... Patrick Gaffney, California Air Resources Board, Sacrament, CA. Jamie Fine, Consultant, San A... more ... Patrick Gaffney, California Air Resources Board, Sacrament, CA. Jamie Fine, Consultant, San Anselmo, CA. Tom Gill, USDA-ARS, Lubbock, TX. John Gillies, Desert Research Institute, Reno, NV. ... Atmospheric Environment 18:1517. Currie, LA, Klouda, GA, Voorhees, KJ (1984). ...
ABSTRACT Vegetation tends to reduce aeolian transport of surface sediments. However, not all vege... more ABSTRACT Vegetation tends to reduce aeolian transport of surface sediments. However, not all vegetation types act in the same way to do so. In general, the more land cover the less erosion will occur; thus grasslands should experience less aeolian erosion than shrublands, which are characterized by patchy cover with open intershrub spaces. Five major ecosystem types are described at the Jornada Basin Long- Term Ecological Research site (Jornada LTER) in south-central New Mexico, USA: mesquite dunes, black grama grasslands, creosote bush shrublands, tarbush alluvial flats, and grass-dominated playas. Here we investigate the dry particle size distribution of material collected by BSNE aeolian particle samplers in 2006 in these five different vegetation types, allowing us to estimate dust production at sites with different land cover. As mesquite and creosote bush continue replacing historical grasslands at Jornada, understanding the characteristics of wind erosion will be important for future management plans. The mesquite sites had the greatest horizontal mass flux, although with substantial variation. M-NORT, a site with large sand dunes, had much greater mass flux than other mesquite sites. For most sites, the dry particle size distributions at 5, 10 and 20 cm heights above the land surface were very similar, dominated by sand, while the distributions for 50 and 100cm heights shifted towards a greater percentage of silt and clay (dust) particles. The playa site and one of three tarbush sites stand out as having the greatest percentages of dust particles, between 33- 52 % of total mass at all heights. After taking into account the differences in mass flux, the mesquite site with the larger dunes and the playa site had the greatest flux of dust-sized particles. These two sites demonstrate different mechanisms of producing dust at the Jornada LTER. The playa is a relatively major dust producer due to its high proportion of fine particles, whereas the mesquite site is a major dust producer because of its far greater overall mass flux. Considering the differential mass flux of aeolian particles produced by each vegetation type, the greatest total mass of dust per unit area at the Jornada LTER occurs at the playa site, followed by the mesquite site with large dunes and tarbush, while creosote bush, grassland, and the other two mesquite sites produce the least dust. Since mesquite dunes cover about 34% of the Jornada Basin, we conclude that mesquite dunes have the potential to produce the most dust from the area overall, with playas and tarbush-dominated alluvial flats (which cover about 7% each) having the potential to emit large amounts of dust if the conditions are correct. These results suggest that the continuing replacement of grasslands with shrubs will likely increase dust emissions from the Jornada Basin.
The White Sands Dune Field, New Mexico (USA), provides a unique opportunity to study sources and ... more The White Sands Dune Field, New Mexico (USA), provides a unique opportunity to study sources and eolian transport of sand. End member mixing analysis provides unbiased correlation of the grain size distributions of populations that mix sands from four different local source surface types. Textural differences between sources allow local transport paths to be deduced. In total, 1214 surface samples from 10 dunes and 2 downwind-oriented transects were collected. Neither elevation on the dune, lee or stoss location nor distance downwind correlated with mean grain size, coarsest 10% (D 90), or sorting. Instead, grain size distributions are controlled by mixing of locally sourced sand populations. Adjacent dunes can have different mean grain sizes, resulting from different local source populations. Local within-dune and between-dune variability resulting from different sand sources dominates any larger-scale trends across and within dunes. Four sand populations are identified, based on microscopically observable differences in grain size, shape and angularity. Each correlates with high loading of a different statistical factor, derived from End Member Mixing Analysis. End Member 1 (EM1) correlates with well-sorted populations of finer-grained, equant, rounded sands. EM2 correlates with samples that contain moderately sorted populations containing angular blades and crystal aggregates associated with erosional interdunes. EM3 is associated with samples of moderately to poorly sorted fine-grained sand containing fine sand-sized gypsum needles collected from areas of vegetated interdunes, and EM4 is associated with moderately well sorted coarse-and very coarse-grained sands collected from granule ripples. These results suggest that downwind mixing of different populations and segregation by different depositional processes influence grain size distributions in the dune field, rather than by dune-scale or erg-scale transport and sorting.
A number of mathematical distributions have been proposed for the description of the particle siz... more A number of mathematical distributions have been proposed for the description of the particle size distribution of unconsolidated sediments. However, few studies have mathematically described aeolian dust particle size distributions. Recent work has shown mathematicallyhowthe sequential fragmentation of materials leads to a Weibull distribution. Since the breakage of aggregates by saltating grains is a primary mode of aeolian dust production, we test the hypothesis that the Weibull distribution may be used to describe airborne soil grains. Surface samples were collected from 52 sites including soils, dirt roads and roadside ditches in the Southern High Plains of west Texas. The samples were tumbled in the Lubbock dust generation, sampling and analysis system to generate a dust cloud. The particle size distribution of the dust was measured in situ by laser diffraction and PM10 concentration was determined gravimetrically (PM10 = airborne particulate matter with diameter 10 m). This study demonstrated that the Weibull cumulative distribution function (c.d.f.) is an excellent choice to describe the particle size distribution of dust suspended from mineral sediment.AWeibull c.d.f. used to describe the dust cloud size distribution, accounted for 94 per cent of the variation in estimates of particles 50mdiameter. The fraction of dust particles 10 m diameter, as estimated using the Weibull, was not correlated to suspended PM10 concentration. However, the fraction of particles 10 m was correlated with properties of the sediment from which the airborne dust was derived. As clay content increased, the total amount of suspended dust increased and the fraction of suspended particles 10min the dust cloud decreased. Analyses of variance showed no significant differences (P < 005) among sampling locations (roads vs ditches vs soils) for cumulative fraction values for 25, 10, 25, 30 and 50 m diameter particles. However, the PM10 concentration values were significantly different among dust generated from these locations. The road samples produced about twice the amount of PM10 (490 mg m ÿ3) as the soil or ditch samples (235 mg m ÿ3)
... Patrick Gaffney, California Air Resources Board, Sacrament, CA. Jamie Fine, Consultant, San A... more ... Patrick Gaffney, California Air Resources Board, Sacrament, CA. Jamie Fine, Consultant, San Anselmo, CA. Tom Gill, USDA-ARS, Lubbock, TX. John Gillies, Desert Research Institute, Reno, NV. ... Atmospheric Environment 18:1517. Currie, LA, Klouda, GA, Voorhees, KJ (1984). ...
ABSTRACT Vegetation tends to reduce aeolian transport of surface sediments. However, not all vege... more ABSTRACT Vegetation tends to reduce aeolian transport of surface sediments. However, not all vegetation types act in the same way to do so. In general, the more land cover the less erosion will occur; thus grasslands should experience less aeolian erosion than shrublands, which are characterized by patchy cover with open intershrub spaces. Five major ecosystem types are described at the Jornada Basin Long- Term Ecological Research site (Jornada LTER) in south-central New Mexico, USA: mesquite dunes, black grama grasslands, creosote bush shrublands, tarbush alluvial flats, and grass-dominated playas. Here we investigate the dry particle size distribution of material collected by BSNE aeolian particle samplers in 2006 in these five different vegetation types, allowing us to estimate dust production at sites with different land cover. As mesquite and creosote bush continue replacing historical grasslands at Jornada, understanding the characteristics of wind erosion will be important for future management plans. The mesquite sites had the greatest horizontal mass flux, although with substantial variation. M-NORT, a site with large sand dunes, had much greater mass flux than other mesquite sites. For most sites, the dry particle size distributions at 5, 10 and 20 cm heights above the land surface were very similar, dominated by sand, while the distributions for 50 and 100cm heights shifted towards a greater percentage of silt and clay (dust) particles. The playa site and one of three tarbush sites stand out as having the greatest percentages of dust particles, between 33- 52 % of total mass at all heights. After taking into account the differences in mass flux, the mesquite site with the larger dunes and the playa site had the greatest flux of dust-sized particles. These two sites demonstrate different mechanisms of producing dust at the Jornada LTER. The playa is a relatively major dust producer due to its high proportion of fine particles, whereas the mesquite site is a major dust producer because of its far greater overall mass flux. Considering the differential mass flux of aeolian particles produced by each vegetation type, the greatest total mass of dust per unit area at the Jornada LTER occurs at the playa site, followed by the mesquite site with large dunes and tarbush, while creosote bush, grassland, and the other two mesquite sites produce the least dust. Since mesquite dunes cover about 34% of the Jornada Basin, we conclude that mesquite dunes have the potential to produce the most dust from the area overall, with playas and tarbush-dominated alluvial flats (which cover about 7% each) having the potential to emit large amounts of dust if the conditions are correct. These results suggest that the continuing replacement of grasslands with shrubs will likely increase dust emissions from the Jornada Basin.
The White Sands Dune Field, New Mexico (USA), provides a unique opportunity to study sources and ... more The White Sands Dune Field, New Mexico (USA), provides a unique opportunity to study sources and eolian transport of sand. End member mixing analysis provides unbiased correlation of the grain size distributions of populations that mix sands from four different local source surface types. Textural differences between sources allow local transport paths to be deduced. In total, 1214 surface samples from 10 dunes and 2 downwind-oriented transects were collected. Neither elevation on the dune, lee or stoss location nor distance downwind correlated with mean grain size, coarsest 10% (D 90), or sorting. Instead, grain size distributions are controlled by mixing of locally sourced sand populations. Adjacent dunes can have different mean grain sizes, resulting from different local source populations. Local within-dune and between-dune variability resulting from different sand sources dominates any larger-scale trends across and within dunes. Four sand populations are identified, based on microscopically observable differences in grain size, shape and angularity. Each correlates with high loading of a different statistical factor, derived from End Member Mixing Analysis. End Member 1 (EM1) correlates with well-sorted populations of finer-grained, equant, rounded sands. EM2 correlates with samples that contain moderately sorted populations containing angular blades and crystal aggregates associated with erosional interdunes. EM3 is associated with samples of moderately to poorly sorted fine-grained sand containing fine sand-sized gypsum needles collected from areas of vegetated interdunes, and EM4 is associated with moderately well sorted coarse-and very coarse-grained sands collected from granule ripples. These results suggest that downwind mixing of different populations and segregation by different depositional processes influence grain size distributions in the dune field, rather than by dune-scale or erg-scale transport and sorting.
A number of mathematical distributions have been proposed for the description of the particle siz... more A number of mathematical distributions have been proposed for the description of the particle size distribution of unconsolidated sediments. However, few studies have mathematically described aeolian dust particle size distributions. Recent work has shown mathematicallyhowthe sequential fragmentation of materials leads to a Weibull distribution. Since the breakage of aggregates by saltating grains is a primary mode of aeolian dust production, we test the hypothesis that the Weibull distribution may be used to describe airborne soil grains. Surface samples were collected from 52 sites including soils, dirt roads and roadside ditches in the Southern High Plains of west Texas. The samples were tumbled in the Lubbock dust generation, sampling and analysis system to generate a dust cloud. The particle size distribution of the dust was measured in situ by laser diffraction and PM10 concentration was determined gravimetrically (PM10 = airborne particulate matter with diameter 10 m). This study demonstrated that the Weibull cumulative distribution function (c.d.f.) is an excellent choice to describe the particle size distribution of dust suspended from mineral sediment.AWeibull c.d.f. used to describe the dust cloud size distribution, accounted for 94 per cent of the variation in estimates of particles 50mdiameter. The fraction of dust particles 10 m diameter, as estimated using the Weibull, was not correlated to suspended PM10 concentration. However, the fraction of particles 10 m was correlated with properties of the sediment from which the airborne dust was derived. As clay content increased, the total amount of suspended dust increased and the fraction of suspended particles 10min the dust cloud decreased. Analyses of variance showed no significant differences (P < 005) among sampling locations (roads vs ditches vs soils) for cumulative fraction values for 25, 10, 25, 30 and 50 m diameter particles. However, the PM10 concentration values were significantly different among dust generated from these locations. The road samples produced about twice the amount of PM10 (490 mg m ÿ3) as the soil or ditch samples (235 mg m ÿ3)
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Papers by Tom Gill
unconsolidated sediments. However, few studies have mathematically described aeolian dust particle size distributions.
Recent work has shown mathematicallyhowthe sequential fragmentation of materials leads to a Weibull distribution. Since
the breakage of aggregates by saltating grains is a primary mode of aeolian dust production, we test the hypothesis that the
Weibull distribution may be used to describe airborne soil grains. Surface samples were collected from 52 sites including
soils, dirt roads and roadside ditches in the Southern High Plains of west Texas. The samples were tumbled in the Lubbock
dust generation, sampling and analysis system to generate a dust cloud. The particle size distribution of the dust was
measured in situ by laser diffraction and PM10 concentration was determined gravimetrically (PM10 = airborne particulate
matter with diameter 10 m). This study demonstrated that the Weibull cumulative distribution function (c.d.f.) is an
excellent choice to describe the particle size distribution of dust suspended from mineral sediment.AWeibull c.d.f. used to
describe the dust cloud size distribution, accounted for 94 per cent of the variation in estimates of particles 50mdiameter.
The fraction of dust particles 10 m diameter, as estimated using the Weibull, was not correlated to suspended PM10
concentration. However, the fraction of particles 10 m was correlated with properties of the sediment from which the
airborne dust was derived. As clay content increased, the total amount of suspended dust increased and the fraction of
suspended particles 10min the dust cloud decreased. Analyses of variance showed no significant differences (P < 005)
among sampling locations (roads vs ditches vs soils) for cumulative fraction values for 25, 10, 25, 30 and 50 m
diameter particles. However, the PM10 concentration values were significantly different among dust generated from these
locations. The road samples produced about twice the amount of PM10 (490 mg m
ÿ3) as the soil or ditch samples (235 mg
m
ÿ3)
unconsolidated sediments. However, few studies have mathematically described aeolian dust particle size distributions.
Recent work has shown mathematicallyhowthe sequential fragmentation of materials leads to a Weibull distribution. Since
the breakage of aggregates by saltating grains is a primary mode of aeolian dust production, we test the hypothesis that the
Weibull distribution may be used to describe airborne soil grains. Surface samples were collected from 52 sites including
soils, dirt roads and roadside ditches in the Southern High Plains of west Texas. The samples were tumbled in the Lubbock
dust generation, sampling and analysis system to generate a dust cloud. The particle size distribution of the dust was
measured in situ by laser diffraction and PM10 concentration was determined gravimetrically (PM10 = airborne particulate
matter with diameter 10 m). This study demonstrated that the Weibull cumulative distribution function (c.d.f.) is an
excellent choice to describe the particle size distribution of dust suspended from mineral sediment.AWeibull c.d.f. used to
describe the dust cloud size distribution, accounted for 94 per cent of the variation in estimates of particles 50mdiameter.
The fraction of dust particles 10 m diameter, as estimated using the Weibull, was not correlated to suspended PM10
concentration. However, the fraction of particles 10 m was correlated with properties of the sediment from which the
airborne dust was derived. As clay content increased, the total amount of suspended dust increased and the fraction of
suspended particles 10min the dust cloud decreased. Analyses of variance showed no significant differences (P < 005)
among sampling locations (roads vs ditches vs soils) for cumulative fraction values for 25, 10, 25, 30 and 50 m
diameter particles. However, the PM10 concentration values were significantly different among dust generated from these
locations. The road samples produced about twice the amount of PM10 (490 mg m
ÿ3) as the soil or ditch samples (235 mg
m
ÿ3)