Encyclopedia of Environmental Science and Engineering, Volume I and II

392 EUTROPHICATION

shallow water prevents depth-dwelling algae from escaping

the intensity of the sunlight penetration. Often muddy rivers

are virtually algae-free due to the lack of penetration of the

sunlight, the Missouri and the Mississippi being two such

rivers.

The distribution of algae at the various depths in a

body of water is directly correlated with the intensity of

illumination at the respective depths. This distribution

would be diffi cult to express in general terms when dealing

with algae on their species level. In addition, the depths at

which these species would be found would change with

such variables as growth phase of the organism, tempera-

ture and the absorptive and refl ective characteristics of the

water. It can be stated, however, that certain fresh-water

red algae and blue-green algae are found only at consid-

erable depths and that some diatoms exist in the bottom

mud. In the most general terms it can also be stated that

algae are found at all levels, but most commonly near the

surface.

The vertical distribution may also be related to the divi-

sion of light rays into various spectral colors. This division

varies with the concentration of dissolved color material,

plankton and particulate matter, with the seasons, and with

the depth. In colored water the violet-blue end of the spec-

trum is absorbed more readily. As depth increases light rays

divide differently with greater absorption occurring at the

red end of the spectrum.

The depth to which light penetrates has a direct infl uence

on photosynthetic activity. The seasonal variation in this

light and the resulting availability of certain dominant wave

lengths may be the reason for fl uctuations in the composition

of the algal population from spring to fall. Much more work

is needed in this area.

TEMPERATURE

In general, temperature is not the key factor in determining

the nature of the algal fl ora. Most species are able to grow

and reproduce if other environmental conditions are favor-

able. According to Patrick, however, the above statement is

not true in the case of diatoms, where temperature changes

are more important than any other environmental factor in

infl uencing their rate of growth. Additional work in this area

by Cairns indicates that certain diatoms grow best only at a

specifi c temperature, and that at some temperatures they will

not grow at all.

Most algae are not affected by minor changes in pH

brought about by the seasonal variations, growths of carbon-

dioxide producing organisms, etc. Large changes such as

would be caused by the introduction of industrial wastes or

acid mine waters, will greatly affect algae, usually causing a

decrease in population.

The majority of algae thrive when the pH is near 7.0.

Some blue-green algae prefer high pHs. Anacystis and coc-

cochloric are found at about pH 10.0 with little or no growth

below pH 8.0. Other algae such as eugleny mutabilis, cryp-

tomonas erosa and ulothrix zonata prefer low pHs.

NUTRITIONAL REQUIREMENTS AND TOXIC

ELEMENTS FOR ALGAE

Calcium

Calcium is not an essential element for most algae, although

some cannot develop without it.

Calcium and Magnesium

As bicarbonates they are a supplemental supply of carbon

dioxide for photosynthesis. This accounts for the greater

abundance of algae in hard-water lakes than in soft-water

lakes.

Iron

Most algae grow best when the ferric oxide content of the

water is between 0.2 to 2.0 mg per liter. Above 5 mg per liter

there is a toxic effect unless it is overcome by the buffering

action of organic compounds or calcium salts. Certain dia-

toms (eunotia and pinnularia) are found in iron-rich water.

Effl uent from steel mills may be toxic to most algae if the

resulting iron concentration exceeds the toxic limitation.

Copper

Copper is extremely toxic to algae in the range of 0.1 to 3.0

ppm as copper sulfate; the sulfate form being used as an algi-

cide. Some algae are able to tolerate large amounts of copper

ion and are considered copper-sulfate resistant. Protococcus,

for example, is not destroyed by 10 ppm of copper sulfate.

Phenol

At a concentration of up to 1.9 mg per liter, phenol appar-

ently has no toxic effect on diatoms.

Nitrates, Phosphates and Ammonia

These are essential food elements necessary for growth.

Nitrogen may be obtained from nitrates, nitrites or simple

ammonia compounds. The primary source of these nutrients

is from sewage treatment plant effl uents, although nitro-

gen may be derived from the atmosphere, land runoff, etc.

(See section on EUTROPHICATION.) In general as little

as 0.3 to 0.015 ppm of nitrates and phosphates will produce

blooms of certain species of algae, other conditions being

favorable.

Oil

Streams polluted with oil are usually low in algae. One vari-

ety of diatoms may be dominant in such waters.

Salinity

Increases in salinity up to about one percent do not affect

the algae population. Signifi cant increases, such as caused

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