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Excessive nutrient loads represent a major source of water pollution globally. Best Management Practices (BMPs) are typically implemented in agricultural and urban landscapes to reduce nutrient losses at individual parcels. However, the effectiveness of BMPs in reducing nutrient loads at regional watershed domains remains an open question. This study aims to evaluate the effectiveness of parcel-based agricultural and urban BMP implementations in reducing watershed-wide phosphorus (P) and nitrogen (N) loads. The Lake Okeechobee watershed in Florida (USA), covering 10,600 km2 of mixed agricultural and urban land-use/land-cover, is used as a case study. Hydrological and nutrient transport processes were simulated using the Watershed Assessment Model (WAM). The model was calibrated and validated for river discharge and nutrients for each of the six sub-watersheds, with R2 values ranging from 0.43 to 0.80 for flows and 0.24 to 0.85 for nutrients. Four what-if scenarios were simulated representing different regional BMP implementations: No BMPs implemented, current conditions (1032 km2 area influenced), maximum potential scenario (5923 km2 area influenced), and optimal BMP placement. Simulations indicated that currently implemented BMPs could be reducing P loads from 482 to 468 tons/year (3%) and N loads from 4384 to 3796 tons/year (13%). Implementation of all potential BMPs could reduce P to 307 tons/year (36%) and N to 3036 tons/year (31%). Dividing the watershed into subwatersheds illustrated that BMPs in Taylor Creek-Nubbin Slough (50% agriculture) have the potential to reduce P by 55%, and in Upper Kissimmee (23.5% urban) BMPs have the potential to reduce N by 42%. In addition, optimal BMP spatial distributions in each subwatershed could reduce P loads and N loads by 10% and 4%, respectively, providing a cost-effective solution to nutrient pollution mitigation. Our simulations suggest that other strategies would be needed to further reduce P and N, especially in subwatersheds that have low BMPs reduction potential. [ABSTRACT FROM AUTHOR]

Nitrate pollution of surface water from farms and urban runoff is widespread – impairing drinking water supplies, recreation, and wildlife habitat. The scale of the problem in rivers has overwhelmed most watershed-based best management practices. A new paradigm is needed. In this paper we highlight the 119 ha (294 acres) Prado Wetlands in southern California, USA as an example of a gravity-enabled, free surface flow vegetated wetlands to treat a river – the nitrate-rich, effluent-dominated Santa Anna River. The wetland treats ∼1–2 m3/s of the 7.1 m3/s (250 cfs) flow of the river in 28 wetland cells in two parallel trains (residence time 2–4 d, hydraulic loading rate 10–20 cm/d). The cleaner water is returned to the river and infiltrated downstream into a managed groundwater basin supplying 2.4 million customers. Since 1998, ∼1200 t of nitrate-N have been permanently removed from the river and released as N 2 -gas into the air. Over 24 years, in the warm summers an average of 6.1 mg-N/L entered the wetland and 3.7 mg-N/L flowed out, a removal efficiency of 57%. In the cooler winters, an average of 6.4 mg NO 3 -N/L entered and 2.6 mg NO 3 -N/L flowed out, a removal efficiency of 45%. Individual months varied widely in concentration removal efficiency from 7% (winter) to 98% (high summer). Areal summer removal averaged 137 mg NO 3 -N/m2/d and the apparent "k" was around 46 m/y. All-year rates were 129 mg NO 3 -N/m2/d or 47 g/m2/y, a reasonable performance considering the size of the system and its configuration for both nitrate removal and duck hunting (i.e., more open water). Annual average nitrate removal efficiency increased substantially over time (45 to 72% for 1998–2004 versus 2016–22) and is attributed to an increase in hydraulic residence time, upgraded internal plumbing, and increased winter temperatures (+3C°). Prado Wetlands also removes phosphorus, though not as well as nitrate; average warm season removal efficiency was 23% (inflow 1.20 mg PO 4 -P/L, outflow 0.93 mg PO 4 -P/L). The aerial removal rate was high at 23 mg P/m2/d or 8.5 g/y, probably due to the high inflowing P-concentrations and the hard water. Wildlife was also enhanced. Least Bell's Vireo (Vireo belli pusillus) , an endangered bird in the Prado Basin, increased from 19 pairs (1998) to a recent average of 444 pairs due to habitat improvement and reduction of cowbird parasitism. Results from the Prado Wetlands show that cleaning up rivers via diversion through wetlands benefits both water quality and wildlife. [ABSTRACT FROM AUTHOR]

Abstract Miyun reservoir watershed is a major source of drinking water for China's capital, Beijing, which has a population of 21.75 million. Recently, the capacity of the Miyun reservoir to supply clean drinking water has been threatened by increasing eutrophication (or algae bloom), mainly due to the discharge of wastewater and excessive fertilization application in the upstream watershed. Therefore, there is an urgent need to design effective best management practices (BMPs) to reduce upstream nutrient load and improve water quality in the Miyun reservoir. In this study, we built a watershed model (the Soil and Water Assessment Tool) for the Miyun Reservoir Watershed (MRW) and calibrated and validated it using long-term sediment, nitrogen (N) and phosphorus (P) data. Furthermore, we developed a Markov Chain based multi-objective optimization program to explore optimal BMPs with tradeoffs between economic costs and water quality responses. Using the watershed model and multi-objective optimization algorithms, we explored the potential effectiveness of BMPs under two scenarios that are currently being considered. Scenario 1 assumes that funding for BMP implementation comes from national grants and targets high water quality standards, whereas scenario 2 assumes funding is provided by farmers and targets water quality that meet the drinking water standards. We found substantial discrepancies between the two scenarios with respect to the types and spatial configurations of BMPs and associated economic costs, highlighting the need to reconcile concerns from different stakeholders in order to arrive at a BMP plan that all parties will agree upon. In addition, we found that cross-subwatershed coordination and targeting flood season instead of year-round water quality standards could pronouncedly reduce the economic costs of BMP implementations without substantially degrading water quality. The watershed scale optimization method developed here holds promise to serve as an effective tool to explore tradeoffs between economic costs, water quality improvements, and decision makers' and stakeholders' concerns in BMP design, thereby informing sustainable watershed scale water resources management and ecosystem maintenance. [ABSTRACT FROM AUTHOR]

Highlights • Assessing ecological effects of selective harvesting on subtropical streams is rare. • Paired-catchment experiments with pools nested in streams are powerful tests. • Selective forest harvesting did not alter stream particulate organic matter dynamics. • Invertebrate detritivores varied among pools yet were not altered by harvesting. • Best management practices protect these facets of subtropical stream ecosystems. Abstract Best management practices (BMPs) for forestry activities have been developed to mitigate the impacts of timber harvesting on stream ecosystems in New South Wales, Australia. These BMPs include selective harvesting within the catchment, exclusion of harvesting in riparian zones, and restrictions on harvesting and machinery operations during wet weather or on steep slopes. The few studies assessing the ecological effects of forestry BMPs have largely focussed on operations in temperate climates and are often based on a single pair of control and impact streams. But what are the effects in subtropical regions where climatic and hydrological variability may be greater? Are the effects of selective harvesting dependent on the proximity of harvesting to the locations of monitoring? We used a multiple paired-catchment study to assess effects of forestry BMPs on standing stocks of benthic coarse particulate organic matter (CPOM) and densities of invertebrate detritivores in streams draining subtropical eucalypt catchments that were either harvested using BMPs (‘impact’) or unharvested (‘control’). CPOM and detritivores in three pools in each of the four streams were sampled multiple times before and after the impact catchments were harvested. Harvesting intensity and proximity of harvesting to stream monitoring sites differed between ‘impact’ catchments. Benthic CPOM was dominated by leaves and leaf fragments in all streams. There were no post-harvesting differences in CPOM composition, standing stocks of different CPOM fractions or densities of detritivorous stream invertebrates in two feeding groups (collector-gatherers and shredders) between stream pairs despite differences in the proximity (minimum of ∼50 m and 1.6 km) of harvesting to monitoring sites. We conclude that relative to matched control sites, selective forestry BMPs do not alter CPOM stocks and stream detritivore densities in this subtropical Australian eucalypt forest, implying that these BMPs are effective in mitigating effects of harvesting across similar subtropical forests. [ABSTRACT FROM AUTHOR]

Climate change is a primary driver that alters water pollution hotspots in watersheds, which complicates the use of Best management practices (BMPs) for diffuse pollution mitigation strategies. The objective of this study is to evaluate future changes in BMPs on total phosphorus (TP) loads to the river system, depending on climate change. Current weather data were collected from 2000 to 2010 and future weather data from 2040 to 2050 were obtained from regional climate model simulations based on Representative Concentration Pathways (RCP) 2.6, 4.5, and 8.5 scenarios. This study describes various BMP implementation plans at affordable cost that are adapted to different weather conditions, current (for 2000–2010) and future climate scenarios (for 2040–2050). The Soil and Water Assessment Tool (SWAT), i.e., one of the deterministic models for watershed management, was used to estimate total phosphorus (TP) removal efficiency of various types of BMP at two crop fields (rice paddy and soybean fields) in the Yeongsan River (YR) watershed of Korea. The Non-dominated Sorting Genetic Algorithm II (NSGA-II), i.e., one of the artificial intelligence (AI) models for decision support framework, was applied to obtain allow for trade-off analysis between two conflict objectives, the maximum TP load reduction against implementation costs. The SWAT simulation results showed that the model performance based on the Nash-Sutcliffe efficiency and percent bias was acceptable for simulating three parameters; daily flow discharge, monthly sediment loads, and TP loads in the river. As a result, monthly sediment loads and TP loads increase remarkably under all future climate change scenarios except for July, when a comparable amount of precipitation is recorded during the present and future conditions. New implementation of BMPs, therefore, will be required for future climate change scenarios to achieve 50% TP load reduction in the given watershed condition. Interestingly, parallel terraces which showed good efficiency in reducing TP loads at both fields under the current weather condition cannot be effective any more under the worst-case weather scenario in the future climate. In such a case, detention ponds can be proposed as BMP alternative to parallel terraces. Overall, this study not only demonstrates that watershed management plans using BMPs should be adjusted according to climate change scenarios, but also that the hybrid use of SWAT model and AI can help in refining existing and future BMPs at affordable cost. [ABSTRACT FROM AUTHOR]

A five-year study was conducted in Orange County, California to document the presence of standing water and the presence or absence of larval mosquitoes within 23 stormwater treatment Best Management Practices (BMPs) installed along State Route 73 by the California Department of Transportation. Findings were used to guide incremental improvements to BMP design and function with the aim of reducing the occurrence of standing water that persisted more than 96 h after precipitation. During the first year of monitoring, a number of structural and non-structural factors were identified as causes for standing water within BMPs suitable for mosquitoes. Uneven grades, inlet design and construction, and novel structural features were most frequently responsible for standing water, often exacerbated by sediment and debris accumulations and periodic or perennial non-stormwater flows. Subsequent modifications to BMPs eliminated or reduced the size of persistent standing water pools. The study demonstrated that mosquito larval habitat can be mitigated in BMPs designed to remain dry between precipitation events by collecting field data that identifies where post-construction structural and managerial changes are needed to eliminate or reduce unintended sources of standing water. [ABSTRACT FROM AUTHOR]

Sediment in forested watersheds is produced primarily from highly disturbed areas such as skid trails. Forestry best management practices (BMPs) have been developed to minimize erosion and water quality problems, but the efficacies of various BMP options such as water bars are not well documented. The aim of this study was to evaluate the effects of different distances (slope lengths) between water diversion structures (water bars) on runoff volume and soil loss on different skid trail gradients on two soils with different textures. The treatments were located in an Iranian temperate forest and included combinations of three levels of trail gradient (<10%, 10–20% and >20%), four different distances between water bars (25, 50, 75, and 100 m), and two soil textures (clay loam and silt loam). Results showed that runoff volume increased curvilinearly and soil loss linearly with distances between water bars regardless of the soil texture and trail gradient. The greater distances on trail gradients >20% resulted in the highest amounts of runoff and soil loss; shorter distances on trail gradients <10% resulted in the lowest runoff and soil loss amount for the two tested soil textures. On the clay loam soil, 50 and 75 m were the most effective distances between water bars for trail gradients >20 and <20%, respectively. On the silt loam soil, 25 m and 50 m were the most effective distances between water bars for trail gradients >20 and <20%, respectively. The results of our study confirm that slope angle is a primary factor in controlling surface runoff and soil loss on skid trails and that soil texture becomes increasingly important as slope gradients become steeper. Therefore, reducing skid trail slope during construction skid trails is recommended to decrease surface runoff and soil loss in forest operations. Further, BMPs should consider soil texture in addition to slope gradient when recommending spacing between water bars. [ABSTRACT FROM AUTHOR]

Regenerative streamwater conveyances (RSCs) are a relatively new stream restoration best management practice (BMP) being extensively implemented in degraded perennial streams and stormwater drainages throughout the mid-Atlantic. Although there is currently a great deal of interest in this type of BMP as a means of reducing nutrient and sediment export from disturbed catchments, little is known of its pollutant reduction capabilities and whether there are unintended ecological consequences associated with these structures. For example, dense accumulations of flocculate from iron-oxidizing bacteria (FeOB) have been observed at numerous RSC sites, yet it is unknown whether this flocculate is predominately natural, a consequence of leached iron (Fe) from the materials used in the RSC construction, or because of mobilized Fe from catchment soils influenced by higher groundwater levels that may occur after construction. We analyzed Fe and other solute concentrations in groundwater and perennial streams at RSC and control sites located in the Coastal Plain and Piedmont physiographic provinces of MD and DC, and conducted leaching experiments using RSC soils and construction materials. Iron flocculate from FeOB in RSCs is commonly localized and depends on several factors including a source of reduced Fe, the availability of dissolved organic carbon (DOC), and specific hydrological (i.e., low flow) and physical (i.e., warmer temperatures) conditions. Sources of reduced Fe are derived from both construction materials and catchment soils, which leach Fe in the presence of DOC originating from natural organic matter (OM) deposits and OM incorporated into the RSCs (i.e., wood chips, leaves, logs). Using construction materials that have relatively low Fe content in areas strongly influenced by OM will likely decrease the spatial and temporal presence of dense mats of Fe flocculate thereby improving stream habitat. [ABSTRACT FROM AUTHOR]

Increasing awareness of hypoxia in ocean regions across the globe has led to creation of nutrient reduction strategies targeting this coastal problem. In the Mississippi River Basin, the Governor’s Action Plan has called for a 45% load reduction of both nitrogen (N) and phosphorous (P) to reduce the Gulf of Mexico hypoxic zone. One documented best management practice (BMP) for nutrient reduction is low-grade weirs (hereafter “weirs”). Recent studies have highlighted advantages of using low-grade weirs in agricultural ditches for controlled drainage by increasing hydraulic residence time (HRT) and mitigating nutrient loading from storm water and sedimentation. This study aimed to assess the ability of weirs to reduce nutrients in agriculture runoff at field-scale in the Mississippi Delta. Nutrient load reductions were observed in drainage ditches with and without weirs. However, nutrient and sediment loads varied widely, with observed load reductions ranging from −885 to 96% and −1 to 65% for total inorganic N and total inorganic P, respectively, in ditches with weirs. Maximum nutrient load reductions highlight that systems, with and without weirs, have the capability to reduce nutrients under certain conditions, while minimum nutrient reductions highlight when drainage ditch capacity limitations were exceeded. Differences in nutrient and sediment concentrations between storm- and low-flow samples ranged from 28 to 97%, indicating water velocity as the driving force behind observed differences. Seasonal analysis of nutrient runoff revealed significantly higher concentrations of total inorganic N, total inorganic P, and total suspended solids in the spring ( p = 0.003, p < 0.0001, and p < 0.0001, respectively), while an N also increased in the fall ( p = 0.007). Differences in annual sediment and P trends showed lower concentrations in systems with weirs. While this investigation highlighted both the successes and limitations of utilizing low-grade weirs as a BMP, results suggest that capture capacity of BMPs should be tailored to drainage acreage and site variability. [ABSTRACT FROM AUTHOR]

Sustainability and the health of freshwater ecosystems are vital to insure their safe and continued use. This study introduces a new approach to improve stream health to a desirable condition at the lowest cost by optimizing the best management practice (BMP) implementation plan. Several hydrological models including the Soil and Water Assessment Tool (SWAT) and Hydrologic Index Tool were integrated and the results were used to develop a stream health model. SWAT model was calibrated and validated against daily streamflow data from nine US geological gauging stations for a 10-year-period while the stream health model was calibrated and validated against 193 biological monitoring sites operated by the Michigan Department of Natural Resources. The stream health model was guided by a genetic algorithm to design the watershed-scale management strategies that included five BMPs. Out of 182 BMP implementation scenarios, eight unique scenarios resulted in an overall excellent stream health for the Honeyoey Creek-Pine Creek Watershed in Michigan. In addition, no tillage was the most selected BMP in three of the eight implementation scenarios. The BMP implementation costs for these eight scenarios ranged from 4.28 to 6.41 million dollars. Therefore, the integration of genetic algorithm techniques in stream health modeling resulted in a savings of over 2 million dollars. In addition, the implementation of the lowest costing scenario resulted in a 52% improvement and 36% reduction in stream health scores, with respect to stream length, compared to current conditions. The technique introduced here can be successfully adapted in different regions to identify the optimal solution from both environmental and economic points of view. [ABSTRACT FROM AUTHOR]

To enhance nitrogen transformations and increase agricultural nitrogen removal, best management practices (BMPs) need to focus on identifying and improving mechanistic removal pathways. Best management practices can be implemented which favor denitrification, the single most effective removal pathway in the nitrogen cycle. Low-grade weirs in agricultural drainage ditches provide conditions conducive for denitrification to occur; however, there is very little information on denitrification potential of agricultural drainage ditches, let alone low-grade weirs in these systems. This study aimed to provide the first examination of denitrification potential of agricultural drainage ditches with and without low-grade weirs and highlight how the age of weirs may result in changes in denitrification rates. Samples were collected in three distinct seasons (summer, winter, spring) during 2011 and 2012 from ditches with and without weirs. Sediment cores were plumbed as flow-through chemostats and inflow and outflow samples were analyzed for N 2 gas to determine net denitrification rates. Overall there were no significant differences between net denitrification rates between sites with weirs and sites under conventional drainage ( z = 0.4526, P = 0.65). Average net denitrification rates for weirs and conventional drainage were 2215 ± 440 and 2541 ± 727 μg m −2 h −1 , respectively. This finding suggests that the potential for denitrification exists within both weired and conventional ditches, but a precipitating environment is limiting. Denitrification rates were significantly different between seasons ( F = 6.1879, P = 0.0004) in all sediment cores, regardless of drainage characteristics, with summer > winter > spring. Differences due to age were also significant ( F = 2.6483, P = 0.0224), with higher rates of denitrification in younger systems (≤1 year) vs. older systems (≥2 years), suggesting denitrification potential of weirs decreases with time. These data suggest that use of weirs can provide enhanced hydrological residence time in these systems, and thus promote conditions conducive for nitrogen removal via denitrification to occur. Thus low-grade weirs should be considered as BMPs for nitrogen removal in source agricultural landscapes, as they promote conditions conducive for denitrification. [ABSTRACT FROM AUTHOR]

Urban runoff can impact the thermal regime of surface waters and degrade valuable aquatic ecosystems. Some stormwater control measures (SCMs) have been shown to mitigate the effects of thermally-enriched runoff, but previous studies lacked consistency when characterizing the thermal behavior of SCMs. Ecologically-relevant parameters such as maximum outflow temperature, duration of temperatures exceeding thresholds for coldwater species, and thermal load have all been considered in past research. Standard metrics that properly represent the downstream impacts of urban stormwater were needed. This paper evaluated thermal metrics to provide designers and regulators with catchment-scale methods for assessing thermal performance and compliance. It was concluded that multiple metrics must be employed to account for both thermal load and biologically-based reference temperature limits. Metrics for temperature evaluations were broken out by data requirements. When only SCM temperature data are available, event mean temperature estimation appears to be the most rigorous metric. Groundwater temperature may also be employed as a surrogate metric for SCM discharge temperatures if conservative protection of coldwater stream health is desired. When SCM temperature and flow data exist, thermal load reductions should be explored. Efficacy of the low impact development (LID) strategy for temperature mitigation (retaining onsite greater than the 95th percentile storm event) was evaluated using field-collected permeable pavement data. Based on these data, retaining the 95th percentile storm event was determined to be an effective technique for thermal protection of surface waters. However, the most rigorous metrics involve long-term temperature and flow data from local reference streams. The best metric currently available is the uniform continuous above threshold (UCAT) method, in which it is necessary to consider continuous exposure duration when comparing against biological thresholds. These analyses can be tailored to specific species of interest within a targeted ecoregion. Combined with thermal load and mixing analysis in-stream, the UCAT method can provide a real-world estimation of the impacts of development. Additionally, evaluation of mixing zones in-stream should also be employed to adequately assess thermal impacts. However, these methods are the most data intensive. The metrics discussed in this paper can be used to inform new and existing design methodologies for regulating stormwater temperature, duration, and thermal load. [ABSTRACT FROM AUTHOR]

Abstract: Wetlands provide various ecosystem services. One of these services includes nutrient storage in soils. Soils retain and release nutrients such as phosphorus (P). This dynamic can be controlled by soil characteristics, overlying water quality, environmental conditions and historical nutrient loading. Historical nutrient loading contributes to a legacy of P stored in soils and this may influence present day P dynamics between soil and water. We quantified P characteristics of wetland soils and determined the availability and capacity of soils to retain additional P loadings. We sampled surface (0–10) and subsurface (10–30) wetland soils within dairy, improved and unimproved pastures. Surface soils had much greater concentrations of organic and inorganic P. Wetland soils in dairy had greatest concentrations of Ca and Mg, probably due to inputs of inorganic fertilizer. They also had much greater total P, inorganic P, and P sorption capacity; however, these soils were P saturated and had little capacity to retain additional P loading. Improved and unimproved pasture wetland soils had greatest amounts of organic P (>84%) and a capacity to store additional P loadings. Using multivariate statistics, we determined that rather than being different based on land use, wetland soils in improved and unimproved pasture were dissimilar based upon organic matter, organic P fractions, residual P, and soil metal (Fe and Al) content. The legacy of stored P in soils, particularly wetland soils from dairies, combined with best management practices (BMPs) to reduce nutrient loading to these systems, could contribute to a short-term release of soil-stored P to overlying wetland water. [Copyright &y& Elsevier]

Abstract: Ditch fencing and culvert cattle crossing Best Management Practice (BMP) was evaluated in this study with regard to phosphorus (P) and nitrogen (N) load reductions and economic feasibility in the Lake Okeechobee (LO) basin. The BMP was implemented at a 170m section of a drainage ditch within a ranch in the LO basin and flow and concentration (N and P) data at the upstream and downstream of the ditch were collected for one pre-BMP (June–October, 2005) and three post-BMP (June–October, 2006–2008) periods. During the pre-BMP period, downstream total P (TP) load was 20% (67.0kg) higher than the upstream, indicating the cattle crossing to be a source of P. Downstream loads of TP in 2006 and 2008 (post-BMP periods) became 26% (14.7kg) and 11% (85.9kg) lower than the upstream loads, respectively indicating that the BMP reduced the P loads. The site was a sink for N for all periods except the 2007. Unusual dry conditions during 2007 resulted in the addition of P and N at the BMP site, probably due to the release of P and N from soil and plants. Average of three post-BMP period load showed a 10% reduction of TP loads at the downstream (251.8kg) compared to the upstream (281.0kg) location. To consider potential P contributions from the soil and plant, two scenarios, conservative and liberal, were considered to estimate P load reductions due to the BMP. For the conservative scenario, P contribution from soil and plant was considered, while for liberal it was not. Reductions in P loads for conservative and liberal scenarios were 0.35 and 0.44kg/day, respectively. Phosphorus removal cost for the conservative scenario was $12.61/kg of P, which is considerably less than the cost of other P reduction strategies in the basin. Overall, results show that the BMP can reduce P concentration and loads from ranches without causing adverse impact on cattle production. [Copyright &y& Elsevier]

Abstract: Runoff quantity and quality from a 248m2 extensive green roof and a control were compared in Connecticut using a paired watershed study. Weekly and individual rain storm samples of runoff and precipitation were analyzed for TKN, NO3 +NO2–N, NH3–N, TP, PO4–P, and total and dissolved Cu, Pb, Zn, Cd, Cr, and Hg. The green roof watershed retained 51.4% of precipitation during the study period based on area extrapolation. Overall, the green roof retained 34% more precipitation than predicted by the paired watershed calibration equation. TP and PO4–P mean concentrations in green roof runoff were higher than in precipitation but lower than in runoff from the control. The green roof was a sink for NH3–N, Zn, and Pb, but not for TP, PO4–P, and total Cu. It also reduced the mass export of TN, TKN, NO3 +NO2–N, Hg, and dissolved Cu primarily through a reduction in stormwater runoff. Greater than 90% of the total Cu, Hg, and Zn concentrations in the green roof runoff were in the dissolved form. The growing media and slow release fertilizer were probable sources of P and Cu in green roof runoff. Overall, the green roof was effective in reducing stormwater runoff and overall pollutant loading for most water quality contaminants. [Copyright &y& Elsevier]