Encyclopedia of Environmental Science and Engineering, Volume I and II

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EUTROPHICATION

INTRODUCTION

For a considerable time, scientists have been aware of the

natural aging of lakes, a process so slow that it was consid-

ered immeasurable within the lifetime of human beings. In

recent years, however, that portion of the nutrient enrichment

or eutrophication of these and other natural bodies of water

contributed by man-made sources have become a matter of

concern. Many bodies of water of late have exhibited biologi-

cal nuisances such as dense algal and aquatic weed growths

whereas in the past they supported only incidental populations

of these plants.

Excessive nutrients are most often blamed in the scien-

tifi c literature for the creation of the plant nuisances. Among

the nutrients, dominant roles have been assigned by most

researchers to nitrogen and phosphorus. These elements can

be found in natural waters, in soils, in plants and animals, and

in precipitation. Man-made sources for these nutrients are in

domestic wastes and often in industrial wastes.

This chapter concerns itself with the nature of algae, the

environmental factors affecting their growth, the nature of

the entrophication problem (sources, relative quantities of

nutrients contributed by these sources, threshold limits for

the growth of aquatic plants), and various techniques for the

removal of those nutrients usually associated with the eutro-

phication problem.

THE PHYSICAL NATURE OF ALGAE

Most bodies of water which can be considered eutrophic

exhibit various predominant forms of algae at different times

of the year. Algae that are important to investigators concerned

with the eutrophication problem may be classifi ed into four

groups which exclude all but a few miscellaneous forms. The

four groups are:

1) Blue-green algae (Myxophyceae)

2) Green algae (Chlorophyceae)

3) Diatoms (Bacillariophyceae)

4) Pigmented flagellates (Chrysophyceae,

Euglenophyceae)

The basis for this classifi cation is the color of the organ-

ism. Blue-green and green algae are self descriptive, whereas

diatoms are brown or greenish-brown. Pigmented fl agellates

can be brown or green. They possess whip-like appendages

called fl agella, which permit them to move about in the water.

It is not inferred by the above list that all algae are restricted to

these colors. Rhodophyceae, for example, which are primarily

marine algae, are brilliant red.

Aquatic biologists and phytologists do not agree on the

number of divisions that should be established to identify

algae. Some authorities use as many as nine divisions while

others use seven, fi ve and four. Nevertheless, the four divi-

sions as suggested by Palmer will be used as they are adequate

for the ensuing discussions.

BLUE-GREEN ALGAE

Blue-green algae as a group are most abundant in the early

fall at a temperature range of 70 to 80°F. Data obtained

from water sources in the southwestern and southcentral

United States indicate that for this section of the country

maximum growth occurs at the end of February and through-

out much of April, May and June. When blue-green algae

becomes predominant, it frequently indicates that the water

has been enriched with organic matter, or that previously there

had been a superabundance of diatoms. Blue-green algae are

quite buoyant due to the oil globules and gas bubbles which

they may contain. For this and other reasons they live near

the surface of the water often producing offensive mats or

blankets. Since these algae are never fl agellated, they are not

considered swimmers although a few, such as oscillatoria

and spirulina, are able to creep or crawl by body movements.

Some of the common blue-green algae are anabaena, aphani-

zomenon, rivularia, gomphosphaeria and desmonema.

GREEN ALGAE

Green algae are most abundant in mid-summer at a tem-

perature range of 60 to 80°F. For water bodies in the south-

western and southcentral United States, maximum growth

occurs during the fi rst half of September with little variation

throughout the remainder of the year. Like the blue-green

algae, green algae usually contain oil globules and gas bub-

bles which contribute to the reasons why they are found near

the surface of the water. Green algae are distinguished by

their green color which comes from the presence of chloro-

phyll in their cells. Many of the green algae are fl agellates

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