Jeffrey J. Whicker

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.

Evaluation of continuous air monitor placement in a plutonium facility.

Department of Energy appraisers found continuous air monitors at Department of Energy plutonium facilities alarmed less than 30% of the time when integrated room plutonium air concentrations exceeded 500 DAC-hours. Without other interventions, this alarm percentage suggests the possibility that workers could be exposed to high airborne concentrations without continuous air monitor alarms. Past research has shown that placement of continuous air monitors is a critical component in rapid and reliable detection of airborne releases. At Los Alamos National Laboratory and many other Department of Energy plutonium facilities, continuous air monitors have been primarily placed at ventilation exhaust points. The purpose of this study was to evaluate and compare the effectiveness of exhaust register placement of workplace continuous air monitors with other sampling locations. Polydisperse oil aerosols were released from multiple locations in two plutonium laboratories at Los Alamos National Laboratory. An array of laser particle counters positioned in the rooms measured time-resolved aerosol dispersion. Results showed alternative placement of air samplers generally resulted in aerosol detection that was faster, often more sensitive, and equally reliable compared with samplers at exhaust registers.

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…

137Cs in sediments of Utah Lakes and reservoirs: Effects of elevation, sedimentation rate and fallout history

Abstract Cesium-137 in lentic sediments was measured in 15 impoundments in Utah, two in Oregon, and one in Colorado, Cesium-137 sediment profiles were used to investigate areas that may have received additional fallout from aboveground nuclear weapons testing at the Nevada Test Site (NTS). Factors that affected sedimentation rates and patterns in the impoundments were explored. Estimated cumulative deposition and mean sedimentation rates were correlated, and both were inversely related to impoundment elevation. There was evidence for enhanced fallout 137 Cs deposition during the period of most intense aboveground testing from 1951 to 1957 at the Nevada Test Site (NTS) at two locations in southwestern Utah. However, our technique for estimating relative NTS fallout generally yielded greater within-lake variability than between-lake variability. Furthermore, most of the observed 137 Cs deposition in sediments deposited in the 1951–1957 time period could be attributed to global rather than NTS fallout. Thus, in general, differences between impoundments in the relative deposition from NTS fallout could not be statistically demonstrated.

Quantitative measurements of airflow inside a nuclear laboratory.

Abstract—Dispersion dynamics of accidentally released radioactive aerosols or gases through laboratory workrooms are determined primarily by airflow, which impacts the level of human exposure and the response of air monitoring instrumentation. Therefore, applying conclusions derived from measurements of the fundamental aspects of airflow (velocity, direction, and turbulence) can lead to better protection of workers by suggesting appropriate locations for air monitoring and sampling. Historically, it has been very difficult to quantitatively measure these fundamental aspects of indoor airflow because of the low flow rates (often <10 cm s−1) and difficulties in quantitative measurement of three-dimensional airflow. Recent advances in sonic anemometry have enabled such measurements. For this study, a sonic anemometer was used that was capable of measuring airflow velocities with a sensitivity of about 0.5 cm s−1 for each of the three-directional components. A sampling frequency of 1 Hz was selected to measure the fluctuations in the air velocity associated with turbulence and expressed in terms of “turbulence intensity.” Point measurements of airflow velocities, directions, and turbulence intensities were made at 69 locations in a mechanically ventilated plutonium laboratory located at Los Alamos National Laboratory. Although the measurements were not made with workers present, all measurements were made at a height of 1.5 m, approximately the height of a worker’s breathing zone (BZ). Velocities ranged from 8 cm s−1 to 41 cm s−1, with a median velocity of 18 cm s−1. Percent turbulence intensities ranged from 13% to 57% with a median of 34%. The measured velocities and turbulence intensities in the laboratory showed that forced convective flows and turbulent eddy diffusion drive dispersion of released aerosols or gases. Results show that after an airborne release, mixing within the room can take minutes and may not always be complete. This is contrary to simplifying assumptions made by some risk modeling of accidentally released materials in a room. Our results also suggest that the mixing pattern would not be omnidirectional at most release locations, especially in the early stages of the release. Finally, airflow directions were upwards in breathing zones at most workstations. Because most releases in the plutonium laboratory occur at a height immediately below the BZ, the concentrated aerosol could be lifted into the BZ, followed by dispersal to the air monitor with the initiation of alarm.

Uranium partition coefficients (Kd) in forest surface soil reveal long equilibrium times and vary by site and soil size fraction.

The environmental mobility of newly deposited radionuclides in surface soil is driven by complex biogeochemical relationships, which have significant impacts on transport pathways. The partition coefficient (Kd) is useful for characterizing the soil-solution exchange kinetics and is an important factor for predicting relative amounts of a radionuclide transported to groundwater compared to that remaining on soil surfaces and thus available for transport through erosion processes. Measurements of Kd for 238U are particularly useful because of the extensive use of 238U in military applications and associated testing, such as done at Los Alamos National Laboratory (LANL). Site-specific measurements of Kd for 238U are needed because Kd is highly dependent on local soil conditions and also on the fine soil fraction because 238U concentrates onto smaller soil particles, such as clays and soil organic material, which are most susceptible to wind erosion and contribute to inhalation exposure in off-site populations. We measured Kd for uranium in soils from two neighboring semiarid forest sites at LANL using a U.S. Environmental Protection Agency (EPA)-based protocol for both whole soil and the fine soil fraction (diameters <45 &mgr;m). The 7-d Kd values, which are those specified in the EPA protocol, ranged from 276–508 mL g−1 for whole soil and from 615–2249 mL g−1 for the fine soil fraction. Unexpectedly, the 30-d Kd values, measured to test for soil-solution exchange equilibrium, were more than two times the 7-d values. Rates of adsorption of 238U to soil from solution were derived using a 2-component (FAST and SLOW) exponential model. We found significant differences in Kd values among LANL sampling sites, between whole and fine soils, and between 7-d and 30-d Kd measurements. The significant variation in soil-solution exchange kinetics among the soils and soil sizes promotes the use of site-specific data for estimates of environmental transport rates and suggests possible differences in desorption rates from soil to solution (e.g., into groundwater or lung fluid). We also explore potential relationships between wind erosion, soil characteristics, and Kd values. Combined, our results highlight the need for a better mechanistic understanding of soil-solution partitioning kinetics for accurate risk assessment. Health Phys. 93(1):36–46; 2007

A quantitative method for optimized placement of continuous air monitors.

Abstract— Alarming continuous air monitors (CAMs) are a critical component for worker protection in facilities that handle large amounts of hazardous materials. In nuclear facilities, continuous air monitors alarm when levels of airborne radioactive materials exceed alarm thresholds, thus prompting workers to exit the room to reduce inhalation exposures. To maintain a high level of worker protection, continuous air monitors are required to detect radioactive aerosol clouds quickly and with good sensitivity. This requires that there are sufficient numbers of continuous air monitors in a room and that they are well positioned. Yet there are no published methodologies to quantitatively determine the optimal number and placement of continuous air monitors in a room. The goal of this study was to develop and test an approach to quantitatively determine optimal number and placement of continuous air monitors in a room. The method we have developed uses tracer aerosol releases (to simulate accidental releases) and the measurement of the temporal and spatial aspects of the dispersion of the tracer aerosol through the room. The aerosol dispersion data is then analyzed to optimize continuous air monitor utilization based on simulated worker exposure. This method was tested in a room within a Department of Energy operated plutonium facility at the Savannah River Site in South Carolina, U.S. Results from this study show that the value of quantitative airflow and aerosol dispersion studies is significant and that worker protection can be significantly improved while balancing the costs associated with CAM programs.

Influence of room geometry and ventilation rate on airflow and aerosol dispersion: implications for worker protection.

Knowledge of dispersion rates and patterns of radioactive aerosols and gases through workrooms is critical for understanding human exposure and for developing strategies for worker protection. The dispersion within rooms can be influenced by complex interactions between numerous variables, but especially ventilation design and room furnishings. For this study, dependence of airflow and aerosol dispersion on workroom geometry (furnishings) and ventilation rate were studied in an experimental room that was designed to approximate a plutonium laboratory. Three different configurations of simulated gloveboxes and two ventilation rates (approximately 6 and 12 air exchanges per hour) were studied. A sonic anemometer was used to measure airflow parameters including all three components of air velocity vectors and turbulence intensity distributions at multiple locations and heights. Aerosol dispersion rates and patterns were measured by releasing aerosols multiple times from six different locations. Aerosol particle concentrations resolved in time and space were measured using 16 multiplexed laser particle counters. Comparisons were made of air velocities, turbulence, and aerosol transport across different ventilation rates and room configurations. A strong influence of ventilation rate on aerosol dispersion rates and air velocity was found, and changes in room geometry had significant effects on aerosol dispersion rates and patterns. These results are important with regards to constant evaluation of placement of air sampling equipment, benchmarking numerical models of room airflow, and design of ventilation and room layouts with consideration of worker safety.