Plant Selection, Installation, and Management to Affect Groundwater - Introduction to Phytoremediation of Contaminated Groundwater - page 160

even in arid areas. Such habitats have been observed for
some time, as exemplified by the following:
By the waters (streams) of Babylon,
there we sat down and wept

In the western United States, one of the most widespread
phreatophytes is the greasewood ( Sarcobatus spp. ). It grows
where the depth to water table is shallow or as deep as 60 ft
(18 m). As stated in Chap. 1, USGS hydrologist W.N. White
set up experimental tanks in Utah to determine the propor-
tion of groundwater used by greasewood (White 1932). He
determined that the seasonal use of groundwater ranged
between 0.08 and 0.38 ft (0.02-0.1 m) when measured in
natural stands of greasewood, whereas in his tank
experiments with an artificially controlled water table the
use was greater, nearly 2 ft (0.6 m) of groundwater.

...
On the willows (poplars) there
we hung up our lyres.

Psalm 137:1-2 (RSV)

All 250-plus willow species are native to the United
States. Like cottonwoods, willows are most likely to be
found along streams or in flood plains where the depth to
groundwater is 10 ft (3 m) or less. Unlike poplars, willows
are pollinated by insects rather than wind.
Based on their location with respect to regional, interme-
diate, and local groundwater-flow systems, it should not be
surprising that evidence of the interaction between willows
and groundwater exists. For example, in the nineteenth cen-
tury, this relation between willows and groundwater was
noted in the following:
When the thalweg [middle] of a valley is uncultivated and one
sees there growing naturally willows, poplars, alders, osiers,
rushes, reeds, wild mint, silver weed, ground ivy, and other
water-loving trees or plants, one should presume that the course
of water is not deep in that place. However, as these kinds of
plants thrive in all humid terranes they can only serve to indi-
cate the presence of groundwater in so far as they are on a
thalweg or at the bottom of a hollow.

7.1.2.3 Saltcedar
Whereas greasewood is native to the western United States,
another phreatophyte that has become widespread but is not
indigenous is saltcedar, or tamarisk ( Tamarix spp. ). The
saltcedar is native to western Europe and Asia, and charcoal
from Tamarix plants has been found in caves near Mount
Carmel, Israel, that date between 12,300 and 10,500 BC
(Ley-Yadun and Weinstein-Evron 1994). Saltcedar probably
was brought to the United States in the 1800s. For example,
Robinson (1958) cites an observation in Bowser (1957)
that saltcedar was found to be thriving in the San Jacinto
River in Harris County, TX, in 1884. The flood plains of
rivers throughout the arid southwestern United States
characterized by shallow groundwater apparently have
provided the imported saltcedar a niche in which to outcom-
pete other riparian plants. Saltcedar can tolerate both wet
years and dry years, because of its deep, branched root
system, produced during dry years, and adventitious roots
from the bark produced during wet years, and a prodigious
amount of seeds produced regardless (Robinson 1958). The
photosynthetic organs of saltcedar are not true leaves but
cladophylls, which are cylindrical stems that look like
whirled leaves, perhaps more readily recognized to exist in
asparagus. Saltcedar has replaced up to 90% of the native
cottonwoods and willows in the lower Colorado River valley
(Sala and Smith 1996).
There are differences between species of this genus.
Whereas T. aphylla does not have to reproduce by seed
and can retain its leaves throughout the year T. gallica
produces seed and drops its leaves annually. Because of
the massive seed production of T. gallica , it is more wide-
spread throughout the western United States. This fecundity
coupled with its copious use of groundwater make saltcedar
a management problem for water managers in that area. For
example, measurements taken in Carlsbad, New Mexico,
indicate that the average use of groundwater by saltcedar
grown in tanks was 5.48 ft/year (1.6 m/year; Blaney et al.
1942). Tank experiments performed by Gatewood et al.
(1950) indicated that as the depth to water table increased,
the amount of groundwater use decreased but was still high.

(Paramelle 1856).

Observations such as these were later confirmed by
experimental testing. For example, White (1932) recorded
the water-table fluctuation in a well near willows to be 0.3 ft
(0.09 m) during August 1926, where depth to groundwater
was 5-6 ft (1.5-1.8 m) below land surface. Another study on
the use of groundwater by willows was performed by Blaney
et al. (1933) in California. They transplanted a willow
( S. laevigata ) from the field into a 6-ft (1.8 m) diameter,
3-ft (0.9 m) deep tank, where a depth to water table was
maintained at about 2 ft (0.6 m). They recorded the water use
to be equivalent to 4.4 ft (1.3 m) between May 1930 and
April 1931. A similar experiment was conducted in New
Mexico, but multiple plants were transplanted into a similar
sized tank. These researchers recorded water use near 2.5 ft
(0.7 m) between June 1936 and May 1937 (Young and
Blaney 1942).
Willows have an advantage over poplars with respect to
the water quality of groundwater. Willows tend to be more
tolerant of salt stress than cottonwoods and are the predomi-
nant riparian plant along the Colorado River (Busch and
Smith 1995). This information may be useful in designing
a phytoremediation planting if site-assessment and charac-
terization activities indicate high salt concentrations in the
soil or groundwater. Transpiration rates between 10 and
45 mm/day have been reported for willows (Interstate Tech-
nology Regulatory Council 2009).