Significance of Algae
There are three general benefits attributed to algae:
(1) reoxygenation via photosynthesis,
(2) mineralization, and
(3) primary production in the food chain.
Also associated with algae are three detrimental effects:
(1) the production of toxic compounds,
(2) aesthetic harm from algal blooms including odors and tastes, and
(3) an increase in BOD due to excessive oxygen consumption for decomposition of the organic material.
Algae are the basic link in the conversion of inorganic constituents in water into organic matter. When present in sufficient number, these plants impart a green, yellow, red or black color to the water.
They may also congregate at or near the surface and form blooms or scums. Some blue-green algae, many green algae, and some Diatoms produce odors and scums that make water less desirable for swimming.
Several species of blue-green algae produce, under certain conditions, toxic organic substances that kill fish, birds, and domestic animals. Some of the genera which may produce toxins are Anabena, Anacyetics, Aphanizomenon,Coleolosphaerium, Gloeotrichia, Microcystis, Nodularia, and Nostoc. Some species of Chlorella, a green algae, are also toxic.
Excessive algal growths that interfere with beneficial uses of a particular water are termed nuisance growths. For example, abnormally abundant growths of algae may make bathing beaches unattractive, produce unpleasant odors and foul the bottoms of boats. Algal growths can impart color or turbidity to water.
There have been reports of rapid deaths of a great variety of animals after drinking water containing high concentrations of blue-green algae such as Anacystis, Aphanizomenon, Nostoc, Rivulari, Nodularia, Gloeotrichia, Gomphosphaeria, and Anabena.
Fresh algae have been reported to be more toxic than decaying algae. Fatal poisoning has occurred among cattle, sheep, pigs, dogs, horses, turkeys, ducks, geese, and chickens. It is believed that such algae may be toxic to all warm blooded animals.
Algal poisoning is considered a menace to migratory water fowl and has been suspected as a cause of mass deaths of ducks. Fatal doses can be very small, on the order of a few milliliters of water suspension taken orally, but animals vary in their susceptibility.
Also, algae can be a severe pollutant to fish in two respects. First, they can cause heavy fish mortality through direct poisoning, and second, they can be responsible for oxygen imbalance thereby killing fish through oxygen depletion or oxygen supersaturation of the waters.
Dead algae have caused the death of fish by clogging their gills and by accumulating in a mat on the surface so dense as to present a barrier to the penetration of oxygen underneath the algal mat.
In terms of recreation, excessive algal growths destroy recreational aesthetic values of lakes and also cause accidents. Algae can be an aesthetic nuisance in another way. Wave action may concentrate a large mass of algae on the shore where, if not removed immediately, decomposition will cause the usual annoyances of septic odors.
As for Diatoms, they discolor water and cause taste and odor problems. Asterionella (a Diatom) blooms have been known to use up all the available silica in their environment, thereby creating conditions detrimental to their own survival. The Diatoms Melosira and Synedra sometimes in small or moderate numbers are responsible for tastes and odors.