process called photosynthesis. In this process of cell growth, oxygen is also produced. It has been estimated that ¾ of the Earth’s supply of oxygen is generated by
algae in the ocean. In terms of the food chain, the algae may be consumed by the
zooplankton, which in turn are consumed by larger animal forms, which may be
consumed by small fish, which may be consumed by larger fish, which may be
consumed by larger vertebrates, including humans. The microscopic algae are the
start of this food chain.
All biological systems require the presence of the proper nutrients to grow and
reproduce. For larger organisms, the smaller organisms provide both the nutrients and
the energy. However, algae obtain their nutrients from dissolved inorganic materials
and their energy from the sun. Organisms that rely on inorganic nutrients are called
autotrophic, whereas those that rely on organic matter are called heterotrophic.
Besides nutrients and energy, growth may depend upon other factors such as temperature, light, etc. Nutrients in a lake may vary with location, including depth, and
time. Specific organisms may have individual nutrient and environmental requirements. However, common to most are carbon, hydrogen, oxygen or another electron
acceptor, nitrogen, and phosphorus. Carbon may be obtained from the solution of
carbon dioxide. Hydrogen may be obtained from electrolysis or from bicarbonates
dissolved in the water. Oxygen is most frequently obtained from the dissolved oxygen
in the water. Nitrogen is secured from dissolved nitrogenous materials including
ammonia, nitrites, and nitrates. Certain blue-green algae can obtain gaseous nitrogen
from the atmosphere. Phosphorus is usually obtained from geological materials and
from the breakdown of other organic materials. A general rule for the ratio of nutrients
to support the growth of organisms is 60 parts carbon to 15 parts nitrogen to 1 part
phosphorus. Some trace substances may also be essential. One of these is sulfur,
which may be present in the soil, and is available in decaying organic matter. Another
is silicon, which is required to form the shell case, called the frustule, of diatoms.
Every species of organism has a specific requirement for nutrients. Other factors
being satisfactory, organisms will continue to grow until one of the essential
nutrients has been completely utilized. Then growth may be retarded or completely
stopped. Conversely, providing the limited nutrient will encourage additional
growth. Frequently limiting nutrients such as nitrogen and phosphorus are contained
in wastes, including human wastes. Conventional wastewater treatment does not
remove nitrogen and phosphorus. Thus additional treatment to remove these nutrients is frequently required before discharge into a lake.
Productivity in a lake is commonly expressed as the amount of fishable fish in a
lake. Since the number of fish is directly related to the fish’s food and the food
ultimately is a function of algae in the food chain, which in turn is a function of the
available nutrients, we can use measurement of the nutrients to estimate the potential
productivity of a lake. Whether or not productivity is desirable is up to individual
taste. A lake that is low in productivity will be clear and have a low fish population. A
lake that is high in fish population tends to be turbid and frequently accompanied by
extensive shoreline weed growths. Moreover, the fish population will vary in each
case with game fish such as trout and salmon predominant in less productive lakes and
pan fish such as bass, pickerel, and catfish predominant in highly productive lakes.
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algae in the ocean. In terms of the food chain, the algae may be consumed by the
zooplankton, which in turn are consumed by larger animal forms, which may be
consumed by small fish, which may be consumed by larger fish, which may be
consumed by larger vertebrates, including humans. The microscopic algae are the
start of this food chain.
All biological systems require the presence of the proper nutrients to grow and
reproduce. For larger organisms, the smaller organisms provide both the nutrients and
the energy. However, algae obtain their nutrients from dissolved inorganic materials
and their energy from the sun. Organisms that rely on inorganic nutrients are called
autotrophic, whereas those that rely on organic matter are called heterotrophic.
Besides nutrients and energy, growth may depend upon other factors such as temperature, light, etc. Nutrients in a lake may vary with location, including depth, and
time. Specific organisms may have individual nutrient and environmental requirements. However, common to most are carbon, hydrogen, oxygen or another electron
acceptor, nitrogen, and phosphorus. Carbon may be obtained from the solution of
carbon dioxide. Hydrogen may be obtained from electrolysis or from bicarbonates
dissolved in the water. Oxygen is most frequently obtained from the dissolved oxygen
in the water. Nitrogen is secured from dissolved nitrogenous materials including
ammonia, nitrites, and nitrates. Certain blue-green algae can obtain gaseous nitrogen
from the atmosphere. Phosphorus is usually obtained from geological materials and
from the breakdown of other organic materials. A general rule for the ratio of nutrients
to support the growth of organisms is 60 parts carbon to 15 parts nitrogen to 1 part
phosphorus. Some trace substances may also be essential. One of these is sulfur,
which may be present in the soil, and is available in decaying organic matter. Another
is silicon, which is required to form the shell case, called the frustule, of diatoms.
Every species of organism has a specific requirement for nutrients. Other factors
being satisfactory, organisms will continue to grow until one of the essential
nutrients has been completely utilized. Then growth may be retarded or completely
stopped. Conversely, providing the limited nutrient will encourage additional
growth. Frequently limiting nutrients such as nitrogen and phosphorus are contained
in wastes, including human wastes. Conventional wastewater treatment does not
remove nitrogen and phosphorus. Thus additional treatment to remove these nutrients is frequently required before discharge into a lake.
Productivity in a lake is commonly expressed as the amount of fishable fish in a
lake. Since the number of fish is directly related to the fish’s food and the food
ultimately is a function of algae in the food chain, which in turn is a function of the
available nutrients, we can use measurement of the nutrients to estimate the potential
productivity of a lake. Whether or not productivity is desirable is up to individual
taste. A lake that is low in productivity will be clear and have a low fish population. A
lake that is high in fish population tends to be turbid and frequently accompanied by
extensive shoreline weed growths. Moreover, the fish population will vary in each
case with game fish such as trout and salmon predominant in less productive lakes and
pan fish such as bass, pickerel, and catfish predominant in highly productive lakes.
264
L. K. Wang et al.