Effects of land use, climate, and imperviousness on urban stormwater quality: A meta-analysis

Characterizing nitrogen deposited on urban road surfaces: Implication for stormwater runoff pollution control

Nitrogen (N) is one of the most important pollutants on urban road surfaces. Understanding the N deposition forms, load characteristics, and influential factors can help to provide management and control strategies for road stormwater runoff pollution. This study focuses on a highly urbanized area in Guangzhou, China, and presents the characteristics of both dissolved and particulate N deposition forms as well as their correlations with land-use types and traffic factors. In addition, an artificial neural network (ANN) based classification model is utilized to estimate N pollution hotspot area and total nitrogen (TN) flux from road to receiving water bodies. The results showed that N on urban road surfaces mainly existed in the form of particulate organic nitrogen. Land use types dominated by residential area (RA) and urban village (UV) have higher TN build-up loads. Geodetector analysis indicated that land use has a greater impact on nitrogen build-up loads than traffic factors. Through classification and estimation using the ANN model, RA, and UV were classified as hotspot areas, and the TN flux from roads in the study area was calculated to be 3.35 × 105 g. Furthermore, it was estimated that the annual TN flux from roads in Guangzhou accounts for 19 % of the city's total urban domestic discharge. These findings are expected to contribute to the pollution control of stormwater runoff from urban road surfaces and provide valuable guidance for enhancing the ecological health of urban water environments.

Effects of mixed land use on urban stormwater quality under different rainfall event types

The joint effect of mixed land uses and rainfall event types was studied using a two-year field monitoring program in four urban catchments in Calgary, Alberta, Canada. Event mean concentration (EMC) and event pollutant load (EPL) were employed to evaluate the total suspended sediment (TSS), nitrogen and phosphorus. The correlation analysis showed that most nitrogen and phosphorus components (except for NO2-/NO3- and TDP) predominantly exist in particulate form in the study areas. The correlation for EPL was notably stronger than EMC, which can be attributed to varying rainfall characteristics. The differences in EMCs and EPLs of TSS, nitrogen and phosphorus across catchments indicated that the complexity and spatial distribution of mixed land use can influence the generation and transportation of pollutants in urban runoff. The impacts of rainfall characteristics on stormwater quality are integrated rather than driven by a single rainfall characteristic. Brief but intense events tended to elevate TSS, nitrogen and phosphorus concentrations, especially in complex land-use catchments. Events with long antecedent dry days and short duration also resulted in increased pollutant concentrations, while events with long duration and low intensity could result in higher EPLs. The effect of mixed land use on water quality can vary depending on rainfall event types. Seasonal variations were found in EMC and EPL of TSS, nitrogen and phosphorus, with higher values in the spring and summer than the fall. Seasonal variations are mainly influenced by rainfall conditions, temperature and anthropogenic activities (e.g. lawn fertilization and de-icing with sands). MLR considering rainfall characteristics is an effective method for predicting stormwater quality within a single catchment. Considering complexity and spatial distribution of mixed land use can improve the accuracy of the harmonized MLR model. This research provided insights into understanding the complexities introduced by mixed land use and rainfall event types in urban stormwater quality.

The interaction of microplastic and heavy metal in bioretention cell: Contributions of water-soil-plant system

The effectiveness of bioretention cells for heavy metals (HMs) and microplastics (MPs) removal from stormwater runoff has been demonstrated. Knowledge of the mechanisms that dictate the interactions between MPs and HMs would be helpful in pollution control. In this study, the performances of different water-soil-plant bioretention cells for HMs removal through the interception of polyethylene MPs (PE-MPs) were investigated. The results showed that PE-MPs bound to HMs and preferentially tended to bind to Pb (32%-44%) in the complex HMs (Cu, Zn, Cd, and Pb). This could be the reason that the concentration of Pb significantly increased in the effluent under low-intensity simulated rainfall events over a long duration. The accumulation of 1.49 g/kg PE-MPs caused a significant soil pH value decrease and a notable soil zeta potential increase in the bioretention cell, while the low sand/silt ratio media buffered this process. The retention of PE-MPs increased 138.5% in the 0-10 cm soil surface layer when the sand/silt ratio reduced from 2:1 to 1:1 and planted with Canna indica. Meanwhile, PE-MPs amplified the instability of Zn removal in bioretention cells under low-intensity rainfall events in long-duration, high silt percentage substrate and vegetation coverage. The study would contribute to developing a long-term management program for PE-MPs and HMs trapped in bioretention cells to reduce the risk of pollution transport.

Effects of landscape changes on water quality: A global meta-analysis

Landscape changes resulting from anthropogenic activities and climate changes severely impact surface water quality. A global perspective on understanding their relationship is a prerequisite for pursuing equity in water security and sustainable development. A sequent meta-analysis synthesizing 625 regional studies from 63 countries worldwide was conducted to analyze the impacts on water quality from changing landscape compositions in the catchment and explore the moderating factors and temporal evolution. Results exhibit that total nitrogen (TN), total phosphorus (TP), and chemical oxygen demand (COD) in water are mostly concerned and highly responsive to landscape changes. Expansion of urban lands fundamentally degraded worldwide water quality over the past 20 years, of which the arid areas tended to suffer more harsh deterioration. Increasing forest cover, particularly low-latitude forests, significantly decreased the risk of water pollution, especially biological and heavy metal contamination, suggesting the importance of forest restoration in global urbanization. The effect size of agricultural land changes on water quality was spatially scale-dependent, decreasing and then increasing with the buffer radius expanding. Wetland coverage positively correlated with organic matter in water typified by COD, and the correlation coefficient peaked in the boreal areas (r=0.82, p<0.01). Overall, the global impacts of landscape changes on water quality have been intensifying since the 1990s. Nevertheless, knowledge gaps still exist in developing areas, especially in Africa and South America, where the water quality is sensitive to landscape changes and is expected to experience dramatic shifts in foreseeable future development. Our study revealed the worldwide consistency and heterogeneity between regions, thus serving as a research roadmap to address the quality-induced global water scarcity under landscape changes and to direct the management of land and water.

Assessing the removal of heavy metals and polycyclic aromatic hydrocarbons and occurrence of metal resistance genes and antibiotic resistance genes in a stormwater bioretention system

Bioretention basins are extensively used in urban areas to manage stormwater by reducing peak flows and pollution. This study evaluated the performance of a bioretention basin in removing heavy metals, polycyclic aromatic hydrocarbons (PAHs), and oil and grease. Using droplet digital PCR (ddPCR), the presence of metal resistance genes (MRGs) and antibiotic resistance genes (ARGs) in the basin's soil was analyzed. The results indicated effective removal of Zn (67%), but higher concentration of Mg was observed at the outlet. Cu, Fe and Pb showed no significant differences in the in- and outflow concentrations. The system successfully removed 82% of influent PAHs. Soil samples collected in summer and fall revealed higher MRG abundance in summer, with copA being the most prevalent MRG (1.2 to 4.8 log10 copies/g soil). Among the ARGs, sul1 was consistently found throughout the basin (2.5 to 6.7 log10 copies/g soil), while tetW was detected primarily at the basin's start and end in the topsoil layer. Rubellimicrobium and Geobacter were identified as potential carriers of ARGs/MRGs. Although the concentration of metals in soil was not measured in the current study, these findings emphasize the need to understand heavy metal distribution and the occurrence of MRGs and ARGs in stormwater control systems to improve their design and effectiveness. ENVIRONMENTAL IMPLICATION: Various chemical pollutants, including heavy metals, polycyclic aromatic hydrocarbons (PAHs), and organic compounds, pose significant health concerns in stormwater. While bioretention basins mitigate peak flows and pollution in urban areas, their role as reservoirs of metal resistance genes (MRGs) and antibiotic resistance genes (ARGs) remains understudied. This study examined heavy metal, PAH, and oil & grease removal in an urban retention basin. Additionally, sulfonamide and tetracycline ARGs, and lead, zinc, and copper MRGs were assessed in the basin soil. Understanding the distribution of these elements and genes is vital for improving stormwater management design and effectiveness.

A model-based analysis for trapping suspended sediment in stormwater inlets of urban drainage network

Raised awareness of environmental constraints in recent decades has led stormwater management to incorporate quality components and focus on the treatment of urban runoff water at pollutant source areas. This study evaluated the impact of a developed type of sediment trap, installed into stormwater inlets, on the total suspended solids (TSS) load in an urban city center catchment in Finland. The objective was to outline a modelling approach to assess efficiency of the traps to treat TSS originating from different land uses (green areas, pavement, parking, roof, street, and other areas not belonging to the main land uses). A Storm Water Management Model (SWMM) parametrization of a 5.87 ha catchment in the Lahti city center, Finland was utilized as the computation engine. The model had separate subcatchments for each land use, allowing the use of literature-based Event Mean Concentrations (EMC) to estimate the TSS pollutant washoff for the land uses. A method to assess the individual stormwater inlet pollutant loads and potential removal effect of the sediment traps was introduced. The hydrological and TSS load simulations covered a period of 6 months. The stormwater network inlets installed with sediment traps were ranked according to their potential removal of TSS. One out of five EMC sets was selected to be representative of the urban land uses in the study site (green areas 75 mg/l, pavement 46 mg/l, parking 44 mg/l, roof 20 mg/l, street 64 mg/l, other 46 mg/l). The simulation results showed the influence of land uses on the pollutant load and revealed the optimal set of locations for the sediment traps. Additionally, the effect of regular maintenance intervals on the pollutant load, given a maximum storage capacity of the traps, was explored. The results showed a large variation in TSS removal depending on the inlets chosen for the sediment traps, with removal rates ranging from about 0 % to 10 % of catchment TSS load. The maximum TSS removal was 63 %, which was the reported efficiency of the traps. These results highlighted the need for an informed decision when selecting trap locations. Streets and parking lots were the largest TSS contributors, with stormwater inlets on streets being the desired sediment trap locations. While the absolute level of simulated TSS load was found to be dependent on the EMCs, the ranking of sediment trap locations was similar for the simulations with different EMC data sets.

Review of trace organic chemicals in urban stormwater: Concentrations, distributions, risks, and drivers

Urban stormwater, increasingly seen as a potential water resource for cities and towns, contains various trace organic chemicals (TrOCs). This study, conducted through a comprehensive literature review of 116 publications, provides a detailed report on the occurrence, concentration distribution, health, and ecological risks of TrOCs, as well as the impact of land use and rainfall characteristics on their concentrations. The review uncovers a total of 629 TrOCs detected at least once in urban stormwater, including 228 pesticides, 132 pharmaceutical and personal care products (PPCPs), 29 polycyclic aromatic hydrocarbons (PAHs), 30 per- and polyfluorinated substances (PFAS), 28 flame retardants, 24 plasticizers, 22 polychlorinated biphenyls (PCBs), nine corrosion inhibitors, and 127 other industrial chemicals/intermediates/solvents. Concentration distributions were explored, with the best fit being log-normal distribution. Risk assessment highlighted 82 TrOCs with high ecological risk quotients (ERQ > 1.0) and three with potential health risk quotients (HQ > 1.0). Notably, 14 TrOCs (including six PAHs, five pesticides, three flame-retardants, and one plasticizer) out of 68 analyzed were significantly influenced by land-use type. Relatively weak relationships were observed between rainfall characteristics and pollutant concentrations, warranting further investigation. This study provides essential information about the occurrence and risks of TrOCs in urban stormwater, offering valuable insights for managing these emerging chemicals of concern.

Developing simple indicators of nitrogen and phosphorus removal in constructed stormwater wetlands

Quantifying pollutant removal by stormwater wetlands requires intensive sampling which is cost-prohibitive for authorities responsible for a large number of wetlands. Wetland managers require simple indicators that provide a practical means of estimating performance and prioritising maintenance works across their asset base. We therefore aimed to develop vegetation cover and metrics derived from monitoring water level, as simple indicators of likely nutrient pollutant removal from stormwater wetlands. Over a two-year period, we measured vegetation cover and water levels at 17 wetlands and used both to predict nitrogen (N) and phosphorus (P) removal. Vegetation cover explained 48 % of variation in total nitrogen (TN) removal; with a linear relationship suggesting an approximate 9 % loss in TN removal per 10 % decrease in vegetation cover. Vegetation cover is therefore a useful indicator of TN removal. Further development of remotely-sensed data on vegetation configuration, species and condition will likely improve the accuracy of TN removal estimates. Total phosphorus (TP) removal was not predicted by vegetation cover, but was weakly related to the median water level which explained 25 % of variation TP removal. Despite weak prediction of TP removal, metrics derived from water level sensors identified faults such as excessive inflow and inefficient outflow, which in combination explained 50 % of the variation in the median water level. Monitoring water levels therefore has the potential to detect faults prior to loss of vegetation cover and therefore TN removal, as well as inform the corrective action required.

Modelling relationships between land use and water quality using statistical methods: A critical and applied review

Land use/land cover (LULC) can have significant impacts on water quality and the health of aquatic ecosystems. Consequently, understanding and quantifying the nature of these impacts is essential for the development of effective catchment management strategies. This article provides a critical review of the literature in which the use of statistical methods to model the impacts of LULC on water quality is demonstrated. A survey of these publications, which included hundreds of original research and review articles, revealed several common themes and findings. However, there are also several persistent knowledge gaps, areas of methodological uncertainty, and questions of application that require further study and clarification. These relate primarily to appropriate analytical scales, the significance of landscape configuration, the estimation and application of thresholds, as well as the potentially confounding influence of extraneous variables. Moreover, geographical bias in the published literature means that there is a need for further research in ecologically and climatically disparate regions, including in less developed countries of the Global South. The focus of this article is not to provide a technical review of statistical techniques themselves, but to examine important practical and methodological considerations in their application in modelling the impacts of LULC on water quality.

New optimization strategies for SWMM modeling of stormwater quality applications in urban area

Build-up/wash-off models were originally developed for small-scale laboratory facilities with uniform properties. The effective translation of these models to catchment scale necessitates the meticulous calibration of model parameters. The present study combines the Mat-SWMM tool with a genetic algorithm (GA) to improve the calibration of build-up and wash-off parameters. For this purpose, Mat-SWMM was modified to equip it with the capacity to provide comprehensive water quality analysis outcomes. Additionally, this research also conducts a comparative examination of two distinct types of objective functions in the optimization. Rather than depending on previous literature, this study undertook a numerical campaign to ascertain an appropriate range for the relevant parameters within the case study, thereby ensuring the optimization algorithm's efficient functionality. This research also implements an integrated event calibration approach, i.e., a novel method that calibrates all rainfall events collectively, thus improving systemic interaction representation and model robustness. The findings indicate that employing this methodology significantly enhances the reliability of the outcomes, thereby establishing a more robust procedure. The first objective function (TSS instantaneous less squared difference function, OF 1), which is widely employed in the literature, was designed to minimize the difference between observed and predicted instantaneous Total Suspended Solids (TSS) concentrations. In contrast, the second function (mass and mass peak consistency function, OF 2) considers integral model outputs, i.e., the overall mass balance, the time of the peak mass flow rate, and its intensity. The analysis of the outputs revealed that both objective functions demonstrated sufficient performance. OF 1 provided slightly better performance in predicting the TSS concentrations, whereas OF 2 demonstrated superior ability in capturing global event characteristics. Notably, the optimal parameter set identified through OF 2 aligned with the physically plausible ranges traditionally recommended in technical manuals for urban catchments. In contrast, OF 1's optimal set necessitated an expansion in the acceptable parameter ranges. Finally, from a computational burden viewpoint, OF 1 demanded a significantly higher number of function evaluations, thus implying an escalating computational cost as the range expands. Conversely, OF 2 necessitated fewer evaluations to converge toward the optimal solution.

Monitoring the impacts of rainfall characteristics on sediment loss from road construction sites

Exposed soils associated with active construction sites provide opportunities for erosion and sediment transport during storm events, introducing risks associated with excess sediment to downstream infrastructure and aquatic biota. A better understanding of the drivers of sediment transport in construction site runoff is needed to improve the design and performance of erosion and sediment control measures (ESCMs). Eleven monitoring locations on 3 active road construction sites in central Ohio were established to characterize runoff quality from points of concentrated flow during storm events. Grab samples were analyzed for total suspended solids (TSS), turbidity, and particle size distribution (PSD). Median TSS concentrations and turbidity levels across all samples were 626 mg/L (range 25-28,600 mg/L) and 759 NTU (range 22-33,000 NTU), respectively. The median PSD corresponded to a silty clay loam, mirroring the soil texture of much of Ohio's subsoils. TSS concentrations and turbidity were significantly positively correlated with the rainfall intensity 10 min prior to sample collection, suggesting that higher flow rates created greater shear stress on bare soil which resulted in more erosion. Conversely, rainfall duration was negatively correlated with particle size, indicating that prolonged moisture from rainfall promoted the dispersion of soil aggregates which mobilized smaller particles. Multivariable linear regression models revealed that higher rainfall intensities corresponded to higher turbidity values, while higher TSS concentrations were associated with higher rainfall intensities, depths, and durations. Results from this study highlight the importance of reducing raindrop impact and subsequent shear stress applied by concentrated flows through the use of ESCMs to limit sediment export from construction sites.

Influence of landscape patterns on nitrate and particulate organic nitrogen inputs to urban stormwater runoff

This study investigated the effect of the landscape pattern of permeable/impermeable patches on NO3--N and particulate organic nitrogen (PON) concentrations during stormwater runoff transport and their source contributions. Six landscape pattern indices, namely, mean proximity index (MPI), largest patch index (LPI), mean shape index (MSI), landscape shape index (LSI), connect index (CONNECT), and splitting index (SPLIT), were selected to reflect the fragmentation, complexity, and connectivity of permeable patches in urban catchments. The results show that lower fragmentation, higher complexity, and greater connectivity can reduce NO3--N concentrations in road runoff and drainage flow (i.e., the flow in the stormwater drainage network), as well as PON concentrations in road runoff. Further, the above landscape pattern is effective for mitigating the contributions of NO3--N and PON from road runoff. Low impact development (LID) can be incorporated with the landscape pattern of permeable/impermeable patches to mitigate nitrogen pollution in urban stormwater at the catchment scale by optimizing the spatial arrangement.

Measuring sediment loads and particle size distribution in road runoff: Implications for sediment removal by stormwater control measures

Road runoff contributes an array of pollutants which degrade the quality of receiving waters. Sediment conveyed in runoff results in loss of habitat and loss of reservoir capacity, among other undesirable impacts. To select and design stormwater control measures (SCMs), the sediment particle size distribution (PSD) is needed to quantify the required hydraulic retention time for particle settling and to understand what other treatment processes (e.g., filtration) are needed to meet sediment removal targets. A two-year field monitoring study was undertaken across the state of Ohio, USA, to evaluate the PSD of sediment in runoff at twelve roads. The highest TSS concentrations were observed on interstate highways (highest annual average daily traffic [AADT]) and minor arterials (low AADT), suggesting factors beyond AADT, such as antecedent dry period, rainfall intensity, and windborne dust and particulates, contribute to the varied sediment characteristics in runoff. The median TSS load across all samples collected was 2.7 kg/ha per storm event, while annual TSS loads for the monitoring sites varied from 98 kg/(ha·yr) to 519 kg/(ha·yr), with a mean value of 271 kg/(ha·yr). Particle size distributions varied across the monitoring sites, with mean and median d50 of 48.6 μm and 52.5 μm, respectively. Interstate highways (highest AADT) had significantly finer PSDs than other functional classes, while roads in low density residential areas had coarser PSDs than other land uses. Observed differences in PSD across road characteristics may guide SCM selection; dry detention basins and wet ponds/wetlands were predicted to provide effective removal across a variety of PSDs, while TSS reductions provided by hydrodynamic separators and high-flow media filters (which effectively remove larger particles) may be maximized in areas with coarser PSDs (e.g., roads surrounded by low density residential areas studied herein).

Curbing sediment: The effects of added surface roughness in the curb and gutter as a novel pretreatment for green infrastructure stormwater control measures

Stormwater control measures (SCMs) are employed to reduce the multitude of deleterious impacts of urban runoff on receiving waters. Sediment accumulation in infiltration-based SCMs can clog these systems, resulting in lack of hydraulic function and reduced stormwater treatment efficacy. As such, pretreatment devices, such as forebays, filter strips, or catch basin sumps, are typically employed upstream of SCMs to remove sediment and prolong maintenance intervals. However, the tendency of SCMs to be retrofitted into space-constrained, ultra-urban areas makes including pretreatment technologies difficult. An alternative pretreatment device for green infrastructure SCMs was developed and tested in the laboratory; alterations were made to the standard curb and gutter, which is ubiquitous within urban environments, to increase the roughness of these surfaces. Roughness was added to the curb and/or gutter of mock road sections constructed of expanded polystyrene (EPS) foam using a computer numerical control (CNC) router. Twenty-one patterns with varying degrees of depth, shape, and spacing were implemented to trap sediment from simulated runoff; samples were collected upstream and downstream of the added roughness and analyzed for sediment removal and particle capture. Patterns which included added roughness in both the curb and gutter reduced total suspended solids (TSS) concentrations by up to 95% (median 85%) and reduced median d50 and d90 in runoff from 46.9 to 39.4 μm and 322 to 100 μm, respectively. Continued TSS removal was observed during repeated testing designed to simulate up to seven runoff events, indicating the potential for sustained sediment accumulation before the need for maintenance via regular street sweeping. With routine maintenance performed at appropriate intervals, these findings indicate that added roughness to curb and gutters could be utilized as a viable pretreatment technology for green infrastructure SCMs.

Environmental regulations in the United States lead to improvements in untreated stormwater quality over four decades

Identifying sources of pollutants in watersheds is critical to accurately predicting stormwater quality. Many existing software used to model stormwater quality rely on decades-old data sets which may not represent current runoff quality in the United States. Because of environmental regulations promulgated at the federal level over previous decades, there is a need to understand long-term trends (and potential shifts) in runoff quality to better parameterize models. Pollutant event mean concentrations (EMCs) from the National Stormwater Quality Database (NSQD) were combined with those from recent sources to understand if untreated stormwater quality has changed over the past 40 years. A significant decreasing monotonic trend (i.e., continually decreasing in a nonuniform fashion) was observed for total suspended solids (TSS), total phosphorus (TP), total Kjeldahl nitrogen (TKN), total copper (Cu), total lead (Pb), and total zinc (Zn) in the resultant database, suggesting that runoff quality has become less polluted with time. Median EMCs decreased from 99.2 to 42 mg/L, 0.34 to 0.26 mg/L, 1.27 to 1.03 mg/L, 40 to 6.8 µg/L, 110 to 3.7 µg/L, and 375 to 53.3 µg/L for TSS, TP, TN, Cu, Pb, and Zn, respectively, from the 1980s to the 2010s. These significant reductions often aligned temporally with advancements in clean manufacturing, amendments of the Clean Air Act, and other source control efforts which impact pollutant bioavailability and atmospheric deposition. Results suggest environmental regulations not specifically targeting stormwater management have had a positive impact on stormwater quality and that temporal fluctuations should be considered in modeling.

Spatial variations in the associations of surface water quality with roads and traffic across an urbanization gradient in northern Georgia, USA

Roads and traffic are important elements of urbanization, but their spatial associations with surface water quality in watersheds have been seldom studied. In this study, the spatially varying associations of three urbanization indicators, including road density, traffic density, and percentages of urban land, with twenty water quality indicators, including dissolved oxygen (DO), specific conductance (SC), dissolved solids (DS), suspended solids (SS), biochemical oxygen demand (BOD), dissolved nutrients, dissolved ions, heavy metals, and coliform bacteria, across the watersheds in the northern part of the state of Georgia, USA, have been examined by a conventional statistical method, ordinary least squares regression (OLS), and a spatial statistical method, geographically weighted regression (GWR). The results from OLS show that the urbanization indicators all have significant positive associations with the majority of the studied water pollutants, indicating that water pollution is significantly contributed by human activities related to urbanization in northern Georgia. In contrast, GWR results show that the associations vary across the watersheds affected by their urbanization levels. Significant positive associations are found between each urbanization indicator and each of the studied water pollutants, but not in all watersheds. The associations of suspended solids, nitrogen nutrients, and coliform bacteria with all three urbanization indicators are more significant in less-urbanized watersheds, while the associations of dissolved ions, BOD, and orthophosphate (PO4) with road density and traffic density are more significant than those with urban land in more-urbanized watersheds, indicating that those water pollutants are more contributed by human activities associated with roads and traffic than other activities in more-urbanized areas. As a pilot study to explore how and why the associations of surface water quality with roads and traffic change across watersheds with different urbanization levels, its findings suggest that the policies of watershed management, land-use planning, and transportation planning should be tailored in local areas based on the locally important water pollutants and their associated urbanization indicators.

Impact of wood-derived biochar on the hydrologic performance of bioretention media: Effects on aggregation, root growth, and water retention

Bioretention systems are one example of green stormwater infrastructure that may mitigate the hydrologic impact of stormwater runoff. To improve water retention while maintaining rapid stormwater infiltration, conventional bioretention soil media (BSM) might be augmented with biochar. Biochar may improve the BSM's structure by increasing soil aggregation, which might improve water retention and increase stormwater infiltration while also improving root growth. Pots with BSMs representing high and moderate sand content media were amended with a wood-derived biochar, planted with switchgrass, and subjected to weekly storms for 20 weeks, followed by a 10-week drought. In the high sand content medium (NC mix), biochar amendment increased hydraulic conductivity (K_sat), and this effect increased with time. At 0 weeks, 2% and 4% (w/w) biochar increased K_sat by 4 ± 2% and 10 ± 4%, respectively, while at 30 weeks the increase was 30 ± 10 and 70 ± 20%, respectively, above biochar-free media. Similar improvements were seen in plant available water (PAW) in NC mix. However, minimal improvements in K_sat and PAW from biochar amendment were found in the moderate sand content BSM that contained compost and mulch (DE mix). Where biochar promoted K_sat, this was correlated with increased water-stable aggregate size (r = 0.86), fine root volume (r = 0.88), and below ground biomass (r = 0.83). Important factors affecting K_sat and aggregation in the NC mix were biochar's influence on organo-mineral association, fungal hyphae length, and plant roots. Wood-derived biochar amendment to BSM may obviate the need for compost/mulch since biochar has similar effects on improving BSM hydrology and root growth without the risk of undesired nutrient leaching.

Monitoring the effects of urban and forested land uses on runoff quality: Implications for improved stormwater management

Urban stormwater is a substantial source of non-point source pollution. Despite considerable monitoring efforts, little is known about stormwater quality in certain geographic regions. These spatial gaps induce uncertainty when extrapolating data and reduce model calibration capabilities, thereby limiting pollutant load reduction strategies. In this study, stormwater quality was monitored from 15 watersheds to characterize pollutant event mean concentrations (EMCs) and loads as a function of urban and forested (i.e., surrogates for pre-development) land use and land covers (LULCs) and rainfall patterns from a geographic region where these data are sparse. Residential and heavy industrial, heavy industrial, and industrial and commercial LULCs, respectively, were the primary generators of nutrients, total suspended solids (TSS), and heavy metals. Increased rainfall intensities (average and peak) significantly increased the EMCs of all particulate bound pollutants. Pollutant loads increased with rainfall depth and, in general, did not follow the same LULC trends as EMCs, suggesting loads were influenced substantially by watershed hydrologic responses. Mean annual urban loads of total phosphorus, total nitrogen, TSS, and zinc (Zn) ranged from 0.4 (low density residential [LDR]) to 1.5 (heavy industrial), 3.2 (single family residential [SFR]) to 11.5 (heavy industrial), 122.6 (SFR) to 1219.9 (heavy industrial), and 0.1 (LDR) to 0.7 (commercial) kg/ha/yr, respectively. Annual urban loads of TSS were 3.5 to 34 and - 1.5 to 6.8-fold greater than annual loads from forested and agricultural watersheds, respectively. Mean annual loads of heavy metals from urban LULCs were substantially greater than loads produced by forested and agricultural watersheds (e.g., 8.6 to 92 and 6.8 to 73-fold greater, respectively, for Zn), while loads of nutrients were generally similar between urban and agricultural watersheds. Findings herein suggest non-point source pollution will continue to threaten surface water quality as land is developed; results can help guide the development of cost-efficient stormwater management strategies.

Appraisal of stormwater-induced runoff quality influenced by site-specific land use patterns in the south-eastern region of Bangladesh

Urban stormwater runoff is considered as one of the major contributors to nonpoint source that contributes to the pollution of all water resources in the surrounding environment. Pollutant concentrations of urban stormwater runoff are directly or indirectly linked with land use types in a catchment that is quite different in different places, and hence, site-specific studies are necessary, unless otherwise the modelling of runoff quality using modelling tools may not be rationally reflected the actual field scenarios. This paper portrays the influence of land use types on stormwater runoff physicochemical quality in Chattogram city, where land use's demarcation is often complicated due to the different natural and human-induced anthropogenic factors. The stormwater runoff samples were collected from the residential, commercial, institutional, and industrial land use types, in the city of Chattogram, Bangladesh, during the period from July to September 2020. The standard laboratory protocol for elemental concentrations and principal component analysis was performed in addition to basic statistics to identify the influence of urban surface characteristics on the quality of stormwater runoff. In general, pollutant concentrations were identified by analysing key physical and chemical quality parameters including colour, temperature, turbidity, total suspended solids (TSS), total dissolved solids (TDS), electrical conductivity (EC), salinity, pH, dissolved oxygen (DO), biochemical oxygen demand (BOD₅), chemical oxygen demand (COD) and ammonia nitrogen (NH₃-N) and exhibited 2 to 3 times higher concentrations than reported elsewhere. Furthermore, the present study reported the greater concentrations of few pollutants, such as TSS, BOD₅, and EC, derived from the residential land uses compared to other land use types that are surprising; however, it confirmed the distinct complexity of unplanned land use patterns that should not be overlooked rather discussed. The strong correlation between land use types and stormwater runoff quality indicates the site-specific influences of runoff quality. The outcomes of this study would be particularly helpful in calibrating water quality models considering different land use types. Additionally, datasets and information obtained from this research will assist engineers and practitioners in developing decision-making tools for effective stormwater management.

Optimizing floating treatment wetland and retention pond design through random forest: A meta-analysis of influential variables

Floating treatment wetlands (FTWs), artificial systems constructed from buoyant mats and planted with emergent macrophytes, represent a potential retrofit to enhance the dissolved nutrient removal performance of existing retention ponds. Treatment occurs as water flows through the dense network of roots suspended in the water column, providing opportunities for pollutants to be removed via filtration, sedimentation, plant uptake, and adsorption to biofilms in the root zone. Despite several recent review articles summarizing the growing body of research on FTWs, FTW design guidance and strategies to optimize their contributions to pollutant removal from stormwater are lacking, due in part to a lack of statistical analysis on FTW performance at the field scale. A meta-analysis of eight international FTW studies was performed to investigate the influence of retention pond, catchment, and FTW design characteristics on effluent concentrations of nutrients and total suspended solids (TSS). Random forest regression, a tree-based machine learning approach, was used to model complex interactions between a suite of predictor variables to identify design strategies for both retention ponds and FTWs to enhance treatment of nutrient and sediment. Results indicate that pond design features, especially loading ratio and pond depth (which should be limited to 200:1 and 1.75 m, respectively), are most influential to effluent water quality, while the benefits of FTWs were limited to improving mitigation of phosphorus species and TSS which was primarily influenced by FTW coverage and planting density. Findings from this work inform wet retention pond and FTW design, as well as guidance on scenarios where FTW implementation is most appropriate, to improve dissolved nutrient and sediment removal in urban runoff.