Jason P. Field

The ecology of dust

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.

Sediment capture by vegetation patches: Implications for desertification and increased resource redistribution

[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.

Interactive effects of grazing and burning on wind‐ and water‐driven sediment fluxes: rangeland management implications

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 + grazed > burned >> grazed > or = 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.

On the ratio of wind- to water-driven sediment transport: Conserving soil under global-change-type extreme events

Wind 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 worlds 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…

Phytoremediation Reduces Dust Emissions from Metal(loid)-Contaminated Mine Tailings

Environmental and health risk concerns relating to airborne particles from mining operations have focused primarily on smelting activities. However, there are only three active copper smelters and less than a dozen smelters for other metals compared to an estimated 500000 abandoned and unreclaimed 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 remain 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 2323 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 PM1, PM2.5, and PM4, 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.

Controls on Yardang Development and Morphology: 1. Field Observations and Measurements at Ocotillo Wells, California

Yardangs are streamlined hills formed in part by the erosive action of wind and wind-blown sediments. Here we examine the controls on yardang development and morphology using the Ocotillo Wells State Vehicular Recreation Area (OWSVRA), California, as a study site. We measured the compressive strengths, strikes, and dips of bedrock strata, eolian sediment fluxes (including their vertical profiles and spatial variations around yardangs), and erosion rates derived from geologic constraints and multitemporal Terrestrial Laser Scanning (TLS). We used a combination of TLS-based and airborne lidar-based Digital Elevation Models (DEMs) to test the applicability of an asymmetric Gaussian function for characterizing yardang form and quantify the relationships among yardang lengths, widths, heights, spacings, and their controlling factors. Yardang aspect ratios are controlled by bedrock structural attributes, specifically by the tangent of the dip and the angle between the strike and the prevailing wind direction. Yardang spacings scale linearly with yardang width. Yardang heights increase as the square root of width such that larger yardangs tend to have gentler side slopes. Sediment fluxes reach amaximum in the troughs among yardangs, consistent with the hypothesis that yardang development involves the focusing of wind and wind-blown sediments into troughs. The vertical distribution of eolian sediment flux follows a power law with an exponent of 2.5, a result consistent with an advection-diffusion-settling model of transport near the saltation-suspension transition. Erosion rates are several mm/yr over time scales of ~10 and ~10 years.

A Dirty Dozen Ways to Die: Metrics and Modifiers of Mortality Driven by Drought and Warming for a Tree Species

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.

Candidate halophytic grasses for addressing land degradation: Shoot responses of Sporobolus airoides and Paspalum vaginatum to weekly increasing NaCl concentration

ABSTRACT 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 quality compared to seashore paspalum. The shoot fresh and dry weights of both grasses were greatest at the low to medium levels of salinity, with the greatest response observed at EC 16 dSm−1. At the highest level, salinity significantly reduced shoot fresh and dry weights of both grasses. Because growth of both halophytic species exhibited high tolerance to salinity stress and were stimulated under low to medium levels of salinity, both species could be considered suitable candidates for re-establishing plant cover in drylands to combat desertification and land degradation associated with high levels of soil salinity.