Portable Chamber Measurements of Evapotranspiration 

at the Amargosa Desert Research Site near Beatty, 

Nye County, Nevada, 2003–06

Scientific Investigations Report 2008–5135

U.S. Department of the Interior

U.S. Geological Survey
Cover:

Photograph of U.S. Geological Survey field crew, Michael Johnson and Chris 

Stone, collecting evapotranspiration measurements using a hemispherical 

chamber at the Amargosa Desert Research Site near Beatty, Nye County, Nevada. 

(Photograph taken by Brian Andraski, Research Hydrologist, Carson City, Nevada, 

2003).
Portable Chamber Measurements of 

Evapotranspiration at the Amargosa Desert 

Research Site near Beatty, Nye County, 

Nevada, 2003–06

By C. Amanda Garcia, Michael J. Johnson, Brian J. Andraski, Keith J. Halford, 

and C. Justin Mayers

Scientific Investigations Report 2008–5135

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

DIRK KEMPTHORNE, Secretary

U.S. Geological Survey

Mark D. Myers, Director

U.S. Geological Survey, Reston, Virginia: 2008

For product and ordering information:

World Wide Web: http://www.usgs.gov/pubprod

Telephone: 1-888-ASK-USGS

For more information on the USGS--the Federal source for science about the Earth, its natural and living resources, 

natural hazards, and the environment:

World Wide Web: http://www.usgs.gov

Telephone: 1-888-ASK-USGS

Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the 

U.S. Government.

Although this report is in the public domain, permission must be secured from the individual copyright owners to 

reproduce any copyrighted materials contained within this report.

Suggested citation:

Garcia, C.A., Johnson, M.J., Andraski, B.J., Halford, K.J., and Mayers, C.J., 2008, Portable chamber measurements of 

evapotranspiration at the Amargosa Desert Research Site near Beatty, Nye County, Nevada, 2003–06: U.S. Geological 

Survey Scientific Investigations Report 2008–5135, 10 p.
iii

Contents

Abstract ..........................................................................................................................................................1

Introduction.....................................................................................................................................................1

Purpose and Scope ..............................................................................................................................1

Description of Study Area ...................................................................................................................2

Study Design and Methods..........................................................................................................................2

Portable Chamber Construction.........................................................................................................2

Chamber Measurements of Evapotranspiration .............................................................................2

Landscape-Scale Evapotranspiration ..............................................................................................4

Evapotranspiration Measurements ............................................................................................................5

Summary..........................................................................................................................................................6

References Cited............................................................................................................................................7

Figures

Figure 1. Map showing location of (A) the Amargosa Desert Research Site (ADRS)

near Beatty, Nye County, Nevada, and (B), eddy-covariance station and

chamber measurement locations adjacent to the waste-disposal facility ......... 3

Figure 2. Graph showing time series of vapor density during two consecutive

measurements showing best fit lines of the steepest intervals at the

Amargosa Desert Research Site near Beatty, Nye County, Nevada, May 1, 2005... 4

Figure 3. Graphs showing chamber (A), component-scale evapotranspiration fluxes

and net radiation, and (B), total landscape evapotranspiration fluxes at the

Amargosa Desert Research Site near Beatty, Nye County, Nevada, May 2, 2005... 5

Appendix A. Plant Characteristics Including Plant Crown Height, Ratio of Plant Crown 

Cover to Chamber Area, and Relative-Plant-Crown Cover of Creosote Bush, 

Shadescale, Burrobush, and Wolfberry at the Amargosa Desert Research 

Site Near Beatty, Nye County, Nevada, August 2003 through January 2006 ...... 9

Appendix B. Partitioned Bare-Soil Evaporation and Plant Transpiration from Chamber

Measurements of Evapotranspiration at the Amargosa Desert 

Research Site Near Beatty, Nye County, Nevada, January 2003 

through January 2006..................................................................... 9

Appendix C. Computed Landscape-Scale Evapotranspiration Using Chamber 

Measurements of Bare-Soil, Creosote Bush, Shadescale, Burrobush, 

and Wolfberry, and the Fractional Cover of Each Plant Species Across 

the Landscape at the Amargosa Desert Research Site Near Beatty, 

Nye County, Nevada, August 2003 through January 2006 ........................... 9
iv

Conversion Factors and Datums

Conversion Factors

Multiply By To obtain

Length

millimeter (mm) 0.03937 inch (in.)

meter (m) 3.281 foot (ft) 

kilometer (km) 0.6214 mile (mi)

Area

square meter (m2

) 10.76 square foot (ft2)

square kilometer (km2

) 247.1 acre

square kilometer (km2

) 0.3861 square mile (mi2)

Volume

cubic meter (m3

) 6.290 barrel (petroleum, 1 barrel = 42 gal)

cubic meter per cubic meter (m3

/ m3) 1.0 cubic foot per cubic foot (ft3/ ft3)

Flow Rate

millimeter per day (mm/d) 0.03937 inch per day (in/d)

millimeter per year (mm/yr) 0.03937 inch per year (in/yr)

Density

gram per cubic centimeter (g/cm3

) 62.4220 pound per cubic foot (lb/ft3) 

Power

Watts per square meter (W/m2

) 0.005290 BTU per square foot per minute 

[(BTU/ft2

)/min]

Datums

Vertical coordinate information is referenced to the North American Vertical Datum of 1988 

(NAVD 88).

Horizontal coordinate information is referenced to the North American Datum of 1983 (NAD 83).
Abstract 

Portable chamber measurements of evapotranspiration 

(ET) were made at the U.S. Geological Survey’s Amargosa 

Desert Research Site in southern Nevada to help quantify 

component- and landscape-scale contributions to ET in an 

arid environment. Evapotranspiration data were collected 

approximately every 3 months from 2003 to 2006. Chamber 

measurements of ET were partitioned into bare-soil 

evaporation and mixed-species transpiration components. 

The component-scale ET fluxes from native shrubs typically 

surpassed those from bare soil by as much as a factor of four. 

Component-scale ET fluxes were extrapolated to landscapescale ET using a one-layer, multi-component canopy model. 

Landscape-scale ET fluxes predominantly were controlled 

by bare-soil evaporation. Bare soil covered 94 percent of the 

landscape on average and contributed about 70 percent of the 

landscape-scale vapor flux. Creosote bush, an evergreen shrub, 

accounted for about 90 percent of transpiration on average 

due to its dominance across the landscape (80 percent of the 

6 percent shrub cover) and evergreen character. 

Introduction

Evapotranspiration (ET) measurements are essential 

when quantifying soil-plant-atmosphere controls on 

hydrologic transport processes in arid environments. Current 

research at the U.S. Geological Survey’s Amargosa Desert 

Research Site (ADRS), adjacent to a low-level radioactive and 

hazardous chemical-waste facility, includes analysis of soilplant atmosphere interactions as they relate to transport and 

release of waterborne contaminants. In support of this ongoing 

research, the ET components of transpiration and evaporation 

from distinct plant species and bare soil were differentiated 

with periodic portable chamber measurements of ET. The 

components were combined in a one-layer, multi-component 

canopy model to estimate total landscape-scale ET (Stannard, 

1988; Stannard and Weltz, 2006).

Portable chambers have been used to measure ET from 

cultivated alfalfa fields (Reicosky and others, 1983), bare soil, 

and sparsely vegetated plant communities (Stannard, 1988; 

Stannard and Weltz, 2006). Chambers also have been used 

to determine ET from distinct vegetation types within mixed 

species communities (Stannard, 1988). Chambers measure 

the water vapor exchange between the Earth’s surface and 

the atmosphere from small areas (Dugas and others, 1997) by 

enclosing a known volume of a plant canopy, soil surface, or 

both, and then measuring the increase in vapor density within 

the chamber. The maximum rate of change in vapor density 

with time is proportional to the ET flux from the surface area 

enclosed by the chamber (Stannard, 1988). 

Purpose and Scope

This report documents the measuring of ET from 

different desert-shrub species and bare soil using a portable 

chamber at an arid mixed-vegetation site, partitioning of 

ET measurements into transpiration and evaporation, and 

compiling chamber measurements into landscape-scale ET. 

From 2003 to 2006, chamber ET measurements over creosote 

bush, shadescale, and bare soil were collected approximately 

every 3 months; measurements over burrobush and wolfberry 

were collected annually. Partitioning of chamber ET 

measurements into evaporation and transpiration components 

and assembly of these components into landscape-scale 

ET using a one-layer, multi-component canopy model are 

described. The magnitude and variability in component- and 

landscape-scale ET are compared between shrub species and 

bare soil. 

Portable Chamber Measurements of Evapotranspiration at 

the Amargosa Desert Research Site near Beatty, 

Nye County, Nevada, 2003–06

By C. Amanda Garcia, Michael J. Johnson, Brian J. Andraski, Keith J. Halford, and C. Justin Mayers
2 Portable Chamber Measurements of Evapotranspiration at the Amargosa Desert Research Site, Nye County, Nevada, 2003–06

Description of Study Area

The ADRS borders a waste-disposal facility in the 

Mojave Desert, 17 km southeast of Beatty, Nev., near Death 

Valley (fig. 1A). The ADRS is in one of the most arid regions 

of the United States. Annual precipitation averaged 

130 mm during 2001–05 and was highly variable from month 

to month and year to year (Johnson and others, 2007). Annual 

potential evaporation is about 1,900 mm (Nichols, 1987). The 

Amargosa Desert in the Basin and Range Province is bounded 

by lower Paleozoic rock and Tertiary volcanic-rock mountains 

(Fischer, 1992). Surface soils are mapped as the YermoArizo association. The Yermo soils are loamy-skeletal and 

the Arizo soils are sandy-skeletal. Subsurface sediments are 

predominantly fluvial deposits, consisting of several sand and 

gravel sequences (Andraski, 1996). Depth to the water table 

ranges from 85 to 115 m below land surface (Fischer, 1992).

The sparsely vegetated (6–8 percent of the landscape; 

Andraski and others, 2005) study site is dominated by creosote 

bush [Larrea tridentata (Sessé & Moc. Ex DC.) Coville], an 

evergreen shrub (Smith and others, 1997). The root system 

of a creosote bush can exceed 4 m radially (Gile and others, 

1998) and the root system depth generally corresponds with 

the penetration depth of annual precipitation, about 0.75 

to 1 m at the ADRS (Andraski, 1997). Root-zone (0–1 m 

depth) volumetric soil-water content ranges from 0.02 to 

0.12 m3

/m3 and near-surface soil-water content ranges from 

0.02 to 0.31 m3/m3 (2001–05; Johnson and others, 2007). 

Drought deciduous plant species include shadscale [Atriplex 

confertifolia (Torr. & Frém) S. Wats.], burrobush [Ambrosia 

dumosa (Gray) Payne], and wolfberry [Lycium pallidum

Miers]. 

Portable chamber measurements of ET were collected 

periodically at locations 1 and 2 shown in figure 1B. Site 

selections were based on four 400-m transects measured in 

2001 using the line-transect method (Smith, 1974); and chosen 

for their proximity to an eddy-covariance ET station (fig. 1B), 

for representative plant size and shape, and for having 

replicate plants within close proximity. 

Study Design and Methods

Portable Chamber Construction

The chamber consists of a 2.4-mm thick, 1-m diameter 

hemispherical dome made of Plexiglass G (Stannard, 1988). 

A cylindrical 0.305-m high skirt of similar thickness, 

diameter, and material typically was added to the bottom 

of the hemisphere to measure taller plants. The combined 

hemisphere and cylindrical skirt has a total height of 0.805 m, 

an internal volume of 0.5 m3, and covers a 0.79 m2 landsurface area. Two 12-volt fans were mounted inside the 

chamber (about 0.3 m above the hemisphere base) and

positioned opposite each other to keep the air and water vapor 

well mixed. Internal fan speed was adjusted to approximate 

the average wind speed at the site. External wind speed was 

measured using a portable wind gage mounted at one-half the 

combined chamber and skirt height (0.4 m) and a rheostat was 

used to adjust the internal fan speed to match the external wind 

speed. Between the fans, a temperature and relative humidity 

probe was used to measure vapor density. 

Chamber Measurements of Evapotranspiration

Chamber measurements at mixed-vegetation sites were 

collected over approximately 15-min intervals during daylight 

hours. Bare-soil evaporation was measured from a single 

site near the eddy-covariance ET station in January and May 

2003, and from two replicate sites at location 1 from August 

2003 through January 2006 (fig. 1B). Plant transpiration 

was measured in conjunction with bare-soil evaporation at 

location 1. Plant transpiration was measured from replicate 

creosote bush plants (August 2003 through January 2006) 

and a single shadescale plant (October 2003 through January 

2006). Shrubs from the four primary plant species (creosote 

bush, shadescale, burrobush, and wolfberry) were measured 

on three separate occasions at location 2 (May 4, 2004, May 2, 

2005, August 4, 2005) (fig. 1B). 

The chamber was positioned over soil and plant sites 

while a data logger collected measurements every 2 seconds 

for about a 2-min interval. Between measurements, the 

chamber was raised above the land surface for a minimum of 

2 min to obtain ambient humidity and air temperature inside 

the chamber. Datasets consisting of at least one measurement 

per site typically were collected within 15 min; datasets were 

repeated at or greater than hourly intervals. 

The evapotranspiration rate was estimated at each soil 

and plant site using (Stannard, 1988):

ET MVC

A

ET

= 86 4.

,

 ,

where

is the evapotranspiration rate in millimeters per

day,

M is the maximum slope of the vapor density time

series in grams per cubic meter per second,

is t

,

V he volume inside the chamber in cubic meters,

is the cal

,

C ibration factor of the chamber unitless,

is the land-sur

,

A face area covered by the chamber

in square meters, and 

86

,

.4 is a factor that converts grams per cubic meter 

per second to millimeters per day using the 

density of water .

(1)

Evapotranspiration reported as millimeters per day is an 

instantaneous rate that occurs at the time of measurement. 

The maximum constant-slope section of the vapor density 

time series was determined using an automated spreadsheet 
Study Design and Methods 3

Ash Meadows

NV19-4018_fig01

95

95

0 10

10

20 30 KILOMETERS

0 20 MILES

A

Amargosa Desert

Hydrographic Area 

of the Mojave Desert

Amargosa Desert

Amargosa

Valley

Beatty

ADRS

study area

(fig. 1B)

To

Las

Vegas

Nye County

Inyo County

CALIFORNIA

NEVADA

Death

Valley

117°00’

37°00’

45’

30’

15’

36°00’

116°45’ 116°30’

116°15’ 116°00’

Amargosa

River

Carson

City

Las

Vegas

C

NEVADA

ALIFORNIA

Amargosa Desert

hydrographic area

Chemicalwaste

area

Low-level

radioactive

waste

area Access/service

road

116°41’30’’ 116°41’

36°46’15’’

0

0

500 METERS

1,500 FEET

B

36°45’45’’

Buffer zone

Base from U.S. Geological Survey digital data, 1:100,000, 1978-88

North American Datum of 1983

 Eddy-covariance ET station 

Location 1 Location 2

Bare

Mountain

Spector

Range

Bullfrog Hills

Funeral Mountains

Figure 1. Location of (A) the Amargosa Desert Research Site (ADRS) near Beatty, 

Nye County, Nevada, and (B), eddy-covariance station and chamber measurement 

locations adjacent to the waste-disposal facility.
4 Portable Chamber Measurements of Evapotranspiration at the Amargosa Desert Research Site, Nye County, Nevada, 2003–06

program that applied ordinary least-squares analysis within a 

10- to 20-second measurement interval. A typical time series 

of vapor density inside the chamber during two consecutive 

measurements (creosote bush and bare soil) is shown in 

figure 2. Beginning with the first 5–10 points on the vapor 

density curve, the program stepped through the whole curve 

calculating the slopes while maintaining the same number of 

points. The final slope selection then was manually verified 

or adjusted as necessary to represent the best fit line of the 

steepest time interval. The maximum vapor density slope 

for creosote bush was measured between 15 and 25 seconds 

after chamber emplacement while the maximum slope for the 

bare soil site was reached between 54 and 64 seconds after 

emplacement. 

The chamber calibration factor, which accounted for the 

slight hydrophilicity of the chamber material, was determined 

using methods described by Stannard (1988). The procedure 

involved evaporating a mass of water from a beaker at a known 

rate and then placing the chamber over the beaker to determine 

the chamber-measured rate. This procedure was repeated 

several times at each of the several known evaporation rates. 

Chamber and known evaporation rates were plotted against 

one another and the slope of the best fit line through the origin 

was the calibration factor used (in this case, C = 1.037).

Landscape-Scale Evapotranspiration 

Plant and soil ET rates computed from eq. (1) were 

extrapolated to compute ET on a component- and landscapescale using a one-layer, multi-component model representing 

a sparse canopy on a planar surface (Stannard, 1988; Stannard 

and Weltz, 2006): 

ET Fc

ET E Rc

Rc

Fc

ET E Rc

Rc

ls i

i s i

i

us

i s i

i

i

n

i

= − −

− −

=

=

∑

+

1

1

1

1

[ ( )]

[ ( )] n

i

n s s

Fc

Fc

Fc E

ET

i

i

ls

∑ ∑=

⎛

⎝

⎜

⎜

⎜

⎜

⎞

⎠

⎟

⎟

⎟

⎟

+

1

,

where

is the total landscape-scale ET in millimeters

per day,

is an index re

,

i presenting each of the measured

plant species,

n is the number of measured species,

Fc is the fractional cover of the i th plant species

unitless,

is the site ET flux from

i

ETi

,

the th plant species

in millimeters per day,

is the ba

i

Es

,

re-soil evaporation in millimeters per 

day,

is the rel

,

Rci ative canopy crown cover of the th

plant species within

i

the chamber area

unitless,

is the fractional cover of

,

Fcs bare soil unitless, and

is the fractional cover of un

,

Fcus measured plant 

species , . unitless

(2)

The first two terms on the right-hand side of eq. (2) 

represent landscape-scale transpiration from specific and 

unmeasured plant species; the last term represents landscapescale evaporation from bare soil. Unmeasured plant species 

were assigned the average, weighted plant transpiration 

of measured species. Component-scale transpiration and 

evaporation fluxes were computed by dividing eq. (2) terms by 

representative Fc values. Negligible transpiration was assumed 

when ETi was less than or equal to Es

. 

Fractional cover of bare soil and all individual plant 

species was measured using the line-transect method (Smith, 

1974). Four 200-m transects extending outward in the 

northwest, northeast, southwest, and southeast directions 

from the eddy-covariance ET station (fig. 1B) were measured 

quarterly, representing a 0.16 km2 area. Plant coverage 

was estimated from additive measurements of the vertical 

Figure 2. Time series of vapor density during two 

consecutive measurements showing best fit lines of the 

steepest intervals at the Amargosa Desert Research Site 

near Beatty, Nye County, Nevada, May 1, 2005.

4

8

12

16

20

24

12:04 :05 :06 :07 12:08 :10 12:12 :09 :11

MAY 1, 2005 PACIFIC STANDARD TIME

Chamber emplaced

Chamber emplaced

Raw 2-second measurements

Best-fit line of steepest interval Chamber removed

Chamber removed

Bare Soil

Creosote Bush

VAPOR DENSITY, IN GRAMS PER CUBIC METER
Evapotranspiration Measurements 5

projection of plant canopies overlaying line transects. Baresoil coverage comprised gaps between plants and within plant 

canopies. The Fcs was computed as the total coverage of bare 

soil for all four transects divided by the total transect length 

(800 m); Fci and Fcus were computed as the total coverage of 

an individual plant species for all four transects divided by the 

total transect length; and Fcus was differentiated for species 

that were excluded from chamber measurements. During the 

period of study, non-dormant, leafed shrubs covered 4–10 

percent of the landscape. 

The relative plant crown cover, Rc, was estimated using 

photographs of the measured plant sites and the following 

equation (Stannard, 1988):

Rc

H h

H

Rc

H

= ⎡( ) −

⎣

⎢ ⎤

⎦

⎥

2

' ,

where

is the camera height, in meters (typically 2 13 m

is the height of the major axis of t

. ),

h he plant crown 

in meters (estimated here as one-half the

,

average plant height for the th plant species

and

is

i

Rc

),

' the ratio of plant crown cover to chamber area

unitless (plant crown and chamber area were 

digitized from digital photographs). 

,

(3)

Measured variables h and Rc' and computed Rc are given in 

appendix A. Average relative crown cover for creosote bush, 

shadescale, burrobush, and wolfberry was 0.64, 0.21, 0.27, 

and 0.68, respectively. Evaporation from canopy shaded soil 

(excluding gaps within plant canopies) was assumed negligible 

and was not separated from the plant transpiration component. 

Chamber ET measurements at location 2 excluded bare 

soil on all dates and creosote bush in May 2003. Therefore, 

component-scale evaporation and transpiration fluxes 

measured the previous day, during a similar time interval at 

location 1 were substituted in eq. (2). 

Evapotranspiration Measurements

An example time series of component-scale 

evapotranspiration fluxes (wolfberry, creosote bush, 

shadescale, burrobush, and bare soil) and net radiation (15-min 

intervals; Johnson and others, 2007) measured on May 2, 

2005, is shown in figure 3A. Using plant crown measurements 

(Rc) from appendix A, bare-soil evaporation was subtracted 

from chamber measurements of ET, yielding transpiration for 

each species. Cloud cover on May 2, 2005, alternated between 

partly cloudy and clear. The mean root-zone (0.15–1.0-m 

depth) soil moisture measured with a neutron probe was 

0.06 ± 0.01 m3/m3 and was twice the soil moisture 

(0.03 m3/m3; Johnson and others, 2007) measured in near 

surface soils (0–0.08-m depth) using a water-content 

reflectometer. Net radiation (Rn

) and component-scale ET 

fluxes followed similar patterns reflecting the diurnal solar 

cycle. 

Figure 3. Chamber (A), component-scale 

evapotranspiration fluxes and net radiation, and 

(B), total landscape evapotranspiration fluxes at the 

Amargosa Desert Research Site near Beatty, Nye 

County, Nevada, May 2, 2005. 

Evapotranspiration reported as millimeters per day 

is an instantaneous rate that occurs at the time of 

measurement.

nv08tac-4141_fig03

MAY 2, 2005 PACIFIC STANDARD TIME 10:00 13:00

16:00

7:00

11:0012:0014:0015:00

8:009:00

10:0013:0016:00

7:00

11:0012:0014:0015:00

8:009:00

NET RADIATION, IN WATTS PER SQUARE METER

0

200

400

600

800

COMPONENT-SCALE EVAPOTRANSPIRATION FLUX, 

IN MILLIMETERS PER DAY

5

10

15

20

0

LANDSCAPE-SCALE EVAPOTRANSPIRATION FLUX, 

IN MILLIMETERS PER DAY

0

1

2

3

4

Shades c ale

Creos ote Bus h

Bare Soil

Burrobush

Wolfberry

Shadescale

Creosote Bush

Bare Soil

Burrobush

Wolfberry

Net Radiation

A.

B.
6 Portable Chamber Measurements of Evapotranspiration at the Amargosa Desert Research Site, Nye County, Nevada, 2003–06

In addition, substantial fluctuations in 15-min Rn

measurements occurred during partly cloudy periods (fig. 3A). 

Sudden increasing and decreasing Rn values (caused by 

intermittent cloud cover) were reflected in burrobush, creosote 

bush, and shadscale chamber flux measurements (for example, 

Rn period beginning at 12:00 and 13:15 PST). Although, some 

variable fluctuations in Rn did not correspond to fluctuating 

ET fluxes (14:30–15:45), most variability affecting short 

(about 2 min) chamber measurements during intermittent 

cloud cover was captured by 15-min Rn measurements. Unlike 

the flux patterns for burrobush, creosote bush, and shadescale, 

wolfberry and bare-soil chamber fluxes were less sensitive to 

fluctuations in Rn (fig. 3A), indicating that measurements were 

likely collected when overhead skies were clear. In addition to 

Rn, variability in component-scale ET fluxes measured in May 

2005 and during additional quarters (appendix B) occasionally 

corresponded with lesser factors affecting ET variability (such 

as air temperature, wind speed, and vapor pressure; data not 

shown). Erratic chamber fluctuations that did not correspond 

with measureable weather factors were likely from random 

noise in the chamber method (Stannard and Weltz, 2006). 

Component-scale ET fluxes for vegetation typically were 

greater than for bare soil and varied by a factor of 1–3 between 

species on May 2, 2005 (fig. 3A) and by as much as a factor 

of 4 for all periods measured (appendix B). Creosote bush, 

which had an Rc that was, on average, a factor of 3.5 greater 

than shadescale (2003–05; appendixes A and B), exhibited the 

greatest component-scale ET fluxes during summer, autumn, 

and winter months (except Oct. 2004 and Jan. 2005 when 

vegetative fluxes were negligible). During the spring when 

all four plant species were measured, component-scale ET 

fluxes from wolfberry (which had a high leaf density and the 

largest Rc) typically were greatest, followed by burrobush and 

creosote bush (fig. 3A). 

An example time-series of landscape-scale ET fluxes 

(combination of wolfberry, burrobush, creosote bush, 

shadescale, and bare soil) measured on May 2, 2005, is shown 

in figure 3B. Bare-soil evaporation dominated the total water 

flux at this scale, despite drier surface soil (twice as dry as 

the aggregate root zone). Expansive bare-soil cover across 

the landscape (Fcs = 0.90) magnified lower bare-soil fluxes 

and reduced greater plant fluxes measured on a component 

scale. Plant transpiration from wolfberry and burrobush, 

which dominated ET on the component scale (fig. 3A), was 

minimized when extrapolated to the landscape scale (Fc = 

0.01 in spring 2005; appendix C). At the landscape scale (Fc = 

0.06), transpiration from creosote bush was greater than from 

wolfberry and burrobush despite having a lower componentscale transpiration than these plant species. On average, 

transpiration on May 2, 2005, accounted for about 40 percent 

of total landscape-scale ET. Variation in transpiration fluxes 

among species at the landscape-scale (a factor of 2–17; 

fig. 3B) was substantially greater than the variation for 

component-scale fluxes (a factor of 1–3; fig. 3A). 

Transpiration accounted for about 30 percent of 

landscape-scale ET on average and bare-soil evaporation for 

about 70 percent over all periods measured. Landscape-scale 

fluxes measured for all periods are given in appendix C. 

For all measurement periods, bare-soil evaporation was the 

predominant contributor of moisture loss to the atmosphere 

as a result of its large landscape cover (Fc = 0.94 on average). 

The relative rank of transpiration contributions varied among 

creosote bush and the three drought deciduous species. Due to 

its abundance across the landscape (80 percent of vegetative 

cover), creosote bush accounted for about 90 percent of 

transpiration on average and ranged from about 50 to 

100 percent of transpiration for all measurement periods. 

Summary

Portable chamber measurements of ET helped to quantify 

component-scale and landscape-scale contributions to ET 

from bare soil and sparsely vegetated, mixed species plant 

communities. Measurements were collected approximately 

every 3 months from 2003 to 2006 at the Amargosa Desert 

Research Site in southern Nevada. Chamber measurements of 

the four primary plant species and bare soil were combined 

in a one-layer, multi-component canopy model to estimate 

(1) transpiration and evaporation components from individual 

plant species and bare soil, respectively, and (2) landscapescale ET. Although chamber measurements of ET from 

native shrubs typically surpassed those from bare soil, soil 

evaporation dominated landscape-scale ET during all periods 

measured. 

Component-scale chamber ET from vegetation typically 

was greater and more variable throughout a given day than that 

from bare soil. Variability in net radiation and other factors 

affecting ET were more notably reflected in 15-min chamber 

measurements from vegetation than from bare soil. Creosote 

bush typically exhibited the greatest chamber ET fluxes 

during summer, autumn, and winter as a result of its evergreen 

character and high relative-plant-crown cover. During spring 

when all four plant species were measured, component-scale 

ET fluxes from wolfberry typically were greatest as a result of 

its high leaf density, followed by burrobush and creosote bush. 

Landscape-scale ET fluxes predominantly were 

controlled by bare-soil evaporation; bare soil covered 

94 percent of the landscape on average. Sparsely distributed 

vegetation (6 percent of the landscape), in turn, caused the 

relative importance of creosote bush and other plant species 

to be substantially overwhelmed. Due to its abundance across 

the landscape (80 percent of vegetative cover), creosote bush 

accounted for about 90 percent of transpiration on average 

and ranged from about 50 to 100 percent of transpiration for 

all measurement periods. Overall, transpiration accounted for 

about 30 percent of ET on average and bare-soil evaporation 

for 70 percent.
References Cited 7

References Cited

Andraski, B.J., 1996, Properties and variability of soil and 

trench fill at an arid waste-burial site: Soil Science Society 

of America Journal, v. 60, p. 54–66.

Andraski, B.J., 1997, Soil-water movement under natural-site 

and waste-site conditions–A multiple-year field study in the 

Mojave Desert, Nevada: Water Resources Research, v. 33, 

p. 1901–1916.

Andraski, B.J., Stonestrom, D.A., Michel, R.L., Halford, K.J., 

and Radyk, J.C., 2005, Plant-based plume-scale mapping of 

tritium contamination in desert soils: Vadose Zone Journal, 

v. 4, p. 819-827, accessed June 10, 2008, at http://vzj.

scijournals.org/cgi/reprint/4/3/819

Dugas, W.A., Reicosky, D.C., and Kiniry, J.R., 1997, Chamber 

and micrometeorological measurements of CO2 and 

H2O fluxes for three C4 grasses: Agricultural and Forest 

Meteorology, v. 83, p. 113–133.

Fischer, J.M., 1992, Sediment properties and water movement 

through shallow unsaturated alluvium at an arid site for 

disposal of low-level radioactive waste near Beatty, Nye 

County, Nevada: U.S. Geological Survey Water-Resources 

Investigations Report 92-4032, 48 p.

Gile, L.H., Gibbens, R.P., and Lenz, J.M., 1998, Soilinduced variability in root systems of creosotebush (Larrea 

tridentate) and tarbush (Flourensia cernua): Journal of Arid 

Environments, v. 39, p. 57–78. 

Johnson, M.J., Mayers, C.J., Garcia, C.A., and Andraski, B.J., 

2007, Selected micrometeorological, soil-moisture, and 

evapotranspiration data at Amargosa Desert Research Site in 

Nye County near Beatty, Nevada, 2001–05: U.S. Geological 

Survey Data Series 284, 28 p., accessed October 26, 2007, 

at http://pubs.usgs.gov/ds/2007/284/

Nichols, W.D., 1987, Geohydrology of the unsaturated zone 

at the burial site for low-level radioactive waste near Beatty, 

Nye County, Nevada: U.S. Geological Survey Water-Supply 

Paper 2312, p. 57–78.

Reicosky, D.C., Sharratt, B.S., Ljungkull, J.E., and Baker, 

D.G., 1983, Comparison of alfalfa evapotranspiration 

measured by a weighing lysimeter and a portable chamber: 

Agricultural Meteorology, v. 28, p. 205–211. 

Smith, R.L., 1974, Ecology and field biology (2nd ed.): New 

York, Harper and Row.

Smith, S.D., Monson, R.K., and Anderson, J.E., 1997, 

Physiological ecology of North American desert plants: 

Berlin, Springer-Verlag, 286 p.

Stannard, D.I., 1988, Use of a hemispherical chamber for 

measurement of evapotranspiration: U.S. Geological Survey 

Open-File Report 88-452. 

Stannard, D.I., and Weltz, M.A., 2006, Partitioning 

evapotranspiration in sparsely vegetated rangeland using 

a portable chamber: Water Resources Research, v. 42, 

doi:10.1029/2005WR004251.
8 Portable Chamber Measurements of Evapotranspiration at the Amargosa Desert Research Site, Nye County, Nevada, 2003–06

This page intentionally left blank.
Appendixes 9

Appendixes

Data files that contain plant characteristics (appendix A) and the complete chamber component- and landscape-scale ET 

flux measurements (appendixes B and C) are presented in three spreadsheets in a Microsoft© Excel workbook. The appendixes 

can be accessed and downloaded at URL http://pubs.usgs.gov/sir/2008/5135/sir20085135_appendixes.xls

Appendix A. Plant Characteristics Including Plant Crown Height, Ratio of Plant Crown Cover to Chamber Area, and Relative-PlantCrown Cover of Creosote Bush, Shadescale, Burrobush, and Wolfberry at the Amargosa Desert Research Site Near Beatty, Nye County, 

Nevada, August 2003 through January 2006.

Appendix B. Partitioned Bare-Soil Evaporation and Plant Transpiration from Chamber Measurements of Evapotranspiration at the 

Amargosa Desert Research Site Near Beatty, Nye County, Nevada, January 2003 through January 2006. 

Appendix C. Computed Landscape-Scale Evapotranspiration Using Chamber Measurements of Bare-Soil, Creosote Bush, Shadescale, 

Burrobush, and Wolfberry, and the Fractional Cover of Each Plant Species Across the Landscape at the Amargosa Desert Research Site 

Near Beatty, Nye County, Nevada, August 2003 through January 2006. 
10 Portable Chamber Measurements of Evapotranspiration at the Amargosa Desert Research Site, Nye County, Nevada, 2003–06

This page intentionally left blank.
For more information concerning the research in this report, contact the 

Director, Nevada Water Science Center

U.S. Geological Survey 

2730 N. Deer Run Road

Carson City, Nevada 89701

http://nv.water.usgs.gov
Garcia and others— Portable Chamber Measurements of Evapotranspiration at the Amargosa Desert Research Site, Nye County, Nevada, 2003–06—Scientific Investigations Report 2008–5135