The Effect of Varying
Amounts and Ratios of Nitrogen and
Phosphate on Algae Blooms
RUTH PATRICK, Chairman
Department of Limnology
Academy of Natural Sciences of Philadelphia
Philadelphia, Pennsylvania
The people of the United States have only recently appreciated the fact that
the enrichment of our surface waters by effluents from raw and treated sewage from
towns and farms and from some industries is having a profound effect on the quality
of water and the aquatic life in our lakes and streams. One very evident effect is
the excessive standing crops of algae, often referred to as algae blooms. Such
standing crops are often the cause of taste and odor problems and may alter the
quality of water in other ways. Another effect of excessive enrichment is to change
the kinds of species which are dominant. For example, diatoms which are one of
the most important --if not the most important -- algal food source for aquatic
life, may be replaced by bluegreen algae which have very little food value for
most forms of aquatic life. Indeed they may be toxic to animals drinking the
water containing them.
Algae blooms may result from several different causes. One of the ones which
generally comes to mind is the increase of nutrients flowing through a system.
Under such conditions all species of algae have increased populations and if the
predator pressure is not great enough this condition will result in large standing
crops and the presence of algae blooms. Such blooms may also result from a shift
in kinds of species without increasing the nutrients flowing through a system. For
example, diatoms are highly desirable as a source of food for most aquatic animals. In contrast, bluegreen algae are rarely eaten by any species. Thus a shift
in conditions which enable bluegreen algae to develop instead of diatoms could
bring about an algae bloom because of a lack of predator pressure. Likewise
slightly toxic conditions may produce an algae bloom. In this case the toxicity
lowers the numbers of species that can tolerate the environmental conditions, thus
predators are often reduced and likewise the numbers of species of algae are reduced. Thus the nutrients which formerly flowed through many species and were
eaten by many kinds of predators now under these conditions flow through a few
species which may have very few predators, thus a large standing crop of algae
results and we call it an algae bloom.
It, therefore, is important that we try to define the causes of such excessive
algae growths. A series of experiments was undertaken at the Waterloo Mills Field
Research Station of the Academy of Natural Sciences to try to determine the effect of nitrogen as nitrates or ammonium and phosphates in varying amounts and
ratios on natural communities of diatoms. Also some experiments were carried
out to determine the effects of adding small amounts of glucose to these enriched
waters. Experiments by Lewin (1) have shown that glucose can be utilized as a
carbon source by several species of diatoms.
In order to undertake these studies an experimental set-up had to be designed
so that a natural community of diatom species could be grown under semi-laboratory
conditions, and so that concentrations of various chemicals could be maintained
in high flows of water without much variation.   Previous experiments have shown
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