Plant Selection, Installation, and Management to Affect Groundwater - Introduction to Phytoremediation of Contaminated Groundwater - page 161

Similarly, high groundwater use was observed in natural
stands of saltcedar by the same researchers.

1918). G.E.P. Smith, who, as described in Chap. 1, first used
automatic water-level recorders in wells installed in stands
of trees to record the diurnal water-level fluctuation of trees
transpiring groundwater, also noted in 1915

7.1.2.4 Mesquite and Rabbitbrush
A phreatophyte native to the western United States is mes-
quite ( Prosopis juliflora ). Mesquite is a deep-rooted plant
with roots that penetrate at least 50 ft (15.2 m) in search of
the water table. It also uses precipitation or surface water if
available. Interestingly, even though mesquite is considered
to be an arid plant, its capacity to take up and retain ground-
water is evident from accounts that upon cutting down a
mesquite tree, its green wood is heavy, similar to the wood
of eastern hardwood trees that are not water limited
(Spalding 1909). Moreover, Spalding (1909) observed a
relation between the distribution and depth of mesquite
roots and groundwater:
The root system of these plants consists of a taproot which grows
rapidly downward and when developed is always within reach of
a permanent, deep water supply, and a system of widely spread-
ing lateral roots which are in relation to more superficial layers
of the soil

... that the trees [mesquite] send their roots down to the water

table is easily proved, for the caving banks of rivers and arroyos
reveal them. The mesquite, in particular, has deep, strong
taproots, with a generous development of feeders.
(Smith 1915).

A short list of woody plants classified as phreatophytes is
presented in Table 7.2 . These plants are primarily observed

Table 7.2 Representative woody phreatophytes native to the western
United States that may have phytoremediation potential (Modified
from Robinson 1958).

Common
name

Scientific name Relation to groundwater
Depth to
water table below
land, ft (m)

Remarks

Boxelder Acer negundo Found along

streams in
mountains.

The contrast between this and the shallow root
system of many of the great trees of eastern mesophytic forests,
familiar to everyone who has seen them uprooted by heavy
winds, is instructive.

...

Alder Alnus Found near

streams.

Hackberry Celtis reticulata Found near

streams, and can
reach 50-ft height.

(Spalding 1909)

The depth to water table also controls, to some extent, the
vigor of mesquite trees. In areas where the water table is at
shallow depths, mesquite can reach a height of 50 ft (15.2 m);
in areas where the depth to water table is greater, the height of
the tree is considerably shorter (Cannon 1911, 1913). Cannon
(1911) conveys that ranchers in Arizona often locate wells
based on the presence of mesquite. About the same time,
Meinzer and Kelton (1913) were investigating the water
resources of the Sulphur Spring Valley in Arizona. As part
of that study, mesquite growth was measured in relation to
measured or estimated depth to water table. Typically, the
depth to water table ranged from 11 to 50 ft (3.3-15.2 m). The
most vigorous mesquite growth was observed, however, in
locations where depths to the water table were moderate,
between 25 and 35 ft (7.6-10.6 m; Meinzer and Kelton
1913). The shallower depths resulted in less vigorous growth
because of the accumulation of salts near the land surface
by the evaporation of shallow groundwater. Transpiration
rates between 2.8 and 3.5 mm/day have been reported
(Interstate Technology Regulatory Council 2009).
It is interesting that observations of the relation between
mesquite growth and depth to water table were documented
as far back as the late 1880s. Harvard (1884) noted that a 60-
ft (18 m) long taproot of mesquite could reach even a deep
water table and observed that the shallower the water table,
the better the growth (Harvard 1884). Others also noted the
relation between the presence of mesquite and the relation to
the water table (Coville and MacDougal 1903; Schwennesen

Smoketree Dalea spinosa Found in gravel

washes.

Sycamore Platanus

wrightii

Found near
streams.

Cottonwood Populus spp.
Quaking
Aspen

Populus
tremuloides
aurea

Found near
streams and
springs.

Mesquite Prosopis

juliflora

Extensive roots,
up to 50-60 ft.

Live Oak Quercus

agrifolia

35 (10 m)

Willow Salix

Elder Sambucus Found in moist

areas.

Greasewood Sarcobatus
vermiculatus

60 (18.2 m)

Sequoia Sequoia

gigantean

Saltcedar Tamarix gallica

California
palm

Washington
filifera

Shallow roots,
groundwater must
be shallow.

Cowania
stansburiana

Vanadium
Bush

Used to indicate
vanadium-
uranium deposits.

Rabbitbrush Chrysothamnus
spp.

Grows in
moderately
alkaline soils;
contains rubber
(non-latex) up to
6%.