may be complicated first by the fact that the dry soil
assemblage is stimulated by moist conditions, and sec-
ond, that wind can blow diatoms in and out of areas,
potentially causing unrepresentative assemblages in the
sediment. Further, although Busch and Kubly (1980)
examined the diatom flora of 10 playas from around
southern California and found from three to twenty spe-
cies in each, in algal floristic work that included playas
of Edwards Air Force Base, only a single diatom was
found (Brostoff et al. 1996, Brostoff 1998). Thus, there
is a potential technical basis for using diatom species
assemblages to delineate WoUS on playas (based on
identifying previously moist areas); however, some
Figure 6. Desert shrimp remnants embedded in soil
effort would need to be devoted to development of pro-
algal crusts from a small playa at EAFB (larger tic
tocols.
marks are cm).
ifornia, Brostoff (1998) encountered a few square meters
OTHER BIOTIC INDICATORS
with distinct desert shrimp remnants in the surface
The presence of desert shrimp remnant adults or
crusts (Fig. 6). At the same site, desert shrimp hatched
eggs has potential for being an indicator of previously
in the laboratory from virtually all collections of playa
standing water. Several species of desert shrimp (bran-
surface material (Sassaman 1998).
chiopod crustaceans) are characteristic of playa habi-
tats in playas in the southwestern United States. Two
REMOTE SENSING
factors make them potentially useful for delineation.
First, their eggs remain viable just below the surface,
Very little remote sensing work has been published
usually in the top 510 mm (0.1950.39 in.) of surface
specific to playas. Drake and Bryant (1994) used Ad-
crust (Brown and Carpelan 1971), for at least several
vanced Very High Resolution Radiometer (AVHRR) im-
decades, but hatch and complete their life cycles quickly
after inundation. The presence of eggs can be deter-
Tunisian playas. Henley (1988) reports some success
mined quickly and easily by immersing a small quantity
in estimating relative moisture conditions using reflec-
of substratum into water and counting hatchlings after
tance spectra from remote sensing. On dry playas, the
a few days or by sieving suspect substratum (e.g.,
reflectance in the 2100-nm band is equal to or greater
Brown and Carpelan 1971). This method has been used
than the reflectance in the 1650-nm band. For perma-
to compile species lists and quantitatively estimate
nently or intermittently wet playas, the 2100-nm band
abundance in particular areas (e.g., Sassaman 1998).
reflectance is lower than the 1650-nm band. Kokaly et
Many species of these organisms are characteristic of
al. (1994) discussed the application of AVIRIS (Airborne
playa habitats throughout the arid areas of the western
Visible Infrared Imaging Spectrometer) to mapping cryp-
United States (Eng et al. 1990; Belk and Brtek 1995, 1997;
tobiotic crusts and the advantages of this method over
Eriksen and Belk 1999). The species composition of col-
others (e.g., NDVI [Normalized Difference Vegetation
lections made in a particular location is dependent on a
Index]) in arid areas. Because of the probable spectral
suite of factors (e.g., duration of inundation, water tem-
differences between aquatic remnant crusts--both
perature, water chemistry) that are of potential use in
algal- and bacterial-dominated and adjacent substratum
establishing the extent and duration of inundation as
types--it is possible that remote sensing protocols
might be useful for performing delineations (Gallagher
could be developed.
1996, Hathaway and Simovich 1996).
In a delineation of WoUS at the Marine Corps Air
CURRENT PRACTICE BY CORPS DISTRICTS
Ground Combat Center, Twentynine Palms, California,
AND OTHER FEDERAL AGENCIES
shrimp were found outside the area classified as WoUS
in only one instance (Lichvar and Pringle 1993). It has
A telephone survey of Corps District and field offices
not been established whether eggs have been found in
with playas that might include WoUS was conducted
areas that do not pond water. Second, the remains of
during July and August 1998. The personnel with
adults or their impressions may remain in the surface
responsibility for delineations were identified in Los
after drying. In a detailed survey of 0.25 km2 (2.69 ft2)
Angeles, Albuquerque, Fort Worth, Sacramento, and
of mixed playadune habitat near Buckhorn Playa, Cal-
Portland Districts, as well as other Federal agencies with
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