Why Study Continental Aquatic Systems? - Freshwater Ecology: Concepts and Environmental Applications - page 5

can be accomplished with lower quality water. Some uses are consumptive
and preclude further use of the water; for instance, a significant
portion of water used for agriculture evaporates. The most extreme
example of nonrenewable water resource use may be water “mined” (with-
drawal rates in excess of rates of renewal from the surface) from aquifers
(large stores of groundwater) that have extremely long regeneration times.
Such withdrawal is practiced globally (Postel, 1996) and also accounts for
a significant portion of the United States' water use, particularly for agri-
culture (Fig. 1.4). Other uses are less consumptive. For example, hydro-
electric power “consumes” less water (i.e., evaporation from reservoirs in-
creases water loss, but much of the water moves downstream).
Accurate accounting for the economic value of water includes both the
immediate benefit and how obtaining a particular benefit alters future use.
Consumption and contamination associated with each type of use dictate
what steps will be necessary to maintain aquatic ecosystems and water
quality and quantity. Establishing the direct benefits of using the water, in-
cluding patterns and types of uses, is also necessary. Elucidation of bene-
fits will allow determination of economic value of water and how uses
should be managed.
How much water does humankind need? A wide disparity occurs be-
tween per capita water use in developed and less developed arid countries,
particularly in semiarid countries in which surface water is scarce (Table
1.2). Israel is likely the most water-efficient developed country, with per
capita water use of 500 m 3 per year (Falkenmark, 1992), about four times
as efficient as the United States. Increases in standard of living lead to
greater water demands (per capita water use).

400

300

Groundwater
Surface water

200

100

0

1950 1960 1970 1980 1990 2000

Year

FIGURE 1.4 Amounts of surface and groundwater used in the United States from 1950 to
1990. These estimates include only withdrawals and not hydroelectric uses [after Gleick
(1993) and Solley et al. (1983)].