Why Study Continental Aquatic Systems? - Freshwater Ecology: Concepts and Environmental Applications - page 3

the refinement of the concept of an ecosystem, ecological methods for
approaching control of disease, methods to assess and remediate water pol-
lution, ways to manage fisheries, restoration of freshwater habitats, under-
standing of the killer lakes of Africa, and conservation of unique organisms.
Each of these will be covered in this text. I hope to transmit the excitement
and appreciation of nature that comes from studying aquatic ecology.
Further justification for study may be necessary for those who insist on
more concrete benefits from an academic discipline or are interested in pre-
serving water quality and aquatic ecosystems in the broader political con-
text. There is a need to place a value on water resources and the ecosystems
that maintain their integrity and to understand how the ecology of aquatic
ecosystems affects this value. Water is unique, has no substitute, and thus
is extremely valuable. A possible first step toward placing a value on a re-
source is documenting human dependence on it and how much is available
for human use.
Humankind would rapidly use all the water on the continents were it
not replenished by atmospheric input of precipitation. Hydrologic fluxes,
or movements of water through the global hydrologic cycle, are central to
understanding water availability. Much uncertainty surrounds some as-
pects of these fluxes. Given the difficulty that forecasters have predicting
the weather over even a short time period, it is easy to understand why es-
timates of global change and the local and global effects on water budgets
are beset with major uncertainties (Mearns et al., 1990; Mulholland and
Sale, 1998). We are able to account moderately well for evaporation of wa-
ter into the atmosphere, precipitation, and runoff from land to oceans.
This accounting is accomplished with networks of precipitation gauges,
measurements of river discharge, and sophisticated methods for estimating
groundwater flow and recharge.
The global water budget is the estimated amount of water movement
(fluxes) between compartments (the amount of water that occurs in each
area or form) throughout the globe (Fig. 1.2). This hydrologic cycle will be

Atmosphere

73

110

386

423

37

Land

Ocean

FIGURE 1.2 Fluxes (movements among different compartments) in the global hydrologic
budget (in thousands of km 3 per year; data from Berner and Berner, 1987).