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"Grant, Stanley"
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Factoring stream turbulence into global assessments of nitrogen pollution
A combination of physical transport processes and biologically mediated reactions in streams and their sediments removes dissolved inorganic nitrogen (DIN) from the water. Although stream chemistry and biology have been considered the dominant controls on how quickly DIN is removed, Grant et al. show that physics is what sets the limits on removal rates of nitrate (a component of DIN). Residence time in the hyporheic zone (the region below the sediment surface where groundwater and surface water mix) determines the maximum rate at which nitrate can be removed from stream water. Nevertheless, at local scales, chemistry and biology modify how closely to that maximum rate removal occurs. Science , this issue p. 1266 Stream physics determines the maximum rate at which nitrate can be removed from the water. The discharge of excess nitrogen to streams and rivers poses an existential threat to both humans and ecosystems. A seminal study of headwater streams across the United States concluded that in-stream removal of nitrate is controlled primarily by stream chemistry and biology. Reanalysis of these data reveals that stream turbulence (in particular, turbulent mass transfer across the concentration boundary layer) imposes a previously unrecognized upper limit on the rate at which nitrate is removed from streams. The upper limit closely approximates measured nitrate removal rates in streams with low concentrations of this pollutant, a discovery that should inform stream restoration designs and efforts to assess the effects of nitrogen pollution on receiving water quality and the global nitrogen cycle.
Journal Article
Characterizing the social-ecological system for inland freshwater salinization using fuzzy cognitive maps: implications for collective management
Current regulatory tools are not well suited to address freshwater salinization in urban areas, and the conditions under which bottom-up management is likely to emerge remain unclear. We hypothesize that Elinor Ostrom’s social-ecological systems (SESs) framework can be used to explore how current understanding of salinization might foster or impede its collective management. We focus on the Occoquan Reservoir, a critical urban water supply in Northern Virginia, USA, and use fuzzy cognitive maps (FCMs) to characterize stakeholder understanding of the SES that underpins salinization in the region. Hierarchical clustering of FCMs reveals four stakeholder groups with distinct views on the causes and consequences of salinization, and actions that could be taken to mitigate salinization, including technological, policy, and governance interventions and innovations. Similarities and differences across these four groups, and their degree of concordance with measured or modeled SES components, point to actions that could be taken to catalyze collective management of salinization in the region.
Journal Article
Taking the \Waste\ Out of \Wastewater\ for Human Water Security and Ecosystem Sustainability
Humans create vast quantities of wastewater through inefficiencies and poor management of water systems. The wasting of water poses sustainability challenges, depletes energy reserves, and undermines human water security and ecosystem health. Here we review emerging approaches for reusing wastewater and minimizing its generation. These complementary options make the most of scarce freshwater resources, serve the varying water needs of both developed and developing countries, and confer a variety of environmental benefits. Their widespread adoption will require changing how freshwater is sourced, used, managed, and priced.
Journal Article
Batgirl : Stephanie Brown
\"Battling both inner and external demons, Stephanie must learn to balance school and crime-fighting or face the wrath of Barbara Gordon! With guest appearences from Batman and Robin and villains like Man-Bat and Clayface, Batgirl must step up to the mantle! Batgirl must battle the Calculator and stop his plan to unleash a nanovirus upon the citizens of Gotham City that will turn them into mindless techno-zombies, enter the FLOOD!\"-- Provided by publisher.
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Free access to the concert hall: widening university students’ participation in extracurricular activity?
The role of extracurricular activity in higher education is receiving increasing international attention as a means for developing social and cultural resources for steering social and employment networks. The focus of this paper is on a post-1992 English university partnership with an orchestra, enabling students to attend free concerts. The initiative aspired to extend the student experience, break down barriers, and encourage students to try a new musical experience. This study explores students’ experiences and contrasts these with the aspirations of the vice chancellor. In view of studies establishing relationships between extracurricular activity and inequality of opportunity, this paper also investigates whether financial subsidies widen participation.
Journal Article
From yards to cities: a simple and generalizable probabilistic framework for upscaling outdoor water conservation behavior
Outdoor watering of lawns accounts for about half of single-family residential potable water demand in the arid southwest United States. Consequently, many water utilities in the region offer customers cash rebates to replace lawns with drought tolerant landscaping. Here we present a parcel-scale analysis of water savings achieved by a 'cash-for-grass' program offered to 60 000 homes in Southern California. The probability a resident will participate in the program, and the lawn area they replace with drought tolerant landscaping, both increase with a home's outdoor area. The participation probability is also higher if a home is occupied by its owner. From these results we derive and test a simple and generalizable probabilistic framework for upscaling water conservation behavior at the parcel-scale to overall water savings at the city- or water provider-scale, accounting for the probability distribution of parcel outdoor areas across a utility's service area, climate, cultural drivers of landscape choices, conservation behavior, equity concerns, and financial incentives.
Journal Article
Effective diffusivity and mass flux across the sediment-water interface in streams
The exchange of water between a stream and its hyporheic zone (defined as the sediment beneath and immediately adjacent to a stream) underpins many ecological and hydrological functions in turbulent streams. Hyporheic exchange can be parameterized in terms of an effective diffusion coefficient Deffand considerable effort has gone into developing process‐based models and empirical correlations for predicting the value of this transport parameter. In this paper we demonstrate previous laboratory estimates forDeffcan be biased by as much as a factor of 10, due to errors in the equations and/or ambiguities in the variables used to reduce data from transient tracer experiments in flow‐through and recirculating flumes. After correcting these problems, an analysis of 93 previously published flume experiments revealsDeffdepends on properties of the tracer (molecular diffusivity), flow field (shear velocity, kinematic viscosity), and sediment bed (permeability and depth). The shear velocity depends implicitly on the Darcy‐Weisbach friction factor, which captures the influence of bed roughness and bed forms on hyporheic exchange in both laboratory and field studies. The dependence ofDeffon sediment bed depth is consistent with the hypothesis that coherent turbulence in the water column drives mass transport across the sediment‐water interface. Furthermore, the dependence ofDeff on sediment bed depth raises the possibility that hyporheic exchange rates measured in the laboratory are not representative of hyporheic exchange rates in the field. Key Points Errors are identified in formulae used to estimate effective diffusivity Darcy‐Weisbach friction factor parameterizes bed roughness in both lab and field Coherent turbulence in the water column drives hyporheic exchange at the patch s
Journal Article