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 viewed as a distinguishing mark (a freckle, for example) often such things are viewed as a
nuisance. If they pose a medical threat, then such growths are considered health risks. Similarly,
in the aquatic environment, a small quantity of aquatic plant growth may be viewed as
interesting, beneficial, or even sightly. When that growth chokes the waterway it is a nuisance,
possibly harmful. When it produces toxins, it is a health risk. When there is resultant economic
or biological damage, the growth is a harmful algal bloom (HAB).
What Causes Nuisance Growth? Plants grow or die. There is no compromise.
Aquatic systems constantly change with flows, seasons, resource use, and numerous other
factors. The interactions among all these factors have led to some generalizations on what
contributes to plant growth.
Plants and algae require water, light, and nutrients. While temperature obviously affects
the growth of all organisms, there is usually some species that are well adapted to all normally
occurring aquatic temperatures. In aquatic environments the only two factors that usually limit
algal growth are light and nutrients.
>>TRUTH STATEMENT<<: In nature, as long as a habitat offers sufficient or
abundant resources to support growth, something will attempt to utilize those resources and
grow abundantly.
Because the growth controlling resources are often keys to long-term management,
understanding how they affect plant growth is therefore also important. The two types of
resources necessary to support plant growth are briefly described below. They include the
source of energy for growth and the materials needed to support that growth.
Light Energy. The sun is the only source of the light energy that is necessary for
photosynthesis and plant growth. The same factors controlling the distribution of light energy in
water and its absorption by water affect the availability to plants in the water. There are
obviously depths in deeper lakes to which no light effectively penetrates and plants do not
exhibit photosynthetic activity there. Also, because longer wavelengths are usually absorbed
nearer the surface, both the light quality and intensity changes with depth. For this reason, at
certain depths of many lakes, there are specific types of algae adapted to use that light and to
live at that range of depths. The factors controlling available light have been addressed
elsewhere in this course.
Nutrients and Eutrophication. Cultural eutrophication began in North America with
the arrival of European settlers. Cultural eutrophication differs from the original concept of
eutrophication by virtue of its speed and the processes contributing to it. The original concept of
eutrophication applied to the natural tendency of a lake to change with age.
In the original concept, the young natural lake, formed through some natural process like
tectonic activity or glaciation, was initially at its deepest and soon was surrounded by well-
1.2.46
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