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1. Modeling Spatio-Temporal Dynamics of BMPs Adoption for Stormwater Management in Urban Areas

   https://doi.org/10.3390/w15142549  

   Zhang, Zeshu; Montas, Hubert; Shirmohammadi, Adel; Leisnham, Paul T.; Rockler, Amanda K. (July 2023, Water)

   Nonpoint source (NPS) pollution is a severe problem in the U.S. and worldwide. Best management practices (BMPs) have been widely used to control stormwater and reduce NPS pollution. Previous research has shown that socio-economic factors affect households’ adoption of BMPs, but few studies have quantitatively analyzed the spatio-temporal dynamics of household BMP adoption under different socio-economic conditions. In this paper, diverse regression approaches (linear, LASSO, support vector, random forest) were used on the ten-year data of household BMP adoption in socio-economically diverse areas of Washington, D.C., to model BMP adoption behaviors. The model with the best performance (random forest regression, R2 = 0.67, PBIAS = 7.2) was used to simulate spatio-temporal patterns of household BMP adoption in two nearby watersheds (Watts Branch watershed between Washington, D.C., and Maryland; Watershed 263 in Baltimore), each of which are characterized by different socio-economic (population density, median household income, renter rate, average area per household, etc.) and physical attributes (total area, percentage of canopy in residential area, average distance to nearest BMPs, etc.). The BMP adoption rate was considerably higher at the Watts Branch watershed (14 BMPs per 1000 housing units) than at Watershed 263 (4 BMPs per 1000 housing units) due to distinct differences in the watershed characteristics (lower renter rate and poverty rate; higher median household income, education level, and canopy rate in residential areas). This research shows that adoption behavior tends to cluster in urban areas across socio-economic boundaries and that targeted, community-specific social interventions are needed to reach the NPS control goal. 

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2. Freshwater Salinization Syndrome Alters Retention and Release of ‘Chemical Cocktails’ along Flowpaths:  from Stormwater Management to Urban Streams

   https://doi.org/10.1086/721469  

   Kaushal, Sujay; Reimer, Jenna E.; Mayer, Paul M.; Shatkay, Ruth R.; Maas, Carly; Nguyen, William D.; Boger, Walter L.; Yaculak, Alexis M.; Doody, Thomas R.; Pennino, Michael; et al (June 2022, Freshwater Science)

   Freshwater salinization syndrome (FSS) refers to the suite of interactive effects of salt ions on degradation of physical, biological,and social systems. Best management practices (BMPs), which are methods to effectively reduce runoff and nonpoint source pollution (stormwater, nutrients, sediments), do not typically consider management of salt pollution. We investigate impacts of FSS on mobilization of salts, nutrients, and metals in urban streams and storm water BMPs by analyzing original data on concentrations and fluxes of salts, nutrients, and metals from 7 urban watersheds in the Mid-Atlantic USA and synthesizing literature data. We also explore future critical research needs through a survey of practitioners and scientists. Our original data show 1) sharp pulses in concentrations of salt ions and metals in urban streams directly following both road salt events and stream restoration construction (e.g.,similar to the way concentrations increase during other soil disturbance activities); 2) sharp declines in pH (acidification) in response to road salt applications because of mobilization of H+ from soil exchange sites by Na+; 3) sharp increases inorganic matter from microbial and algal sources (based on fluorescence spectroscopy) in response to road salt applications, likely because of lysing cells and changes insolubility; 4) substantial retention (~30–40%) of Na+ in stormwater BMP sediments and floodplains in response to salinization; 5) increased ion exchange and mobilization of diverse salt ions (Na+, Ca2+, K+, Mg2+), nutrients(N, P), and trace metals(Cu, Sr) from stormwater BMPs and restored streams in response to FSS; 6) downstream increasing loads ofCl–, SO42–, Br–, F–,andI–along flowpaths through urbanstreams and P release from urban stormwater BMPs in response to salinization; and 7)a substantial annual reduction (>50%) in Na+concentrations in an urban stream when road salt applications were dramatically reduced, which suggests potential for ecosystem recovery. We compare our original results with published metrics of contaminant retention and release across a broad range of stormwater BMPs from North America and Europe.Overall, urban streams and stormwater BMPs consistently retain Na+ and Cl–but mobilize multiple contaminants based on salt types and salinity levels. Finally, we present our top 10 research questions regarding FSS impacts on urban streams and stormwater BMPs. Reducing diverse chemical cocktails of contaminants mobilized by freshwater salinization is a priority for effectively and holistically restoring urban waters. 

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3. Stormwater control impacts on runoff volume and peak flow: A meta‐analysis of watershed modelling studies

   https://doi.org/10.1002/hyp.13784  

   Bell, Colin D.; Wolfand, Jordyn M.; Panos, Chelsea L.; Bhaskar, Aditi S.; Gilliom, Ryan L.; Hogue, Terri S.; Hopkins, Kristina G.; Jefferson, Anne J. (May 2020, Hydrological Processes)

   Abstract Decades of research has concluded that the percent of impervious surface cover in a watershed is strongly linked to negative impacts on urban stream health. Recently, there has been a push by municipalities to offset these effects by installing structural stormwater control measures (SCMs), which are landscape features designed to retain and reduce runoff to mitigate the effects of urbanisation on event hydrology. The goal of this study is to build generalisable relationships between the level of SCM implementation in urban watersheds and resulting changes to hydrology. A literature review of 185 peer‐reviewed studies of watershed‐scale SCM implementation across the globe was used to identify 52 modelling studies suitable for a meta‐analysis to build statistical relationships between SCM implementation and hydrologic change. Hydrologic change is quantified as the percent reduction in storm event runoff volume and peak flow between a watershed with SCMs relative to a (near) identical control watershed without SCMs. Results show that for each additional 1% of SCM‐mitigated impervious area in a watershed, there is an additional 0.43% reduction in runoff and a 0.60% reduction in peak flow. Values of SCM implementation required to produce a change in water quantity metrics were identified at varying levels of probability. For example, there is a 90% probability (high confidence) of at least a 1% reduction in peak flow with mitigation of 33% of impervious surfaces. However, as the reduction target increases or mitigated impervious surface decreases, the probability of reaching the reduction target also decreases. These relationships can be used by managers to plan SCM implementation at the watershed scale. 

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4. Impacts of Land Cover Change on the Spatial Distribution of Nonpoint Source Pollution Based on SWAT Model

   https://doi.org/10.3390/w15061174  

   Zhang, Zeshu; Montas, Hubert; Shirmohammadi, Adel; Leisnham, Paul T.; Negahban-Azar, Masoud (March 2023, Water)

   Nonpoint source (NPS) pollution is a pressing issue worldwide, especially in the Chesapeake Bay, where sediment, nitrogen (N), and phosphorus (P) are the most critical water quality concerns. Despite significant efforts by federal, state, and local governments, the improvement in water quality has been limited. Investigating the spatial distribution of NPS hotspots can help understand NPS pollutant output and guide control measures. We hypothesize that as land cover changes from natural (e.g., forestland) and agricultural to suburban and ultra-urban, the distribution of NPS pollution source areas becomes increasingly spatially uniform. To test this hypothesis, we analyzed three real watersheds with varying land cover (Greensboro watershed for agriculture, Watts Branch watershed for suburban, and Watershed 263 for ultra-urban) and three synthetic watersheds developed based on the Watts Branch watershed, which ranged from forested and agricultural to ultra-urban but had the same soil, slope, and weather conditions. The Soil and Water Assessment Tool (SWAT) was selected as a phenomenological model for the analysis, and SWAT-CUP was used for model calibration and validation. The hydrologic responses of the three real and synthetic watersheds were simulated over ten years (1993–2002 or 2002–2011), and calibration and validation results indicated that SWAT could properly predict the export of runoff and three target NPS pollution constituents (sediment, total nitrogen, and total phosphorus). The results showed that the distribution of NPS pollutant outputs becomes increasingly uniform as land cover changes from agriculture to ultra-urban across watersheds. This research suggests that the spatial distribution of NPS pollution source areas is a function of the major land cover category of study watersheds, and control strategies should be adapted accordingly. If NPS pollution is distributed unevenly across a watershed, hotspot areas output a disproportionate amount of pollution and require more targeted and intensive control measures. Conversely, if the distribution of NPS pollution is more uniform across a watershed, the control strategies need to be more widespread and encompass a larger area. 

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5. Adaptation of SWAT Watershed Model for Stormwater Management in Urban Catchments: Case Study in Austin, Texas

   https://doi.org/10.3390/w15091770  

   Glick, Roger; Jeong, Jaehak; Srinivasan, Raghavan; Arnold, Jeffrey G.; Her, Younggu (May 2023, Water)

   Computer simulation models are a useful tool in planning, enabling reliable yet affordable what-if scenario analysis. Many simulation models have been proposed and used for urban planning and management. Still, there are a few modeling options available for the purpose of evaluating the effects of various stormwater control measures (SCM), including LID (low-impact development) controls (green roof, rain garden, porous pavement, rainwater harvesting), upland off-line controls (sedimentation, filtration, retention–irrigation) and online controls (detention, wet pond). We explored the utility and potential of the Soil and Water Assessment Tool (SWAT) as a modeling tool for urban stormwater planning and management. This study demonstrates how the hydrologic modeling strategies of SWAT and recent enhancements could help to develop efficient measures for solving urban stormwater issues. The case studies presented in this paper focus on urban watersheds in the City of Austin (COA), TX, where rapid urbanization and population growth have put pressure on the urban stormwater system. Using the enhanced SWAT, COA developed a framework to assess the impacts on erosion, flooding, and aquatic life due to changes in runoff characteristics associated with land use changes. Five catchments in Austin were modeled to test the validity of the SWAT enhancements and the analytical framework. These case studies demonstrate the efficacy of using SWAT and the COA framework to evaluate the impacts of changes in hydrology and the effects of different regulatory schemes. 

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