194
isotope discrimination and environmental influences on c/c a . Some studies have found it useful to
measure both 813C and 8 18 0 to separate out
changes in precipitation input and local environmental conditions (Lipp et al. 1996; Saurer et al.
1997). Although tree rings are most often used to
study long-term changes in the water relations of
ecosystems, they can also be subdivided and provide fine-scale seasonal climatic information
(Loader et al. [1995] subdivided an annual ring into
20 units).
Millennial: Caliche
Pedogenic carbonates are formed from soil-respired
CO2 and are therefore long-term indicators of the
vegetation within an ecosystem. The variation in
paleosol carbonate 8 13 C signals at depth have been
used to indicate shifts in C 3 and C 4 vegetation (Cole
and Monger 1994; Quade and Ceding 1995; Liu et
al. 1996). However, the 8 18 0 in the CO 2 evolved
(using phosphoric acid) can also provide climatic
information. For example, the lack of a change in
8 18 0 with changes in 8 13 C implies that shifts in
photosynthetic pathway may be due more to shifts
in CO2 concentration than climate (Cole and Monger 1994; Quade and Ceding 1995). Variation in
the 8 18 0 of pedogenic carbonates may be caused
by a number of climatic factors, including temperature change, shift in the amount of precipitation, shifts in precipitation patterns (summer vs.
winter), and shifts in regional moisture sources
(Quade and Ceding 1995), and are therefore a valuable long-term record of ecosystem water relations.
10
6
•
~
2
6
co
to -2
-6
•
James R. Ehleringer, John Roden, and Todd E. Dawson
Animals
Short-Term Indicators of Water Source
Stable isotope ratio analyses can provide direct evidence of short-term animal movements across the
landscape. Often, more than 60% of an animal's
mass is water. The isotopic composition of water
in animals reflects that of their drinking source
modified by the isotopic effects of evaporative enrichment, in much the same way that leaf water
reflects both a source water component and an
evaporative enrichment component. Longinelli
(1984) first showed that a strong linear relationship
existed between the 8 18 0 values of blood and an
animal's source water (Fig. 12.6). He further provided evidence for seasonality in the 8 18 0 values
of blood, reflecting the seasonal changes in the
8 18 0 values of precipitation. Because different animals vary in overall water turnover rates and have
different relative water rates of water loss through
evaporation versus excretion, the slope of the 8 18 0
of source water and blood are different across species. Only microliter quantities are required for
these analyses. Consequently, analyses of the 8 18 0
values of blood is a viable and less expensive alternative to radiotransmitters for tracing the recent
movement patterns of animals between ecosystems
and across the landscape.
Long-Term Indicators of Water Source
The 8 18 0 values of water in blood are recorded in
bone phosphate (see Figure 12.6). Longinelli
(1984) first showed that a linear 1: 1 relationship
•
-60
-80
en
0
-100
~
•
-120
-140
-160
-10
-12
-10
-8
-6
-160
-120
-80
-40
0
FIGURE 12.6. Relationships between
source water and oxygen isotope ratios of blood and bone phosphate
(left) (Longinelli 1984), and hydrogen isotope ratios of bird feathers
(right) (Hobson and Wassenaar
1997).
8180 of source water, %.
80 of source water, %.
isotope discrimination and environmental influences on c/c a . Some studies have found it useful to
measure both 813C and 8 18 0 to separate out
changes in precipitation input and local environmental conditions (Lipp et al. 1996; Saurer et al.
1997). Although tree rings are most often used to
study long-term changes in the water relations of
ecosystems, they can also be subdivided and provide fine-scale seasonal climatic information
(Loader et al. [1995] subdivided an annual ring into
20 units).
Millennial: Caliche
Pedogenic carbonates are formed from soil-respired
CO2 and are therefore long-term indicators of the
vegetation within an ecosystem. The variation in
paleosol carbonate 8 13 C signals at depth have been
used to indicate shifts in C 3 and C 4 vegetation (Cole
and Monger 1994; Quade and Ceding 1995; Liu et
al. 1996). However, the 8 18 0 in the CO 2 evolved
(using phosphoric acid) can also provide climatic
information. For example, the lack of a change in
8 18 0 with changes in 8 13 C implies that shifts in
photosynthetic pathway may be due more to shifts
in CO2 concentration than climate (Cole and Monger 1994; Quade and Ceding 1995). Variation in
the 8 18 0 of pedogenic carbonates may be caused
by a number of climatic factors, including temperature change, shift in the amount of precipitation, shifts in precipitation patterns (summer vs.
winter), and shifts in regional moisture sources
(Quade and Ceding 1995), and are therefore a valuable long-term record of ecosystem water relations.
10
6
•
~
2
6
co
to -2
-6
•
James R. Ehleringer, John Roden, and Todd E. Dawson
Animals
Short-Term Indicators of Water Source
Stable isotope ratio analyses can provide direct evidence of short-term animal movements across the
landscape. Often, more than 60% of an animal's
mass is water. The isotopic composition of water
in animals reflects that of their drinking source
modified by the isotopic effects of evaporative enrichment, in much the same way that leaf water
reflects both a source water component and an
evaporative enrichment component. Longinelli
(1984) first showed that a strong linear relationship
existed between the 8 18 0 values of blood and an
animal's source water (Fig. 12.6). He further provided evidence for seasonality in the 8 18 0 values
of blood, reflecting the seasonal changes in the
8 18 0 values of precipitation. Because different animals vary in overall water turnover rates and have
different relative water rates of water loss through
evaporation versus excretion, the slope of the 8 18 0
of source water and blood are different across species. Only microliter quantities are required for
these analyses. Consequently, analyses of the 8 18 0
values of blood is a viable and less expensive alternative to radiotransmitters for tracing the recent
movement patterns of animals between ecosystems
and across the landscape.
Long-Term Indicators of Water Source
The 8 18 0 values of water in blood are recorded in
bone phosphate (see Figure 12.6). Longinelli
(1984) first showed that a linear 1: 1 relationship
•
-60
-80
en
0
-100
~
•
-120
-140
-160
-10
-12
-10
-8
-6
-160
-120
-80
-40
0
FIGURE 12.6. Relationships between
source water and oxygen isotope ratios of blood and bone phosphate
(left) (Longinelli 1984), and hydrogen isotope ratios of bird feathers
(right) (Hobson and Wassenaar
1997).
8180 of source water, %.
80 of source water, %.