Environmental Engineering Reference
In-Depth Information
also observed that ocean water, though
variable from place to place, had those
same three elements in the ratio of
105:15:1, and he went on to argue that the
abundance of those elements in ocean
water was controlled by the synthesis and
decomposition of organic matter. He thus
began a scientific conversation about the
ways in which the abundance of elements
in biotic and abiotic pools might be linked
because of the structural requirements of
organisms. Building on this idea,
Sterner
and Elser (2002)
explored the stoichiomet-
ric requirements of primary producers and
consumers and the ways in which these
requirements influence consumption pat-
terns of organisms and adaptations to dif-
ferent environments. They also developed
further Redfield's ideas about the ways in
which the stoichiometric structure of
organisms, communities, and ecosystems
are linked to ecological processes such as
decomposition.
Linkages among elements also occur via
chemical reactivity and material and energy
flow. Redox reactions (appendix) are one
of the most straightforward ways that ele-
ment cycles are linked through chemical
reactions. For example, the oxidation of
carbon requires an electron acceptor, and if
an environment is anoxic, but rich in free
manganese, it can be used as an electron
acceptor, thus linking the manganese cycle
to that of carbon. While
Redfield (1958)
is often cited for his recognition of struc-
tural stoichiometry, he also calculated the
amount of oxygen and sulfate that might be
consumed to oxidize organic matter and
compared this to observations about the
abundance of oxygen and sulfate in the
ocean. He then discussed the importance of
linkages
availability, and redox reactions involving
sulfur in regulating the oxygen concentra-
tion of the atmosphere. Thus, his work
pointed out not only the linkages of carbon,
nitrogen, and phosphorus cycles across
ecosystem pools, but also the connection
between those cycles and those of oxygen
and sulfur both within the ocean and
atmosphere.
Element cycles can also be linked
because of chemical changes that occur as
material moves through an ecosystem.
For example, when acidic precipitation
percolates through the soil, a variety of
elemental cycles are brought together as
the water moves through different envir-
onments. Water from the atmosphere may
be rich in hydrogen, sulfur, and nitrogen,
but it enters the soil where the elements
most easily exchangedmightincludecal-
cium, potassium, and sodium in much
greater concentrations than in the atmo-
sphere. Because the water encounters
chemical gradients that include a different
array of ions that are more or less tightly
held than those entering in solution—and
yet must maintain charge balance, the
equivalency of positive and negative
charges—therewlbesomeionsle t
behindwh leothersmoveintosolution
(
Figure 5.2
). Thus, the movement of water
through the soil environment will result in
a change in the water's chemical composi-
tion—and new associations of elements.
Notice here that there are many other
chemical reactions that can occur—for
example, the precipitation of calcium car-
bonate or the chelation of metals with
organic material—that bring new assem-
blages of elements into association: the
linkage of biogeochemical cycles through
move,stick,andchange.
among decomposition, oxygen
