Environmental Engineering Reference
In-Depth Information
CHAPTER
5
Element Cycling
Kathleen C. Weathers 1 and Holly A. Ewing 2
1 Cary Institute of Ecosystem Studies, Millbrook, NY
2 Bates College, Lewiston, ME
Element cycling is the transport and transformation of chemicals within and among eco-
systems, and as such is a major focal area for ecosystem scientists. Elements are required
by all life, and element cycles thus link the living and nonliving parts of ecosystems.
Nutrient cycles are an important subset of elemental cycles because they represent ele-
ments that are especially important to living organisms (e.g., the plant macronutrients
nitrogen (N), potassium (K), calcium (Ca), magnesium (Mg), phosphorus (P), and sulfur
(S)) or are the building blocks of life (carbon, C). Because the pathways of nutrient cycling
are those traveled by all elements, whether beneficial or harmful to life, our understanding
of nutrient cycling informs nearly all other areas of ecosystem science. Indeed, we cannot
understand primary production without understanding the availability of nutrients and
the pathways by which those nutrients are transformed in food webs, liberated through
decomposition, and again used for primary production. Nearly every process you might
consider in an ecosystem is linked in some way to nutrient cycling.
Many environmental management issues arise from too much or too little of particular
elements within a system. Not surprisingly, given how essential nutrient cycling is to pri-
mary production and food webs in ecosystems, and to our need to harness large amounts
of primary and secondary production for human food ( Vitousek et al. 1986 ), whole areas
of study examine the elemental requirements for and deterrents to growth of organisms.
Much of this focus is on important macronutrients in agricultural systems: nitrogen, phos-
phorus, calcium, and potassium. However, some elements that are needed for growth in
trace amounts, often because of their presence in enzymes, also garner attention, although
often because they are not only essential but may be toxic in high concentrations. For
example, copper is a micronutrient required for plant growth, but it has been used exten-
sively in high concentration as a toxin to control both parasites and algae in freshwater
and marine systems (e.g., as copper sulfate). Other elements, such as the heavy metals
Search WWH ::




Custom Search