Soil and Biota of Serpentine: A World View 2009 Northeastern Naturalist 16(Special Issue 5):163–177 Plant Colonization Limits Dispersion in the Air of Asbestos Fibers in an Abandoned Asbestos Mine Sergio Enrico Favero-Longo1,2,*, Enrica Matteucci1,2, and Consolata Siniscalco1,2 Abstract - Asbestos exposure has been linked to adverse human health effects including asbestosis and mesothelioma. As such, mining and utilization of asbestos is restricted or has been banned in about 50 countries since 1990. Nevertheless, abandoned asbestos mines, mostly in serpentine areas, persist as sources of hazardous airborne fibers. Revegetation of asbestos mine spoils has been proposed as a way by which to stabilize asbestos-bearing substrate, thereby reducing fiber dispersion into the air. No study to date, however, has evaluated the revegetation's effectiveness of reducing airborne asbestos pollution. In this study, we evaluated the effect of natural revegetation on the air dispersion of asbestos fibers from asbestos-rich serpentine lithosoils at an abandoned chrysotile mine. Air sampling of vegetated and barren plots within the mine demonstrated that vegetative cover significantly reduced asbestos dispersion into the air (50% reduction with 15–40% vegetative cover). Additionally, the effectiveness of several native, locally collected serpentine-tolerant species to revegetate the asbestos mine spoil, including Minuartia and Thymus species, was evaluated. Mat-forming, serpentine endemic Thymus sp. proved to be particularly effective at revegetating the mine spoil, having high transplantation survival, growth rates, and reproductive output. Introduction Asbestos is a general term encompassing fibrous and friable minerals which mainly occur in nature as vein-filling, accessory minerals in serpentinized ultramafic rocks (i.e., serpentinites). Asbestos has been mined for thousands of years for use in domestic, and more recently, industrial products due to its unique qualities of noncombustibility and high resistance to chemical degradation (Compagnoni and Groppo 2006, O’Hanley 1996, Ross and Nolan 2003). Asbestos has been widely used in fire retardant insulation, tiles, and shingles, and as a strengthening additive in bonding compounds, surface coatings, and concrete. Two primary types of asbestos exist including serpentine (i.e., chrysotile; layered, curly fibers) and amphiboles (i.e., crocidolite, amosite, tremolite, anthophyllite; long, straight fibers) (Ross et al. 2008). Inhalation of airborne asbestos has been strongly linked with adverse impacts to human health, including asbestosis (scarring of lung tissue) and 1Plant Biology Department - Centre of Excellence for Plant and Microbial Biosensing (CEBIOVEM), University of Torino, Viale Mattioli 25, Torino, 10125 Italy. 2Interdepartmental Centre “G. Scansetti” for Studies on Asbestos and Other Toxic Particulates, University of Torino, Via Giuria 7, Torino, 10125 Italy. *Corresponding author - sergio.favero@unito.it. 164 Northeastern Naturalist Vol. 16, Special Issue 5 mesothelioma (cancer of the pleural lining) (IARC 1977, Kane et al. 1996, Selikoff et al. 1964). The adverse effects of asbestos on human health is directly related to the quality (asbestos type) and quantity of fibers inhaled (Baron 2001, Fubini and Otero-Areán 1999). Due to the adverse impacts to human health related to inhalation of asbestos, the extraction and utilization of asbestos in products has been restricted or banned in about 50 countries since 1990 (Kane et al. 1996). Nevertheless, abandoned mines still represent potential sources of airborne asbestos, and thus are considered hazardous environmental sites (Dearwent et al. 2006, Hillerdal 1999, Lee et al. 2008, Magnani et al. 2000). Sealing is the typical method for limiting human exposure from highly localized asbestos sources (asbestos-cement roofs or abandoned industrial plants) when removal of the material is not practical (US EPA 2003). This approach, however, is inadequate where asbestos contamination is widespread, such as is the case with abandoned asbestos mines (Favero-Longo et al. 2006, Turci et al. 2007). It has been suggested that revegetation of asbestos-bearing mine spoils may reduce their negative impact both in terms of aesthetic and health problems (Liston and Balkwill 1997, Moore and Zimmermann 1977). Studies have demonstrated that vegetation can naturally re-establish upon asbestos-rich serpentine mine spoils over time, despite the unfavourable physical and nutrient conditions of the substrate, including very low CEC, water-holding capacity, organic matter, macronutrient levels, and Ca:Mg molar ratios and potentially high levels of phytotoxic heavy metals (Baker 1999, Ellery and Walker 1986, Favero- Longo et al. 2006, Liston and Balkwill 1997, Moore and Zimmermann 1977). No study to date has evaluated the effectiveness of revegetation at reducing airborne asbestos pollution. Serpentine-tolerant species and ecotypes have been shown to be the most suitable candidates for serpentine revegetation (Liston and Balkwill 1997, O’Dell and Claassen 2006). Field trials, however, have been limited to just a few species, with positive results partially obtained with seeded grasses, which generally develop a sparse cover (Moore and Zimmermann 1977, O’Dell and Claassen 2006). Nutrient amendment of barren, serpentine substrate in order to promote revegetation has yielded encouraging results, but has rarely been applied due to high costs and may not be practical on steep slopes (e.g., Cyprus Asbestos Mine [Kyrou and Petrides 2004]; Atlas Asbestos Mine [California; US EPA 2006]). Most studies on phytoremediation and phytoextraction of metal-rich substrates using serpentine plant species (without substrate amendments) have primarily focused on biomass production, rather than plant cover, which is important for limiting fiber dispersion (Angle et al. 2001, Chaney et al. 2007, Shah and Nongkynrih 2007, Whiting et al. 2004). Since these studies do not offer reliable models for the remediation of abandoned asbestos mines, further investigations are needed to identify plant species suitable for obtaining self-sustaining communities that will limit the dispersion of fibers into the air. 2009 S.E. Favero-Longo, E. Matteucci, and C. Siniscalco 165 The purpose of this study was to evaluate the influence of natural, vegetative cover on airborne asbestos fiber dispersion within an abandoned asbestos mine. Additionally, the ability of native, locally collected, serpentine- tolerant plant species to establish vegetative cover on unamended asbestos mine tailings was also evaluated. Methods Field site description The Balangero asbestos mine is located approximately 30 km northwest of Torino (NW Italy). The mine (about 4 km2) is located on the Balangero ultramafic (serpentinite) mass, a portion of the Ultramafic Lanzo Massif occurring in the Central Western Alps (Compagnoni et al. 1980). Undisturbed native vegetation surrounding the mine is dominated by a xerophytic oak woodland (Favero-Longo et al. 2006). The climate is transitional between a temperate-continental climate (characteristic of the Po Plane) and a prealpine climate, with high precipitation. Mean annual temperature is 10.3 °C and rainfall is 1160 mm (Fig. 1). Average natural wind speed measured at 6 m height from January 2006 to December 2007 was 2.2 ± 1.3 m s-1 (max = 19.6 m s-1; between 1 and 3 m s-1 = 65% of the time for the two monitored years; <1 m s-1 = 13% of the time for the two monitored years). According Figure 1. Walter and Lieth climatic diagram from the Lanzo T.se weather station, close to the Balangero asbestos mine (data from 1960 to 1990). 166 Northeastern Naturalist Vol. 16, Special Issue 5 to log-height decrease of wind speed (Namikas et al. 2003, Okin et al. 2006) and supplementary field measures (at 3, 50, 100 cm height), wind speed at the ground level is estimated to be between 0.7 and 1.5 m s-1 when wind speed at 6 m height is between 1 and 3 m s-1 (Fig. 2) Mining of chrysotile asbestos at Balangero began in the 1920s and continued until 1990, when it was halted due to new Italian laws that completely banned the exploitation and commercialization of asbestos (Favero-Longo et al. 2006). Early attempts in the 1970s to revegetate spoil banks with the exotic species Pinus nigra Arnold (European Black Pine) (Pinaceae) and Ulmus pumila L. (Siberian Elm) (Ulmaceae) did not yield significant increases in vegetative cover and simultaneously prevented the development of native herbaceous vegetation, due to competition between the transplanted trees and the native species. Topsoil application and hydroseeding with commercial Figure 2. Windspeed profiles for the Balangero asbestos mine measured on the basin terrace and near the spoil bank. Measurement was performed throughout the course of a day and is representative of the average wind conditions for the site: wind speed below 3 m s-1 during 78% of the time for the years 2006– 2007. Solid lines indicate the bestfit regression relation, highlighting the typical log-height decrease of wind speed near the soil surface. Data are displayed as means ± standard error. 2009 S.E. Favero-Longo, E. Matteucci, and C. Siniscalco 167 herbaceous species during the last decade had partial success, but was limited to small areas because of high costs (Favero-Longo et al. 2006). In this study, we examined the dominant native species occurring on asbestos- rich serpentine mine spoil of a mine “basin terrace,” where mining activity continued until 1990, and a post-milling “spoil bank,” abandoned since 1970. Soil texture at both sites is a gravelly loam. The high proportion of gravel (30% by volume) tends to armor the soil surface. The basin terrace is colonized by a metallophytic pioneer community dominated by widely spaced, patch-forming Minuartia laricifolia (L.) Sch. et Th. (Caryophyllaceae) and the serpentine endemic Thlaspi sylvium Gaudin (Brassicaceae). Vegetative cover on the basin terrace varies from 3 to 40%. The spoil bank is colonized by a more developed community dominated by mat-forming Thymus humifusus Bernh., T. pulegioides L. and T. alpestris Tausch (Lamiaceae) (Favero-Longo et al. 2006). Vegetative cover on the spoil bank ranges from 40 to 90% (Fig. 3). Figure 3. Vegetative cover on the basin terrace by widely spaced, patch-forming Minuartia laricifolia (L.) Sch. et Th. (Caryophyllaceae) (A and B) and on the spoil bank by mat-forming Thymus humifusus Bernh., T. pulegioides L. and T. alpestris Tausch (Lamiaceae) (C and D). 168 Northeastern Naturalist Vol. 16, Special Issue 5 Asbestos air monitoring study Monitoring of airborne fibers is usually performed by collecting fibers on filters and counting them by contrast light or electron microscopy (Baron 2001). In this study, a wind-generating and air-sampling unit was utilized to assess the effect of vegetative cover on asbestos fiber dispersion from mine spoil. The sampling methods utilized followed those established to standardize the assessment of the human health risk of asbestos in soils (Swartijes and Tromp 2008). Vegetated areas examined included 15% cover of M. laricifolia on the basin terrace and 40% cover of T. humifusus and T. pulegioides on the spoil bank. For sample collection, each plot was covered with a Plexiglas case (80 cm square at base and 50 cm high), and the ground was subject to mechanical ventilation for 25 minutes, using a fan (ML23-E11231, 23 cm fan dia., 230V, 50Hz, 25W; Esprit, Milano, Italy) (Fig. 4). The “wind speed” produced by the fan in the case at the ground level (3 cm from the surface) was calibrated as follows in order to simulate typical wind speeds characteristic of the site: maximum wind speed = 1.5 m s-1, minimum = 0.5 m s-1, and average = 0.8 m s-1. The interface between the base perimeter of the case and the ground was sealed with strips of foam rubber to avoid influence of the surrounding conditions. During, and for 5 minutes following mechanical ventilation, the air volume within the case (320 L) was sampled using an air-sampling pump Figure 4. Sampling equipment for airborne asbestos fibers dispersed from asbestosrich lithosoils. a. Plexiglas case (height x width x length: 50 x 80 x 80 cm), b. fan, c. filtering device, d. air sampling pump, and e. foam rubber strips. 2009 S.E. Favero-Longo, E. Matteucci, and C. Siniscalco 169 (Buck Libra Pump L-4 with 120 VAC Charger) at 2.5 L min-1, yielding a final sample of 75 L. The 75-L volume was chosen on the basis of preliminary measures of the sample volume needed to obtain an adequate density of fi- bers for counting. Fibers in the sampled air volume were collected over the surface of a cellulose-acetate filter (MFS: diameter = 2.5 cm, pore size = 0.8 μm). The filter was mounted on a microscope slide and made transparent using a dot of triacetin. The collected asbestos fibers (minerals showing an aspect ratio greater than 3:1) were finally counted by high magnification (500x) contrast light microscopy (Olympus CX40). It is worth noting that this method does not detect all fibers because of the limitation of light microscopy (Baron 2001), but it allows comparison between the air dispersion of fibers from vegetated and bare plots. Vegetated plots on the basin terrace were examined on different days during the growing seasons in 2006 and 2007. The number of plots sampled were 2 in spring, 5 in early summer, and 4 in late summer. The number of plots measured in spring was limited due to technical constrains. Vegetated plots on the spoil bank were also examined (4 plots each during early and late summer). During each sampling session, bare plots between the vegetated plots were monitored as controls (basin terrace: 2, 4, and 4 bare plots examined in spring, early summer, and late summer, respectively; spoil bank: 3 and 4 bare plots were examined in early and late summer, respectively). Sampling of the airborne fibers was performed from the morning (9 AM) to the early afternoon (4 PM) on days following at least ten days without rain, thus operating in air-dry soil surface conditions. Climate data for the sampling days are shown in Table 1. The amount of fibers dispersed from bare vs. vegetated plots was statistically analyzed by means of Student’s t-test (P < 0.05 considered significant), using Systat 10.2 (Systat Software, Inc. 2002). Minuartia and Thymus germination study Seeds of M. laricifolia and T. humifusus were collected from the Balangero mine, surface-sterilized by washing with 50% ethanol for 10 min and afterwards with 3.75% sodium hypochlorite for 10 min, and repeatedly Table 1. Climate data from the Balangero asbestos mine (Mt. Vittore station, 890 m). RH = relative humidity (%), T = air temperature (°C). Weather data Measuring Ten days Field Plant Measuring days days* before** sites communities Season Date RH T RH T Basin terrace Minuartia Spring 04 May 2006 44.6 15.9 62.4 11.6 Early summer 19 July 2007 36.8 27.0 95.8 20.2 Late summer 05 September 2007 27.5 15.7 66.6 18.6 Spoil bank Thymus Early summer 22 June 2006 45.5 22.9 48.9 20.4 Late summer 07 September 2007 22.8 18.5 60.9 16.7 *Average values of measures performed hourly from 9 AM to 4 PM. **Average values of measures performed hourly from 12 AM to 12 AM. 170 Northeastern Naturalist Vol. 16, Special Issue 5 rinsed with distilled water. Seeds of M. laricifolia were stratified at 4 °C for 22 days, since preliminary attempts without cold stratification failed. Germination was carried out on two substrate types, including: (1) Petri dishes (9 cm diameter) on sterile agar stored at 20 °C for 14 days (25 seeds per Petri dish, n = 3 Petri dishes per species), and (2) 1200-cm3 pots on sterile sand (90%) and vermiculite (10%) stored at 20 °C for 20 days (3 seeds per pot, n = 12 pots per species). Seed germination was evaluated for both the agar and sand/vermiculite substrate. Plant growth parameters stem length, number of nodes, percentage of nodes with branches, leaf number and leaf area, were measured for plants in the sand/vermiculite mix after twelve weeks of growth. Leaf area was calculated by processing photos of the plants by image analysis using the software WinCAM (Régent Instrument, version 2007b). Thymus field growth study Fifty-three individuals of Thymus (40 of T. humifusus and 13 of T. pulegioides; proportional to the relative species abundance of 3:1 found in the natural community) were transplanted in November from the post-milling spoil bank to an unvegetated mining terrace area representative of the whole area in terms of soil features. Plants were organized in rows of ten or eleven individuals 25 cm apart. Neither irrigation nor soil addition were supplied during the course of the study. Survival (% of live plants, estimated in the field) and development (as maximum diameter in cm, measured in the field) of the plants were thereafter assessed in the subsequent vegetative season (in spring, 28 March 07; summer, 19 July 07; autumn, 25 October 07). Differences in plant diameters along the experimental season were statistically analyzed by means of ANOVA with post-hoc Tukey’s test (P < 0.05 considered significant), using Systat 10.2 (Systat Software, Inc., 2002). Final survival was assessed on 10 June 08. Results Asbestos air monitoring study Following mechanical ventilation, fibers were dispersed in the air from all bare and plant colonized plots, except for two plots covered by Thymus where no fibers were observed on the filters. Fiber dispersion from the soil of the mining terrace (mean = 0.54 fibers L-1) was about one order of magnitude higher than that from the soil of the post-milling spoil bank (mean = 0.05 fi- bers L-1), apart from the occurrence or absence of plants (Fig. 5). In both areas, plant cover significantly (P < 0.05) reduced fiber dispersion by approximately 50%, with the same effect being observed throughout the investigated seasons. On the mining terrace, a progressive decrease of airborne fibers was observed from spring to late summer, while on the post-milling spoil bank, a higher fiber dispersion was observed in early summer relative to late summer. Minuartia and Thymus germination study Germination rate on both agar and sand/vermiculite, and morphometric data for sand/vermiculite are shown in Table 2. Minuartia laricifolia showed a 2009 S.E. Favero-Longo, E. Matteucci, and C. Siniscalco 171 lower germination rate compared to Thymus humifusus, both on agar and sand/ vermiculite. After 12 weeks of growth, M. laricifolia displayed little stem development (mean = 5 cm), and leaf number—although abundant (mean >50)—generated very low cover values (<1 cm2 ). In contrast, T. humifusus displayed a higher developmental rate, both in terms of stem length (mean = 11 cm) and leaf number (mean = 66). Additionally, a high number of nodes with branches, which was mostly absent in Minuartia, yielded relatively higher cover values (mean = 4 cm2) with maximum values exceeding 15 cm2. High Table 2 - Germination and development of Minuartia laricifolia and Thymus humifusus in the laboratory. Data are expressed as means ± standard error. n.d. = not determined Germination (%) Growth on sterile sand after twelve weeks Sterile Stem Number Number Nodes with Cover Agar sand length (cm) of leaves of nodes branches (%) (cm2) Minuartia 9.3 19.4 5.0 ± 0.8 ≈50* n.d. <10* <1.0* Thymus 66.6 47.2 10.6 ± 1.5 66 ± 11 11 ± 1 42 ± 6 4.4 ± 1.3 *The reported value is approximated because of measuring difficulties. Figure 5. Dispersion of asbestos fibers in the air from Bare and vegetated (Veg) plots. Basin terrace: 15% total vegetative cover by Minuartia laricifolia. Spoil bank: 40% total vegetative cover by Thymus humifusus and T. pulegioides. Data are expressed as means ± standard error. *P < 0.05. 172 Northeastern Naturalist Vol. 16, Special Issue 5 variability was observed from individual to individual, as indicated by high standard errors for both nodes with branches and cover values. Thymus field growth study Ninety-six percent of Thymus individuals transplanted in autumn 2006 survived to the end of spring 2008. Morphometric analysis showed that the plants undergo a small reduction in size during the first winter, thereafter reverting to an increasing trend, which yielded highest diameter values in summer 2007 (Fig. 6). In late summer, a reduction in size was again observed, as well as abundant fruiting, in agreement with frequent floral visitation by insects observed during spring and early summer. At the end of spring 2008, several seedlings were observed close to the transplanted plants, suggesting reproductive success and consistent, rapid self-propagation (Fig. 7). Discussion Previous studies have suggested that the revegetation of asbestos-rich mine spoil may reduce airborne asbestos pollution from them (Favero-Longo et al. 2006, Liston and Balkwill 1997, Moore and Zimmermann 1977). Our study has demonstrated that natural revegetation of an abandoned asbestos mine was able to significantly reduce the dispersion of fibers from minespoil into the air by 50%. Figure 6. Development of transplanted Thymus on asbestos bearing lithosoil through the 2007 growing season. Development is estimated on the basis of the maximum individual diameter. Data are expressed as means ± standard error. *P < 0.05. 2009 S.E. Favero-Longo, E. Matteucci, and C. Siniscalco 173 Vegetative cover is able to protect the asbestos-rich minespoil from wind erosion in three ways, including 1) physically covering the soil surface by its canopy, 2) modifying ground-level air flow, and 3) physically stabilizing the soil through anchorage by roots. By covering the substrate on which they grow, Minuartia laricifolia and Thymus spp. directly reduce the area of exposed asbestos-bearing mine spoil (reductions of about 15% and 40%, respectively). Additionally, plants may modify ground-level air flow by causing local reductions in surface wind speed and temperature, coupled with increases in humidity and condensation at the soil surface, which helps to reduce fiber dispersion. Different morphologies, such as leaf shape, leaf orientation, and canopy growth patterns of the two studied taxa (M. laricifolia vs. Thymus), are likely to account for the similar decrease of fiber dispersion (50%) despite the different cover values of the taxa (Whisenant 2002). In comparison, vegetation cover at 15% was considered a threshold over which wind erosion rapidly reduces (Allgaier 2008), coupling covering of the soil surface with creation of effective lee-side areas sheltered from the wind (Okin et al. 2006). Similar vegetation-influenced reductions in wind-blown sand and wind erosion have been demonstrated in grasslands of California and China (Lancaster and Baas 1998, Liu et al. 2008). We also found that the maximum wind speed at ground level (1.5 m s-1) did not differ between bare and colonized plots, although minimum values did vary at 0.5 and 0.0 m s-1 in bare and vegetated plots, respectively. As with many serpentine plants, M. laricifolia (Rune 1953) has a strongly developed root system which may significantly contribute to the stabilization of asbestos-bearing soils (Tordoff et al. 2000). Different types of disturbance impacts between the basin terrace (mining area) and spoil bank (post-milling area) account for the strong difference in fiber counts between the two investigated areas. Milled spoil bank material contained less asbestos due to removal of asbestos during the milling Figure 7. Floral visitation of Thymus pulegioides (A) and fruiting of Thymus humifusus (B) transplanted on the asbestos rich lithosoil. Seedlings (arrows) observed near the plants 18 months after the transplantation (C). 174 Northeastern Naturalist Vol. 16, Special Issue 5 process. Fiber count varied by season as a function of the variation in soilmoisture conditions (precipitation vs. temperature). The highest airborne asbestos levels were observed in spring. This result may be attributed to increased weathering during the winter when soil frost heave can loosen the soil surface. Although seasonal increases in soil moisture can effectively reduce airborne asbestos pollution during the wet season, only plant cover provides year-round protection of the soil surface from wind erosion that generates airborne asbestos pollution (Favero-Longo et al. 2006). Revegetation of abandoned asbestos mines is a major tool to reduce airborne asbestos pollution by providing surface cover and anchoring soil. Revegetation of asbestos mines is not achieved without great difficulty due to the extreme adverse physical and chemical properties of the mine spoil (Baker 1999, Ellery and Walker 1986, Moore and Zimmermann 1977, O’Dell and Claassen 2006). Some success has been achieved utilizing soil amendments and local, native, serpentine-tolerant plant materials (Baker 1999, Ellery and Walker 1986, EPA 2006, Kyrou and Petrides 2004, Liston and Balkwill 1997, Moore and Zimmermann 1977, O’Dell and Claassen 2006). High survival (96%) and vigor of Thymus transplanted into asbestos-rich serpentinite mine spoil terraces indicates that the use of native, site-collected plants, which are ecologically adapted both to serpentine soil factors and to the prevailing climate (Luçon et al. 1997, Tordoff et al. 2000, Whiting et al. 2004), can successfully be used to revegetate asbestos mine spoils. Seeding or transplanting of native species was previously shown to promote revegetation and reclamation of metalliferous mine wastes by enhancing natural colonization processes (Tordoff et al. 2000). Thymus humifusus showed greater vegetative cover development than M. laricifolia, thus appearing more suitable for revegetation. Additionally, higher germination rates of Thymus and field observations on floral visitation, fruiting, and new seedling production suggest that the species will continue to thrive on the mine spoil. Strong differences in plant growth observed between individuals suggest the potential advantages of selecting for the desirable traits of fast growth and high plant cover within the species by classical breeding methods, as suggested by Angle et al. (2001) and Davy (2002). Such a combined laboratory and field approach may reveal practical solutions for the revegetation of asbestos mine spoil, although it should be noted that the examined plant covers (up to 40%) significantly reduce, but do not completely eliminate, asbestos fiber dispersion. Acknowledgments The authors wish to express their gratitude to the R.S.A. s.r.l. staff of the Balangero mine for their constant assistance during the field-work and for soil data, to Rosanna Piervittori (University of Torino) for WinCAM software, and to Ryan O’Dell and two anonymous referees for helpful editorial work and comments to the manuscript. The research has been carried out with the financial support of Regione Piemonte, “Direzione regionale 22, Tutela e Risanamento Ambientale - Programmazione - Gestione Rifiuti,” in the context of a multidisciplinary project “Asbestos hazard in Western Alps.” 2009 S.E. Favero-Longo, E. Matteucci, and C. Siniscalco 175 Literature Cited Allgaier, A. 2008. Aeolian sand transport and vegetation cover. Pp. 211–224, In S.-W. Breckle, A. Yair, and M. Veste (Eds.). Arid Dune Ecosystems. Ecological Studies 200. Springer, Berlin-Heidelberg, Germany. Angle, J.S., R.L. Chaney, A.J.M. Baker, Y. Li, R. Reeves, V. Volk, R. Roseberg, E. Brewer, S. 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