Stormwater Treatment Wetlands Research Articles

Evaluation of the impact of aquatic-animal excretion on nutrient recycling and retention in stormwater treatment wetlands

The relative contribution of aquatic animals to phosphorus (P) and nitrogen (N) cycles of water bodies can be substantial. Excretion rates can be affected by seasonal environmental conditions, physiology, and body size. Determining the importance of particular species or size classes to total fauna-driven internal recycling of nutrients requires measurements of seasonal mass-specific excretion rates (MSER). We used short-term incubation experiments to estimate the contribution of excretion and egestion by eight species of fish and one macroinvertebrate to water column P and N in Stormwater Treatment Areas (STAs) used to retain P from water flowing to the Everglades in Florida, U.S.A. To account for environmental conditions and fish physiology, excretion was estimated during day and night in the wet and dry seasons for nine of the most abundant fish and invertebrates found in the STAs. To yield measurable contributions of analytes in short-duration incubations, large-fish species were incubated individually, whereas small-fish species and invertebrates were incubated in single-species groups. For large-fish species, total excreted nutrients were positively correlated with the mass of individual fish, but MSER decreased with increased individual size. All four small species, three fish and invertebrate, excreted P and N at greater MSERs than all five large-fish species. Most MSERs were not correlated with incubated mass (stocked density) of small animals (80%), indicating that there were no density-dependent effects on excretion rates. Most species excreted more N and less P during the South Florida wet season (May to October) though this was not the case for one or more analytes for three of the large species. Most species excreted more during the day, except large herbivores that excreted more at night. Small species excreted higher proportions of particulate P and N, while the larger species had higher proportions of dissolved nutrients. Using measured MSERs and areal biomass estimates for the nine species, we estimated mass of P and N excreted annually. Based on known inflow P and N loads for four STAs, a preliminary and conservative estimate is that fish excretion can recycle between 50% to 92% of the annual total P entering the system and 15% to 29% of the annual total N entering the system. These preliminary results underestimate the actual amounts because they do not account for STA cells that were not sampled, nor known under-estimation of large-fish biomass, as well as other animal effects on nutrient cycles such as bioturbation. Though preliminary, our results suggest that altering aquatic animal abundance or species composition could improve the efficiency of STAs to remove and retain nutrients from inflowing waters.

Bibliometric Analysis and Comprehensive Review of Stormwater Treatment Wetlands: Global Research Trends and Existing Knowledge Gaps

Stormwater treatment wetlands are widely recognized as efficient and cost-effective solutions to growing stormwater problems. This study presented a new approach to evaluating the current status and trends in stormwater treatment wetlands research. The annual scientific productivity of different states was identified using a bibliometric analysis approach. The number of publications related to stormwater treatment wetlands has exhibited an increasing trend since the earliest record of publication. USA and China were among the states that had the most number of stormwater treatment wetlands-related publications and international collaborations. In terms of the population-to-publication ratio, Australia, Canada, and South Korea were found to have a higher level of scientific productivity. Analysis of frequently used keywords and terms in scientific publications revealed that the efficiency of stormwater treatment wetlands and the processes involved in the removal of nutrients and trace elements were adequately investigated; however, inquiries on the removal of organic micropollutants and emerging pollutants, such as pharmaceuticals and personal care products, microplastics, and industrial compounds, among others, are still lacking. Through the comprehensive review of related scientific works, the design, components, and primary factors affecting the performance of stormwater treatment wetlands were also identified. Future works that address the aforementioned knowledge gaps are recommended to optimize the benefits of stormwater treatment wetlands.

Typing Colonial Perceptions of Carrum Carrum Swamp: The Expected and the Surprising

Carrum Carrum Swamp was a vast wetland to the south-east of Melbourne, Victoria, Australia, at the time that it was first sighted by white colonists in 1803. By 1878, the colonists had commenced converting the swamp to dry land for agricultural and horticultural pursuits, and 100 years later it was predominantly residential land. Shifting values in the 1970s led to environmental concerns about water quality in local creeks and Port Phillip Bay and subsequent residential development on the former swamp included the construction of stormwater treatment wetlands. Perceptions of wetlands are now diverse, including positive perceptions that support their presence in urban settings. In contrast, traditionally, wetlands have been perceived negatively, as waste lands, leading to their drainage. Nevertheless, alternative, perhaps positive, perceptions could have existed, only to be overwhelmed by the negative perceptions driving drainage. Understanding the full range of past perceptions is important to ensure that the historical record is correct and to provide historical context to contemporary perceptions of wetlands. It will better equip natural resource managers and designers and managers of constructed wetlands in urban locations to ensure that wetlands are healthy, functioning and appreciated by their local and wider communities. Thus, the perceptions of Carrum Carrum Swamp by colonists from 1803 to 1878 were examined through qualitative content analysis of historical documents, and a typology was developed. Seven different perceptions were identified: scientific, premodern, exploitative, romantic, aesthetic, medico-mythic and ecological. Most could be traced to the colonists’ predominantly British heritage, but one perception arose in the colony in response to the specific environmental conditions that the colonists encountered. This ecological perception valued wetlands as places of predictable water supply in a land of unpredictable rainfall. It recognised wetlands as part of a broader hydrological system, with influences on the local climate. Its proponents promoted the need for a different approach to the management of wetlands than in Britain and Europe. Nevertheless, a dominant exploitative perception prevailed, leading to the drainage of Carrum Carrum Swamp. The typology developed in this study will be useful for exploring perceptions of other wetlands, both colonial and contemporary.

Mineralogy of particulate inputs and P-speciation and mineralogy of recently accreted soils within Everglades stormwater treatment wetlands

Phosphorus (P) biogeochemical processes in wetlands are influenced by the chemical composition of both recently accreted and native soils. The evaluation of biogeochemical processes influencing P transformations requires an understanding of the participating chemical components. Here, we use X-ray diffraction (XRD), scanning electron microscopy (SEM)/energy-dispersive X-ray fluorescence spectroscopy (EDS), X-ray absorption near-edge P spectroscopy (P-XANES), and microprobe X-ray fluorescence (μ-XRF) to examine the mineralogy and P speciation of solid phases entering and within selected Everglades Stormwater Treatment Areas (STAs). Suspended particulates in the source waters (upstream of the STAs) to the STAs were examined and compared with those of recently-accreted soil (RAS) from inflow, mid-flow, and outflow locations of two flowways (FWs) within STA-2: one dominated by emergent aquatic vegetation (EAV) and the other dominated by submerged aquatic vegetation (SAV). Source water particulates included carbonates and silicates, whereas mineralogies of STA RAS were less diverse, dominated by CaCO3 and having a lower silicate content, suggesting a strong autochthonous influence on STA RAS composition. No P minerals were detected via XRD. Discrete CaP particles were evident, though uncommonly observed, in two of three STA RAS samples analyzed via SEM/EDS. P-XANES of STA RAS indicated the presence of apatitic minerals. The potential presence of apatitic minerals was supported by μ-XRF correlation analysis that revealed strong correlations of P with both Ca and K. Apatitic minerals are a relatively refractory form of P and their presence in the RAS of both EAV and SAV systems indicate that remobilization and release of this P from the STAs will have a smaller effect on the downstream oligotrophic conditions of the Florida Everglades than more labile forms of P.

Role of emergent and submerged vegetation and algal communities on nutrient retention and management in a subtropical urban stormwater treatment wetland

A 4.6-ha urban stormwater treatment wetland complex in southwest Florida has been investigated for several years to understand its nutrient retention dynamics. This study investigates the role of aquatic vegetation, both submerged vegetation (such as benthic macrophytic and algal communities) and emergent plant communities, on changes in nutrient fluxes through the wetlands. Gross and net primary productivity of water column communities and net primary productivity of emergent macrophytes were used to estimate nutrient fluxes through vegetation in these wetlands using biannual biomass, nutrient concentrations of plant material, and areal coverage data. Emergent macrophyte net primary productivity was estimated as the difference between the increase of productivity during the wet season and the loss during the dry season which, in turn, suggested approximately 0.11g-N m− 2 y− 1 and 0.09g-P m− 2 yr− 2 being removed, primarily from the soil, by emergent vegetation. Water column primary productivity accounted for a much larger flux of nutrients with approximately 39.6g-N m− 2 yr− 1 and 2.4g-P m− 2 yr− 1 retained in algal communities. These fluxes, combined with measurements in parallel studies, allowed us to develop preliminary nutrient budgets for these wetlands and identify gaps, or missing fluxes, in our models for these wetlands. The results further validated previous findings that suggested that there are large inputs of nitrogen (up to 62.3g-N m− 2 yr− 1) that are not accounted for by the pumped inflow. Additionally, management suggestions are provided to improve water quality by identifying vegetative species that are most effective at retaining nutrients.

Internal phosphorus loading rate (iPLR) in a low-P stormwater treatment wetland

Low-phosphorus (P) wetland discharges (e.g., < 20 μg/L), such as those now commonly observed in Stormwater Treatment Areas (STAs) for Everglades restoration, are likely influenced by internal P loads. This study estimated for the first time the “aggregated” internal P loading rate (iPLR) (including soil and biotic vectors) in a low-P treatment wetland along with calculated vertical soil diffusive fluxes. In situ mesocosms (1.5-m diameter polyethylene cylinders) equipped with closeable windows were deployed at three locations in an STA, enclosing parcels of local vegetation and soil. The mesocosms isolated the water column P response from longitudinal P transport (flow) so the local soil-water-biota P dynamics and equilibria could be observed during no-flow conditions. The water column inside and outside the mesocosms was sampled at each location during three two-week no-flow batch incubations. A first-order model was calibrated to mesocosm batch reaction time series to estimate the iPLR (with uncertainty) at each study site. Soil diffusive flux rates were estimated from vertical porewater P concentration profiles measured at each site. Results showed that: 1) strong gradients in water column equilibrium P concentrations existed along the direction of flow (92–20 μg/L from inflow to outflow), 2) a corresponding gradient also existed for model-predicted iPLR (~6.6 to 1.9 mg/m2-d), 3) these aggregated internal loads were more than 20× greater than calculated soil diffusive fluxes, and 4) an annual extrapolation suggested that average iPLR could be approximately equivalent to the average annual inflow P loading rate to the wetland (1.3 g/m2-yr). This study demonstrates that aggregated internal P loading can greatly exceed more commonly estimated vertical soil diffusive fluxes in low-P wetlands and can be a substantial contributor to water column P concentrations. Furthermore, measuring and modeling water P equilibria during no-flow intervals was a useful method to estimate internal loading in these wetlands.

Nutrient retention via sedimentation in a created urban stormwater treatment wetland

Nutrient removal by a 4.6-ha urban stormwater treatment wetland system in a 20-ha water/nature park in southwest Florida has been investigated for several years, suggesting that the wetlands are significant sinks of both phosphorus and nitrogen although with a slightly decreased total phosphorus retention in recent years. This study investigates the role of sedimentation on changes in nutrient concentrations and fluxes through these wetlands. Sedimentation bottles along with sediment nutrient analyses every six months allowed us to estimate gross sedimentation rates of 9.9 ± 0.1 cm yr−1 and nutrient sedimentation rates of approximately 7.8 g-P m−2 yr−1 and 81.7 g-N m−2 yr−1. Using a horizon marker method to account for lack of resuspension in the sedimentation bottles suggested that net nutrient retention by sedimentation may be closer to 1.5 g-P m−2 yr−1 and 33.2 g-N m−2 yr−1. Annual nutrient retention of the wetland system determined from water quality measurements at the inflow and outflow averaged 4.23 g-P m−2 yr−1 and 11.91 g-N m–2 yr−1, suggesting that sedimentation is a significant pathway for nutrient retention in these urban wetlands and that resuspension is playing a significant role in reintroducing nutrients, especially phosphorus, to the water column. These results also suggest that additional sources of nitrogen not in our current nutrient budgets may be affecting overall nutrient retention.

Microplastic pollution in a stormwater floating treatment wetland: Detection of tyre particles in sediment

Synthetic rubber particles released from car tyres are expected to be an important type of microplastics in the environment, with road runoff and stormwater likely to transport tyre particles to the aquatic environment. Stormwater treatment wetlands are one of the key methods for treating road runoff and stormwater, but the presence and concentration of synthetic rubber microplastics from tyre particles in wetlands are largely unknown. In addition, constructed floating wetlands can be built using recycled PET plastic bottles, raising concerns about potential release of microplastics to the environment. In this study, we measured the concentrations of microplastics in water and sediment from the inlet and outlet of a stormwater floating treatment wetland on Queensland's Gold Coast. An average of 0.9 ± 0.3 and 4.0 ± 2.4 microplastic particles/L were detected in the water phase in the inlet and outlet samples, respectively. The sediment contained an average of 595 ± 120 and 320 ± 42 microplastic particles/kg dry sediment in inlet and outlet sediments, respectively. Between 15 and 38% of microplastics in the sediment were identified by FTIR as synthetic rubber-carbon filled particles, most likely derived from car tyres. The presence of synthetic rubber microplastics confirms that tyres can contribute to microplastic pollution in stormwater, with road runoff likely to be an important pathway. No microplastics with the same characteristics and polymer composition as the floating wetland construction material were detected in the water and sediment samples, indicating that the microplastics in the water and sediment detected here did not originate from the floating wetland's material. However, further investigation of older treatment wetlands is required to better understand the potential role of floating treatment wetlands as a source of microplastics.

Balancing biodiversity outcomes and pollution management in urban stormwater treatment wetlands

Wetlands are increasingly being constructed to mitigate the effects of urban stormwater, such as altered hydrological regimes and reduced water quality, on downstream aquatic ecosystems. While the primary purpose of these wetlands is to manage stormwater, they also attract animals whose growth, survival and breeding (i.e. ‘fitness’) may be compromised. Such deleterious effects will be exacerbated if animals are caught in ‘ecological traps’, mistakenly preferring wetlands with unsuitable environmental conditions. Alternatively, wetlands that offer suitable habitat conditions for animals could be beneficial, especially in fragmented urban landscapes. Consequently, a thorough understanding of the potential ecological impacts of stormwater treatment wetlands is critical for managing unintended consequences to urban biodiversity.To help facilitate this understanding, we draw upon findings from a four-year research program conducted in the city of Melbourne in south-eastern Australia as a case study. First, we summarise our research demonstrating that some stormwater wetlands can be ecological traps for native frogs and fish in the study region, whilst others likely provide important habitat in areas where few natural waterbodies remain. We use our work to highlight that while stormwater wetlands can be ecological traps, their effects can be properly managed. We propose the need for a better understanding of the ecological consequences of changes to wetland quality and their population-level impacts across the landscape. We hope that this study will generate discussions about how to most effectively manage constructed wetlands in urban landscapes and more research for a better understanding of the issues and opportunities regarding potential ecological traps.

Using conservation behavior to manage ecological traps for a threatened freshwater fish

AbstractUrban stormwater treatment wetlands are constructed to treat stormwater runoff before it enters waterways, but are often inhabited by animals that can suffer impairments. Such effects will be exacerbated if animals mistakenly prefer sites where their fitness is reduced, and are caught in ecological traps. Traps can compromise the persistence of threatened species in urban landscapes, so assessing how animals respond to stormwater wetlands, and whether their fitness varies between stormwater and natural wetlands, can guide management efforts. We examined the habitat selection behavior of dwarf galaxias (Galaxiella pusilla), a threatened freshwater fish inhabiting wetlands and streams around Melbourne, Australia. We tested whether fish respond to cues that could indicate habitat quality, and whether they can differentiate between water from stormwater and non‐stormwater wetlands. We also tested whether fitness (e.g., survival, development) was lower at stormwater wetlands. Fish responded weakly to cues and did not avoid stormwater wetlands. Survival was lower at stormwater wetlands, and fish suffered delayed ovarian maturation, potentially due to a lack of food. Thus, stormwater wetlands can be equal‐preference ecological traps for G. pusilla, a key finding with direct implications for conservation. For highly dispersive species that are not selective about habitats, managing ecological traps requires a whole‐of‐landscape approach, with consideration given to where wetlands are constructed. Given the investment required to remediate existing ecological traps, this approach can also identify priority wetlands for intervention. We discuss our results in the context of how insights from animal behavior can inform threatened species conservation in fragmented urban landscapes.

Hurricane and seasonal effects on hydrology and water quality of a subtropical urban stormwater wetland

Understanding the hydrology of a created or restored wetland is a critical component in understanding the overall functioning of its design, and in determining if the original goals of the wetland are being met. Freedom Park, a 20-ha park constructed in Naples, Florida in 2009, includes a 4.6-ha subtropical stormwater wetland treatment system for improving the water quality of the downstream impaired Gordon River and estuaries that flow into the Gulf of Mexico. Subtropical wetlands often present significant issues of sustaining viable wetland vegetation communities because of long wet and then long dry patterns in the wetlands’ hydroperiods. The treatment wetland’s watershed includes 1766 ha of an urbanized Naples metro area. The goals of the stormwater wetlands are to improve the water quality, reduce peak flows discharging into Gordon River and further to Naples Bay, and provide an aesthetic water park for the public. A monthly hydrologic budget for the period August 1, 2016 to January 31, 2018 showed the following averages: pumped surface water inflow of 50.1 cm week−1; average surface outflow of 38.8 cm week−1; precipitation of 3.76 cm week−1, potential evapotranspiration (PET) of 5.34 cm week−1; and estimated seepage of 14.8 cm week−1. During the wet season, water pathways are largely influenced by pumped surface inflow and surface outflow, balanced to not produce significant changes in water level from month to month. Groundwater seepage and evapotranspiration are the most important outflows during the dry season. A stormwater pulsing study during Hurricane Irma (September 10, 2017) showed that after an initial inflow flush due primarily to rainfall, total phosphorus and total nitrogen concentrations were higher at the outflow than at the inflow for several days during and immediately after the hurricane. Similarly, the mass of nutrients leaving the system was 130% and 37% higher for TN and TP, respectively, than the mass entering the system during this 6-day period during and immediately after the hurricane. Ironically, the design of the pump-only inflow did not allow for major urban runoff during the hurricane to enter the wetlands. Samples taken at the inflow and outflow of the system for four other storm events throughout the 2017 wet season (July through October) were also analyzed for their effects on water quality. While total phosphorus removal during and after storm events is comparable to normal conditions at the Freedom Park wetlands and other stormwater treatment wetlands in the world, total nitrogen removal decreased during and after storm events.

Stormwater wetlands can function as ecological traps for urban frogs.

Around cities, natural wetlands are rapidly being destroyed and replaced with wetlands constructed to treat stormwater. Although the intended purpose of these wetlands is to manage urban stormwater, they are inhabited by wildlife that might be exposed to contaminants. These effects will be exacerbated if animals are unable to differentiate between stormwater treatment wetlands of varying quality and some function as "ecological traps" (i.e., habitats that animals prefer despite fitness being lower than in other habitats). To examine if urban stormwater wetlands can be ecological traps for frogs, we tested if survival, metamorphosis-related measures, and predator avoidance behaviors of frogs differed within mesocosms that simulated stormwater wetlands with different contaminant levels, and paired this with a natural oviposition experiment to assess breeding-site preferences. We provide the first empirical evidence that these wetlands can function as ecological traps for frogs. Tadpoles had lower survival and were less responsive to predator olfactory cues when raised in more polluted stormwater wetlands, but also reached metamorphosis earlier and at a larger size. A greater size at metamorphosis was likely a result of increased per capita food availability due to higher mortality combined with eutrophication, although other compensatory effects such as selective-mortality removing smaller individuals from low-quality mesocosms may also explain these results. Breeding adults laid comparable numbers of eggs across wetlands with high and low contaminant levels, indicating no avoidance of the former. Since stormwater treatment wetlands are often the only available aquatic habitat in urban landscapes we need to better understand how they perform as habitats to guide management decisions that mitigate their potential ecological costs. This may include improving wetland quality so that fitness is no longer compromised, preventing colonization by animals, altering the cues animals use when selecting habitats, pretreating contaminated water prior to release, providing off-line wetlands nearby, or simply not constructing stormwater treatment wetlands in sensitive areas. Our study confirms the potential for urban stormwater treatment wetlands to function as ecological traps and highlights the need for greater awareness of their prevalence and impact at landscape scales.

Island topographies to reduce short-circuiting in stormwater detention ponds and treatment wetlands

Urban stormwater is an increasing environmental problem for cities worldwide. Many cities have turned to green infrastructure solutions, which provide water treatment and retention while also harnessing other ecosystem services. This study considered the design of detention ponds and treatment wetlands with the goal of improving hydraulic performance (specifically reducing short-circuiting) while also increasing habitat diversity. Fifty-four basin topographies, including a variety of islands and berms, were compared to an open and a traditional serpentine basin. Using scaled physical models the hydraulic performance of each design was evaluated using tracer studies to construct the residence time distribution and to visually observe the circulation pattern. In addition, the earthwork construction cost and habitat diversity index (based on the Shannon-Weaver entropy measure) were estimated at field scale. The results reveal multiple design options that improve hydraulic performance, relative to both the open and serpentine basins, and which represent a range of habit diversity and cost. General guidelines for optimal configurations are discussed.

Identifying critical inundation thresholds to maintain vegetation cover in stormwater treatment wetlands

Vegetation cover, specifically emergent macrophyte cover, is critical to the performance of constructed stormwater treatment wetlands which are widely used to protect receiving waterways. Maintenance of vegetation relies on a suitable water level regime, which in turn is governed by the hydraulic loading rate and efficiency of the outlet control structure. Wetland designers need to take these factors into account to avoid excessive depth and duration of inundation. We investigated the relationship between the water level regime and vegetation cover in 19 stormwater wetlands. We found a strong relationship between the median water level and vegetation cover, where vegetation cover was generally high (>80%) at median depths <0.35 m. Interestingly, poor outlet efficiency, rather than the hydraulic loading rate, was driving the water level regime. While this again highlights the importance of appropriate design and maintenance, we suggest that adjustable outlets in combination with real-time water level monitoring should be used to maintain a suitable water level regime in stormwater wetlands fed by dynamic urban catchments. The results of the study provide firm evidence for threshold depths for emergent macrophytes in stormwater wetlands which can be used to inform design guidelines.

NUTRIENT REMOVAL IN A WET DETENTION POND WITH BAFFLE DIKE - A CASE STUDY OF THE CEDAR RIVER PROJECT

The City of Jacksonville, Florida USA is in the midst of an important program to reduce nutrient load from its municipal storm water system. New regulations promulgated by the US EPA and State of Florida have targeted nutrient reduction within the St. Johns River watershed which includes most of the City of Jacksonville. In order to reduce overall nutrient loads to the St. Johns River, the City of Jacksonville and its consultant team have begun a construction program to build a series of wet detention storm water reservoirs designed to attenuate storm runoff and reduce nutrient discharge. One such facility lies within the Cedar River watershed which is connected downstream to the St. Johns River. This paper describes the layout of the facility and its nutrient removal performance over a period of more than one year. The storage and treatment facility is unique in its design since it includes a longitudinal baffle dike designed to extend the flow path and increase the overall residence time of the facility. The actual nutrient removal performance of the specially-designed facility greatly exceeded its design goals and outperformed other typical wet detention facilities in Florida as well as many storm water treatment wetlands. Overall, the pond removed approximately 31% of total nitrogen, 59% of total phosphorus, and 83% of total suspended solids during the study period.

Accretion of Nutrients and Sediment by a Constructed Stormwater Treatment Wetland in the Lake Tahoe Basin

AbstractThis unique study evaluates the cumulative 16‐year lifetime performance of a wetland retention basin designed to treat stormwater runoff. Sediment cores were extracted prior to basin excavation and restoration to evaluate accretion rates and the origin of materials, retention characteristics of fine particulate matter, and overall pollutant removal efficiency. The sediment and organic layers together accreted 3.2 cm of depth per year, and 7.0 kg/m2/yr of inorganic material. Average annual accretion rates in g/m2/yr were as follows: C, 280; N, 17.7; P, 3.74; S, 3.80; Fe, 194; Mn, 2.68; Ca, 30.8; Mg, 30.7; K, 12.2; Na, 2.54; Zn, 0.858; Cu, 0.203; and B, 0.03. The accretion of C, N, P and sediment was comparable to nonwastewater treatment wetlands, overall, and relatively efficient for stormwater treatment wetlands. Comparison of particle size distribution between sediment cores and suspended solids in stormwater runoff indicated the wetland was effective at removing fine particles, with sediment cores containing 25% clay and 56% silt. A majority of the accretion of most metals and P could be attributed to efficient trapping of allochthonous material, while over half the accretion of C and N could be attributed to accumulation of autochthonous organic matter. Stormwater treatment was shown to be effective when physical properties of a retention basin are combined with the biological processes of a wetland, although sediment accretion can be relatively rapid.

Ecological Analysis Before and After Planting in a Constructed Wetland in the Adirondacks

The assessment of constructed treatment wetland success usually relies on abiotic measures, such as nutrient level reduction. Because constructed wetlands eventually function as whole ecosystems, and their biotic components play a role in water treatment, it is important to consider the development of associated flora and fauna when conducting site assessments. The goal of this two-year case study was to observe ecosystem establishment at a constructed stormwater treatment wetland adjacent to Lake George in the Adirondack Mountains of New York, with a focus on macroinvertebrate and vegetation community development. The first year of the study occurred during a period of natural succession. The second year occurred following the artificial introduction of 85 plant species. The vegetation community predictably improved in richness, evenness, and diversity. The macroinvertebrate community experienced substantial shifts in dominant taxa. Importantly, each pond in the wetland’s treatment train developed unique profiles over time as defined by their vegetation and macroinvertebrate communities, as well as by their water chemistry. While the specific biotic and abiotic drivers creating these unique ponds have not been identified, the disparate profiles and how they function together will determine stormwater treatment efficiency after further site maturation.

Environmental monitoring of selected pesticides and organic chemicals in urban stormwater recycling systems using passive sampling techniques

Water recycling via aquifers has become a valuable tool to augment urban water supplies in many countries. This study reports the first use of passive samplers for monitoring of organic micropollutants in Managed Aquifer Recharge (MAR). Five different configurations of passive samplers were deployed in a stormwater treatment wetland, groundwater monitoring wells and a recovery tank to capture a range of polar and non-polar micropollutants present in the system. The passive samplers were analysed for a suite of pesticides, polycyclic aromatic hydrocarbons (PAHs) and other chemicals. As a result, 17 pesticides and pesticide degradation products, 5 PAHs and 8 other organic chemicals including flame retardants and fragrances were detected in urban stormwater recharging Aquifer Storage and Recovery (ASR) and an Aquifer Storage Transfer and Recovery (ASTR) system. Of the pesticides detected, diuron, metolachlor and chlorpyrifos were generally detected at the highest concentrations in one or more passive samplers, whereas chlorpyrifos, diuron, metolachlor, simazine, galaxolide and triallate were detected in multiple samplers. Fluorene was the PAH detected at the highest concentration and the flame retardant Tris(1-chloro-2-propyl)phosphate was the chemical detected in the greatest abundance at all sites. The passive samplers showed different efficiencies for capture of micropollutants with the Empore disc samplers giving the most reliable results. The results indicate generally low levels of organic micropollutants in the stormwater, as the contaminants detected were present at very low ng/L levels, generally two to four orders of magnitude below the drinking water guidelines (NHMRC, 2011). The efficiency of attenuation of these organic micropollutants during MAR was difficult to determine due to variations in the source water concentrations. Comparisons were made between different samplers, to give a field-based calibration where existing lab-based calibrations were unavailable.

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.

Effects of hydraulic resistance by vegetation on stage dynamics of a stormwater treatment wetland

Summary This work examined the potential effects of large-scale thinning of emergent vegetation on the stage dynamics in a very large (33.3 km2) constructed treatment wetland in South Florida. Dense vegetative biomass in treatment wetlands may restrict water flow and increase water levels, which may in turn have adverse effects on vegetative community structure. Here, we developed a physically-based, spatially-distributed hydrodynamic model of Stormwater Treatment Area 2, Cell 2 (STA2C2) to investigate the spatio-temporal variability of water level (stage) in response to management for thinning of emergent macrophytes (e.g., burning and/or herbicide treatments). The model was calibrated against stage measured at six monitoring stations for 1 year, and subsequently validated against 2 years of stage data from eight stations. Finally, the validated model was extended to simulate various vegetation management scenarios. The model provided an excellent fit to observed stage data in both calibration and validation periods (median model efficiency indices of 0.82 and 0.83, respectively). Higher stages in the treatment cell were dominantly associated with peak inflow magnitude and the timing of event intervals. Prolonged periods of sustained deep water conditions were observed when one flow peak was followed by consecutive peaks. A gradual stage gradient from the inlet to outlet was observed during peak flow periods, with a shift to a sharp gradient at approximately two-thirds distance from the inlet. Stages in the wetland were found to be controlled less by the hydraulic resistance, as indicated by a low sensitivity of simulated water levels for a ±50% perturbation in flow resistance parameter. Water depths were reduced by a maximum of 12 cm at the inlet region by thoroughly thinning the remaining emergent vegetation in STA2C2. Similarly, a maximum of only 2% of the total STA2C2 area was prevented from exceeding a water depth believed to be detrimental to Typha sp. (1.22 m) after the highest peak inflow. Collectively, our findings suggested that vegetation thinning may not be effective for minimizing deep water conditions in STA2C2.