biological characteristics are determined in large part by physical
characteristics of the water
column. Important physical characteristics include temperature,
light transparency, and wave action, as well as the total abundance
nutrients, which is largely a watershed characteristic. In addition,
preceding populations influence successive populations by assimilating
critical nutrients. Populations also have varying susceptibilities to
grazing by zooplankton,
which vary seasonally in type and abundance. As physical, chemical,
and biological conditions in the lake change over time, some species
will be effectively eliminated from a lake because they cannot tolerate
the new conditions. Other species will be out-competed by organisms
that are better adapted to the new environment.
represent an important ecological pattern in lakes known as algal succession.
In most natural systems the seasonal succession of algae
(and macrophytes) is a recurrent, if not exactly repetitive, yearly
cycle. A typical algal succession is shown in Figure 19. Some species
flourish for a period of time and then give way to other species more
compatible with changed conditions, such as warmer water, more daylight,
or lower concentrations of phosphorus
or nitrogen. Short-lived plankton communities are characterized by these
seasonal fluctuations; longer-lived organisms, such as fish, must be
tolerant of lake conditions all year.