📄 metadata.txt
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sample collected from one trap typically weighs less than
1 g/yr). These adaptations generally result in larger
standard errors than normal for the results of different
techniques because the amount of sample used is smaller
than the recommended amount.
Process_Date: 1985
Process_Step:
Process_Description:
Total dust flux is calculated by multiplying the mineral
weight times the fraction less than 2 mm times the pan
area times the fraction of year during which the sample
accumulated (in file labdust.xls, number of days divided
by 365). Other dust-flux values for various components (i.
e. silt flux) are calculated by multiplying the total dust
flux by the percentage of the component.
Preliminary examination of the flux data indicated that
samples from some sites collected in 1985 and 1986, before
the trap design was modified to discourage birds from
roosting, were anomalously large (50-500% greater)
compared to those collected in later years. All of the
anomalous samples had been recorded as having significant
amounts of bird feces at the time of collection.
Consultations with bird biologists confirmed that bird
droppings can contain significant amounts of mineral
matter, mostly derived from cropstones; the amount varies
with the species and with the diet of local populations of
individual species. Moreover, perching birds can
contaminate the sample with material from their feet. In
some cases, we have evidence of near-deliberate
contamination in the form of one or two pebble-sized
clasts of local rocks that were found in samples, possibly
dropped (or swapped for marbles) by large birds such as
ravens. Data from samples with large amounts of bird
droppings were discarded from further analysis and were
excluded from the computations of "selected average" flux
values.
Process_Date: 1987
Process_Step:
Process_Description:
Major elements were measured in U.S. Geological Survey
laboratories on a split of the less-than-2mm fraction
remaining after analysis and removal of carbonate by the
Chittick method. Major elements and zirconium were
analyzed by induction-coupled plasma spectroscopy (Lichte
and others, 1987). In some cases, samples from different
years at the same site or adjacent sites were combined to
obtain enough material for measuring major-oxide
composition.
Process_Date: 1988
Process_Step:
Process_Description:
Major oxides are calculated from elemental compositions
(file dusticp.txt) using the following equations based on
atomic weights:
SiO2 = Si/0.467
Al2O3 = Al/0.529
Fe2O3 = Fe/0.699
MgO = Mg/0.603
CaO = Ca/0.715
Na2O = Na/0.742
K2O = K /0.830
TiO2 = Ti/0.599
MnO = Mn/0.774
ZrO2 = Zr/0.740
The percentages of major oxides and zirconium were then
recalculated to 100%, excluding water, volatiles, and
minor elements, and the ratios of major oxides to ZrO2 are
based on the recalculated values.
Process_Date: 1988
Process_Step:
Process_Description:
Mineralogy was measured in U.S. Geological Survey
laboratories on splits of samples that had been previously
analyzed for grain size. Samples of sand, silt, and clay
were slurried in water (sand samples were ground to a fine
powder) and mounted dropwise on glass slides. Minerals
in the sand and silt fractions were identified by
characteristic peaks on X-ray diffractograms and their
relative amounts were estimated by measuring peak
heights. Minerals in the clay samples were identified by
characteristic peaks obtained after the following
treatments: air-dried, glycolated, and heated to 300
degrees C and 550 degrees C. The relative abundances of
clay minerals were estimated by measuring the following
peak heights (in degrees 2 theta) and adjusted for
intensity variations between runs using the peak height of
quartz at 26.65 2 theta: chlorite, 6.3 on the 550 degrees
C trace; kaolinite, 12.6 on the glycolated trace minus the
amount of chlorite; mica, 8.8 on the glycolated trace;
smectite, 5.2 on the glycolated trace; mixed-layer mica-
smectite, 8.85 on the 550 degrees trace minus the amounts
of mica and smectite.
Process_Date: 1988
Process_Step:
Process_Description:
The National Climatic Data Center no longer publishes mean
climatic data for the entire length of record at weather
stations. To obtain mean annual temperature (MAT) and
precipitation (MAP) for the weather stations nearest the
dust traps, averages had to be computed from climatic
summaries of the United States (U.S. Department of
Commerce, 1952, 1965), from station normals for 1961-1990
(National Climatic Data Center, 1992), and from various
climatological data annual summaries. Comparisons could
then be made of the long-term averages with those for the
five years of dust collection (file climate.xls).
Process_Date: 1993
Source_Used_Citation_Abbreviation: DOC 51-60 CA
Source_Used_Citation_Abbreviation: DOC 51-60 NV
Source_Used_Citation_Abbreviation: NCDC 61-90 A CA
Source_Used_Citation_Abbreviation: NCDC 61-90 M CA
Source_Used_Citation_Abbreviation: NCDC 61-90 A NV
Source_Used_Citation_Abbreviation: NCDC 61-90 M NV
Process_Step:
Process_Description:
The dust-trap sites are at different elevations from the
nearest weather stations. To estimate mean annual
temperature (MAT) and precipitation (MAP) at the sampling
sites, annual climate data for the entire period of record
was obtained for every weather station in the region,
including some that are no longer maintained but excluding
those in coastal California. The data in this file was
combined from the data in file aveclim.xls, which included
the weather stations nearest the traps, and from climatic
data for other stations. For many stations with
relatively complete records, this involved computation of
the averages of MAT and MAP (columns under "MAT
calculations" and "MAP calculations") compiled from
records prior to 1961, the last year in which averages for
the entire length of record were published by the U.S.
Department of Commerce (1965), and from station normals
for 1961-1990 (National Climatic Data Center, 1992).
Normals and averages are not published for stations with
missing data or those which were moved at some time; for
these stations, the computation required hand-entering
data for each year of record from the climatological data
annual summaries (columns under "MAT records" and "MAP
records").
Linear regression (bottom left of file) was used to obtain
equations that relate temperature and precipitation to
elevation for these weather stations (columns
"Elevation", "MAT", and "MAP") and to estimate these
parameters at sampling sites with different elevations.
For temperature, only one equation was required; it
provides estimates with a standard error (s.e.) of only
1.3 degrees C. For precipitation, equations were most
useful when the stations were divided into three
geographic regions, including the area of the Mexican
border and the Colorado River-southeast Nevada corridor
(s.e.=2.6 cm), southwestern California east of the
Transverse Ranges (s.e.=8.6 cm), and the interior deserts
(s.e.=2.0 cm).
Process_Date: 1993
Source_Used_Citation_Abbreviation: DOC 51-60 CA
Source_Used_Citation_Abbreviation: DOC 51-60 NV
Source_Used_Citation_Abbreviation: NCDC 61-90 A CA
Source_Used_Citation_Abbreviation: NCDC 61-90 M CA
Source_Used_Citation_Abbreviation: NCDC 61-90 A NV
Source_Used_Citation_Abbreviation: NCDC 61-90 M NV
Process_Step:
Process_Description:
Estimates of MAP and MAT listed under "this study" were
obtained using the linear regression equations calculated
from data in file regclim.xls. These equations are:
MAT = -0.0072E+23.4
MAP (interior deserts) = 0.00555E+7.075
MAP (Colo.R.-Salton Sea) = 0.01013+7.468
MAP (SW Calif.) = 0.05E+5.002
where E is elevation in meters. For comparison, MAP is
also calculated using other published equations. For
stations on the Nevada Test Site (T-1 through T-9) I used
the equation of Quiring (1983), in which y = MAP in inches
and x = elevation in thousands of feet:
y = 1.36x - 0.51
For stations in southern Nevada, including the Nevada Test
Site, I used the equations of French (1983), in which
y = MAP in inches and x = elevation in feet. French (1983)
divided southern Nevada roughly into thirds based on the
paths of moisture-carrying air masses from the west and
south; the eastern third has the most rainfall, the
western third has the least, and the central third is
intermediate:
Eastern: log y = 0.0000933x + 0.486
Central: log y = 0.0000786x + 0.446
Western: log y = 0.0000365x + 0.505
MAP at the closest weather station to the dust-trap site
is also given. Estimates of MAP for sites near Los
Angeles, including T-51 through T-54, using the equations
from this study gave unrealistically low values (see file
trapclim.xls) because this area is under a coastal rather
than an interior climate. Thus, in the papers written
using these data, MAP for these sites is assumed to be
about the same as that at the nearest weather station.
Process_Date: 1993
Process_Step:
Process_Description:
Mean monthly precipitation and temperature from 1984 to
1989 were acquired from the National Climatic Data Center
(1984-1989) for weather stations in southern Nevada and
California that were closest to dust-trap sites and
entered into a spreadsheet in order to calculate mean
annual values for climatic variables and compare them to
long-term means (calculated in file aveclim.xls).
Seasonal precipitation (May-October and November-April)
was calculated from monthly values.
Process_Date: 1993
Process_Step:
Process_Description:
Secondary climatic variables were calculated from the data
in file climate.txt These secondary variables include
monthly and annual potential evapotranspiration (PET) and
the leaching index (LI) of Arkley (1963). The leaching
index is a measure of available moisture obtained by
subtracting monthly evapotranspiration from monthly
precipitation. PET was calculated for all stations with
both temperature and precipitation data using the method
of Thornthwaite (1948), and for stations with mean
minimum and maximum temperatures using the method of
Papadakis (1965). The leaching index is calculated for
both methods of PET. Pan evaporation measurements are
also given where available (National Climatic Data Center
and Farnsworth and others, 1982) for comparison.
PET is more readily calculated by the Thornthwaite method
than by the Papadakis method, because the latter requires
mean minimum and maximum temperatures that are commonly
not recorded at some weather stations. However, according
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