Methane Emission in a Specific Riparian-Zone Sediment Decreased with Bioelectrochemical Manipulation and Corresponded to the Microbial Community Dynamics

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 six 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

Hydrogeomorphology of the Hyporheic Zone: Stream Solute and Fine Particle Interactions With a Dynamic Streambed

Hyporheic flow in streams has typically been studied separately from geomorphic processes. We investigated interactions between bed mobility and dynamic hyporheic storage of solutes and fine particles in a sand-bed stream before, during, and after a flood. A conservatively transported solute tracer (bromide) and a fine particles tracer (5 μm latex particles), a surrogate for fine particulate organic matter, were co-injected during base flow. The tracers were differentially stored, with fine particles penetrating more shallowly in hyporheic flow and retained more efficiently due to the high rate of particle filtration in bed sediment compared to solute. Tracer injections lasted 3.5 h after which we released a small flood from an upstream dam one hour later. Due to shallower storage in the bed, fine particles were rapidly entrained during the rising limb of the flood hydrograph. Rather than being flushed by the flood, we observed that solutes were stored longer due to expansion of hyporheic flow paths beneath the temporarily enlarged bedforms. Three important timescales determined the fate of solutes and fine particles: (1) flood duration, (2) relaxation time of flood-enlarged bedforms back to base flow dimensions, and (3) resulting adjustments and lag times of hyporheic flow. Recurrent transitions between these timescales explain why we observed a peak accumulation of natural particulate organic matter between 2 and 4 cm deep in the bed, i.e., below the scour layer of mobile bedforms but above the maximum depth of particle filtration in hyporheic flow paths. Thus, physical interactions between bed mobility and hyporheic transport influence how organic matter is stored in the bed and how long it is retained, which affects decomposition rate and metabolism of this southeastern Coastal Plain stream. In summary we found that dynamic interactions between hyporheic flow, bed mobility, and flow variation had strong but differential influences on base flow retention and flood mobilization of solutes and fine particulates. These hydrogeomorphic relationships have implications for microbial respiration of organic matter, carbon and nutrient cycling, and fate of contaminants in streams

A social-ecological-technological systems framework for urban ecosystem services

As rates of urbanization and climatic change soar, decision-makers are increasingly challenged to provide innovative solutions that simultaneously address climate change impacts and risks and inclusively ensure quality of life for urban residents. Cities have turned to nature-based solutions to help address these challenges. Nature-based solutions, through the provision of ecosystem services, can yield numerous benefits for people and address multiple challenges simultaneously. Yet, efforts to mainstream nature-based solutions are impaired by the complexity of the interacting social, ecological, and technological dimensions of urban systems. This complexity must be understood and managed to ensure ecosystem-service provisioning is effective, equitable, and resilient. Here, we provide a social-ecological-technological system (SETS) framework that builds on decades of urban ecosystem services research to better understand four core challenges associated with urban nature-based solutions: multi-functionality, systemic valuation, scale mismatch of ecosystem services, and inequity and injustice. The framework illustrates the importance of coordinating natural, technological, and socio-economic systems when designing, planning, and managing urban nature-based solutions to enable optimal social-ecological outcomes

A social-ecological-technological systems framework for urban ecosystem services

As rates of urbanization and climatic change soar, decision-makers are increasingly challenged to provide innovative solutions that simultaneously address climate-change impacts and risks and inclusively ensure quality of life for urban residents. Cities have turned to nature-based solutions to help address these challenges. Nature-based solutions, through the provision of ecosystem services, can yield numerous benefits for people and address multiple challenges simultaneously. Yet, efforts to mainstream nature-based solutions are impaired by the complexity of the interacting social, ecological, and technological dimensions of urban systems. This complexity must be understood and managed to ensure ecosystem-service provisioning is effective, equitable, and resilient. Here, we provide a social-ecological-technological system (SETS) framework that builds on decades of urban ecosystem services research to better understand four core challenges associated with urban nature-based solutions: multi-functionality, systemic valuation, scale mismatch of ecosystem services, and inequity and injustice. The framework illustrates the importance of coordinating natural, technological, and socio-economic systems when designing, planning, and managing urban nature-based solutions to enable optimal social-ecological outcomes

Temporal Evolution of Green Stormwater Infrastructure Strategies in Three US Cities

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

Assessing dissolved methane patterns in central New York groundwater

Study region: Groundwater in Chenango County (central New York State, USA), which is underlain by Devonian sedimentary bedrock. This region has conventional natural gas wells and is under consideration for future shale gas development using high-volume hydraulic fracturing. Study focus: The study examines current patterns of dissolved methane in groundwater, based on 113 samples from homeowner wells in the spring of 2012. Samples were analyzed for methane and other water quality parameters, and each well characterized by its landscape position and geology. Statistical testing and regression modeling was used to identify the primary environmental drivers of observed methane patterns. New hydrological insights for this region: There was no significant difference between methane concentrations in valleys versus upslope locations, in water wells less than or greater than 1 km from a conventional gas well, and across different geohydrologic units. Methane concentrations were significantly higher in groundwater dominated by sodium chloride or sodium bicarbonate compared with groundwater dominated by calcium bicarbonate, indicating bedrock interactions and lengthy residence times as controls. A multivariate regression model of dissolved methane using only three variables (sodium, hardness, and barium) explained 77% of methane variability, further emphasizing the dominance of geochemistry and hydrogeology as controls on baseline methane patterns

The Role of Denitrification in Stormwater Detention Basin Treatment of Nitrogen

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