constructed wetlands in Beijing,China

An integrated wetland system (IWS) including constructed wetlands (CWs) and modified natural wetlands (NWs) for wastewater treatment to replenish water to wetlands located at the Beijing Wetland School (BWS) in Beijing, China, is presented in this paper. The synergistic effects of CWs and NWs on treated water quality are investigated. The IWS is proved to be an effective wastewater treatment technique and a better alternative to alleviate the water shortage for conservation of wetlands based on the monitoring data obtained from October 2007 to 2008. The results show that CWs and NWs play different roles in removing contaminants from wastewater. The COD removal efficiency in CWs is higher than that in modified NWs, whereas the modified NWs can compensate for the deficiency of CWs where a stable and sufficient rhizosphere is not fully formed in the start-up period. All removal rates of COD, TN, and TP in CWs and modified NWs vary from 50 to 70%, while the total removal rate of COD, TN, and TP in IWS is about 85–90%. The operational results show that the maximum area loading of organic pollutants in modified NWs (65 kg/ha d) is slightly higher than the empirical one (60 kg/ha d) recommended by USEPA (2000) for free water surface wetlands.     

青海湖区大型底栖动物群落结构与空间分布格局

为了解青海湖大型底栖动物的群落结构特征、空间分布格局及关键驱动力, 于2011-2012年分4次对青海湖区主体湖、3个子湖和5条入湖河流进行了系统调查。共采集到底栖动物28个分类单元, 隶属于3门5纲15科, 主体湖区、咸水和淡水子湖及入湖河流分布有9、5、9和15种; 它们的密度分别为455.8、1562.7、741.3和331.2 ind./m2; 生物量为1.18、3.70、2.75和4.53 g/m2。优势度分析显示, 喜盐摇蚊为主体湖区绝对优势种（占总密度的83.32%）。Surfer模拟显示, 主体湖区东南部沿岸带的密度和生物量最高, 湖心区最低; 高峰值主要出现在布哈河、菜挤河等大型河流入湖的河口附近。CCA分析表明: 青海湖区大型底栖动物的分布主要受水体pH、水深、总氮和盐度等环境因子的驱动。       

Phosphorus mass load and outflow concentration relationships in stormwater treatment areas for Everglades restoration

Mass loading and outflow phosphorus (P) relationships were investigated for four stormwater treatment area (STA) wetlands in south Florida. These systems, ranging in size from 350 to 2670 ha, were constructed by the South Florida Water Management District (SFWMD) for Everglades restoration, and approaches currently are being investigated for optimizing their design and management. We analyzed 2–7 years of P removal data from 10 independent STA process trains using system classifications based on dominant vegetation type, which was either emergent aquatic vegetation (EAV) or submerged aquatic vegetation (SAV), and prior land use, which was either recently farmed (RF) or historic wetland (HW). We found that a 1–2 year history of mass loading rates (MLR) at or below ∼1.3 g P/m²/year in STA process trains provided a high likelihood of achieving outflow total P (TP) concentrations less than ∼30 μg/L. Statistical analyses revealed that P removal performance of SAV and EAV-HW systems was generally superior to that of EAV-RF systems. These performance differences were corroborated with data from seven other non-STA Florida-based treatment wetlands. Furthermore, in the subset of SAV and continuously flooded EAV-HW data with P MLRs at or below ∼2 g/m²/year, outflow P concentrations were consistently between 10 and 20 μg/L, mass removal efficiencies were consistently above 85%, and the wetlands demonstrated a substantial resilience to small-to-moderate pulsed inflow P loads. Despite 16 occurrences in these full-scale STA data of annual flow-weighted mean outflow P concentrations between 10 and 20 μg/L, no significant MLR–P relationships were identified for targeting specific P concentrations in this range.     

How hydrological and hydraulic conditions affect performance of ponds

During the 1990s there has been a growing interest in (re)constructed wetlands and ponds for treatment of agricultural runoff, sewage water, and stormwater. Some of these facilities, however, are poorly designed in terms of hydrological and hydraulic performance, which strongly affects their treatment capacity. This paper gives an overview of the present knowledge regarding pond hydraulics in terms of effective volume ratio and dispersion. The importance of these parameters is demonstrated by modelling of nitrogen removal in 13 ponds of different design. The results show that effective volume ratio has a clear influence, which increases when removal rate coefficients increase, while dispersion is of minor importance for removal efficiency. Finally, the concept of hydraulic efficiency is discussed in the light of these results.     

Retention of nitrogen, phosphorus and silicon in a large semi-arid riverine lake system

Lakes and reservoirs (impoundments) are often viewed as a sink for nutrients within the river continuum. To date, most studies on nutrient retention within impoundments are derived from the temperate climate zones of Europe and North America, only consider one nutrient, and are often short-term (1–2 years). Here, we present a long-term (17 year) data set and nutrient (nitrogen, phosphorus and silica) budget for two connected semi-arid lakes (the Lower Lakes) at the terminus of the River Murray, Australia. Most of the filterable reactive phosphorus and nitrate entering the lakes were retained (77 and 92%, respectively). Total phosphorus (TP) was also strongly retained (55% of the annual TP load on average) and the annual TP retention rates could be predicted as a function of the areal hydraulic loading rate (annual lake outflow/lake surface area). On average, there was a slight net retention (7%) of the annual total nitrogen (TN) load but a slight net export (6% of the load) of organic N. TN retention as function of the areal hydraulic loading rate was lower than expected from existing models, possibly because of high nitrogen fixation rates in the Lower Lakes. Silica was retained (39%) at similar rates to those observed in previous studies. There was also a marked increase in the TN:TP and TN:Si ratios within the lake (TN:TP~30 and TN:Si~0.67) compared to those entering (TN:TP~15, TN:Si~0.45), as a consequence of the relatively low net retention of nitrogen.     

Waterbird use of artificial wetlands in an Australian urban landscape

With the loss of natural wetlands, artificial wetlands are becoming increasingly important as habitat for waterbirds. We investigated the relationships between waterbirds and various biophysical parameters on artificial wetlands in an Australian urban valley. The densities (birds per hectare) of several species were correlated (mostly positively) with wetland area, and correlations were observed between certain species and other physical and water chemistry variables. Waterbird community structure, based on both abundance (birds per wetland) and density data, was most consistently positively correlated with the relative amount of wetland perimeter that was vegetated, surface area, distance to nearest wetland, public accessibility and shoreline irregularity. We also compared the relative use of the two types of urban wetlands, namely urban lakes and stormwater treatment wetlands, and found for both abundance and density that the number of individuals and species did not vary significantly between wetland types but that significant differences were observed for particular species and feeding guilds, with no species or guild being more abundant or found in greater density on an urban lake than a stormwater treatment wetland. Designing wetlands to provide a diversity of habitat will benefit most species.     

A process-orientated design and performance assessment methodology for passive mine water treatment systems

The aim of this paper is the development of a methodology for assessing the iron removal efficiency of passive mine water treatment settling lagoons and reed beds. Previous work in the design and sizing of coal mine drainage lagoons and wetlands has focussed on the use of standard hydraulic residence times or using the 10 g m⁻² d⁻¹ metric, these criteria have been applied without regard to the fundamental physical and chemical processes controlling iron removal in the system, namely the pH dependent rates of Fe(II) oxidation and physical settling of the particulate Fe(III). In this study field water quality data have been collected from lagoons and reed beds. These data are examined alongside data from the UK Coal Authority database and combined with simple mathematical formulations to provide a framework through which to understand passive treatment schemes from a process-orientated perspective. It is demonstrated that for the sites studied reed beds are more efficient for iron removal. This paper recommends that judgements of iron removal performance should be based on a derived treatment efficiency index (?) and that the modelling approach espoused in this paper should be used when designing passive mine water treatment schemes.     

Evaluation of relative importance of different microbial reactions on organic matter removal in horizontal subsurface-flow constructed wetlands using a 2D simulation model

In this study, we used a two-dimensional (2D) mechanistic mathematical model in order to evaluate the relative contribution of different microbial reactions to organic matter removal (in terms of COD) in horizontal subsurface-flow constructed wetlands that treated urban wastewater. We also used the model to analyse the effect of increasing or decreasing the organic loading rate (changing the hydraulic loading rate (HLR) at a constant influent organic matter concentration, or changing the organic matter concentration at a constant HLR) on both the removal efficiency and the relative importance of the microbial reactions. The model is based on the code RetrasoCodeBright, which we modified to include the main microbial processes related to organic matter and nitrogen transformations in the wetlands: hydrolysis, aerobic respiration, nitrification, denitrification, sulphate reduction and methanogenesis. The model was calibrated and validated with data from two wetlands (each with a surface area of 55 m²) located in a pilot plant near Barcelona (Spain). According to the simulations, anaerobic processes (methanogenesis and sulphate reduction) are more widespread in the wetlands and contribute to a higher COD removal rate (60–70%) than anoxic (denitrification) and aerobic reactions do. These model results are confirmed by experimental observations. In all the cases tested, the reaction that most contributed to COD removal was methanogenesis (33–52%). According to our simulations, decreasing the HLR (for example, from 40 to 25 mm/d) while maintaining a constant COD influent concentration has a clear positive impact on COD removal efficiency (which increases from 65% to 89%). Changing influent COD concentration (for example, from 290 to 190 mg/L) while maintaining a constant HLR has a smaller impact, causing efficiency to increase from 79% to 84%. Changes in influent COD concentration (at a constant HLR) affect the relative contribution of the microbial reactions to organic matter removal. However, this trend is not seen when the HLR changes and the COD influent concentration remains constant.     

Ostracoda as bioindicators of anthropogenic impact in salt lakes,saltpans, and a lagoon: A case study from the Gulf of Saros coast (NE Aegean Sea), Turkey

The study area consists of wetlands and semi-wetlands (saltpan and salt lakes) that are separated from the Gulf of Saros in the northeastern Aegean Sea by a littoral cordon. Twenty-four samples were collected from the Enez Salt Lake; Dalyan, Enez Gala, Kuvalak, Isik, and Tasalti Lakes; Vakif and Erikli Saltpans; and Karagol Lagoon. The overall distribution of the sediment sizes reveals that they consist predominantly of mud and sand and a mixture of mud, sand, and gravel. The average proportion of gravel size particles is 8.36%. Feldspar and mica are abundant in sand and gravel-sized materials. Ecological conditions of these coastal areas were assessed on the basis of ostracod assemblages that can be considered as useful bioindicators and depend on water depth, temperature, and salinity. In this context, the effects of physical and chemical properties of the environment, geochemistry of the sediment, and anthropogenic impact on the meiofauna, in particular ostracoda, was here evaluated. Cyprideis torosa Jones, a cosmopolitan species of ostracoda, was found in salt lakes. Other species of ostracoda were shown to be affected by environmental conditions. The toxicity of some heavy metals in the saltpans, salt lakes, and hypersaline lagoons was evaluated. Lake Dalyan and Erikli Saltpan display high toxicity for Cu and Cd levels. The distribution of hydrocarbon pollution of terrestrial origin was determined.     

Increases in lake phytoplankton biomass caused by future climate‐driven changes to seasonal river flow

For the many lakes world‐wide with short residence times, changes to the rate of water throughput may have important effects on lake ecology. We studied relationships between current and predicted residence times and phytoplankton biomass using a eutrophic lake in the north‐west of England with an annual residence time averaging about 20 days, as a test case. Using 32 years of recent hydrological flow data for Bassenthwaite Lake, multiple sets of scaled flow for each year, and the process‐based phytoplankton response model, PROTECH, we modelled the effects of changing river flow on phytoplankton biomass in the lake. The impact on biomass was shown to depend on seasonal changes in flow rather than annual changes. Furthermore, there was a qualitative difference in impact depending on whether the nutrient loading to the lake came principally from flow‐independent sources, or from flow‐dependent ones. Predictions for changes in river flow under future climate scenarios in the north‐west of England have suggested that, despite little change in the annual flow magnitude, there will be a shift to greater flow in the winter and lesser flow in the summer. Applying these flow predictions to our modelling of Bassenthwaite Lake revealed that, with flow‐independent nutrient loading, and no overall increase in nutrient load, phytoplankton abundance in the summer could increase by up to 70%, including an increased proportion of Cyanobacteria. Conversely, were the loading completely dependent on the flow, the biomass would fall. In many parts of the world, river flow is expected to decrease in the summer even more than in England, suggesting these areas may expect substantial changes to seasonal phytoplankton biomass as a result of climate‐driven changes to seasonal river flow. Such changes would be in addition to any other changes owing to warming effects or eutrophication.     

Lagoonal stormwater detention ponds as promoters of harmful algal blooms and eutrophication along the South Carolina coast

In the rapidly urbanizing coastal zone of South Carolina, intensive landscape maintenance and turf management are significant sources of nonpoint source pollutant loadings. The best management practice of choice for stormwater in this region is wet detention ponds, the majority of which are brackish lagoons. Typically, stormwater is piped directly into the ponds, but ponds have limited capacity for processing pollutants. These eutrophic brackish ponds are “hot spots” for harmful algal blooms (HABs)—over 200 blooms from 23 different species were documented over the last 4 years, many associated with measured toxins, fish kills or shellfish health problems. Because these ponds exchange with tidal creeks, they are potential sources for HAB dispersion into adjacent estuaries. Also, flux measurements indicated that groundwater was both a source of nutrients to the ponds and a mechanism for transporting nutrients from the ponds. These findings suggest that manmade ponds as presently designed along the SC coast may contribute to estuarine eutrophication and HAB prevalence. A summary of HAB occurrences in SC lagoonal ponds from 2001 to 2005 is presented, and a project is described that simulates the effectiveness of constructed wetlands as a supplementary best management practice designed to process stormwater and groundwater and remove nutrients prior to entering wet detention ponds.     

Factors affecting nitrogen loss in experimental wetlands with different hydrologic loads

Constructed or restored wetlands have great potential for reducing nonpoint source contamination of surface and ground waters by agricultural chemical contaminants. The work reported here combines field and experimental studies of factors affecting nitrogen loss in the Des Plaines River Experimental Wetlands, northeastern Illinois, USA. These wetlands receive approximately 5–36 cm/week of pumped river water with significant but seasonally variable loads of nitrate and organic nitrogen. On an annual basis, the wetlands removed 78–95% of the nitrate and 54–75% of the total nitrogen received. At the low hydrologic loading rate, organic nitrogen exports approximately equalled imports. However at the higher hydrologic loading rate, the wetlands exported 22–31% more organic nitrogen than received. Seasonal variation in nitrate and organic nitrogen loads had significant effects on the effectiveness of the wetlands as sinks for total nitrogen. The wetlands were nitrogen sinks during periods of the nitrate loading and nitrogen sources during periods of low nitrate loading. Experimental studies demonstrated the effects of nitrate concentration, temperature, and location on rates of nitrate loss. Results suggest that nitrite loading rates might influence not only nitrate loss rates but also loss rate coefficients.     

Wetlands as Sinks for Reactive Nitrogen at Continental and Global Scales: A Meta-Analysis

Wetlands support physical and ecological functions that result in valuable services to society, including removal of reactive nitrogen (Nr) from surface water and groundwater. We compiled published data from wetland studies worldwide to estimate total Nr removal and to evaluate factors that influence removal rates. Over several orders of magnitude in wetland area and Nr loading rates, there is a positive, near-linear relationship between Nr removal and Nr loading. The linear model (null hypothesis) explains the data better than either a model of declining Nr removal efficiency with increasing Nr loading, or a Michaelis–Menten (saturation) model. We estimate that total Nr removal by major classes of wetlands in the contiguous U.S. is approximately 20–21% of the total anthropogenic load of Nr to the region. Worldwide, Nr removal by wetlands is roughly 17% of anthropogenic Nr inputs. Historical loss of 50% of native wetland area suggests an equivalent loss of Nr removal capacity. Expanded protection and large-scale restoration of wetlands should be considered in strategies to re-balance the global nitrogen cycle and mitigate the negative consequences of excess Nr loading.