Over the last several decades, interest in green stormwater infrastructure (GSI) has rapidly increased, particularly given its potential to provide stormwater management in conjunction with other ...ecosystem services and co-benefits such as urban heat island mitigation or habitat provision. Here we explore the implementation of GSI in three US cities – Baltimore (Maryland), Phoenix (Arizona), and Portland (Oregon). We examine the trends in GSI construction over several decades, highlighting changes in implementation rates and GSI types with concurrent regulatory and economic changes. Additionally, we discuss the implications of these GSI portfolios for ecosystem service delivery in urban areas. Results indicate that Portland's quantity of GSI is approximately ten times greater than the quantity of GSI in Phoenix or Baltimore. However, Baltimore has the most diverse portfolio of GSI types. In Phoenix, regional stormwater policies focused on flood control have led to retention basins being the dominant GSI type for decades. In contrast, Portland and Baltimore both have had substantial changes in their GSI portfolios over time, with transitions from detention or retention basins and underground facilities toward filters, infiltration facilities, and swales. These changes favor increased water quality function as well as provision of other ecosystem services. Additionally, we find evidence that each city followed a different GSI implementation pathway, with Portland's combined sewer overflow program influencing initial development of GSI, while state legislation and regional water quality pressures played a major role in Baltimore's GSI development. By studying the evolution of GSI in these different cities, we can see the variability in stormwater management trajectories and how they manifest in different suites of benefits. We hope that continued research of GSI implementation and performance will identify opportunities for future improvement of these infrastructures.
The nitrogen (N) cycling dynamics of four stormwater basins, two often saturated sites (“Wet Basins”) and two quick draining sites (“Dry Basins”), were monitored over a ∼ 1-year period. This study ...paired stormwater and greenhouse gas monitoring with microbial analyses to elucidate the mechanisms controlling N treatment. Annual dissolved inorganic N (DIN) mass reductions (inflow minus outflow) were greater in the Dry Basin than in the Wet Basin, 2.16 vs 0.75 g N m–2 yr–1, respectively. The Dry Basin infiltrated a much larger volume of water and thus had greater DIN mass reductions, even though incoming and outgoing DIN concentrations were statistically the same for both sites. Wet Basins had higher proportions of denitrification genes and potential denitrification rates. The Wet Basin was capable of denitrifying 58% of incoming DIN, whereas the Dry Basin only denitrified 1%. These results emphasize the need for more mechanistic attention to basin design because the reductions calculated by comparing inflow and outflow loads may not be relevant at watershed scales. Denitrification is the only way to fully remove DIN from the terrestrial environment and receiving waterbodies. Consequently, at the watershed scale the Wet Basin may have better overall DIN treatment.
As the demand for renewable energy increases, solar energy is becoming an increasingly important power source. Implementing solar energy on a large scale requires solar farm installations on land ...covering hundreds of acres of area. Solar farms alter the existing land use and may affect the catchment’s hydrological response. However, the impact of solar farms on catchment hydrology is not well understood, partly due to the lack of established modeling methods tailored to their unique land cover. The areas over which solar panels are installed are impervious on the panel and pervious underneath it, making it challenging to model. This study proposes a framework to model the hydrological response of a solar farm using the United States Environmental Protection Agency (US EPA) Storm Water Management Model (SWMM). The framework divides each row of the solar farm into four sections, the impervious solar panel, a wet section at the dripline that captures the majority of runoff from the panel, a spacer section that encompasses the space between the solar panel rows, and an under-panel section which represents the space under the solar panel. The runoff from one section is routed to the next section in the order of natural water flow. All four sections together represent one row of the solar farm, so runoff from each row is then routed to the next row until the outlet. With this general setup, many variables, such as land cover, the slope of the land and solar panel, panel width, and rainfall events can be easily modified to understand the effect on hydrology for specific scenarios. This relatively simple framework can improve our ability to represent the hydrological response of a catchment before and after the installation of solar farms and can serve as a preliminary tool for the planning and design of solar farms, and identification of stormwater management needs.
Roadside ditches are ubiquitous in developed landscapes. They are designed to route water from roads for safety, with little consideration of water quality or biogeochemical implications in ditch ...design and minimal data on environmental impacts. We hypothesize that periodic saturation and nutrient influxes may make roadside ditches hotspots for nitrogen (N) removal via denitrification as well as biological production of the greenhouse gases (GHGs) nitrous oxide (N2O), methane (CH4), and carbon dioxide (CO2). Research sites included 12 grassed ditches and adjacent lawns with varying fertilization in a suburban watershed in central New York, where lawns represented a reference with similar soils as ditches but differing hydrology. We measured potential denitrification using the denitrification enzyme assay in fall 2014 and GHG fluxes using in situ static chambers between summer 2014 and 2015, including sample events after storms. Potential denitrification in ditches was significantly higher than in lawns, and rates were comparable to those in stream riparian areas, features traditionally viewed as denitrification hotspots. Ditches had higher rates of CH4 emissions, particularly sites that were wettest. Lawns were hotspots for N2O and CO2 respiratory emissions, which were driven by nutrient availability and fertilizer application. Extrapolating up to the watershed, ditches have the potential to remove substantial N loads via denitrification if managed optimally. Ditch GHG emissions extrapolated across the watershed were minimal given their much smaller area compared with lawns, which were the greater contributor of GHGs. These findings suggest that roadside ditches may offer new management opportunities for mitigating nonpoint source N pollution in residential watersheds.
Core Ideas
Greenhouse gases and denitrification were studied in grassed road ditches and lawns.
Nitrous oxide emissions were higher in lawns, particularly in fertilized lawns.
Ditches were hotspots for CH4 emissions and potential denitrification.
Ditches could be better managed to promote beneficial N removal and minimize GHGs.
Extreme events are of interest worldwide given their potential for substantial impacts on social, ecological, and technical systems. Many climate‐related extreme events are increasing in frequency ...and/or magnitude due to anthropogenic climate change, and there is increased potential for impacts due to the location of urbanization and the expansion of urban centers and infrastructures. Many disciplines are engaged in research and management of these events. However, a lack of coherence exists in what constitutes and defines an extreme event across these fields, which impedes our ability to holistically understand and manage these events. Here, we review 10 years of academic literature and use text analysis to elucidate how six major disciplines—climatology, earth sciences, ecology, engineering, hydrology, and social sciences—define and communicate extreme events. Our results highlight critical disciplinary differences in the language used to communicate extreme events. Additionally, we found a wide range in definitions and thresholds, with more than half of examined papers not providing an explicit definition, and disagreement over whether impacts are included in the definition. We urge distinction between extreme events and their impacts, so that we can better assess when responses to extreme events have actually enhanced resilience. Additionally, we suggest that all researchers and managers of extreme events be more explicit in their definition of such events as well as be more cognizant of how they are communicating extreme events. We believe clearer and more consistent definitions and communication can support transdisciplinary understanding and management of extreme events.
Plain Language Summary
Extreme events, such as heat waves, widespread flooding, or very strong storms, are of interest to scientists and managers because of their potential to cause extensive damage and impacts on people, infrastructure, and nature. With climate change causing more of these events to happen, it is important that we understand how or when they might occur, and how to better respond to them to prevent disastrous impacts. For these reasons, researchers from many different subject areas study extreme events. However, we show that researchers from different backgrounds may use very different words to communicate about these events and different ways of deciding what makes an extreme event “extreme.” In order for researchers, managers, and planners to help everyone better prepare for and respond to extreme events, we encourage all researchers to improve how they explain why they are studying a particular event and make greater effort to understand the work that colleagues in other subject areas are doing and how that may affect our own research and practice.
Key Points
What constitutes an extreme event varies by study and discipline; thus we must be explicit in how we define extreme events
Extreme events are often conflated with their impacts, but this will inhibit future recognition of resilience
Bridging across disciplinary differences in communication and definitions is critical for holistic management of extreme events
Storm‐driven flow pulses in rivers destroy and restructure sediment habitats that affect stream metabolism. This study examined thresholds of bed disturbances that affected patch‐ and reach‐scale ...sediment conditions and metabolism rates. A 4 year record of discharge and diel changes in dissolved oxygen concentrations (ΔDO) was analyzed for disturbances and recovery periods of the ΔDO signal. Disturbances to the ΔDO signal were associated with flow pulses, and the recovery times for the ΔDO signal were found to be in two categories: less than 5 days (30% of the disturbances) or greater than 15 days (70% of the disturbances). A field study was performed during the fall of 2007, which included a storm event that increased discharge from 3.1 to 6.9 m3/s over a 7 h period. During stable flow conditions before the storm, variability in patch‐scale stream metabolism values were associated with sediment texture classes with values ranging from −16.4 to 2.3 g O2/m2/d (negative sign indicates net respiration) that bounded the reach‐averaged rate of −5.6 g O2/m2/d. Hydraulic modeling of bed shear stresses demonstrated a storm‐induced flow pulse mobilized approximately 25% of the bed and reach‐scale metabolism rates shifted from −5 to −40 g O2/m2/d. These results suggest that storm‐induced bed disturbances led to threshold behavior with respect to stream metabolism. Small flow pulses resulted in partial‐bed mobilization that disrupted stream metabolism by increased turbidity with short recovery times. Large flow pulses resulted in full‐bed mobilization that disrupted stream metabolism by destroying periphyton habitats with long recovery times.
Key Points
Stream metabolism is affected by floods with partial or full bed mobilization
Variability in sediment texture correlated with patch‐scale metabolism rates
Modeling of storm event showed mobilizing fine sediments disrupted metabolism
This study investigated drivers of denitrification and overall NO
3
−
removal in an agricultural riparian area in central New York. Denitrification was measured using an in situ “push-pull” method ...with
15
N–NO
3
−
as a tracer during summer and fall 2011 at a pair of riparian sites characterized by different hydrologic regimes. Median denitrification rates were 1347 and 703 μg N kg soil
−1
day
−1
for the two study sites. These rates are higher than those reported for other riparian areas, emphasizing the role of some riparian areas as hotspots of NO
3
−
removal. N
2
O production was significantly higher at one site, demonstrating that riparian areas can be a greenhouse gas source under certain conditions. Denitrification was negatively correlated with groundwater flux, suggesting that slower flushing of water, and thus longer residence time, promotes denitrification. A mass balance of NO
3
−
loss revealed that denitrification only accounted for 5–12 % of total NO
3
−
loss, and production of NH
4
+
indicated that dissimilatory NO
3
−
reduction to NH
4
+
(DNRA) may be occurring at both sites. While both sites were characterized by high NO
3
−
removal, differences in denitrification rates and NO
3
−
removal processes demonstrate the need to improve our ability to capture spatial and process heterogeneity in landscape biogeochemical models.
Dissimilatory metal-reducing bacteria are widespread in terrestrial ecosystems, especially in anaerobic soils and sediments. Thermodynamically, dissimilatory metal reduction is more favorable than ...sulfate reduction and methanogenesis but less favorable than denitrification and aerobic respiration. It is critical to understand the complex relationships, including the absence or presence of terminal electron acceptors, that govern microbial competition and coexistence in anaerobic soils and sediments, because subsurface microbial processes can effect greenhouse gas emissions from soils, possibly resulting in impacts at the global scale. Here, we elucidated the effect of an inexhaustible, ferrous-iron and humic-substance mimicking terminal electron acceptor by deploying potentiostatically poised electrodes in the sediment of a very specific stream riparian zone in Upstate New York state. At two sites within the same stream riparian zone during the course of 6 weeks in the spring of 2013, we measured CH4 and N2/N2O emissions from soil chambers containing either poised or unpoised electrodes, and we harvested biofilms from the electrodes to quantify microbial community dynamics. At the upstream site, which had a lower vegetation cover and highest soil temperatures, the poised electrodes inhibited CH4 emissions by ∼45% (when normalized to remove temporal effects). CH4 emissions were not significantly impacted at the downstream site. N2/N2O emissions were generally low at both sites and were not impacted by poised electrodes. We did not find a direct link between bioelectrochemical treatment and microbial community membership; however, we did find a correspondence between environment/function and microbial community dynamics.
•20–29% lower soil moisture and 60–88% lower solar radiation occurred under panels.•There is increased soil moisture and incidence of saturation at the dripline.•Differences in ET and soil moisture ...within the solar farm vary by season.•The interspace zone facilitates infiltration, leading to reduced incidence of saturation.•Stormwater management strategies can manage changes in runoff from solar farms.
As solar energy becomes a cheap source of renewable energy, the number of major utility-scale ground solar panel installations, often called ‘solar farms,’ are growing. With these solar farms often covering hundreds of acres, there is potential for impacts on natural hydrologic processes, including runoff generation and erosion. There is still limited research in this area, and best management practices to address these impacts are variable and not well understood. To fill this gap, we conducted a field investigation of soil moisture patterns, solar radiation, and vegetation at two solar farms in central Pennsylvania, USA that are representative of the complex terrain in the region (e.g., high or variable slopes). Both solar farms also included engineered infiltration basins or trenches that were investigated. Analysis of soil moisture patterns reveals redistribution of water relative to panels, with dripline soil moisture 19 % higher than the reference, and underpanel moisture 25 % lower than the reference, on average at both solar farms over a year. There are also the greatest periods of saturation and runoff generation at the panel driplines. However, an open interspace between panel rows and existing infiltration basins and trenches are playing a critical role in managing runoff. Micrometeorological monitoring indicates reduced evapotranspiration (ET) under panels, with potential underpanel ET 37–67 % lower in summer, and minimal difference in winter. However, a survey of vegetation revealed almost complete ground coverage under panels, which is critical for supporting infiltration and reducing erosion. As solar farms expand to meet important renewable energy goals, it is essential that care be taken to design the landscape to minimize runoff generation and erosion. This work demonstrates that healthy vegetation and well-draining soils can help manage runoff on solar farms; where necessary on more challenging landscapes, engineered stormwater controls can manage any unmitigated runoff.
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