390 EUTROPHICATION
and due to their swimming ability they are frequently found
in rapidly moving streams. Some of the common green algae
are chlorella, spirogyra, chlosterium, hydrodictyon, nitella,
staurastrum and tribonema.DIATOMSDiatoms are usually most prevalent during the cooler months
but thrive over the wide temperature range of from 35 to
75°F. For water bodies in the southwestern and southcen-
tral United States, diatoms thrive best in May, September
and October with the maximum growth observed in mid-
October. It is generally recognized that many diatoms will
continue to fl ourish during the winter months, often under
the ice. The reason for the increase in growth twice a year
is due to the spring and fall overturn, in which food in the
form of carbon, nitrates, ammonia, silica and mineral matter,
is brought to the surface where there is more oxygen and a
greater intensity of light.
Diatoms live most abundantly near the surface, but unlike
the buoyant green and blue-green algae, they may be found
at almost any depth and even in the bottom mud. Diatoms
may grow as a brownish coating on the stems and leaves
of aquatic plants, and in some cases they grow along with
or in direct association with other algae. In rapidly moving
streams they may coat the bottom rocks and debris with a
slimy brownish matrix which is extremely slippery. Lastly,
diatoms are always single-celled and nonfl agellated.PIGMENTED FLAGELLATESNo classifi cation of algae has caused more disagreement
than that of the pigmented fl agellates. The diffi culty arises
from the fact that hey possess the protozoan characteristics
of being able to swim by means of fl agella, and the algae
characteristic of utilizing green chlorophyll in association
with photosynthesis. Thus they could be listed either as
swimming or fl agellated algae in the plant kingdom, or as
pigmented or photosynthetic protozoa in the animal king-
dom. One of many attempts to resolve this problem has been
the proposal to lump together all one-celled algae and all
protozoa under the name “Protista.” This method, however,
has not met with general acceptance. For the sanitary engi-
neer the motility of the organism is of lesser importance than
its ability to produce oxygen. The pigmentation character-
istic associated with green chlorophyll and oxygen produc-
tion is suffi cient criteria for separating these organisms into
a class by themselves. Thus a distinction is made between
pigmented fl agellates (algae) and nonpigmented fl agellates
(protozoa).
Pigmented fl agellates are more abundant in the spring
than at any time of the year although there is generally con-
siderable variation among the individual species. Apparently
fl agellates are dependent on more than temperature. They
are found at all depths, but usually are more prevalent below
the surface of the water than at the surface.For present purposes pigmented fl agellates can be divided
into two groups: euglenophyceae which are grass-green in
color and chrysophyceae which are golden-brown.
Euglenophyceae are usually found in small pools rich in
organic matter, whereas chrysophyceae are usually found in
waters that are reasonably pure.
Some of the more common pigmented fl agellates are
euglena, ceratium, mallomonas, chlamydomonas, cryptomo-
nas, glenodinium, peridinium, synura and volvox.MOTILITYOf additional value in the classifi cation of algae are their
means of motility. Three categories have been established,
namely:Nekton—algae that move by means of flagella.
Plankton—algae that have no means of motility.
Benthic algae—algae that attach themselves to a fixed
object.NEKTONNekton are the most active algae and are often referred to
as “swimmers.” Due to their activity they use more energy
and in turn release more oxygen during the daylight hours.
Their cells are supplied with one, two, or more fl agella
which extend outward from the front, side or back of the
cell. These fl agella enable the organisms to move about
freely in the aquatic environment and to seek food which,
in the case of turbulent water, is constantly changing in
location.
In general nekton have the most complex structure of the
three categories and come nearest to being simple animals.
Nekton are the predominant algae found in swiftly moving
rivers and streams.
According to Lackey, results of tests performed on waters
of the Ohio River show that certain nekton are the only algae
that provide reliable clear-cut responses to the presence of
pollution and thus are true indicator organisms. Five fl ag-
ellates have been singled out on the genus level as being
common and easily recognized. They are (1) cryptomonas,
(2) mallomonas, (3) synura, (4) uroglenopsis, and (5) dino-
bryon. Dinobryon is perhaps the most easily recognized
due to its unique shape which resembles a shaft of wheat.
Samples taken from several rivers indicate that these algae
react adversely to the presence of sewage and are found in
abundance only in clean water. Unfortunately not all experts
agree on what constitutes clean water and what algae serve
as indicator organisms. Patrick states that the “healthy” por-
tion of a stream contains primarily diatoms and green algae.
Rafter states that the absence of large amounts of blue-green
algae is an indicator of clean water. Palmer lists 46 species
which have been selected as being representative of “clean-
water algae,” and these consist of diatoms, fl agellates, green
algae, blue-green algae and red algae. In addition Palmer listsC005_012_r03.indd 390C005_012_r03.indd 390 11/18/2005 10:26:01 AM11/18/2005 10:26:01 AM