Environmental Engineering Reference
In-Depth Information
radioisotopes to trace the movement of materials through ecosystems, rather than adding
radioisotopes to ecosystems. For example,
Caraco and her colleagues (2010
)observedthat
the concentration of
14
C in organic matter washed into the Hudson River from the soils of
its watershed was very different from that of organic matter produced by photosynthesis
within the river. They could therefore use
14
C to trace movement of terrestrial organic
matter through the Hudson River food web, and show that modern zooplankton were
being supported in part by carbon that was captured by primary production thousands of
years ago (
Figure 1.5
).
Stable isotopes have largely taken the place of radioisotopes as tracers outside the labo-
ratory (
Box 1.3
). Although much more difficult to measure and often expensive to use,
stable isotopes do not present a health risk to humans and wildlife. Stable isotopes are
available for many elements of ecological interest, including hydrogen, nitrogen, carbon,
oxygen, sulfur, and others. Stable isotopes often are added to ecosystems (or to laboratory
experiments) and followed as they move through the system. For example, Templer and
her colleagues (
2005
) added a stable isotope of nitrogen,
15
N, to forest plots in the Catskill
100
Modern
terrestrial
Modern
terrestrial
FIAV
FIAV
0
SAV
SAV
Phytoplankton
Phytoplankton
-100
-200
Zooplankton
Zooplankton
-300
Aged
terrestrial
Aged
terrestrial
-400
-250
-200
-150
-100
-35
-30
-25
-20
13
δ
C
(‰)
2
H
(‰)
δ
FIGURE 1.5
Use of stable and radioisotopes to determine the source of organic matter supporting zooplank-
ton in the Hudson River (
Caraco et al. 2010
). Isotope bi-plots show
14
C vs.
13
C (left side) and
14
C vs.
2
H (right
side). Sources of carbon from modern primary production are shown near
the tops of
the graphs
(FlAV
submersed aquatic vegetation). If zooplankton were composed
of carbon and hydrogen from these sources, then the data for isotopic composition of zooplankton should fall in
the same region of the graph as the sources. Instead, zooplankton fall far outside this region of the graph, show-
ing that they must be composed of organic matter from both modern and “aged” sources (i.e., organic matter
thousands of years old from the soils of the Hudson River's watershed). (From Caraco et al. 2010.)
5
floating-leaved aquatic vegetation; SAV
5
