Physiography of Lakes and Reservoirs - Freshwater Ecology: Concepts and Environmental Applications - page 91

6 Physiography of
Lakes and
Reservoirs
Formation: Geological Processes
Lake Habitats and Morphometry
Stratification
Water Movement and Currents in Lakes
Summary
Questions for Thought
Lakes of all sizes provide us with fisheries, recreation, drinking water,
and scenic splendor. Having a clean lake nearby increases property values.
Large lakes (Table 6.1) have played a part in the history, economy, and cul-
ture of many nations. Lakes also provide an excellent system for ecologi-
cal study. The boundaries of the lake community and ecosystem often ap-
pear distinct, the water well mixed, and the bottom relatively homogeneous,
making lakes a tractable system for ecologists. Much effort has been made
to study the physical and biological aspects of lakes (e.g., some of those in
Table 6.2 have been studied intensively for approximately a century) and
to manage pollution. The base of these studies is an understanding of the
geomorphology of the lakes. Different lake morphologies give rise to dif-
ferent levels of productivity and physical effects of water retention, circu-
lation, currents, and waves. For example, the fates of toxins and nutrients
in lakes depend partly on lake circulation, which is a function of lake phys-
iography. In this chapter, I describe formation, lake morphometry, the
process of stratification, and water movement in lakes.
FORMATION: GEOLOGICAL PROCESSES
What is a lake? I define a lake as a very slowly flowing open body of wa-
ter in a depression of ground not in contact with the ocean. This definition
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