Dirk Goossens

Dust dynamics in off-road vehicle trails: Measurements on 16 arid soil types, Nevada, USA.

Soil analyses and measurements with the Portable In Situ Wind Erosion Laboratory (PI-SWERL) were conducted on 16 soil types in an area heavily affected by off-road vehicle (ORV) driving. Measurements were performed in ORV trails as well as on undisturbed terrain to investigate how ORV driving affects the vulnerability of a soil to emit PM10 (particles<10microm), during the driving as well as during episodes of wind erosion. Particular attention is paid to how the creation of a new trail affects those properties of the topsoil that determine its capability to emit PM10. Also, recommendations are given for adequate management of ORV-designed areas. The type of surface (sand, silt, gravel, drainage) is a key factor with respect to dust emission in an ORV trail. Trails in sand, defined in this study as the grain size fraction 63-2000microm, show higher deflation thresholds (the critical wind condition at which wind erosion starts) than the surrounding undisturbed soil. Trails in silt (2-63microm) and in drainages, on the other hand, have lower deflation thresholds than undisturbed soil. The increase in PM10 emission resulting from the creation of a new ORV trail is much higher for surfaces with silt than for surfaces with sand. Also, the creation of a new trail in silt decreases the supply limitation in the top layer: the capacity of the reservoir of emission-available PM10 increases. For sand the situation is reversed: the supply limitation increases, and the capacity of the PM10 reservoir decreases. Finally, ORV trails are characterized by a progressive coarsening of the top layer with time, but the speed of coarsening is much lower in trails in silt than in trails in sand or in drainages. The results of this study suggest that, to minimize emissions of PM10, new ORV fields should preferably be designed on sandy terrain rather than in silt areas or in drainages.

Measuring fast-temporal sediment fluxes with an analogue acoustic sensor: a wind tunnel study.

In aeolian research, field measurements are important for studying complex wind-driven processes for land management evaluation and model validation. Consequently, there have been many devices developed, tested, and applied to investigate a range of aeolian-based phenomena. However, determining the most effective application and data analysis techniques is widely debated in the literature. Here we investigate the effectiveness of two different sediment traps (the BEST trap and the MWAC catcher) in measuring vertical sediment flux. The study was performed in a wind tunnel with sediment fluxes characterized using saltiphones. Contrary to most studies, we used the analogue output of five saltiphones mounted on top of each other to determine the total kinetic energy, which was then used to calculate aeolian sediment budgets. Absolute sediment losses during the experiments were determined using a balance located beneath the test tray. Test runs were conducted with different sand sizes and at different wind speeds. The efficiency of the two traps did not vary with the wind speed or sediment size but was affected by both the experimental setup (position of the lowest trap above the surface and number of traps in the saltation layer) and the technique used to calculate the sediment flux. Despite this, good agreement was found between sediment losses calculated from the saltiphone and those measured using the balance. The results of this study provide a framework for measuring sediment fluxes at small time resolution (seconds to milliseconds) in the field.

Combining surface mapping and process data to assess, predict, and manage dust emissions from natural and disturbed land surfaces

The impact of dust emission on air quality is a significant health and environmental concern. Accurately determining the source (natural versus anthropogenic) and load of dust is an important component of any mitigation effort. We develop an approach to assess dust emission potential based on study of Nellis Dunes Recreation Area, a popular off-road vehicle area close to Las Vegas, Nevada. A mapping approach to assess dust emission potential is presented, which may serve as a template to assess other areas for this hazard. A 1:10,000 map delineating units based upon surficial characteristics affecting dust emission (e.g., soil texture, rock cover, surface crusts, and vegetation) was created. Seventeen surface units are grouped into four major classes (sand, silt and clay, rock covered, and active drainages). A >500 km network of trackways was digitized into a geographic information system (GIS) to determine the distribution of tracks across surface types to assess the density of disturbance. Wind-erosion measurements and off-road experiments using different vehicles (four-wheeler, motorcycle, and dune buggy) were performed on the various surface types to assess the amount of dust generated. Dust emission risk maps for Nellis Dunes Recreation Area are presented for two types of processes: off-road vehicular (ORV) activity and wind erosion. Highest dust emissions for ORV activity occur on map units composed of silt and clay, and on desert pavements. These areas can also produce large amounts of dust through natural wind erosion when disturbed. In contrast, the sandy units produce high emissions through natural wind erosion, and therefore limiting ORV use in those areas provides no benefit to air quality.

A method for dry extracting large volumes of fine particulate matter from bulk soil samples

A significant part of ambient dust consists of fine particles derived from natural soils. Because many toxic constituents are concentrated in the smallest particle fractions, and because these small particulates are the most easily inhaled, the fine-particle fraction of soil (PM10 and smaller) is what presents the greatest health concern. Assessing the potential risk of a soil requires examining its chemical content, its biological and mineralogical composition, its sedimentological characteristics, detailed data on grain size distribution, and other information. This analysis requires a relatively large mass of appropriate size fraction(s), obtained by dry extraction. Most methods for extracting fine particulates from soil collect only small amounts of sediment, or use wet extraction. This paper describes the Soil Fine Particle Extractor, a setup for dry extracting large volumes (dozens of grams and more) of fine particulate matter (PM10 and smaller) from bulk soil samples. Separation takes place in two steps. Primary separation in a cylindrical separator 70xa0cm high and 40xa0cm in diameter removes all coarse particles from the sample. The remaining sediment then flows through a 200xa0cm long and 7xa0cm diameter inclined elutriator connected to a three-engine vacuum cleaner. The setup allows extraction of different size fractions depending on the adjustment of the control parameters (suction rate, length, diameter and inclination of the elutriator, thickness of the sediment layer drawn in by the system). The article presents examples of extractions from soil collected in loess and desert environments, ranging from PM2.5 to PM10. It also evaluates the efficiency of the technique by investigating the extraction efficiency for a large number of particle sizes, varying from 0.1 to 70xa0μm. Extraction occurs most efficiently for particles between 1 and 10xa0μm, with an optimum around 5xa0μm.

Immunotoxicological and neurotoxicological profile of health effects following subacute exposure to geogenic dust from sand dunes at the Nellis Dunes Recreation Area, Las Vegas, NV

Exposure to geogenic particulate matter (PM) comprised of mineral particles has been linked to human health effects. However, very little data exist on health effects associated with geogenic dust exposure in natural settings. Therefore, we characterized particulate matter size, metal chemistry, and health effects of dust collected from the Nellis Dunes Recreation Area (NDRA), a popular off-road vehicle area located near Las Vegas, NV. Adult female B6C3F1 mice were exposed to several concentrations of mineral dust collected from active and vegetated sand dunes in NDRA. Dust samples (median diameter: 4.4 μm) were suspended in phosphate-buffered saline and delivered at concentrations ranging from 0.01 to 100 mg dust/kg body weight by oropharyngeal aspiration. ICP-MS analyses of total dissolution of the dust resulted in aluminum (55,090 μg/g), vanadium (70 μg/g), chromium (33 μg/g), manganese (511 μg/g), iron (21,600 μg/g), cobalt (9.4 μg/g), copper (69 μg/g), zinc (79 μg/g), arsenic (62 μg/g), strontium (620 μg/g), cesium (13 μg/g), lead 25 μg/g) and uranium (4.7 μg/g). Arsenic was present only as As(V). Mice received four exposures, once/week over 28-days to mimic a month of weekend exposures. Descriptive and functional assays to assess immunotoxicity and neurotoxicity were performed 24 h after the final exposure. The primary observation was that 0.1 to 100 mg/kg of this sand dune derived dust dose-responsively reduced antigen-specific IgM antibody responses, suggesting that dust from this area of NDRA may present a potential health risk.

Health effects following subacute exposure to geogenic dusts from arsenic-rich sediment at the Nellis Dunes Recreation Area, Las Vegas, NV

Geogenic dust from arid environments is a possible inhalation hazard for humans, especially when using off-road vehicles that generate significant dust. This study focused on immunotoxicological and neurotoxicological effects following subacute exposure to geogenic dust generated from sediments in the Nellis Dunes Recreation Area near Las Vegas, Nevada that are particularly high in arsenic; the naturally-occurring arsenic concentrations in these surficial sediments ranged from 4.8 to 346μg/g. Dust samples from sediments used in this study had a median diameter of 4.5μm and also were a complex mixture of naturally-occurring metals, including aluminum, vanadium, chromium, manganese, iron, cobalt, copper, zinc, strontium, cesium, lead, uranium, and arsenic. Adult female B6C3F1 mice exposed via oropharyngeal aspiration to 0.01 to 100mg dust/kg body weight, four times, a week apart, for 28days, were evaluated 24h after the last exposure. Peripheral eosinophils were increased at all concentrations, serum creatinine was dose responsively increased beginning at 1.0mg/kg/day, and blood urea nitrogen was decreased at 10 and 100mg/kg/day. Antigen-specific IgM responses and natural killer cell activity were dose-responsively suppressed at 0.1mg/kg/day and above. Splenic CD4+CD25+ T cells were decreased at 0.01, 0.1, 10, and 100mg/kg/day. Antibodies against MBP, NF-68, and GFAP were selectively reduced. A no observed adverse effect level of 0.01mg/kg/day and a lowest observed adverse effect level of 0.1mg/kg/day were determined from IgM responses and natural killer cell activity, indicating that exposure to this dust, under conditions similar to our design, could affect these responses.

Surface and Airborne Arsenic Concentrations in a Recreational Site near Las Vegas, Nevada, USA

Elevated concentrations of arsenic, up to 7058 μg g-1 in topsoil and bedrock, and more than 0.03 μg m-3 in air on a 2-week basis, were measured in the Nellis Dunes Recreation Area (NDRA), a very popular off-road area near Las Vegas, Nevada, USA. The elevated arsenic concentrations in the topsoil and bedrock are correlated to outcrops of yellow sandstone belonging to the Muddy Creek Formation (≈ 10 to 4 Ma) and to faults crossing the area. Mineralized fluids moved to the surface through the faults and deposited the arsenic. A technique was developed to calculate airborne arsenic concentrations from the arsenic content in the topsoil. The technique was tested by comparing calculated with measured concentrations at 34 locations in the NDRA, for 3 periods of 2 weeks each. We then applied it to calculate airborne arsenic concentrations for more than 500 locations all over the NDRA. The highest airborne arsenic concentrations occur over sand dunes and other zones with a surficial layer of aeolian sand. Ironically these areas show the lowest levels of arsenic in the topsoil. However, they are highly susceptible to wind erosion and emit very large amounts of sand and dust during episodes of strong winds, thereby also emitting much arsenic. Elsewhere in the NDRA, in areas not or only very slightly affected by wind erosion, airborne arsenic levels equal the background level for airborne arsenic in the USA, approximately 0.0004 μg m-3. The results of this study are important because the NDRA is visited by more than 300,000 people annually.

Health effects following subacute exposure to geogenic dust collected from active drainage surfaces (Nellis Dunes Recreation Area, Las Vegas, NV)

Graphical abstract

Constructing 3-D wind fields for Nellis Dunes in Nevada

An h-adaptive, mass consistent finite element model (FEM) is used to construct 3-D wind fields over irregular terrain utilizing sparse meteorological tower data. The element size in the computational domain is dynamically controlled by a–posteriori error estimator based on the L2 norm. In the h-adaptive FEM algorithm, large element sizes are typically associated with computational regions where the flow is smooth and small errors; small element sizes are attributed to fast changing flow regions and large errors. The adaptive procedure uses mesh refinement/unrefinement to satisfy error criteria. The application of a mass consistent approach essentially poses a least-squares problem in the computational domain. Preliminary results are obtained for constructing 3-D wind fields for Nellis Dunes in Nevada.Copyright