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With climate change, heat waves are becoming increasingly frequent, intense and broader in spatial extent. However, while the lethal effects of heat waves on humans are well documented, the impacts on flora are less well understood, perhaps except for crops. We summarize recent findings related to heat wave impacts including: sublethal and lethal effects at leaf and plant scales, secondary ecosystem effects, and more complex impacts such as increased heat wave frequency across all seasons, and interactions with other disturbances. We propose generalizable practical trials to quantify the critical bounding conditions of vulnerability to heat waves. Collectively, plant vulnerabilities to heat waves appear to be underappreciated and understudied, particularly with respect to understanding heat wave driven plant die-off and ecosystem tipping points.

We outline the multiple, cross-scale, and complex consequences of terrestrial and marine ecosystem heatwaves in two regions on opposite sides of the planet: the southwestern USA and southwestern Australia, both encompassing Global Biodiversity Hotspots, and where ecosystem collapses or features of it have occurred in the past two decades. We highlight ecosystem shifts that have clearly demonstrated a substantial change from a baseline state over time, although not necessarily across their entire distribution, with evidence of collapse at local scales. Responses to temperature extremes, such as heatwaves, encompass processes at all scales, including population level (e.g. altered demography such as survival, recruitment, and fecundity, together resulting in structural changes), community level (e.g. species compositional shifts), and ecosystem level (e.g. carbon loss), as well as physical properties altered by vegetation loss (e.g. microclimate, fire behaviour on land). These changes impact all trophic levels with foundational species losses (such as seagrasses, kelp, and trees), flowing through to vertebrates (such as sea turtles, penguins, and cockatoos). Where extensive collapse has occurred, shifts in microclimate could affect important biosphere-to-atmosphere feedbacks including fluxes of energy, carbon, and water. Such extensive changes usually do not occur in isolation and frequently interact with other disturbance processes such as fire, storms, pathogen and pest outbreaks, and anthropogenic stressors. Interactions may alter the likelihood, extent, or severity of subsequent disturbances (linked disturbances) as well as condition the ecological response and recovery (compound disturbances). In addition, if ecosystem collapse is extensive enough (e.g. tree die-off), those changes also can impact climate and ecosystems elsewhere via ecoclimate teleconnections. Increasing rates of climatic extremes will drive a host of direct and indirect feedbacks certain to produce large-scale shifts in ecological functioning at unprecedented rates. Understanding how, why, and where these shifts will occur will be critical for effective ecosystem management and climate change mitigation.

To evaluate the optimal approaches to initial surgical management and the potential for prenatal ultrasound detection of patients with closing gastroschisis.We performed a retrospective analysis of patients born with gastroschisis to determine clinical and surgical outcomes and the ability to determine prognosis by prenatal imaging. Data collected included operative findings and postoperative outcome, as well as prenatal imaging features from a subset of cases with and without closing gastroschisis. Statistical analyses were performed as appropriate.We included 197 patients with gastroschisis. No statistical significance was seen in outcomes between closing gastroschisis patients undergoing resection versus intracorporeal parking (n = 18). Ultrasound review was performed on 33 of these patients, 11 with closing gastroschisis, and 22 without. Significantly more closing gastroschisis patients had imaging indicative of progressive defect narrowing and defect diameter ≤8 mm after 30 weeks of gestation versus non-closing patients (p = 0.002).Parking of extruded bowel offers potential for intestinal remodeling. In addition, prenatal ultrasound may be useful in detection of closing gastroschisis in utero.

The occurrence of plant species around the globe is largely constrained by climate. Ecologists use plant-climate relationships such as bioclimatic envelopes to determine environmental conditions th...

In many arid and semiarid regions worldwide, high levels of soil salinity is a key driver of land degradation, as well as a key impediment to re-establishing plant cover. Combating land degradation and erosion associated with soil salinity requires experimental determination of plant species that can grow in soils with high levels of salinity and can be used to re-establish plant cover. Herein, we evaluated the responses of untested candidate cultivars of two halophytic grass species to high soil salinity: alkali sacaton (Sporobolus airoides Torr.) and seashore paspalum (Paspalum vaginatum Swartz). We evaluated the growth responses of both species in a greenhouse under control (no-salt) and various levels of NaCl salinity (EC 8, 16, 24, 32, 40, and 48 dSm−1) using Hoagland solution in a hydroponics system in a randomized complete block design trial. At all salinity levels, sacaton grass had a greater shoot height, shorter root length, lower shoot fresh and dry weights, and poorer color and general...

The fully rough form of the law of the wall is commonly used to quantify velocity profiles and associated bed shear stresses in fluvial, aeolian, and coastal environments. A key parameter in this law is the roughness length, z0. Here we propose a predictive formula for z0 that uses the amplitude and slope of each wavelength of microtopography within a discrete-Fourier-transform-based approach. Computational fluid dynamics (CFD) modeling is used to quantify the effective z0 value of sinusoidal microtopography as a function of the amplitude and slope. The effective z0 value of landscapes with multi-scale roughness is then given by the sum of contributions from each Fourier mode of the microtopography. Predictions of the equation are tested against z0 values measured in ∼ 105 wind-velocity profiles from southwestern US playa surfaces. Our equation is capable of predicting z0 values to 50 % accuracy, on average, across a 4 order of magnitude range. We also use our results to provide an alternative formula that, while somewhat less accurate than the one obtained from a full multi-scale analysis, has an advantage of being simpler and easier to apply.

Tree mortality events driven by drought and warmer temperature, often amplified by pests and pathogens, are emerging as one of the predominant climate change impacts on plants. Understanding and predicting widespread tree mortality events in the future is vital as they affect ecosystem goods and services provided by forests and woodlands, including carbon storage needed to help offset warming. Additionally, if extensive enough, tree die-off events can influence not only local climate but also climate and vegetation elsewhere via climate teleconnections. Consequently, recent efforts have focused on improving predictions of tree mortality. The most commercially important genera of trees is Pinus, and the most studied species for tree mortality is the pinon pine, Pinus edulis. Numerous metrics have been developed in association with predicting mortality thresholds or variations in mortality for this species. In this Mini Review we compiled metrics associated with drought and warming related mortality that were developed for P. edulis or for which P. edulis was a key example species used in a calculation or prediction. We grouped these metrics into four categories: (i) those related to simple climate variables, (ii) those related to physiological responses, (iii) those that require multi-step calculations or modeling using climate, ecohydrological, and/or ecophysiological data, and (iv) modifiers of rates or sensitivities of mortality. We identified the spatial-temporal scale of each of these metrics. The metrics to predict mortality include empirical ones which often have implicit linkages to expected mechanisms, and more mechanistic ones related to physiological drivers. The metrics for P. edulis have similarities with those available for other species of Pinus. Expected future mortality events will provide an opportunity to observationally and experimentally test and compare these metrics related to tree mortality for P. edulis via near-term ecological forecasting. The metrics for P. edulis may also be useful as potential analogs for other genera. Improving predictions of tree mortality for this species and others will be increasingly important as an aid to move towards anticipatory management.

Environmental and health risk concerns relating to airborne particles from mining operations have focused primarily on smelting activities. Yet there are only three active copper smelters and less than a dozen smelters for other metals compared to an estimated 500,000 abandoned and un-reclaimed hard rock mine tailings in the US, that have the potential to generate dust. The problem can also extend to modern tailings impoundments, which may take decades to build and remaining barren for the duration, before subsequent reclamation. We examined the impact of vegetation cover and irrigation on dust emissions and metal(loid) transport from mine tailings during a phytoremediation field trial at the Iron King Mine and Humboldt Smelter Superfund (IKMHSS) site. Measurements of horizontal dust flux following phytoremediation reveals that vegetated plots with 16% and 32% canopy cover enabled an average dust deposition of 371.7 and 606.1 g m(−2) y(−1), respectively, in comparison to the control treatment which emitted dust at an average rate of 2,323 g m(−2) y(−1). Horizontal dust flux and dust emissions from the vegetated field plots are comparable to emission rates in undisturbed grasslands. Further, phytoremediation was effective at reducing the concentration of fine particulates, including PM(1), PM(2.5,) and PM(4), which represent the airborne particulates with the greatest health risks and the greatest potential for long-distance transport. This study demonstrates that phytoremediation can substantially decrease dust emissions as well as the transport of windblown contaminants from mine tailings.

Monitoring of aeolian transport is needed for assessment and management of human health risks as well as for soil resources. Human health risks are assessed based on duration of exposure as well as concentration. Many aeolian studies focus on periods of high wind speed when concentrations are greatest but few studies focus on “background” conditions when concentrations are likely lower but which represent the most prevalent conditions. Such “background” conditions might be especially important at sites with recent disturbance such as fire. Exposure assessments also require improved understanding relating longer-term (days to weeks) measurements of saltation of larger particles to shorter-term (minutes to hours) measurements of smaller inhalable dust particles. To address these issues, we employed three commonly used instruments for measuring dust emissions for unburned and recently-burned sites: Big Springs Number Eight (BSNE) samplers for larger saltating soil particles (>50 μm) with weekly to monthly sampling resolution, DustTraks for suspended particles (diameters

Aeolian processes driving sediment flux and corresponding erosion are inherently 3-dimensional, but are primarily studied either with respect to the horizontal flux component, or to a lesser extent the vertical component. Understanding the relationship between horizontal flux and the vertical component of sediment and dust is critical to predicting fundamental processes such as erosion, and to assessing human and environmental risks associated with contaminated sediment and dust. Multiple mathematical approaches to calculate vertical flux of dust exist but are limited in their ability to predict vertical flux across a wide variety of landscapes and soil conditions. To address these issues, here we explore the relationship between horizontal and vertical fluxes from three perspectives: mathematical, based on existing equations; empirical, based on existing and new data; and risk-based, based on translating the former two into a risk context. Mathematical derivations suggest, depending on the approach, the two components could either be a constant ratio or that the vertical flux could be more dependent on the shear stress and particle size than horizontal flux. Empirical data highlight a wide range of ratios, varying by more than two orders of magnitude, though the ratios can be relatively similar within a given site and set of conditions. Risk-based assessment indicates the vertical flux component is relatively important in dose calculations, and consequently further improvement in mathematical and empirical relationships is needed. Collectively, these three perspectives expand insights on horizontal and vertical sediment fluxes and could aide future risk assessment from dust contaminants.

Atmospheric particulate have deleterious impacts on human health. Predicting dust and aerosol emission and transport would be helpful to reduce harmful impacts but, despite numerous studies, prediction of dust events and contaminant transport in dust remains challenging. In this work, we show that relative humidity and wind speed are both determinants in atmospheric dust concentration. Observations of atmospheric dust concentrations in Green Valley, AZ, USA, and Juárez, Chihuahua, México, show that PM10 concentrations are not directly correlated with wind speed or relative humidity separately. However, selecting the data for high wind speeds (> 4 m/s at 10 m elevation), a definite trend is observed between dust concentration and relative humidity: dust concentration increases with relative humidity, reaching a maximum around 25% and it subsequently decreases with relative humidity. Models for dust storm forecasting may be improved by utilizing atmospheric humidity and wind speed as main drivers for dust generation and transport.

Contaminants can be transported rapidly and over relatively long distances by atmospheric dust and aerosol relative to other media such as water, soil and biota; yet few studies have explicitly evaluated the environmental implications of this pathway, making it a fundamental but understudied transport mechanism. Although there are numerous natural and anthropogenic activities that can increase dust and aerosol emissions and contaminant levels in the environment, mining operations are notable with respect to the quantity of particulates generated, the global extent of area impacted, and the toxicity of contaminants associated with the emissions. Here we review (i) the environmental fate and transport of metals and metalloids in dust and aerosol from mining operations, (ii) current methodologies used to assess contaminant concentrations and particulate emissions, and (iii) the potential health and environmental risks associated with airborne contaminants from mining operations. The review evaluates future research priorities based on the available literature and suggest that there is a particular need to measure and understand the generation, fate and transport of airborne particulates from mining operations, specifically the finer particle fraction. More generally, our findings suggest that mining operations play an important but underappreciated role in the generation of contaminated atmospheric dust and aerosol and the transport of metal and metalloid contaminants, and highlight the need for further research in this area. The role of mining activities in the fate and transport of environmental contaminants may become increasingly important in the coming decades, as climate change and land use are projected to intensify, both of which can substantially increase the potential for dust emissions and transport.

Aeolian and fluvial processes play a fundamental role in dryland regions of the world and have important environmental and ecological consequences from local to global scales. Although both processes operate over similar spatial and temporal scales and are likely strongly coupled in many dryland systems, aeolian and fluvial processes have traditionally been studied separately, making it difficult to assess their relative importance in drylands, as well as their potential for synergistic interaction. Land degradation by accelerated wind and water erosion is a major problem throughout the world's drylands, and although recent studies suggest that these processes likely interact across broad spatial and temporal scales to amplify the transport of soil resources from and within drylands, many researchers and land managers continue to view them as separate and unrelated processes. Here, we illustrate how aeolian and fluvial sediment transport is coupled at multiple spatial and temporal scales and highlight the need for these interrelated processes to be studied from a more integrated perspective that crosses traditional disciplinary boundaries. Special attention is given to how the growing threat of climate change and land-use disturbance will influence linkages between aeolian and fluvial processes in the future. We also present emerging directions for interdisciplinary needs within the aeolian and fluvial research communities that call for better integration across a broad range of traditional disciplines such as ecology, biogeochemistry, agronomy, and soil conservation. This article is a US Government work and is in the public domain in the USA. Published in 2011 by John Wiley & Sons, Ltd.

W ind and water are fundamental drivers of land surface dynamics through their net effects on sediment transport and associated soil erosion. In arid and semiarid environments, where vegetation cover is usually sparse, wind- and water-driven sediment transport can potentially occur over similar spatial and temporal scales and both can contribute substantially to total erosion (Oldeman et al. 1990; Breshears et al. 2003; Field et al. 2009). Sediment transport and associated soil erosion remains a serious and persistent environmental problem worldwide because of its potential adverse impacts on soil productivity, air and water quality, and ecosystem health (Trimble and Crosson 2000; MEA 2005). Notably, roughly two-thirds of the world's arable land is affected by moderate to severe soil degradation (Pimentel et al. 1995), most of which is attributed to wind and water erosional processes (Oldeman et al. 1990). The combined impact of wind and water erosion on agricultural land translates directly into considerable financial costs (Pimentel et al. 1995), and their effects permeate across all major types of ecosystem goods and services (MEA 2005). Further, synergistic relationships between wind- and water-driven sediment transport could be particularly important in dryland ecosystems because both processes can operate on the soil surface to redistribute…

Wind erosion and associated dust emissions play a fundamental role in many ecological processes and provide important biogeochemical connectivity at scales ranging from individual plants up to the entire globe. Yet, most ecological studies do not explicitly consider dust-driven processes, perhaps because most relevant research on aeolian (wind-driven) processes has been presented in a geosciences rather than an ecological context. To bridge this disciplinary gap, we provide a general overview of the ecological importance of dust, examine complex interactions between wind erosion and ecosystem dynamics from the scale of plants and surrounding space to regional and global scales, and highlight specific examples of how disturbance affects these interactions and their consequences. It is likely that changes in climate and intensification of land use will lead to increased dust production from many drylands. To address these issues, environmental scientists, land managers, and policy makers need to consider wind erosion and dust emissions more explicitly in resource management decisions.

Regional-scale tree die-off events driven by drought and warming and associated pests and pathogens have occurred recently on all forested continents and are projected to increase in frequency and extent with future warming. Within areas where tree mortality has occurred, ecological, hydrological and meteorological consequences are increasingly being documented. However, the potential for tree die-off to impact vegetation processes and related carbon dynamics in areas remote to where die-off occurs has rarely been systematically evaluated, particularly for multiple distinct regions within a given continent. Such remote impacts can occur when climate effects of local vegetation change are propagated by atmospheric circulation—the phenomena of 'ecoclimate teleconnections'. We simulated tree die-off events in the 13 most densely forested US regions (selected from the 20 US National Ecological Observatory Network [NEON] domains) and found that tree die-off even for smaller regions has potential to affect climate and hence Gross Primary Productivity (GPP) in disparate regions (NEON domains), either positively or negatively. Some regions exhibited strong teleconnections to several others, and some regions were relatively sensitive to tree loss regardless of what other region the tree loss occurred in. For the US as a whole, loss of trees in the Pacific Southwest—an area undergoing rapid tree die-off—had the largest negative impact on remote US GPP whereas loss of trees in the Mid-Atlantic had the largest positive impact. This research lays a foundation for hypotheses that identify how the effects of tree die-off (or other types of tree loss such as deforestation) can ricochet across regions by revealing hot-spots of forcing and response. Such modes of connectivity have direct applicability for improving models of climate change impacts and for developing more informed and coordinated carbon accounting across regions.

Soil erosion is driven by not only aeolian but also fluvial transport processes, yet these two types of processes are usually studied independently, thereby precluding effective assessment of overall erosion, potential interactions between the two drivers, and their relative sensitivities to projected changes in climate and land use. Here we provide a perspective that aeolian and fluvial transport processes need to be considered in concert relative to total erosion and to potential interactions, that relative dominance and sensitivity to disturbance vary with mean annual precipitation, and that there are important scale-dependencies associated with aeolian–fluvial interactions. We build on previous literature to present relevant conceptual syntheses highlighting these issues. We then highlight relative investments that have been made in soil erosion and sediment control by comparing the amount of resources allocated to aeolian and fluvial research using readily available metrics. Literature searches suggest that aeolian transport may be somewhat understudied relative to fluvial transport and, most importantly, that only a relatively small number of studies explicitly consider both aeolian and fluvial transport processes. Numerous environmental issues associated with intensification of land use and climate change impacts depend on not only overall erosion rates but also on differences and interactions between aeolian and fluvial processes. Therefore, a more holistic viewpoint of erosional processes that explicitly considers both aeolian and fluvial processes and their interactions is needed to optimize management and deployment of resources to address imminent changes in land use and climate.

ARTICLE I NFO Aeolianprocesses are of particular importance in dryland ecosystems where ground cover is inherently sparse because of limited precipitation. Dryland ecosystems include grassland, shrubland, savanna, woodland, and forest, and can be viewed collectively as a continuum of woody plant cover spanning from grasslands with no woody plant cover up to forests with nearly complete woody plant cover. Along this continuum, the spacing and shape of woody plants determine the spatial density of roughness elements, which directly affects aeolian sediment transport. Despite the extensiveness of dryland ecosystems, studies of aeolian sediment transport have generally focused on agricultural fields, deserts, or highly disturbed sites where rates of transport are likely to be greatest. Until recently, few measurements have been made of aeolian sediment transport over multiple wind events and across a variety of types of dryland ecosystems. To evaluate potential trends in aeolian sediment transport as a function of woody plant cover, estimates of aeolian sediment transport from recently published studies, in concert with rates from four additional locations (two grassland and two woodlandsites),arereportedhere.Thesynthesisofthesereportsleadstothedevelopmentofanewconceptual framework for aeolian sediment transport in dryland ecosystems along the grassland-forest continuum. The findings suggest that: (1) for relatively undisturbed ecosystems, shrublands have inherently greater aeolian sediment transport because of wake interference flow associated with intermediate levels of density andspacingofwoodyplants;and(2)fordisturbedecosystems,theupperboundforaeoliansedimenttransport decreases as a function of increasing amounts of woody plant cover because of the effects of the height and density of the canopy on airflow patterns and ground cover associated with woody plant cover. Consequently, aeolian sediment transport following disturbance spans the largest range of rates in grasslands and associated systems with no woody plants (e.g., agricultural fields), an intermediate range in shrublands, and a relatively small range in woodlands and forests. These trends are consistent with previous observations relating large rates of wind erosion to intermediate values for spatial density of roughness elements. The framework for aeolian sediment transport,which isalso relevanttodust fluxes,wind erosion,andrelatedaeolianprocesses,is applicable to a diverse suite of environmental challenges, including land degradation and desertification, dust storms, contaminant transport, and alterations of the hydrological cycle.

Assessment of ecosystem services—the benefits society receives from ecosystems—can be improved by including broader spatial and temporal scales of geosciences perspectives.

On-site wastewater treatment systems can be a potential source of groundwater contamination in regions throughout the United States and other parts of the world. Here, we evaluate four conventional trench systems and four seepage pit systems to determine the relative effectiveness of these systems for the treatment of septic tank effluent in medium- to coarse-textured arid and semiarid soils. Soil borings were advanced up to twice the depth of the trenches (4 m) and seepage pits (15 m) at two horizontal distances (30 cm and 1.5 m) from the sidewalls of the systems. Soil samples were analyzed for various biological and chemical parameters, including Escherichia coli, total coliform, pH, total organic carbon, total dissolved solids, total nitrogen, ammonium-nitrogen, and nitrate-nitrogen. Most soil parameters investigated approached background levels more rapidly near the trenches than the seepage pits, as sampling distance increased both vertically and horizontally from the sidewalls of the systems. Water Environ. Res., 79, 310 (2007).

Site preparation practices are frequently utilized in Southern pine ecosystems to facilitate planting and seedling establishment. Soil and nutrient losses were monitored in 12 bordered erosion plots following four site preparation treatments in a clearcut harvested loblolly pine (Pinus taeda L.) forest in east Texas. Three replications of four site preparation treatments were used: (1) chemical herbicide followed by prescribed fire and mechanical tillage, (2) chemical herbicide followed by prescribed fire, (3) chemical herbicide only, and (4) unprepared control. Annual soil loss from the mechanical tillage and prescribed fire treatments (1273 kg ha-1 and 885 kg ha-1, respectively) was significantly greater than annual soil loss from the chemical herbicide and control treatments (240 kg ha-1 and 219 kg ha-1, respectively). During the first post-treatment year, sediment concentration and overland flow increased significantly in the mechanical tillage and prescribed fire treatments with respect to control. Nutrient (N, P, K, Ca, Mg, and S) concentrations and losses in sediment and overland flow temporarily increased after the mechanical tillage and prescribed fire treatments, but not after the chemical herbicide and control treatments. Nutrient concentrations and losses for all site preparation treatments were relatively small and should have little or no effects on water quality and long-term site productivity.

Soil loss and nutrient concentrations in runoff were evaluated to determine the effects of site preparation burning on a recently harvested loblolly pine (Pinus taeda L.) site in east Texas. Soil and nutrient losses prior to treatment were approximately the same from control plots and pretreatment burn plots. Nutrient analysis of runoff samples indicated that the prescribed burn caused increased losses of N, P, K, Ca, and Mg from treatment plots. Results also indicate a significant increase in sediment concentration and soil loss from plots following the prescribed burning application. The data indicate a gradual decline in soil loss and nutrient concentration over time from treatment plots with respect to control plots. Soil loss following treatment was within the normal range of soil loss for an uncut forest in the south.

Mining operations are a potential source of metal and metalloid contamination by atmospheric particulate generated from smelting activities, as well as from erosion of mine tailings. In this work, we show how lead isotopes can be used for source apportionment of metal and metalloid contaminants from the site of an active copper mine. Analysis of atmospheric aerosol shows two distinct isotopic signatures: one prevalent in fine particles (< 1 μm aerodynamic diameter) while the other corresponds to coarse particles as well as particles in all size ranges from a nearby urban environment. The lead isotopic ratios found in the fine particles are equal to those of the mine that provides the ore to the smelter. Topsoil samples at the mining site show concentrations of Pb and As decreasing with distance from the smelter. Isotopic ratios for the sample closest to the smelter (650 m) and from topsoil at all sample locations, extending to more than 1 km from the smelter, were similar to those found in fine particles in atmospheric dust. The results validate the use of lead isotope signatures for source apportionment of metal and metalloid contaminants transported by atmospheric particulate.

The Technical Area 54 (TA-54) Area G disposal facility is used for the disposal of radioactive waste at Los Alamos National Laboratory (LANL). U.S. Department of Energy (DOE) Order 435.1 (DOE, 2001) requires that radioactive waste be managed in a manner that protects public health and safety and the environment. In compliance with that requirement, DOE field sites must prepare and maintain site-specific radiological performance assessments for facilities that receive waste after September 26, 1988. Sites are also required to conduct composite analyses for facilities that receive waste after this date; these analyses account for the cumulative impacts of all waste that has been (and will be) disposed of at the facilities and other sources of radioactive material that may interact with these facilities. LANL issued Revision 4 of the Area G performance assessment and composite analysis in 2008. In support of those analyses, vertical and horizontal sediment flux data were collected at two analog sites, each with different dominant vegetation characteristics, and used to estimate rates of vertical resuspension and wind erosion for Area G. The results of that investigation indicated that there was no net loss of soil at the disposal site due to wind erosion, and suggestedmore » minimal impacts of wind on the long-term performance of the facility. However, that study did not evaluate the potential for contaminant transport caused by the horizontal movement of soil particles over long time frames. Since that time, additional field data have been collected to estimate wind threshold velocities for initiating sediment transport due to saltation and rates of sediment transport once those thresholds are reached. Data such as these have been used in the development of the Vegetation Modified Transport (VMTran) model. This model is designed to estimate patterns and long-term rates of contaminant redistribution caused by winds at the site, taking into account the impacts of plant succession and environmental disturbance. Aeolian, or wind-driven, sediment transport drives soil erosion, affects biogeochemical cycles, and can lead to the transport of contaminants. Rates of aeolian sediment transport depend in large part on the type, amount, and spatial pattern of vegetation. In particular, the amount of cover from trees and shrubs, which act as roughness elements, alters rates of aeolian sediment transport. The degree to which the understory is disturbed and the associated spacing of bare soil gaps further influence sediment transport rates. Changes in vegetation structure and patterns over periods of years to centuries may have profound impacts on rates of wind-driven transport. For recently disturbed areas, succession is likely to occur through a series of vegetation communities. Area G currently exhibits a mosaic of vegetation cover, with patches of grass and forbs over closed disposal units, and bare ground in heavily used portions of the site. These areas are surrounded by less disturbed regions of shrubland and pinon-juniper woodland; some ponderosa pine forest is also visible in the canyon along the road. The successional trajectory for the disturbed portions of Area G is expected to proceed from grasses and forbs (which would be established during site closure), to shrubs such as chamisa, to a climax community of pinon-juniper woodland. Although unlikely under current conditions, a ponderosa pine forest could develop over the site if the future climate is wetter. In many ecosystems, substantial and often periodic disturbances such as fire or severe drought can rapidly alter vegetation patterns. Such disturbances are likely to increase in the southwestern US where projections call for a warmer and drier climate. With respect to Area G, the 3 most likely disturbance types are surface fire, crown fire, and drought-induced tree mortality. Each type of disturbance has a different frequency or likelihood of occurrence, but all 3 tend to reset the vegetation succession cycle to earlier stages. The Area G performance assessment and composite analysis evaluate the impacts of disposing of radioactive waste over a period of hundreds to thousands of years. An assessment of aeolian sediment transport over this timeframe needs to account for the impacts of changes in vegetation structure and other surface conditions that occur under normal circumstances and as a result of environmental disturbance. Recent aeolian sediment transport studies undertaken in diverse dryland systems on both undisturbed and disturbed lands have yielded a suite of empirical measurements. These studies do not take into account changes in long-term conditions at the sites being investigated. Although studies of dune systems have begun to account for different types of vegetation due to succession and the effects of disturbance under current and projected climate, similar information for drylands that are not dominated by dunes is almost entirely lacking.« less

[1] Desertification impacts a large proportion of drylands and can be driven by a variety of climate and land use factors. Most conceptual models of desertification include the underlying assumption that when herbaceous cover is reduced, increased erosion from bare patches is redistributed to shrub canopy patches, resulting in self-reinforcing “islands of fertility.” Notably, however, this underlying assumption has not been explicitly tested with direct field measurements. Here we provide direct measurements of horizontal sediment flux moving into and out of bare-, herbaceous-, and shrub-dominated patch types in a semiarid ecosystem for both simulated and natural dust events, as well as in response to simulated disturbance. Horizontal sediment flux out of the bare patches was 20% greater than the herbaceous patches and 50% greater than sediment flux out of the shrub-dominated patches. Differences among vegetation patch types indicate that shrub patches capture more sediment than herbaceous patches and, importantly, that bare patches serve as amplified sediment sources following disturbance. Our results provide explicit support for the pervasive but untested desertification redistribution assumption, highlighting that loss of grass cover is a compounding problem that not only increases dust emissions but also precludes capture, and may have global relevance for coupled human-environmental systems at risk due to current or potential desertification.

Ravi, S., D'Odorico, P., Breshears, D. D., Field, J. P., Goudie, A. S., Huxman, T. E., Li, J., Okin, G. S., Swap, R. J., Thomas, A. D., Pelt, S. V., Whicker, J. J., Zobeck, T. M. (2011). Aeolian processes and the biosphere. Reviews of Geophysics, 49 (3).

Rangelands are globally extensive, provide fundamental ecosystem services, and are tightly coupled human-ecological systems. Rangeland sustainability depends largely on the implementation and utilization of various grazing and burning practices optimized to protect against soil erosion and transport. In many cases, however, land management practices lead to increased soil erosion and sediment fluxes for reasons that are poorly understood. Because few studies have directly measured both wind and water erosion and transport, an assessment of how they may differentially respond to grazing and burning practices is lacking. Here, we report simultaneous, co-located estimates of wind- and water-driven sediment transport in a semiarid grassland in Arizona, USA, over three years for four land management treatments: control, grazed, burned, and burned + grazed. For all treatments and most years, annual rates of wind-driven sediment transport exceeded that of water due to a combination of ongoing small but nontrivial wind events and larger, less frequent, wind events that generally preceded the monsoon season. Sediment fluxes by both wind and water differed consistently by treatment: burned + grazedburnedgrazedor = control, with effects immediately apparent after burning but delayed after grazing until the following growing season. Notably, the wind:water sediment transport ratio decreased following burning but increased following grazing. Our results show how rangeland practices disproportionally alter sediment fluxes driven by wind and water, differences that could potentially help explain divergence between rangeland sustainability and degradation.

Aeolian research focuses primarily on the fundamental processes of dust emissions and transport (Ravi et al., 2011) but this scientific focus is also particularly relevant for the related consequences of the emissions of airborne mineral dust contaminants (Csavina et al., 2012), which have important implications for human health and the environment. Linking from “dust to dose” is particularly important in the context of human health (Whicker et al., 2006). However, expertise in the relevant research areas tends to be fragmented, with researchers looking at different spatial and temporal scales related to the processes, often with insufficient integration (Field et al., 2010; Ravi et al., 2011; Csavina et al., 2012). To help foster interdisciplinary interactions, a conference sponsored with support from the US National Environmental Institute of Health Sciences was held in Tucson, AZ in the USA in May 2013 with the goal “to stimulate interaction among different research communities interested in dust and to promote better integration of research on airborne mineral dust from emissions to environmental exposure” (http://www.superfund.pharmacy.arizona.edu/content/airborne-mineral-dust-contaminants-conference-report). Linking from dust emissions to contaminant transport through atmospheric processes and to toxicological and epidemiological relevance is complex and requires multidisciplinary perspectives and initiatives. Here we summarize the main points of the papers in this special issue in the context of a previous framework linking potential for dust emissions, potential contaminant concentration in dust, and potential risk to human health and the environment (Fig. 1, modified from Csavina et al., 2012). We also listed future needs identified in a survey from the meeting. Fig. 1 Natural and anthropogenic sources of dust associated with potential emission rates, contaminant concentration, and risk to human health and the environment (modified from Csavina et al., 2012). Papers in this special issue are related to airborne mineral ... A first section of papers emphasize basic processes and modeling of dust emissions and transport that are relevant for airborne mineral dust contaminants. Belnap et al. (2014) present a large data set evaluating threshold friction velocities as a function of soil type and surface type for two southwestern US deserts. Their results highlight the importance of soil surface conditions and their sensitivity to disturbances. Judger et al. (2014) quantify increases in dust concentrations during dust events in Mongolia as function of health-relevant particle sizes (PM10 and PM2.5), documenting increases of more than an order of magnitude in some cases. Merino-Martin et al. (2014) focus on “background” conditions that do not include very windy periods but do include brief gusts; these periods, while less windy, are the most common, and the results highlight an interplay between spatial and temporal scale of measurement from different sampler types and particle size. Many field measurement methods capture horizontal dust flux using samplers such as the Big Spring Number Eight (BSNE) collector, but these horizontal fluxes are not equivalent to vertical fluxes relevant for dust emission suspension and transport; Whicker et al. (2014) consider previous formulations for horizontal and vertical fluxes based on theoretical, empirical and risk-based perspectives, yielding several potential relationships between horizontal and vertical fluxes that can serve as hypotheses for future testing. Sprigg et al. (2014) highlight improved dust emission forecasting approaches for dust avoidance, which is particularly relevant for Valley Fever. Stovern et al. (2014) highlight advances in modeling of dust and contaminant transport; importantly they also highlight how management of surface conditions can aid in controlling dust emissions. A second section of the special issue focuses more directly on contaminant emissions, transport and risks related to toxicology and/or epidemiology. Kim et al. (2014) quantify surface enrichment of arsenic in mine tailings environments due to windborne transport and the bioaccessibility of arsenic in fine-grained tailings through the inhalation pathway. Xiao et al. (2014) evaluates characteristics of toxicity of emissions, which is directly relevant to human health risks. And Taylor et al. (2014) highlight issues related to the public health impacts in mining and smelting communities affected by the transport of metal-rich dust and aerosol contaminants, and to associated regulatory relationships. A survey of participants at the conference highlighted the following gaps in the field (http://www.superfund.pharmacy.arizona.edu/content/airborne-mineral-dust-contaminants-conference-report): Stronger links needed between the dust community and epidemiologists. More specific information needed on the health impacts of dust (moving beyond generic PM2.5 and PM10; immune system suppression; biological responses of various human organs). Needed improvements in dust modeling (forecast severity of dust storms; quantitative dust fluxes; verification of model predictions). Improved information on effects of dust storms on public safety (highways, airports). We also note other challenges highlighted in pulling together this special section. These include issues of scaling (e.g. from small source patches of dust up through large urban area impacts) (Ravi et al., 2011); issues related to climate change (Field et al., 2011) as well as land use change (Ravi et al., 2011); the relative roles of background conditions with gusts vs. windy periods vs. dust storms; consideration of longer term processes and environmental disturbances (Breshears et al., 2012); and the need to link studies of dust and contaminant emission and transport processes more directly to epidemiology studies, including more integration with the medical community to evaluate causality of emissions. The papers in this issue reveal the value of interdisciplinary collaboration and integration spanning from source terms to human health and ecological consequences. Collectively, these papers serve as an important baseline for further advancing aeolian research in the context of airborne mineral dust contaminants, which is likely to become as increasingly important issue under pressures of future population growth, urbanization, land use change and climate change.

Processes within the critical zone—spanning groundwater to the top of the vegetation canopy—have important societal relevance and operate over broad spatial and temporal scales that often are not included in existing frameworks for ecosystem services evaluation. Here we expand the scope of ecosystem services by specifying how critical zone processes extend context both spatially and temporally, determine constraints that limit provision of services, and offer a potentially powerful currency for evaluation. Context : A critical zone perspective extends the context of ecosystem services by expressly addressing how the physical structure of the terrestrial Earth surface (e.g., parent material, topography, and orography) provides a broader spatial and temporal template determining the coevolution of physical and biological systems that result in societal benefits. Constraints : The rates at which many ecosystem services are provided are fundamentally constrained by rate-limited critical zone processes, a phenomenon that we describe as a conceptual “supply chain” that accounts for rate-limiting soil formation, hydrologic partitioning, and streamflow generation. Currency : One of the major challenges in assessing ecosystem services is the evaluation of their importance by linking ecological processes to societal benefits through market and nonmarket valuation. We propose that critical zone processes be integrated into an evaluation currency, useful for valuation, by quantifying the energy flux available to do thermodynamic work on the critical zone. In short, characterization of critical zone processes expands the scope of ecosystem services by providing context, constraints, and currency that enable more effective management needed to respond to impacts of changing climate and disturbances.