Plant Selection, Installation, and Management to Affect Groundwater - Introduction to Phytoremediation of Contaminated Groundwater - page 155

7

Plant Selection, Installation, and Management
to Affect Groundwater

... like a tree planted by water, that sends out its roots by the

stream,
And does not fear when heat comes, for its leaves remain green,
And is not anxious in the year of drought ,
for it does not cease to bear fruit .

similar to the values of groundwater than of surface water
(Dawson and Ehleringer 1991). Riparian plants thrive
near surface water because they tap groundwater dis-
charge. Many of the plants used for phytoremediation of
contaminated groundwater can be found naturally near
streams, such as cottonwoods, poplars, birch, and sycamore.
Incidentally, the Hebrew version of Jeremiah 17:8 suggests
that the trees near the stream actually were using groundwa-
ter discharge. As revealed by Ross (2007) with emphasis by
the author, the hydrologic importance of the passage is
related to one word

Jeremiah 17:8 (RSV)

This quote from the Bible states what, up until recently, was
thought to be a long-held observation—that trees growing
near streams use surface water. We now know that trees
near streams often use groundwater. Conversely, early
observations indicated that a connection between plants
and groundwater near surface water may exist, and that the
occurrence of certain plants indicated the relative depth
that groundwater could be found below land surface. For
example, the Roman architect Vitruvius stated that (with
emphasis by the author),
Besides these there are other indications of places where water
can be found—namely, the presence of small rushes, willows
which are not planted, alder trees, vitex, reeds, ivy, and all other
such plants which occur and thrive only in places where there is
water. One must solely rely on these plants, however, if they
occur in marshes, which, being lower than the surrounding
country, receive and collect and for some time retain waters
that fall on the near-by fields in winter; but if these plants occur
naturally in places that are not marshes, one can seek for
water in these places.

They shall be like a tree planted above water,
sending down its roots by a stream.

This translation suggests that the trees indeed used
groundwater rather than surface water, which would have
been infrequent in the arid area of the story. It took almost
2,000 years and the use of stable isotopes of water to verify
that groundwater can be a source of water to trees, as we will
see in Chap. 9.
Since the term phreatophyte was introduced in 1927 by
O.E. Meinzer, at least 70 species of plants have been
characterized as phreatophytes. Such plants are not from
one family but cross many different families, from herba-
ceous grasses to woody trees. Plants that rely solely on
groundwater are called obligate phreatophytes, and those
that rely on groundwater and other sources of water are
facultative phreatophytes, as described in Chap. 1.
Much of what currently is understood about phreato-
phytes and water use, especially in regard to contaminated
groundwater, is based, somewhat ironically, on efforts to
control these plants or rid areas of them where they use
large volumes of groundwater that otherwise could be used
by man, as was introduced in Chap. 5. Therefore, the plant-
ing of phreatophytes at sites characterized by contaminated
groundwater is actually a beneficial aspect of consumptive
use that could, perhaps, be termed consumptive restoration.

Even in the Saharan and Sahel desert regions of northern
Africa, it has long been known that some trees, such as
acacia and tamarisk, prefer groundwater such that

Trees and plants sometimes afford invaluable assistance in
locating successful wells, the position of master joints or belts
of fissured or decomposed rock, along which underground water
percolates, being not infrequently indicated at the surface by
lines of trees or shrubs, known as 'aars.'

Wagner (1916)

The use of groundwater rather than surface water by
plants was confirmed by the discovery that the stable isoto-
pic values of water in trees that grow along streams are more