Environmental Engineering Reference
In-Depth Information
have higher diffusional loss rates across a shorter length of
stem than a larger tree.
Ma and Burken (2004) used the data presented in Ma and
Burken (2003) to develop a model that accounts for the
effects of various contaminant transport and fate processes
in plants to explain the loss of contaminants from the tree
tissue with ascending height. In both ring- and diffuse-
porous trees, the water is conducted near the outer surface
of the plant, closer to the bark. As such, the potential for
diffusive loss of waterborne solutes increases.
and vapor. On average, roughly 170 g of plant matter pro-
duced about 23 mL of water. This approach is non-invasive
to the subsurface, and has the advantage that the water
transpiring from the leaves has entered in some part of
the full volume of the root zone. The data indicated that
plant-water tritium concentrations and soil-water tritium
concentrations were directly related.
The measurement of contaminants in leaf samples
directly or in gas bags many not necessarily indicate that
the source of the detected compound was from the subsur-
face. This is because the atmosphere also can be a source of
contaminants deposited on leaf surfaces. Atmospheric
compounds can remain on the leaf surface or be taken into
the leaf tissue, such as how the widely used herbicide
glyphosphate enters target plants.
15.1.4 Gas Bags
Various gases enter and exit plant leaves based on concen-
tration gradients. The most important movement of gas is
related to photosynthesis. Water vapor also exits plant leaves
during photosynthesis. Couple this with the ability of plants
to translocate and transpire VOCs and the study of gaseous
exudates at the whole stand, whole plant, leaf, or bark
surface is warranted.
Conditions that affect gas exchange are controlled at the
leaf level. Knowledge of leaf-level gas exchange can often
be used to scale up the results to the whole tree, but can be
problematic. As an alternative, whole-canopy measurements
typically involve infrared gas analyzers (IRGA) to measure
CO
2
and H
2
O vapor exchange. Open systems have been
developed to amend these problems (Alterio et al. 2006).
Collection of gas emission of water vapor and other
compounds can be performed while the leaves remain on
the plant. For example, Tedlar
15.1.5 Infrared Analysis
The reaction of photosynthesis indicates that the measure-
ment of CO
2
uptake by plants in a phytoremediation system
over time could be used as an indicator of the impact that
plants were having on contaminant remediation, or con-
versely, the impact that the contaminants were having on
plant growth. Although laboratory methods to measure
changes in CO
2
have been used widely in the plant sciences,
these methods require the use of radiolabeled CO
2
, as a gas
for terrestrial studies, and bicarbonate for aquatic studies as a
tracer of CO
2
uptake and photosynthesis. IRGA is a safer
alternative to measuring photosynthesis and has been shown
to be useful at the field scale.
bags were used by Martin
et al. (1999) to detect the release of various hydrocarbons
from the branches and leaves of a wide variety of deciduous
and coniferous plants (see Chap. 16 for more details).
Ferrieri et al. (2006) used Teflon
®
15.1.6 Plant Fluorescence
-lined plastic bags sealed
around individual plants grown hydroponically. The bags
encased all the foliage and were secured around the base of
the plant's main stem. To capture any emitted volatile
contaminants from the leaves into the air, each bag
contained a carbon-based molecule sieve cartridge of
500 mg of Tenax
®
Light energy captured by a plant in chloroplasts can be
radiated back out of the plant at wavelengths between 650
and 800 nm. This characteristic of all photosynthetic plants
is called fluorescence. Fluorescence begins when photons
split water by oxidizing it into oxygen, hydrogen, and
electrons. This process is 97% efficient, which means 3%
of the energy is “lost” in the form of fluorescence. Dark-
adapted leaves fluoresce when exposed to light. The degree
of response is referred to as the Kautsky effect. The
properties of bioluminescence and fluorescence can be con-
sidered as photosynthesis in reverse.
In many studies, the degree of fluorescence is used to
determine the response of a plant to a variety of factors.
Inhibitors of photosynthesis or stresses from water deficits,
pest invasion, or contamination can affect photosynthesis
and, therefore, fluorescence. Such fluorescence by chloro-
phyll
a
is directly related to the amount of chlorophyll
a
.In
GR placed in small-diameter tubes. In
this study, CCl
4
and isoprene were measured.
A simple approach was presented by Andraski et al.
(2003, 2005), who used gas bags to trap plant gas for analy-
sis. Their goal was to investigate the fate of tritium contami-
nation of the vadose zone at the USGS Amargosa Desert
Research Site, near Death Valley National Park, NV.
Andraski et al. (2003, 2005) developed a method where
foliage from the native, deep-rooted creosote bush (
Larrea
tridentate
) was manually stripped from plants, put into plas-
tic bags, and then placed in the sun for evaporation
and collection of water vapor. Tritiated water (
3
HHO) and
vapor behaves identically as non-tritiated water (HHO)
®
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