Ecosystem service provision by stormwater wetlands and ponds - a means for evaluation?

Habitat complexity, connectivity, and introduced fish drive pond community structure along an urban to rural gradient

Urbanization can influence local richness (alpha diversity) and community composition (beta diversity) in numerous ways. For instance, reduced connectivity and land cover change may lead to the loss of native specialist taxa, decreasing alpha diversity. Alternatively, if urbanization facilitates nonnative species introductions and generalist taxa, alpha diversity may remain unchanged or increase, while beta diversity could decline due to the homogenization of community structure. Wetlands and ponds provide critical ecosystem services and support diverse communities, making them important systems in which to understand the consequences of urbanization. To determine how urban development shapes pond community structure, we surveyed 68 ponds around Madison, Wisconsin, USA, which were classified as urban, greenspace, or rural based on surrounding land use. We evaluated how landscape and local pond factors were correlated with the alpha diversity of aquatic plants, macroinvertebrates, and aquatic vertebrates. We also analyzed whether surrounding land use was associated with changes in community composition and the presence of specific taxa. We found a 23% decrease in mean richness (alpha diversity) from rural to urban pond sites and a 15% decrease from rural to greenspace pond sites. Among landscape factors, adjacent developed land, mowed lawn cover, and greater distances to other waterbodies were negatively correlated with observed pond richness. Among pond level factors, habitat complexity was associated with increased richness, while nonnative fishes were associated with decreased richness. Beta diversity was relatively high for all ponds due to turnover in composition between sites. Urban ponds supported more nonnative species, lacked a subset of native species found in rural ponds, and had slightly higher beta diversity than greenspace and rural ponds. Our results suggest that integrating ponds into connected greenspaces, maintaining riparian vegetation, preventing nonnative fish introductions, and promoting habitat complexity may mitigate the negative effects of urbanization on aquatic richness. While ponds are small in size and rarely incorporated into urban conservation planning, the high beta diversity of distinct pond communities emphasizes their importance for supporting urban biodiversity.

Tradeoffs and synergies in wetland multifunctionality: A scaling issue

Wetland area in agricultural landscapes has been heavily reduced to gain land for crop production, but in recent years there is increased societal recognition of the negative consequences from wetland loss on nutrient retention, biodiversity and a range of other benefits to humans. The current trend is therefore to re-establish wetlands, often with an aim to achieve the simultaneous delivery of multiple ecosystem services, i.e., multifunctionality. Here we review the literature on key objectives used to motivate wetland re-establishment in temperate agricultural landscapes (provision of flow regulation, nutrient retention, climate mitigation, biodiversity conservation and cultural ecosystem services), and their relationships to environmental properties, in order to identify potential for tradeoffs and synergies concerning the development of multifunctional wetlands. Through this process, we find that there is a need for a change in scale from a focus on single wetlands to wetlandscapes (multiple neighboring wetlands including their catchments and surrounding landscape features) if multiple societal and environmental goals are to be achieved. Finally, we discuss the key factors to be considered when planning for re-establishment of wetlands that can support achievement of a wide range of objectives at the landscape scale.

Knowledge Atlas on the Relationship between Water Management and Constructed Wetlands—A Bibliometric Analysis Based on CiteSpace

Water management is a crucial resource conservation challenge that mankind faces, and encouraging the creation of manmade wetlands with the goal of achieving long-term water management is the key to long-term urban development. To summarise and analyse the status of the research on the relationship between water management and constructed wetlands, this paper makes use of the advantages of the bibliometric visualization of CiteSpace to generate country/region maps and author-collaboration maps, and to analyse research hotspots and research dynamics by using keywords and literature co-citations based on 1248 pieces of related literature in the core collection in the Web of Science (WoS) database. The existing research shows that the research content and methods in the field of constructed-wetland and water-management research are constantly being enriched and deepened, including the research methods frequently used in constructed wetlands in water management and in the research content under concern, the functions and roles of constructed wetlands, the relevant measurement indicators of the purification impact of constructed wetlands on water bodies, and the types of water bodies treated by constructed wetlands in water management. We summarise the impact pathways of constructed wetlands on water management, as well as the impact factors of constructed wetlands under water-management objectives, by analysing the future concerns in the research field to provide references for research.

Hydrologic processes regulate nutrient retention in stormwater detention ponds

Managed stormwater ponds are abundant in urban landscapes in much of the world, performing vital but under-studied functions for attenuation of urban runoff and nutrient pollution. Water quality improvements are widely assumed to arise from settling of nutrients and other contaminants bound to particulates, with less consideration of hydrological and biogeochemical processes. To inform improved management of ponds for nutrient retention, we studied three mature urban detention ponds in the Twin Cities, MN, USA using continuous monitoring of pond hydrology and concentrations of nitrogen and phosphorus, coupled with periodic measurement of physiochemical conditions in the ponds. Across the three sites, annual nutrient retention was high for both nitrogen (>58%) and phosphorus (>48%) despite expectations of poor performance for phosphorus due to old age and internal loading linked to hypolimnetic anoxia. Both annual and event-scale analyses suggested strong hydrologic controls on nutrient retention, with retention for individual storm events strongly regulated by antecedent pond storage capacity. Events with net nutrient export occurred primarily due to low volume retention rather than relatively high outflow concentrations. Together these results suggest that understanding and improving pond hydrologic function is crucial to improving managed stormwater pond performance for meeting downstream water quality goals.

Wetland Construction, Restoration, and Integration: A Comparative Review

In response to the global loss and degradation of wetland ecosystems, extensive efforts have been made to reestablish wetland habitat and function in landscapes where they once existed. The reintroduction of wetland ecosystem services has largely occurred in two categories: constructed wetlands (CW) for wastewater treatment, and restored wetlands (RW) for the renewal or creation of multiple ecosystem services. This is the first review to compare the objectives, design, performance, and management of CW and RW, and to assess the status of efforts to combine CW and RW as Integrated Constructed Wetlands (ICW). These wetland systems are assessed for their ecological attributes and their relative contribution to ecosystem services. CW are designed to process a wide variety of wastewaters using surface, subsurface, or hybrid treatment systems. Designed and maintained within narrow hydrologic parameters, CW can be highly effective at contaminant transformation, remediation, and sequestration. The ecosystem services provided by CW are limited by their status as high-stress, successionally arrested systems with low landscape connectivity and an effective lifespan. RW are typically situated and designed for a greater degree of connection with regional ecosystems. After construction, revegetation, and early successional management, RW are intended as self-maintaining ecosystems. This affords RW a broader range of ecosystem services than CW, though RW system performance can be highly variable and subject to invasive species and landscape-level stressors. Where the spatial and biogeochemical contexts are favorable, ICW present the opportunity to couple CW and RW functions, thereby enhancing the replacement of wetland services on the landscape.

Effects of two submerged macrophyte species on microbes and metazoans in rooftop water-storage ponds with different labile carbon loadings

Nature-based solutions including rooftop-water storage ponds are increasingly adopted in cities as new eco-designs to address climate change issues, such as water scarcity and storm-water runoff. Macrophytes may be valuable additions for treating stored rooftop waters and provisioning other services, including aquaponics, esthetic and wildlife-conservation values. However, the efficacy of macrophyte treatments has not been tested with influxes of different labile carbon loadings such as those occurring in storms. Moreover, little is known about how macrophytes affect communities of metazoans and microbes, including protozoans, which are key players in the water-treatment process. Here, we experimentally investigated the effectiveness of two widely distributed macrophytes, Ceratophyllum demersum and Egeria densa, for treating drained rooftop water fed with two types of leaf litter, namely Quercus robur (high C lability) and Quercus rubra (low C lability). C. demersum was better than E. densa at reducing water conductivity (by 10 ̶ 40 µS/cm), TDS (by 10-18 mg/L), DOC (by 4-5 mg/L) and at increasing water transparency (by 4-9%), water O₂ levels (by 19-27%) and daylight pH (by 0.9-1.3) compared to leaf-litter only microcosms after 30 days. Each treatment developed a different community of algae, protozoa and metazoa. Greater plant mass and epiphytic chlorophyll-a suggested that C. demersum was better at providing supporting habitat than E. densa. The two macrophytes did not differ in detritus accumulation, but E. densa was more prone to develop filamentous bacteria, which cause sludge bulking in water-treatment systems. Our study highlights the superior capacity of C. demersum and the usefulness of whole-ecosystem experiments in choosing the most adequate macrophyte species for nature-based engineered solutions.

Variability of Potential Soil Nitrogen Cycling Rates in Stormwater Bioretention Facilities

Low-impact development (LID) is a common management practice used to infiltrate and filter stormwater through vegetated soil systems. The pollutant reduction potential of these systems is often characterized by a single pollutant removal rate; however, the biophysical properties of soils that regulate the removal of pollutants can be highly variable depending on environmental conditions. The goal of this study was to characterize the variability of soil properties and nitrogen (N) cycling rates in bioretention facilities (BRFs). Soil properties and potential N cycling processes were measured in nine curbside bioretention facilities (BRFs) in Portland, OR during summer and winter seasons, and a subset of six sites was sampled seasonally for two consecutive years to further assess temporal variability in soil N cycling. Potential N cycling rates varied markedly across sites, seasons, and years, and higher variability in N cycling rates was observed among sites with high infiltration rates. The observed seasonal and annual changes in soil parameters suggest that nutrient removal processes in BRFs may be highly variable across sites in an urban landscape. This variability has important implications for predicting the impacts of LID on water quality through time, particularly when estimated removal rates are used as a metric to assess compliance with water quality standards that are implemented to protect downstream ecosystems.

Valuing stakeholder preferences for environmental benefits of stormwater ponds: Evidence from choice experiment

With population growth driving urban expansion in many cities in the United States, there is a need for a sustainable way to manage stormwater. Green stormwater infrastructure (GSI) is considered an innovative way to handle stormwater because of its potential to provide multiple ecosystem services (ES) beyond flooding reduction. However, there is limited research regarding the society's perceived value for GSI practices' co-benefits. This study utilized stated-preference data obtained from a choice experiment in an online survey of 1159 South Carolina (SC) residents to estimate a monetary value for the ES provided by wet detention ponds- the most widely adopted stormwater practice in coastal counties of SC. The benefits examined are flooding reduction, water quality, wildlife habitat, recreation, and scenic beauty. The data were analyzed using a Mixed logit formulation. Considering the differences across the state, the model was estimated separately for five counties. Findings indicate that residents are willing to pay $13.8 to $37.8 annually for a 50% improvement in pollutant removal efficiency of ponds in addition to their current stormwater fee. Also, they are willing to pay $12.5 to $42.9 per year for the nearest pond to have buffer vegetation and wildlife. They are also likely to pay $5 to $22.5 for ponds to contribute to their neighborhood's scenic beauty. Furthermore, the results indicate that respondents from three counties are willing to pay $5.4 to $13.2 for a 50% improvement in flooding reduction, while those from two counties are likely to pay $3.9 to $4.9 for ponds to have recreational benefits. The findings of the study could help stormwater managers in designing their stormwater management programs, especially for better evaluation of stormwater utility fees.

Evaluation of measured dissolved and bio-met predicted bioavailable Cu, Ni and Zn concentrations in runoff from three urban catchments

Urban runoff is a diffuse source of pollution contributing to the poor ecological and chemical status of surface waters. Whilst the EU Priority Hazardous Substances Directive now identifies environmental quality standards for selected metals in relation to the bioavailable metal fraction the relationship between analytically determined metal size fractions transported by urban runoff and the often variably defined concept of bioavailability has not been thoroughly evaluated. This paper provides a review of the terminology used within urban runoff studies to characterise metal fractions and behaviour. Measured dissolved and truly dissolved (determined by ultrafiltration; <3000 molecular weight cutoff) Cu, Ni, and Zn concentrations are also compared to the bioavailable metal fraction (as predicted using Bio-met, a simplified biotic ligand model) in snowmelt and rainfall derived runoff samples from three urban catchments. The study shows that predicted bioavailable concentrations were significantly lower than truly dissolved concentrations for all metals and discusses current bioavailability modelling parameters in relation to rainfall and snowmelt runoff data sets. Statistical analysis of relationships between field and predicted bioavailable data sets indicate that the bioavailable fractions originate from both colloidal and truly dissolved fractions.

Spatial-Temporal Changes in Removal of Fecal Indicators and Diversity of Bacterial Communities in a Constructed Wetland with Ornamental Plants

The present study was undertaken in a constructed wetland (CW), setup in a tourism house, for domestic wastewater treatment. The influence of season variations on the abundance of fecal indicator organisms (total coliforms and Escherichia coli) in the wastewater and in the substrate and the roots of plants inhabiting the inlet and outlet zones of the CW was evaluated along three consecutive years. The structure and diversity of bacterial communities associated to the CW’s substrate of inlet and outlet zones was also analyzed overtime. Wastewater was characterized for physicochemical and microbiological parameters and the bacterial communities colonizing the substrate surface, were analyzed by Denaturing Gradient Gel Electrophoresis (DGGE). The CW was effective in removing COD, BOD5, TSS, PO43−, NH4+, NO3−, and NO2−. It was also effective in removing fecal indicators, with a generalized decrease of total coliforms and E. coli in the substrate and in the wastewater from inlet to outlet of up to 2–3 log. The structure and composition of bacterial communities associated with the substrate was mainly influenced by the year rather than by the season or the CW zone.

Ecological health and water quality of village ponds in the subtropics limiting their use for water supply and groundwater recharge

Ponds are a typical feature of many villages in the subtropics, and have been widely used as important sources of water for agriculture, aquaculture and groundwater recharge, as well as enhancing village resilience to floods and drought. Currently many village ponds are in a very poor state and in dire need of rejuvenation. This paper assesses the current water quality status and ecological health of twelve sub-tropical village ponds, situated in western Uttar Pradesh, India. This assessment is used to evaluate their wastewater treatment needs in relation to potential village uses of the water. Physico-chemical (Secchi depth, Total phosphorus and Total nitrogen) and biological (Phytoplankton chlorophyll-a) indicators highlight hypertrophic conditions in all the ponds. The study indicates that the status of village ponds requires significant investments in wastewater treatment to restore their use for many purposes, including aquaculture, although some may still be acceptable for irrigation purposes, as long as pathogenic bacteria are not abundant. We propose increased implementation of decentralised systems for wastewater treatment, such as septic tanks and constructed wetlands, to reduce the organic and nutrient loads entering village ponds and allow their use for a wider range of purposes.

Contribution of Irrigation Ponds to the Sustainability of Agriculture. A Review of Worldwide Research

The use of irrigation ponds has proved to be an efficient alternative for increasing the availability and quality of water resources for irrigation and contributing to the sustainability of agriculture. This article analyses the dynamics of worldwide research on this topic over the last two decades. To do this, a review including a qualitative systematic analysis and a quantitative bibliometric analysis was carried out on a sample of 951 articles. The results reveal that this line of research is becoming more relevant within agricultural research, particularly in recent years. The research in this topic has focused on the sustainable development of vulnerable regions, the contribution to the agronomic improvement of crops and farms, environmental impact assessment, the joint management of water resources, the restoration of groundwater bodies, and the use of rainfall. Gaps have been found in the literature with respect to the capacity of irrigation ponds to cover the irrigation needs in different agricultural contexts, the perceptions and attitudes of farmers towards the use of irrigation ponds, and the economic–financial feasibility of these systems.

Stormwater ponds: An overlooked but plentiful urban designer ecosystem provides invasive plant habitat in a subtropical region (Florida, USA)

Designed ecosystems are built as part of ongoing urban expansion, providing a suite of valued ecosystem services. However, these new ecosystems could also promote disservices by facilitating the colonization and spread of invasive species. We conduct the first assessment of the quantity and invasion of an overlooked designed ecosystem: stormwater ponds. These ponds are commonly recommended for managing urban hydrology, but little is known about their ecology or extent of proliferation. Using a broad-scale survey of pond coverage in Florida, USA, we found that over 76,000 stormwater ponds have been built just in this state, forming 2.7% of total urban land cover. This extensive pondscape of manufactured habitats could facilitate species spread throughout urban areas and into nearby natural waterbodies. We also conducted a survey of the severity of plant invasion in 30 ponds in Gainesville, FL, US across two pond types (dry vs. wet), and a gradient of management intensities (low, medium, high) and pond ages. We unexpectedly found a high number of invasive plant species (28 in just 30 ponds). Ninety-six percent of surveyed ponds contained from one to ten of these species, with ponds exhibiting high turnover in invader composition (i.e., high beta diversity). The bank sections of dry unmanaged ponds exhibited the highest mean invasive species richness (5.8 ± 1.3) and the inundated centers of wet medium managed ponds exhibited the highest mean invasive species cover (34 ± 12%). Invasive plant richness and cover also tended to be greater in dry ponds with higher soil nutrient levels, and in older wet ponds. Therefore, we found that highly maintained and younger wet ponds were the least invaded. Nevertheless, common management practices that limit plant invasions may also limit native species establishment and invasion may increase in the decades following pond construction.

Can Constructed Wetlands be Wildlife Refuges? A Review of Their Potential Biodiversity Conservation Value

The degradation of wetland ecosystems is currently recognized as one of the main threats to global biodiversity. As a means of compensation, constructed wetlands (CWs), which are built to treat agricultural runoff and municipal wastewater, have become important for maintaining biodiversity. Here, we review studies on the relationships between CWs and their associated biodiversity published over the past three decades. In doing so, we provide an overview of how wildlife utilizes CWs, and the effects of biodiversity on pollutant transformation and removal. Beyond their primary aim (to purify various kinds of wastewater), CWs provide sub-optimal habitat for many species and, in turn, their purification function can be strongly influenced by the biodiversity that they support. However, there are some difficulties when using CWs to conserve biodiversity because some key characteristics of these engineered ecosystems vary from natural wetlands, including some fundamental ecological processes. Without proper management intervention, these features of CWs can promote biological invasion, as well as form an ‘ecological trap’ for native species. Management options, such as basin-wide integrative management and building in more natural wetland components, can partially offset these adverse impacts. Overall, the awareness of managers and the public regarding the potential value of CWs in biodiversity conservation remains superficial. More in-depth research, especially on how to balance different stakeholder values between wastewater managers and conservationists, is now required.

It Is Not Easy Being Green: Recognizing Unintended Consequences of Green Stormwater Infrastructure

Green infrastructure designed to address urban drainage and water quality issues is often deployed without full knowledge of potential unintended social, ecological, and human health consequences. Though understood in their respective fields of study, these diverse impacts are seldom discussed together in a format understood by a broader audience. This paper takes a first step in addressing that gap by exploring tradeoffs associated with green infrastructure practices that manage urban stormwater including urban trees, stormwater ponds, filtration, infiltration, rain gardens, and green roofs. Each green infrastructure practice type performs best under specific conditions and when targeting specific goals, but regular inspections, maintenance, and monitoring are necessary for any green stormwater infrastructure (GSI) practice to succeed. We review how each of the above practices is intended to function and how they could malfunction in order to improve how green stormwater infrastructure is designed, constructed, monitored, and maintained. Our proposed decision-making framework, using both biophysical (biological and physical) science and social science, could lead to GSI projects that are effective, cost efficient, and just.

Hydrologic and water quality performance of two aging and unmaintained dry detention basins receiving highway stormwater runoff

Dry detention basins (DDBs) are a type of stormwater control measure (SCM) designed to provide flood storage, peak discharge reduction, and some water quality improvement through sedimentation. DDBs are ubiquitous in the urban environment, but are expensive to maintain. In this study, two overgrown DDBs near Raleigh, NC, receiving highway runoff were monitored for up to one year to quantify their water quality and hydrologic performance. Both basins, B1 and B2, have not received vegetation maintenance since construction in 2007. Flow-weighted composite samples were collected during storm events and analyzed for nutrients (Total Phosphorus (TP), Ortho-phosphorus (OP), Ammonia-N (NH₃), NO_2-3-N (NO_X), and Total Kjeldahl Nitrogen (TKN)), total suspended solids (TSS), and total Cd, Cu, Pb, and Zn. An annual water balance was also conducted to quantify runoff volume reduction. Despite low influent concentrations from the highway, significant removal efficiencies were found for all constituents except NH₃ in B1. TP, OP, NO_X, TSS, and Zn were reduced in B2. Both basins achieved greater than 41% volume reduction through soil infiltration and evapotranspiration, resulting in significant pollutant load reductions for all detected constituents, between 59% and 79% in B1 and 35% and 81% in B2. This study provides evidence that overgrown and unmaintained DDBs can reduce pollutant concentrations comparable to those reported for maintained DDBs, while reducing more volume than standard DDBs. Moreover, carbon sequestration likely increases while maintenance costs decrease.

A dynamic life cycle assessment of green infrastructures

As stormwater and its associated nutrients continue to impair our nation's waterways, green infrastructures (GIs) are increasingly applied in urban and suburban communities as a means to control combined sewer system overflows and stormwater related pollutants. Although GIs have been widely studied for their life cycle impacts and benefits, most of these studies adopt a static approach which prevents that information from being scaled or transferred to different spatial and temporal settings. To overcome this limitation, this research utilizes a dynamic life cycle assessment (LCA) approach to evaluate seven different GIs by integrating a traditional LCA with a system dynamics model which simulates the daily loadings and treatments of nutrients by the GIs across a 30-year life span. A base model was first developed, calibrated, and validated for seven GIs that are currently installed on the campus of the University of New Hampshire. The base model was then expanded to assess different scenarios in terms of geographic locations, land uses, GI design sizes, and climate changes. Our results show these aforementioned factors have significant influences on GIs' life cycle performances, with life cycle nitrogen reductions varying -100.90 to 512.09kgNeq. and life cycle phosphorous reductions varying from -23.77 to 63.43kg P eq. Furthermore, nutrient loading thresholds exist for certain GIs to offset nutrient emissions from their construction and maintenance activities. Accordingly, an optimal GI design size can be estimated for a given spatial and temporal setting. Such thresholds and optimal sizes are important to be identified to inform the decision-making and future planning of GIs.

The Low-Impact Development Demand Index: A New Approach to Identifying Locations for LID

The primary goal of low impact development (LID) is to capture urban stormwater runoff; however, multiple indirect benefits (environmental and socioeconomic benefits) also exist (e.g., improvements to human health and decreased air pollution). Identifying sites with the highest demand or need for LID ensures the maximization of all benefits. This is a spatial decision-making problem that has not been widely addressed in the literature and was the focus of this research. Previous research has focused on finding feasible sites for installing LID, whilst only considering insufficient criteria which represent the benefits of LID (either neglecting the hydrological and hydraulic benefits or indirect benefits). This research considered the hydrological and hydraulic, environmental, and socioeconomic benefits of LID to identify sites with the highest demand for LID. Specifically, a geospatial framework was proposed that uses publicly available data, hydrological-hydraulic principles, and a simple additive weighting (SAW) method within a hierarchical decision-making model. Three indices were developed to determine the LID demand: (1) hydrological-hydraulic index (HHI), (2) socioeconomic index (SEI), and (3) environmental index (ENI). The HHI was developed based on a heuristic model using hydrological-hydraulic principles and validated against the results of a physical model, the Hydrologic Engineering Center-Hydrologic Modeling System model (HEC-HMS). The other two indices were generated using the SAW hierarchical model and then incorporated into the HHI index to generate the LID demand index (LIDDI). The framework was applied to the City of Toronto, yielding results that are validated against historical flooding records.

Associations between microplastic pollution and land use in urban wetland sediments

Microplastic pollution is concerning because it is widespread in aquatic environments and there is growing evidence of negative biological effects. Here, we present one of the first studies to examine microplastic pollution (plastic particles < 1 mm) in urban wetlands and investigate relationships between contamination and urban land use. Sediment samples were collected from 20 independent urban wetlands, each with different types of urban land use within their catchments. Microplastics were observed at all wetlands, with an average abundance of around 46 items/kg of dry sediment. Plastic fragments were the most common type of microplastic, accounting for 68.5% of all microplastics found. Consistent with other studies, microplastic abundance was positively correlated with increased catchment urbanisation. On closer examination, plastic fragments and beads correlated with catchment urbanisation. Fragment abundance also increased in wetlands with catchments that had a higher proportion of industrial land use and decreased in catchments with higher residential densities. This study demonstrates the susceptibility of urban wetlands to microplastic pollution, further highlighting the ubiquitous nature of microplastic pollution. The prevalence of microplastic fragments indicates that plastic litter degradation is a significant source of microplastics in urban environments, especially in industrial areas.

Investigation on the carbon sequestration capacity of vegetation along a heavy traffic load expressway

Carbon sequestration by vegetation plays an important role in the global carbon cycle. More emphasis on the carbon sequestration of roadside vegetation will help to reduce the total carbon emissions from the transportation sector. In the current study, the Shanghai-Nanjing G42 expressway in east China was selected to investigate and calculate the carbon sequestration of roadside vegetation including trees, shrubs and herbs. Findings of the current study revealed that the total carbon sequestration of all the vegetation was about 97,000 tons per year. Results also indicated that trees have a higher carbon sequestration capacity (γ) in unit land area compared to shrubs and herbs. The γ value of most of the shrubs was lower than that of tree; however, species such as Nerium indicum, Jasminum mesnyi and Forsythia suspense have better carbon sequestration capacity than some other tree species. The γ value of herbs was too low, compared with trees and shrubs. The findings of the current study will be of great benefit to make the vegetation planting strategy for express highways in the areas with similar geographic characteristics and climate.

Impact of Urban Stormwater Runoff on Cyanobacteria Dynamics in A Tropical Urban Lake

Worldwide, eutrophication and cyanobacteria blooms in lakes and reservoirs are a great concern for water resources management. Coupling a catchment hydrological model and a lake model has been a strategy to assess the impact of land use, agricultural practices and climate change on water quality. However, research has mainly focused on large lakes, while urban reservoirs and their catchments, especially in tropical regions, are still poorly studied despite the wide range of ecosystem services they provide. An integrated modelling approach coupling the hydrological model Storm Water Management Model SWMM and the lake ecological model DYRESM-CAEDYM is proposed for Lake Pampulha (Brazil). Scenarios of increased imperviousness of the catchment and of reduction in the load of nutrients and total suspended solids (TSS) in dry weather inflow were simulated. Runoff water quality simulations presented a fair performance for TSS and ammonium (NH4+) while the dynamics of total phosphorus (TP) and nitrate (NO3−) were poorly captured. Phytoplankton dynamics in the lake were simulated with good accuracy (Normalized Mean Absolute Error, NMAE = 0.24 and r = 0.89 in calibration period; NMAE = 0.55 and r = 0.54 in validation period). The general trends of growth, decline and the magnitude of phytoplankton biomass were well represented most of the time. Scenario simulations suggest that TP reduction will decrease cyanobacteria biomass and delay its peaks as a consequence of orthophosphate (PO43−) concentration reduction in the lake surface layers. However, even decreasing TP load into Lake Pampulha by half would not be sufficient to achieve the water quality objective of a maximum concentration of 60 µg chla L−1. Increased imperviousness in the catchment will raise runoff volume, TSS, TP and NO3− loads into Lake Pampulha and promote greater cyanobacteria biomass, mainly in the beginning of the wet season, because of additional nutrient input from catchment runoff. Recovering Lake Pampulha water quality will require the improvement of the sanitation system. The lake water quality improvement will also require more sustainable and nature-based solutions for urban drainage in order to reduce non-point pollution through infiltration and retention of stormwater and to enhance natural processes, such as chemical sorption, biodegradation and phytoremediation. The integrated modelling approach here proposed can be applied for other urban reservoirs taking advantage of existing knowledge on Lake Pampulha.

Nitrogen cycling processes within stormwater control measures: A review and call for research

Stormwater control measures (SCMs) have the potential to mitigate negative effects of watershed development on hydrology and water quality. Stormwater regulations and scientific literature have assumed that SCMs are important sites for denitrification, the permanent removal of nitrogen, but this assumption has been informed mainly by short-term loading studies and measurements of potential rates of nitrogen cycling. Recent research concluded that SCM nitrogen removal can be dominated by plant and soil assimilation rather than by denitrification, and rates of nitrogen fixation can exceed rates of denitrification in SCM sediments, resulting in a net addition of nitrogen. Nitrogen cycling measurements from other human-impacted aquatic habitats have presented similar results, additionally suggesting that dissimilatory nitrate reduction to ammonium (DNRA) and algal uptake could be important processes for recycling nitrogen in SCMs. Future research should directly measure a suite of nitrogen cycling processes in SCMs and reveal controlling mechanisms of individual rate processes. There is ample opportunity for research on SCM nitrogen cycling, including investigations of seasonal variation, differences between climatic regions, and trade-offs between nitrogen removal and phosphorus removal. Understanding nitrogen dynamics within SCMs will inform more efficient SCM design and management that promotes denitrification to help mitigate negative effects of urban stormwater on downstream ecosystems.

Linking hydrological and bioecological benefits of green infrastructures across spatial scales - A literature review

Green infrastructure (GI) mitigates the negative effects of urbanization and provides hydrological and bioecological benefits. However, these benefits are highly scale-dependent because the processes involved vary at different spatial scales; there are thus additional challenges in GI planning when multiple benefits are targeted. Therefore, it is necessary to review and summarize the theoretical understandings and practical experience obtained from previous studies and projects related to the hydrological and bioecological benefits of GI practices. In this review, we elaborate the conceptual linkages between the hydrological and bioecological benefits of GI practices across different scales. Smaller-scale benefits lay the foundation for larger-scale benefits. Hydrological benefits drive bioecological benefits by providing consistent water flows and maintaining a suitable soil environment. Bioecological benefits in turn enhance hydrological benefits by increasing water uptake and filtration via more active biological processes. We next summarize the study area sizes of existing studies and categorize them according to their study approaches and targeted benefits. The study area sizes in studies that make use of laboratory experiments, numerical modeling, and remote sensing have increased in recent years and vary greatly between each type of study; the study area size in studies of bioecological benefits was larger than in studies of hydrological and water quality benefits. However, there is a research gap in studies of bioecological benefits at the catchment scale. Furthermore, we summarize the major research topics and findings of bioecological benefits of GI practices at different spatial scales. We conclude this review with recommendations for future research, which include performing more studies at the catchment scale, developing hydro-bioecological statistical relationships to simplify the quantification of bioecological benefits, and developing databases to document the bioecological benefits of GI practices.

Coastal landscape planning for improving the value of ecosystem services in coastal areas: Using system dynamics model

Coastal areas provide important ecosystem services and affect local tourism. However, these areas are also sensitive to coastal erosion. The purpose of this study was to simulate a landscape plan scenario to improve the value of ecosystem services. The Shinduri coastal area in South Korea which has important natural resources, such as coastal sand dunes and coastal forests. To simulate landscape changes, this study was conducted using system dynamics. The study progressed in three stages: first, an analysis of the landscape change behavior model of Shinduri in its current state and an evaluation of the value of ecosystem services was conducted. Second, a simulation was carried out by applying a coastal erosion scenario. Third, a simulation of landscape change was run, and the value of ecosystem services was estimated, with regard to afforestation, thinning, weeding and coastal sand dune restoration plan scenarios. The results were as follows: in the absence of disturbances, current landscape change models are stable, and the value of ecosystem services, which was $859,259 in 2014, has increased over time. However, the value of ecosystem services decreased when subjected to a coastal erosion scenario. The evaluation of value of ecosystem services under afforestation, thinning, weeding and coastal sand dune plan scenarios revealed an optimal landscape plan that focuses on a coastal sand dune restoration plan suggesting restoration of these dunes at a rate of 27.05 ha per year. When the coastal sand dune restoration plan is applied, the value of ecosystem services increases to $ 895,474 by 2054. The coastal sand dune restoration plan should prioritize the protection of the coastal sand dune area as component of the restoration of coastal ecological resources in the area. These findings could contribute to the ecological management and improvement of coastal ecosystem services.

The Challenge of Maintaining Stormwater Control Measures: A Synthesis of Recent Research and Practitioner Experience

The methods for properly executing inspection and maintenance of stormwater control measures are often ambiguous and inconsistently applied. This paper presents specific guidelines for inspecting and maintaining stormwater practices involving media filtration, infiltration, ponds, and permeable pavements because these tend to be widely implemented and often unsatisfactorily maintained. Guidelines and examples are based on recent scientific research and practitioner experience. Of special note are new assessment and maintenance methods, such as testing enhanced filtration media that targets dissolved constituents, maintaining proper vegetation coverage in infiltration practices, assessing phosphorus release from pond sediments, and the development of compressed impermeable regions in permeable pavements and their implications for runoff. Inspection and maintenance examples provided in this paper are drawn from practical examples in Northern Midwest USA, but most of the maintenance recommendations do not depend on regional characteristics, and guidance from around the world has been reviewed and cited herein.

Integrated modelling of stormwater treatment systems uptake

Nature-based solutions provide a variety of benefits in growing cities, ranging from stormwater treatment to amenity provision such as aesthetics. However, the decision-making process involved in the installation of such green infrastructure is not straightforward, as much uncertainty around the location, size, costs and benefits impedes systematic decision-making. We developed a model to simulate decision rules used by local municipalities to install nature-based stormwater treatment systems, namely constructed wetlands, ponds/basins and raingardens. The model was used to test twenty-four scenarios of policy-making, by combining four asset selection, two location selection and three budget constraint decision rules. Based on the case study of a local municipality in Metropolitan Melbourne, Australia, the modelled uptake of stormwater treatment systems was compared with attributes of real-world systems for the simulation period. Results show that the actual budgeted funding is not reliable to predict systems' uptake and that policy-makers are more likely to plan expenditures based on installation costs. The model was able to replicate the cumulative treatment capacity and the location of systems. As such, it offers a novel approach to investigate the impact of using different decision rules to provide environmental services considering biophysical and economic factors.

Technical and natural conditions and operating efficiency of a municipal stormwater treatment plant

A decade of observations provided grounds for assessing the operation of one of the few stormwater treatment plants in Poland (system: screens-grit chambers-settler-retention pond) which collects effluents from 471 ha of the city. Among other aspects, the following were evaluated: treatment efficiency, relationship between the quality of treated stormwater and that of waters in the receiving body (the ox-bow lake of the Vistula river), operating stability of key units, significance of the facility for nature. During the assessment, the plant had a positive effect on the quality of stormwater effluents-the content of the analysed pollutants was reduced (more than 80% average efficiency for mineral forms of nitrogen and suspension matter) and oxygen ratios improved (23% increase in the average concentration of dissolved oxygen and more than 50% decrease in 5-day biochemical oxygen demand and chemical oxygen demand). Although the overall assessment of the facility's operation was good, some omissions and operating errors were noted (method of removing retained pollutants, stormwater flow control). Eliminating them is a prerequisite for maintaining the expected reliability of the system. An effect of stormwater ponds on the increase in biodiversity in the poor urbanised landscape has also been observed. The structures, forming a uniform system along with urban green areas, constitute specific enclaves which attract living organisms.

Coastal stormwater wet pond sediment nitrogen dynamics

Wet ponds are a common type of stormwater control measure (SCM) in coastal areas of the southeastern US, but their internal nitrogen dynamics have not been extensively studied. Using flow-through intact sediment core incubations, net sediment N₂ fluxes before and after a nitrate addition from five wet ponds spanning a range of ages (3.25-10years old) were quantified through membrane inlet mass spectrometry during early summer. Multiple locations within a single wet pond (6.16years old) were also sampled during ambient conditions in late summer to determine the combined effects of depth, vegetation, and flow path position on net N₂ fluxes at the sediment-water interface. All pond sediments had considerable rates of net nitrogen fixation during ambient conditions, and net N₂ fluxes during nitrate-enriched conditions were significantly correlated with pond age. Following a nitrate addition to simulate storm conditions, younger pond sediments shifted towards net denitrification, but older ponds exhibited even higher rates of net nitrogen fixation. The pond forebay had significantly higher rates of net nitrogen fixation compared to the main basin, and rates throughout the pond were an order of magnitude higher than the early summer experiment. These results identify less than optimal nitrogen processing in this common SCM, however, data presented here suggest that water column mixing and pond sediment excavation could improve the capacity of wet ponds to enhance water quality by permanently removing nitrogen.

Air quality considerations for stormwater green street design

Green streets are increasingly being used as a stormwater management strategy to mitigate stormwater runoff at its source while providing other environmental and societal benefits, including connecting pedestrians to the street. Simultaneously, human exposure to particulate matter from urban transportation is of major concern worldwide due to the proximity of pedestrians, drivers, and cyclists to the emission sources. Vegetation used for stormwater treatment can help designers limit the exposure of people to air pollutants. This goal can be achieved through the deliberate placement of green streets, along with strategic planting schemes that maximize pollutant dispersion. This communication presents general design considerations for green streets that combine stormwater management and air quality goals. There is currently limited guidance on designing green streets for air quality considerations; this is the first communication to offer suggestions and advice for the design of green stormwater streets in regards to their effects on air quality. Street characteristics including (1) the width to height ratio of the street to the buildings, (2) the type of trees and their location, and (3) any prevailing winds can have an impact on pollutant concentrations within the street and along sidewalks. Vegetation within stormwater control measures has the ability to reduce particulate matter concentrations; however, it must be carefully selected and placed within the green street to promote the dispersion of air flow.

Variability of zinc, copper and lead contents in sludge of the municipal stormwater treatment plant

Several years of observations enabled us to assess the extent and variability of heavy metal contamination (Zn, Cu and Pb) of the sludge of the municipal stormwater treatment plant (the town of Puławy, Poland). In terms of size (high capacity) and innovation, it is the only facility of this kind in the country. It collects rainwater run-offs from two catchments (separate inlets) with a total area of about 500 ha. The concentration of the analysed metals is characterised by a large spatial and temporal diversity. The reason for this may be differences in the manner and intensity of use of drained surfaces and different hydraulic conditions (of sedimentation) prevailing in the particular treatment devices. The highest pollution was found in sediments in the grit chamber and in the part of the settler from the side of the interceptor supplying sewage, i.e. from the main traffic route of the town (heavy traffic and developed technical infrastructure). The best-quality sludge was retained in the pond for treated wastewater. In the pool of analysed components, the largest share is Zn, which amounts to about 85%. The content of heavy metals limits the possibility of the natural use of sludge from the municipal stormwater treatment plant. In chemical terms, they should be seen as a potentially dangerous waste and undergo remediation.

Evaluating the performance of a retrofitted stormwater wet pond for treatment of urban runoff

This paper describes the performance of a retrofitted stormwater retention pond (Ashby Pond) in Northern Virginia, USA. Retrofitting is a common practice which involves modifying existing structures and/or urban landscapes to improve water quality treatment, often compromising standards to meet budgetary and site constraints. Ashby Pond is located in a highly developed headwater watershed of the Potomac River and the Chesapeake Bay. A total maximum daily load (TMDL) was imposed on the Bay watershed by the US Environmental Protection Agency in 2010 due to excessive sediment and nutrient loadings leading to eutrophication of the estuary. As a result of the TMDL, reducing nutrient and sediment discharged loads has become the key objective of many stormwater programs in the Bay watershed. The Ashby Pond retrofit project included dredging of accumulated sediment to increase storage, construction of an outlet structure to control flows, and repairs to the dam. Due to space limitations, pond volume was less than ideal. Despite this shortcoming, Ashby Pond provided statistically significant reductions of phosphorus, nitrogen, and suspended sediments. Compared to the treatment credited to retention ponds built to current state standards, the retrofitted pond provided less phosphorus but more nitrogen reduction. Retrofitting the existing stock of ponds in a watershed to at least partially meet current design standards could be a straightforward way for communities to attain downstream water quality goals, as these improvements represent reductions in baseline loads, whereas new ponds in new urban developments simply limit future load increases or maintain the status quo.

Evaluation of factors affecting soil carbon sequestration services of stormwater wet retention ponds in varying climate zones

The carbon sequestration services of stormwater wet retention ponds were investigated in four different climates: U.S., Northern Sweden, Southern Sweden, and Singapore, representing a range of annual mean temperatures, growing season lengths and rainfall depths: geographic factors that were not statistically compared, but have great effect on carbon (C) accumulation. A chronosequence was used to estimate C accumulations rates; C accumulation and decomposition rates were not directly measured. C accumulated significantly over time in vegetated shallow water areas (0-30cm) in the USA (78.4gCm^-2yr^-1), in vegetated temporary inundation zones in Sweden (75.8gCm^-2yr^-1), and in all ponds in Singapore (135gCm^-2yr^-1). Vegetative production appeared to exert a stronger influence on relative C accumulation rates than decomposition. Comparing among the four climatic zones, the effects of increasing rainfall and growing season lengths (vegetative production) outweighed the effects of higher temperature on decomposition rates. Littoral vegetation was a significant source to the soil C pool relative to C sources draining from watersheds. Establishment of vegetation in the shallow water zones of retention ponds is vital to providing a C source to the soil. Thus, the width of littoral shelves containing this vegetation along the perimeter may be increased if C sequestration is a design goal. This assessment establishes that stormwater wet retention ponds can sequester C across different climate zones with generally annual rainfall and lengths of growing season being important general factors for C accumulation.

Stormwater nutrient attenuation in a constructed wetland with alternating surface and subsurface flow pathways: Event to annual dynamics

Among different Water Sensitive Urban Design (WSUD) options, constructed wetlands (CWs) are widely used to protect and support downstream urban waterways from stormwater nutrients. This analysis assessed the nutrient attenuation ability of a novel CW in Western Australia that combined multiple alternating surface flow (SF) and laterite-based subsurface flow (SSF) compartments within a parkland context to improve the urban landscape and amenity. The CW was designed to maximise nutrient reduction despite experiencing a large range of hydrologic conditions, from low transit time nutrient-rich pulses during the wet periods to prolonged low to zero flow conditions during the dry periods. The CW design was further complicated by the possibility of ungauged water inputs after wet antecedent conditions, seasonal macrophyte senescence and a recirculation system to maintain flow during the dry periods. From analysis of data over a range of time scales, we determined that overall the CW attenuated up to 62% total nitrogen (TN) and 99% total phosphorus (TP) loads during dry weather conditions, and 54-76% TN and 27-68% TP during episodic flow pulses. N species attenuation was dominant in the SF compartments, while P species were attenuated mostly within the SSF compartments. Nutrient accumulation in the sediments, and above and below ground biomass of the macrophytes were found to increase during the early stages of operation, suggesting the system reached equilibrium within four years. Further, by comparing trends in nutrient attenuation within the context of diel changes in high frequency oxygen data from different compartments, it was demonstrated that changes in dissolved oxygen were related to changes in nutrient concentration across the CW, although interpretation of this was complicated by changing hydro-climatological conditions. The implementation of this CW concept in a highly seasonal Mediterranean climate demonstrates that urban liveability and environmental health can both be improved through careful design.

Analysis of intensity and spatial patterns of public use in natural treatment systems using geotagged photos from social media

Patterns of public use in 273 natural treatment systems worldwide are investigated by means of geotagged data from two popular photo-sharing websites, using spatial analysis and regression techniques. Standardized Major Axis (SMA) regression is found to perform better than other univariate calibration models in terms of goodness of fit with reported visitation frequencies and predictive accuracy, and is used to predict visitation rates in 139 systems that are associated with at least one geotagged photograph. High visitation rates are found in free-water surface (FWS) constructed wetlands and mixed pond-constructed wetlands systems, as well as systems treating surface water or stormwater runoff. Geographic Information System (GIS) techniques are used to map hot and cold spots of public use in two highly visited systems. Binomial logit regression reveals that the probability to be associated with at least one geotagged photograph is a function of system size, system type, and influent water quality. The findings are discussed in terms of their implications for the evaluation of public use in multifunctional ecologically engineered systems as well as the applicability of the proposed methodology to other natural and man-made ecosystems.

Balancing the Ecological Function of Residential Stormwater Ponds with Homeowner Landscaping Practices

Stormwater ponds are installed in urban developments to provide the ecosystem services of flood control and water treatment. In coastal areas, these ponds are connected to watersheds that can drain directly into protected estuaries, making their design, function, and maintenance critical to environmental protection. However, stormwater ponds in residential areas are increasingly managed as aesthetic amenities that add value to real estate rather than as engineered devices with special maintenance requirements. To help extend the life of neighborhood stormwater systems and improve ecosystem services, homeowners should follow best management practices for nutrient management and add shoreline plantings and non-invasive, beneficial aquatic plants to their ponds. This study used focus group and survey research to document the knowledge, behaviors, and attitudes of homeowners living near stormwater ponds in a master-planned community in Florida. The study was designed to use a social marketing research approach to promote Extension best practices. Findings indicate that many residents were aware of the functional components of stormwater systems and respondents' receptivity to best management practices was mediated by age, their attitudes about water quality and whether their home was adjacent to a pond. These findings can be used to target Extension audiences and improve adoption of stormwater pond best management practices for increased protection of water quality.

Replacing natural wetlands with stormwater management facilities: Biophysical and perceived social values

Urban expansion replaces wetlands of natural origin with artificial stormwater management facilities. The literature suggests that efforts to mimic natural wetlands in the design of stormwater facilities can expand the provision of ecosystem services. Policy developments seek to capitalize on these improvements, encouraging developers to build stormwater wetlands in place of stormwater ponds; however, few have compared the biophysical values and social perceptions of these created wetlands to those of the natural wetlands they are replacing. We compared four types of wetlands: natural references sites, natural wetlands impacted by agriculture, created stormwater wetlands, and created stormwater ponds. We anticipated that they would exhibit a gradient in biodiversity, ecological integrity, chemical and hydrologic stress. We further anticipated that perceived values would mirror measured biophysical values. We found higher biophysical values associated with wetlands of natural origin (both reference and agriculturally impacted). The biophysical values of stormwater wetlands and stormwater ponds were lower and indistinguishable from one another. The perceived wetland values assessed by the public differed from the observed biophysical values. This has important policy implications, as the public are not likely to perceive the loss of values associated with the replacement of natural wetlands with created stormwater management facilities. We conclude that 1) agriculturally impacted wetlands provide biophysical values equivalent to those of natural wetlands, meaning that land use alone is not a great predictor of wetland value; 2) stormwater wetlands are not a substantive improvement over stormwater ponds, relative to wetlands of natural origin; 3) stormwater wetlands are poor mimics of natural wetlands, likely due to fundamental distinctions in terms of basin morphology, temporal variation in hydrology, ground water connectivity, and landscape position; 4) these drivers are relatively fixed, thus, once constructed, it may not be possible to modify them to improve provision of biophysical values; 5) these fixed drivers are not well perceived by the public and thus public perception may not capture the true value of natural wetlands, including those impacted by agriculture.