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 Chemical constituents of the atmosphere such as water vapor, carbon dioxide, and ozone
selectively absorb certain wavelengths of incoming solar radiation. The preferential absorbtion of longer
wavelengths by such constituents is the basis for the so-called `greenhouse effect' and the constituents
are often termed `greenhouse gases'. In the ultraviolet, diminishing ozone is responsible for decreased
absorbance of harmful ultraviolet wavelengths. And obviously, all
Table 1.2.1. Some Characteristics of Reservoirs Compared to Natural Lakes
Natural Lakes
Reservoirs
Characteristic
Distribution
Mostly in glaciated regions
Located mostly outside region
also near rivers , their
of glaciation. Mostly in south
floodplains and often associated
region of U.S. Often in regions
with karst regions or coastal plains.
of water resource need.
Shape
Rounder, less shoreline complexity
Dendritic, greater shoreline
complexity (shoreline development).
Morphometry
Basin with central deep areas
Basin with deeper areas near one
end (the dam)
Drainage area
Smaller ratio of drainage area to
Larger ratio of drainage area
to lake surface area.
to lake surface area.
Theoretical retention
Longer, sometimes many years
Shorter, often less than 1 year.
time
Inflows
Often many smaller order streams
Often dominated by one or a
few major inflows (sometimes
other lake outflows).
Outflows
More stable, lake surface
Releases according to
fluctuations smaller
demand schedules, lake
surface fluctuations
greater
Longevity
Longer
Shorter
Nutrient loading
This depends on the watershed characteristics and the size of the watershed.
Water clarity
Greater
Lesser, especially near headwaters.
plants in aquatic ecosystems are affected by the distribution and availability of wavelengths in the visible
range.
Whereas all wavelengths can act to input energy to an aquatic system, the visible wavelengths
are those most important to biological activity. Visible wavelengths represent about one-half of the total
1.2-6
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