Environmental Engineering Reference
In-Depth Information
Rain and snow
Lake
Glacier
Rapids
Waterfall
Tributary
Flood plain
Oxbow lake
Salt marsh
Delta
Deposited
sediment
Ocean
Source Zone
Transition Zone
Water
Figure 5-36 Natural capital: three zones in the down-
hill flow of water: source zone containing mountain
(headwater) streams; transition zone containing wider,
lower-elevation streams; and floodplain zone containing
rivers, which empty into the ocean.
Sediment
Floodplain Zone
before water covers them again. In such cases, scien-
tists must use the composition of the soil or the pres-
ence of certain plants (such as cattails, bulrushes, or
red maples) to determine that a particular area is really
a wetland. Inland wetlands provide a number of free
ecological and economic services. For example, they
filter toxic wastes and pollutants, absorb and store
excess water from storms, and provide habitats for
many species.
ings. More than half of the inland wetlands estimated to
have existed in the continental United States during the
1600s no longer exist. This loss of natural capital has
been an important factor in increased flood and drought
damage in the United States. Many other countries have
suffered similar losses. For example, 80% of all wet-
lands in Germany and France have been destroyed.
Scientists have made a good start in understanding
important aspects of the ecology of the world's terres-
trial and aquatic systems. One of the major lessons from
their research: In nature, everything is connected. Accord-
ing to scientists, we urgently need more research on
how the world's terrestrial and aquatic systems work
and are connected to one another and to the atmo-
sphere. With such information we will have a clearer
picture of how our activities affect the earth's biodiver-
sity and what we can do to live more sustainably.
Natural Capital Degradation: Effects of
Human Activities on Freshwater Systems
We have built dams, levees, and dikes that reduce the
flow of water and alter wildlife habitats in rivers;
established cities and farmlands that pollute streams
and rivers; and filled in inland wetlands to grow food
and build cities.
Human activities affect freshwater systems in four ma-
jor ways. First, dams, diversions, or canals fragment
almost 60% of the world's 237 large rivers. They alter
and destroy wildlife habitats along rivers and in
coastal deltas and estuaries by reducing water flow.
Second, flood control levees and dikes built along
rivers alter and destroy aquatic habitats. Third, cities
and farmlands add pollutants and excess plant nutri-
ents to nearby streams and rivers. Fourth, many inland
wetlands have been drained or filled to grow crops or
have been covered with concrete, asphalt, and build-
When we try to pick out anything by itself, we find it hitched
to everything else in the universe.
J OHN M UIR
CRITICAL THINKING
1. List a limiting factor for each of the following eco-
systems: (a) a desert, (b) arctic tundra, (c) alpine tundra,
(d) the floor of a tropical rain forest, (e) a temperate
deciduous forest, (f) the surface layer of the open sea,
and (g) the bottom of a deep lake.
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