Green Chemistry and the Ten Commandments

growth of photosynthetic algae. The oxygen-rich epilimnion generally contains a high
concentration of oxidized chemical species, which normally have high oxygen contents.
These include CO 2 and HCO 3 - for carbon, NO 3 - for nitrogen, and SO 42 - for sulfur. The
hypolimnion is often deficient in O 2 and tends to contain chemically reduced species
with low oxygen contents and high H contents, including CH 4 , NH 3 (or NH 4 +), and
H 2 S for carbon, nitrogen, and sulfur, respectively. Under the reducing conditions of the
hypolimnion, iron may be present as soluble Fe, whereas in the hypolimnion it exists as
solid Fe(OH) 3 or Fe 2 O 3

Evaporation fromocean, 1

164

Pr

ecipitation

to ocean, 1055Runoff toocean, 1^10

Pr

ecipitation

over

land, 304

Snow,

glaciers

Plant transpirationplus evaporation, 195

Condensation

of water vapor

Water vapor

to land, 1 10

Surface water

Water infiltrating soil and rock

Groundwater in aquifers

Solar energy

Figure 7.3. The hydrologic cycle, quantities of water in trillions of liters per day.

Living Organisms in Water

A normal body of water provides a habitat for large numbers of organisms ranging
from single-celled algae to fish. Such a body of water can be regarded as an ecosystem,
usually based upon a food supply consisting of the biomass produced photosynthetically
by the algae and plants living in it:

6CO 2 + 6H 2 O Light    energy C 6 H 12 O 6 + 6O 2 (7.4.1)

Chap. 7. Water, The Ultimate Green Solvent 165