Environmental Engineering Reference
In-Depth Information
Figure 3-23 The pH scale, used to measure acidity and alkalin-
ity of water solutions based on their concentrations of hydrogen
ions (H ). Values shown are approximate. A solution with a pH
less than 7 is acidic, a neutral solution has a pH of 7, and a so-
lution with a pH greater than 7 is basic. Each whole-number
drop in pH represents a tenfold increase in acidity. (Used by
permission from Cecie Starr, Biology: Concepts and Applica-
tions, 4th ed., Pacific Grove, Calif.: Brooks/Cole, 2000)
The acidity or alkalinity of a soil, as measured by
its pH (Figure 3-23), influences the uptake of nutrients
by plants. Chemicals can be added to raise or lower
the acidity of soils.
that organisms need to live, grow, and reproduce are
continuously cycled between air, water, soil, rock, and
living organisms. These cycles, driven directly or indi-
rectly by incoming solar energy and gravity, include
the carbon, oxygen, nitrogen, phosphorus, and hydro-
logic (water) cycles (Figure 3-6, p. 39).
The earth's chemical cycles also connect past, pre-
sent, and future forms of life. Some of the carbon
atoms in your skin may once have been part of a leaf, a
dinosaur's skin, or a layer of limestone rock. Your
grandmother, Plato, or a hunter-gatherer who lived
25,000 years ago may have inhaled some of the oxygen
molecules you just inhaled.
Compare soil profiles from grassland, desert, and three
types of forests at Environmental ScienceNow.
3-6
MATTER CYCLING IN ECOSYSTEMS
Nutrient Cycles: Global Recycling
Global cycles recycle nutrients through the earth's air,
land, water, and living organisms and, in the process,
connect past, present, and future forms of life.
All organisms are interconnected by vast global recy-
cling systems known as nutrient cycles, or biogeo-
chemical cycles (literally, life-earth-chemical cycles).
In these cycles, nutrient atoms, ions, and molecules
The Water Cycle
A vast global cycle collects, purifies, distributes, and
recycles the earth's fixed supply of water.
The hydrologic cycle, or water cycle, which collects,
purifies, and distributes the earth's fixed supply of wa-
ter, as shown in Figure 3-24 (p. 54).
Search WWH ::




Custom Search