ENCYCLOPEDIA OF ENVIRONMENTAL SCIENCE AND ENGINEERING - EUTROPHICATION pdf

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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
© 2006 by Taylor & Francis Group, LLC
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.
DIATOMS
Diatoms 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 FLAGELLATES
No 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.
MOTILITY
Of 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.
NEKTON
Nekton 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 lists
© 2006 by Taylor & Francis Group, LLC
EUTROPHICATION 391
47 species of algae condensed from a list of 500 prepared
from reports of more than 50 workers, as being representative
of “polluted-water algae.” These consist of blue-green algae,
green algae, diatoms and fl agellates.
PLANKTON
Plankton are free-fl oating algae which are most commonly
found in lakes and ponds, although they are by no means lim-
ited to these waters. Most species are unicellular; however,
they tend to become colonial when their numbers increase,
as in the formation of a heavy concentrated growth known
as a “bloom.” An arbitrary defi nition of a bloom is that con-
centration of plankton that equals or exceeds 500 individual
organisms per ml. of raw water. Blooms usually show a pre-
dominance of blue-green algae although algae from other
classes can also form blooms.
An algae bloom often becomes suffi ciently dense as
to be readily visible on or near the water surface, and its
presence usually indicates that a rich supply of nutrients is
available. Other environmental factors may stimulate the
formation of blooms, and a bloom of the same organism
in two bodies of water may or may not result from identi-
cal favorable environmental conditions. These growths are

extremely undesirable in bodies of water, in general, and in
potential water supply sources in particular for the following
reasons:
1) They are very unsightly.
2) They interfere with recreational pursuits.
3) When the water becomes, turbulent, fragments of
the mat become detached and may enter a water
treatment system clogging screens and filters.
4) When the algae die (as a result of seasonal changes
or the use of algicides), decomposition occurs,
resulting in foul tastes and odors.
5) They may act as a barrier to the penetration of
oxygen into the water which may result in fish
kills.
6) They may reduce the dissolved oxygen in the water
through decay or respiration within the bloom.
7) Some blooms release toxic substances that are
capable of killing fish and wild life.
8) They may cause discoloration of the water.
9) They attract waterfowl which contribute to the
pollution of the water.
Some of the common blue-green algae that form blooms
are anabaena, aphanizomenon, oscillatoria, chlorella and
hydrodictyon. Synedra and cyclotella are common diatoms
that form blooms and synura, euglena and chlamydomo-
nas are common fl agellates that form blooms. Filamentous
green plankton, such as spirogyra, cladophora and zyg-
nema form a dense fl oating mat or “blanket” on the surface
when the density of the bloom becomes suffi cient to reduce
the intensity of solar light below the surface. Like blooms,

these blankets are undesirable, and for the same reasons
cited earlier. However, in addition, blankets also serve
as a breeding place for gnats and midge fl ies, and after
storms they may wash up on the shores where they become
offensive. In many cases hydrogen sulfi de and other gases
which are able to spread disagreeable odors considerable
distances through the air are liberated. In large amounts,
hydrogen sulfi de has been known to seriously discolor the
paint on lakeside dwellings.
BENTHIC ALGAE
Benthic algae are those algae which grow in close associa-
tion with a supply of food. That is, they seek out an aquatic
environment where nutrients are adequate, then attach
themselves to a convenient stationary object such as a sub-
merged twig or rock. They may be found in quiet ponds and
lakes or in fast-moving rivers and streams. In some cases
they break away from their attachments and form unsightly
surface mats, or they may re-attach themselves somewhere
else. Chlamydomonas is such an organism, where in one
growth phase it may be found attached to a fi xed object,
and in another phase it may be dispersed throughout the
water.
Benthic algae include diatoms, blue-green algae, green
algae and a few species of red fresh-water algae. None of the
pigmented fl agellates are benthic. Most attached algae grow
as a cluster of branched or unbranched fi laments or tubes
and are fastened at one end to some object by means of an
anchoring device. Others take the shape of a green felt-like
mat (gomphonema), a thin green fi lm or layer (phytoconis),
or a soft fragile tube (tetraspora). Some of the most common

benthic algae are cladophora, chara, nitella, ulothrix, cym-
bella, vaucheria and gomphonema.
ENVIRONMENTAL FACTORS AFFECTING GROWTH
OF ALGAE
The effects of certain environmental factors on the growth
of the aforementioned forms of algae have been fairly well
defi ned. The most important parameters to be considered in
the growth pattern are light intensity, temperature, pH and
nutritional requirements.
LIGHT INTENSITY
Light is essential to all organisms which carry on photo-
synthesis; however, requirements or tolerance levels differ
greatly with the organism. For example, terrestrial species
of vaucheria grow equally well in fully-illuminated soil and
densely-shaded soil, while a number of blue-green algae
grow only in shaded habitats. In addition, some algae are
unable to endure in the absence of sunlight caused by sev-
eral consecutive cloudy days, whereas certain submerged
algae are unable to withstand exposure to full sunlight.
Thus, an algae kill may be noted during a drought where
© 2006 by Taylor & Francis Group, LLC
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

© 2006 by Taylor & Francis Group, LLC
EUTROPHICATION 393
by salt-brine wastes, may destroy most of the algae present,
however. Certain fresh-water algae may become adapted to
water with slowly increasing salinity.
Hydrogen Sulfide
At a concentration of 3.9 ppm, hydrogen sulfi de is toxic to most
diatoms. Some resistant species are achnanthese affi nis, cymbella
ventricosa, hantzschia amphioxys and nitzschia palea.
Silica
Silica is necessary for the growth of diatoms whose cell wall is
composed of silica. Presently no limits have been determined
(to the author’s knowledge).
Vitamins
Several vitamins in small quantities are a requisite to growth
in certain species of algae. Chief among these vitamins are
vitamin B-12, thiamine and biotin. These vitamins are sup-
plied by bottom deposits, soil runoff and by the metabolites
produced by other organisms.
Micronutrients
Substances such as manganese, zinc, molybdenum, vana-
dium, boron, chlorine, cobalt, etc. are generally present in
water in the small concentrations suffi cient for plant growth.
Carbon Dioxide
Carbon dioxide is necessary for respiration. If it is defi cient,
algae may remove carbon dioxide from the atmosphere.
Chlorine
Chlorine is toxic to most algae and is used as an algicide in
the range of 0.3 to 3.0 ppm. It is used as an algicide in the
treatment plant and distribution system. Some algae, cos-

marium for example, are resistant to chlorine. Protococcus,
which is resistant to copper sulfate, is killed by 1 ppm of
chlorine. Therefore, algae resistant to the copper ion may not
be resistant to the chlorine ion and vice versa.
Calcium Hydroxide (lime)
An excess of lime in the water, as may be introduced during
pH adjustment for coagulation, results in the death of certain
algae. Five ppm of lime with an exposure of 48 hours has
been lethal to melosira, nitzschia and certain protozoa and
crustacea.
THE EUTROPHICATION PROBLEM
Of the factors previously discussed which promote the growth
of algae, that factor which man has altered is the nutrient
concentration in may of the natural waterways.
In simplest terms, eutrophication is the enrichment of
waters by nutrients from natural or man-made sources. Of
the many nutrients which are added to the waters by man-
made sources, nitrogen and phosphorous are most often cited
by researchers as being the key nutrients responsible for the
promotion of algae growth. In nearly all cases when the
nitrogen and phosphorus level of a body of water increases,
there will be a corresponding increase in the growth of algae
and aquatic plants. Such growth greatly speeds up the aging
process whereby organic matter invades and gradually dis-
places the water until eventually a swamp or marsh is formed.
Unfortunately, the process of eutrophication is often diffi cult
to reverse in bodies of water such as large lakes where the
fl ushing or replacement time for the waters can be in the
order of years.
The following sections provide the relative magnitude of

natural and man-made sources of nutrient material associated
with plant growth.
SOURCES OF NUTRIENTS
While it is recognized that certain algae require a number
of chemical elements for growth, it is also known that
algae can absorb essential as well as superfl uous or even
toxic elements. Although every essential element must be
present in algae, this does not mean that every element is
essential. On the other hand, the absence of certain nutrient
elements will prevent growth. Nutrients may be classifi ed
as (1) “absolute nutrients,” which are those which cannot
be replaced by other nutrients, (2) “normal nutrients,”
which are the nutrients contained in the cell during active
growth, and (3) “optimum maximum growth.” It may also
be well to assign a broad meaning to the word “nutrient”
and defi ne it as anything that can be used as a source of
energy for the promotion of growth or for the repair of
tissue.
In evaluating the effects of nutrients on algae, care must
be exercised to consider the interaction between nutrients
and other physical, chemical or biological conditions. Rapid
growth of algae may be stimulated more by factors of sun-
light, temperature, pH, etc., than by an abundance of nutrient
material. Tests performed with nitzschia chlosterium, in order
to study the interaction of environmental factors showed that
two identical cultures of the organism, when supplied with a
reduced nutrient level, had a lower optimum light intensity
and optimum temperature for maximum growth. Thus light
intensity and temperature data should accompany data on
nutrient concentration and growth rate.

Of all the possible nutrients, only nitrogen and phosphorus
have been studied in depth both in the fi eld and in the labo-
ratory. This is because of the relative diffi culties associated
with the study, analysis and measurement of trace elements,
compounded by the minute impurities present in the regents
and distilled water. In addition, nitrates and phosphates
have a long history of use in agricultural fertilizers where
determination of their properties have been essential to their
economical use.
© 2006 by Taylor & Francis Group, LLC
394 EUTROPHICATION
The following are the most common sources of nitrogen
and phosphorus in bodies of water:
1) Rainfall—Based on experimental data, it has been
found that rainwater contains between 0.16 and
1.06 ppm of nitrate nitrogen and between 0.04 and
1.70 ppm of ammonia nitrogen. Computations
based on the nitrogen content of rainwater show
that for Lake Mendota, Wisconsin, approximately
90,000 pounds of nitrogen are available each year
as a result of rainfall. Thus it can be seen that
rainfall plays a significant role in building up the
nitrogen content of a lake or reservoir especially
if the surface area is large.
An examination of the phosphorus content of rainwater
of different countries shows that a number of concentrations
may exist ranging from 0.10 ppm to as little as an unmeasur-
able trace, the latter reported in the Lake Superior region
of the United States. In view of the wide variation in the
determinations, little can be stated at present regarding the

degree of phosphorus build-up in impoundments resulting
from rainwater.
2) Groundwater—Studies conducted on sub-surface
inflows to Green Lake, Washington, show that this
water contains approximately 0.3 ppm of phospho-
rus. Other reports, however, claim that the amount
of phosphorus in groundwater is negligible.
Investigations into the nitrate content of groundwater pro-
duced variable results; however, it can be stated that 1.0 ppm
is a reasonable fi gure. The results of the above studies on both
nitrogen and phosphorus can be summarized by stating that
groundwater should not be discounted as a possible source of
nutrients and that quantitative values should be obtained for
the specifi c locality in question.
3) Urban Runoff—Urban runoff contains storm
water drainage, overflow from private disposal
systems, organic and inorganic debris from paved
and grassed areas, fertilizers from lawns, leaves,
etc. In view of the variable concentration of the
above material, precise figures cannot be obtained
on the phosphorus or nitrate content that would be
meaningful for all areas.
Studies conducted in 1959 and 1960 by Sylvester on
storm water from Seattle street gutters shows the following
nutrients:
Organic nitrogen—up to 9.0 ppm
Nitrate nitrogen—up to 2.8 ppm
Phosphorus—up to 0.78 ppm soluble and up to 1.4 ppm
total.
4) Rural Runoff—Rural runoff for the purposes

of definition may be considered as runoff from
sparsely-populated, wooded areas with little or
no land devoted to agriculture. Investigations by
Sylvester showed that the phosphorus content
of drainage from three such areas in the state of
Washington contained 0.74, 0.77 and 0.32 lb./acre/
year, or a total concentration of 0.069 ppm. The
corresponding nitrate nitrogen concentration and
organic nitrogen concentration amounted to 0.130
and 0.074 ppm, respectively.
5) Agricultural Runoff—Agricultural runoff is one
of the largest sources of enrichment material and
may be derived from two sources—wastes from
farm animals and the use of nitrogen and phos-
phorus-containing fertilizers.
Farm-animal wastes add both large quantities and high
concentrations of nutrients to adjacent streams and rivers.
The large concentrations are due primarily to the practice of
herding animals in relatively confi ned areas. A comparison
on the nutrient value of animal wastes and human wastes has
been made in a study by the President’s Science Advisory
Committee. According to the fi ndings, a cow generates the
waste equivalent of 16.4 humans, a hog produces as much as
1.9 humans and a chicken produces as much as 0.14 humans.
The use of chemical fertilizers in the United States has
grown almost 250% in the decade from 1953 to 1963. In
1964 the use of phosphorus-containing fertilizers and the use
of nitrogen-containing fertilizers reached approximately 1.5
and 4.4 million tons, respectively, per year. Most all of this
fertilizer is distributed to soil already high in natural-occurring

nitrogen. When nitrogen fertilizer and natural soil nitrogen
combine, there is a great increase in crop production, but
also a greater opportunity for loss of this nitrogen in runoff.
This loss will increase if the fertilizer is not properly applied,
if it is not completely utilized by the crops, if the crops have
a short growing season (the land being non-productive for a
time), if the land is irrigated, and if the land is sloped.
The addition of nitrogen-bearing fertilizers also increase
the quantity of mineral elements in the soil runoff which are
necessary for the growth of aquatic plants and algae. When
applied, the nitrogen in the fertilizer is converted into nitric
acid which combined with the minerals in the soil, such as
calcium and potassium, rendering them soluble and subject
to leaching.
6) Industrial Wastes—The nutrient content of indus-
trial waste effluents is variable and depends
entirely upon the nature, location and size of the
industry. In some cases the effluents are totally
free of nitrogen and phosphorus.
The meat packing industry is one of the chief producers of
nitrogen-bearing wastes. The greatest producer of phosphate-
bearing wastes is most likely the phosphate-manufacturing
industry itself. Most phosphate production in the United States
is concentrated in Florida and as a result many severe local-
ized problems of eutrophication have resulted in that state.
Fuel processing industries and petroleum refi neries dis-
charge vast quantities of nitrogen into the atmosphere both
in the gaseous state and solid state as particulate matter. This
nitrogen is then washed from the atmosphere by the rain and
carried back to earth. In 1964, the 500 billion tons of coal

used in the United States released about 7.5 million tons of
nitrogen into the atmosphere, most of which has returned to
be combined with the soil. This greatly exceeds the use of
nitrogen in the form of fertilizers which, as previously stated,
amounted to 4.4 million tons for that year. Thus, through the
atmosphere we are bringing more nitrogen into the soil than
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EUTROPHICATION 395
we are taking out, and much of this excess ultimately gets
washed out into our waterways.
7) Municipal Water Treatment—The water treatment
plants themselves are to a degree responsible for
adding to the eutrophication problem as approxi-
mately 33% of the municipal water in the United
States is treated with compounds containing
phosphorus or nitrogen. Some of the commonly
used nutrient-bearing chemicals or compounds
are ammonia (in the use of chloramines) organic
polyelectrolytes, inorganic coagulant aids, sodium
hexametaphosphate, sodium tripolyphosphate,
and sodium pyrophosphate.
8) Waterfowl—It has been estimated that wild ducks
contribute 12.8 pounds of total nitrogen/acre/year
and 5.6 pounds of total phosphorus/acre/year to
reservoirs or lakes. A number of studies have
been conducted on waterfowl, but it may be con-
cluded that, although there may be some bearing
on localized eutrophication, in general the overall
effect is negligible.
9) Domestic Sewage Effluent—Undoubtedly the

greatest contributor toward the eutrophication
of rivers and lakes is the discharge from sewage
treatment plants. Conventionally treated domestic
sewage usually contains from 15 to 35 ppm total
nitrogen and from 6 to 12 ppm total phosphorus.
In addition there are a large number of minerals
present in sewage which serve as micro-nutrients
for algae and aquatic plants.
Phosphorus in domestic sewage may be derived from
human wastes, waste food (primarily from household garbage-
disposal units), and synthetic detergents. Human wastes have
been reported in domestic sewage at the rate of 1.4 pounds
of phosphorus/capita/year. The largest source of phospho-
rus, however, is from synthetic detergents which amounts to
approximately 2.1 pounds/capita/year. Sawyer indicates that
detergent-based phosphorus represents between 50 and 75%
of the total phosphorus in domestic sewage. It should be
noted that both the use of household garbage-disposal units
and detergents is fairly recent, and accordingly they may be
considered as contributing strongly to the development of
the recently magnifi ed eutrophication problem.
Not all the phosphorus entering a sewage treatment
plant will leave the plant since chemical removal does occur
during the treatment process. Calcium and metallic salts in
large concentrations form insoluble phosphates which are
readily removed. Very often phosphate-precipitating agents
are present in waters containing industrial wastes, and when
these agents are received at the plant, removals in the neigh-
borhood of 60% may be realized.
Nitrogen in domestic sewage is derived from human

wastes and from waste food primarily from household
garbage-disposal units. Human wastes, the major source of
nitrogen, contributes an average of about 11 pounds of nitro-
gen/capita/year. Some reduction in the nitrogen also takes
place during the treatment of the sewage. Many plants treat
the sludge anerobically which permits signifi cant release of
the nitrogen. In general the removal amounts to between 20
and 50%. The higher percentage of removal occurs when
fresh wastes are given complete treatment with no return of
sludge nutrients to the effl uent.
EUTROPHICATION STUDIES
In recent years a considerable number of studies have been
made on eutrophication and related factors. Most of the studies
can be grouped into the following categories:
1) nutrient content of runoff, rainwater, sewage efflu-
ent, bottom mud, etc.
2) nutrient analysis and physical distribution of
nutrients in bodies of water before and/or after
enrichment.
3) methemoglobinemia (illness in infants due to
drinking high nitrate-content water)
4) toxicological and other effects on fish of high
nitrate/high phosphate-content water
5) the chemical composition of plants in both eutro-
phied and non-eutrophied waters
6) the nutrient values of various fertilizers, manures
and other fertilizing elements
7) the nutrient value of various soils
8) the effects of eutrophication on aquatic plants,
animals and fish

9) studies on specific algae under either controlled
laboratory conditions or in a particular body of
water, using artificial or natural environmental
conditions
10) methods for the removal or reduction of nitrogen
and phosphorus
11) nutrient thresholds for growth of algae and aquatic
weeds
12) the effects of eutrophication on the oxygen
balance.
Of the above list, only studies conducted in the areas of
(11) and (12) will be presented below. Work done in regard
to (1) has already been presented. The removal or reduction
of nitrogen and phosphorus (10) will be discussed separately
as part of the subject matter in “CONTROL METHODS.”
NUTRITIONAL THRESHOLDS FOR THE GROWTH
OF ALGAE
Studies conducted by Chu indicate that for growth on artifi cial
media most planktonic algae fl ourish if the total nitrogen con-
tent ranges from 1.0 to 7.0 ppm and the total phosphorus content
ranges from 0.1 to 2.0 ppm. If the nitrogen is reduced below
0.2 ppm and the phosphorus below 0.05 ppm, the growth of
algae appears to be inhibited. The same inhibiting effect is cre-
ated when the nitrogen or phosphorus content is raised above
20.0 ppm. The lower limit of the optimum range of nitrogen
© 2006 by Taylor & Francis Group, LLC
396 EUTROPHICATION
varies with the organism and with the type of nitrogen. For
ammonia nitrogen the optimum range varies from 0.3 to 5.3
ppm and for nitrate nitrogen the optimum range falls between

0.3 and 0.9 ppm. Below these values the growth rate decreases
as the concentration of nitrogen decreases.
Apparently the use of the various forms of nitrogen by
algae is not constant throughout the year. Tests conducted
at Sanctuary Lake in Pennsylvania (1965) indicate that the
order of preference for the three forms of nitrogen—ammonia-
nitrogen, nitrate-nitrogen, and nitrite-nitrogen—are defi ned
by three seasonal periods, which are:
Spring (1) Ammonia nitrogen
(2) Nitrate nitrogen
(3) Nitrite nitrogen
Midsummer (1) Ammonia nitrogen
(2) Nitrite nitrogen
(3) Nitrate nitrogen
Fall (1) Ammonia nitrogen
(2) Nitrate nitrogen
(3) Nitrite nitrogen
The amount of nitrogen in the aquatic environment is
important to algae because it determines the amount of chlo-
rophyll that may be formed. Too much nitrogen, however,
inhibits the formation of chlorophyll and limits growth.
Laboratory studies on algae conducted by Gerloff indicate
that of all the nutrients required by algae, only nitrogen, phos-
phorus and iron may be considered as limiting elements, and
of these three, nitrogen exerts the maximum limiting infl u-
ence. Approximately 5 mg of nitrogen and 0.08 mg of phos-
phorus were necessary for each 100 mg of algae produced.
The corresponding nitrogen/phosphorus ratio is 60 to 1.
Hutchinson cites phosphorus as being the more impor-
tant element since it is more likely to be defi cient. When

phosphorus enters a body of water, only about 10% is in the
soluble form readily available for algal consumption. During
midsummer total phosphate may increase greatly during the
formation of algal blooms, while soluble phosphate is unde-
tectable due to rapid absorption by the growing algae. Very
often during warm weather these blooms are stimulated by
the decomposition and release of soluble phosphates from
the bottom sediments, deposited by the expired blooms of
previous seasons. Thus when phosphates are added to a
lake, only a portion of the phosphates are used in produc-
ing blooms. The blooms thrive and consume phosphates for
only a short time, and a signifi cant amount fi nds its way to
the bottom sediments where it will be unavailable to further
growth of aquatic vegetation.
Prescott examined a number of algae and concluded
that most blue-green algae are highly proteinaceous.
Aphanizomenon fl os-aquae, for example, was shown to con-
tain 62.8% protein. Green algae were found to be less pro-
teinaceous. Spirogyra and cladophora, for example, contain
23.8 and 23.6% respectively. Thus it can be concluded that
the nitrogen requirement (for the elaboration of proteins)
depends on the class of algae, and that blue-green algae
would require more nitrogen than green algae.
Provasoli examined 154 algal species to determine the
requirements for organic micronutrients. He found that
although 56 species required no vitamins, 90 species were
unable to live without vitamins such as B
12
, thiamin and
biotin, either alone or in various combinations. He concluded

that these vitamins are derived from soil runoff, bottom muds,
fungi and bacterial production (B
12
), and from a natural resid-
ual in the water.
Ketchum and Pirson conducted a series of examina-
tions on the inorganic micronutrient requirements of algae
and concluded that a number of elements are necessary for
growth. No numerical values were assigned to the require-
ment levels. Those elements shown to be essential were C,
H, O, P, H, S, Mg, Ca, Co, Fe, K and Mo. Those elements
which may be essential (subject to further study) were Cu,
An, B, Si, Va, Na, Sr, and Rb.
In summation, absolute values and nutrient thresholds
cannot be set at this time because too little is known regard-
ing the requirements of individual species. It might be stated
in general terms, however, that nitrogen and phosphorus are
two essential nutrient elements related to the production of
blooms, and that if they are present in the neighborhood
of 0.2 ppm and 0.05 ppm, respectively, algal growths will
increase signifi cantly.
NUTRITIONAL THRESHOLDS FOR THE GROWTH
OF AQUATIC PLANTS
Studies conducted by Harper and Daniel indicate that sub-
merged aquative plants contain 12% dry matter of which
1.8% are nitrogen compounds and 0.18% are phosphorus
compounds. Hoagland indicates that when the nitrate content
of water is high, nitrates may be stored in aquatic plants to
be reduced to the usable ammonia nitrogen form as required.
Subsequent investigations show that ammonia nitrogen can

be substituted for nitrate nitrogen and used directly. Light
apparently is not a necessary factor in the reduction of the
nitrogen.
Muller conducted a number of experiments on both algae
and submerged aquatic plants, and concludes that exces-
sive growths of plants and algae can be avoided in enriched
waters if the concentration of nitrate nitrogen is kept below
0.3 ppm, and if the concentration of total nitrogen remains
below 0.6 ppm.
OXYGEN BALANCE
Recently, attention has been given to the effect of the intense
growths of algae on the oxygen balance of natural water-
ways. It has been established that the dissolved oxygen
concentrations may exhibit wide variation throughout the
course of the day. This variation is attributed to the ability of
algae to produce oxygen during the daylight hours, whereas
they require oxygen for their metabolic processes during the
hours of darkness.
© 2006 by Taylor & Francis Group, LLC
EUTROPHICATION 397
In addition, since algae are organic in nature, they exert
a biochemical oxygen demand (BOD) on the stream oxygen
resources as does other materials which are organic.
Extensive tests were run on the Fox River in Wisconsin
by Wisniewski in 1955 and 1956 to examine the infl uence
of algae on the purifi cation capacity on rivers. In the most
general terms, the studies indicate that algae increase the
B.O.D. by adding organic matter capable of aerobic bacte-
rial decomposition and by the respiration of the live cells
which utilize oxygen during the absence of light. In the

presence of light, algae produce oxygen and as a result
may cause a “negative” B.O.D. for a production of oxygen
in excess of that required for the normal B.O.D. require-
ments or aerobic bacterial stabilization. In addition to the
above, the following specifi c conclusions were drawn from
the tests:
1) The oxidation rate resulting from the respiration
of live algae was much lower than that obtained
by the biological oxidation of the dead algae.
2) The ultimate B.O.D. of live algae was practically
the same as for dead algae.
3) A linear relationship was found to exist between the
five-day B.O.D. of suspended matter and volatile
suspended solids concentration.
4) The B.O.D. increases with increases in suspended
solids, the latter consisting largely of algae.
Additional work was done in this area and reported
in 1965 by O’Connell and Thomas. They note that the
oxygen produced by photosynthetic plants is affected
greatly by changes in the availability of light due to cloud
cover, turbidity in the water, etc., and therefore it may be
too variable to be used as a reliable factor in evaluating
the oxygen resources of a river. Another variable may be
the loss of oxygen to the atmosphere during the daylight
hours, caused by excess oxygen production and localized
supersaturation.
An important consideration is the type of photosynthetic
plants which are prevalent in a river. According to the above
authors, if benthic algae and/or rooted aquatic plants are
predominant (in lieu of phytoplankton), there will be little

benefi cial effect on the oxygen balance. In addition night-
time absorption of oxygen through respiration can seriously
reduce daily minimum concentrations of dissolved oxygen.
Determination of the effects of the benthic algae oscillato-
ria along a fi vemile stretch of the Truckee River in Nevada
indicated that on the average of the organism produced 72.5
pounds/acre/day of oxygen through photosynthesis. Oxygen
uptake for these same organisms amounted to an average of
65.4 pounds/acre/day.
An examination of the oxygen profi les indicated that the
oxygen variation throughout the day ranged from 2 (at night)
to 13 (during daylight) parts per million.
It is dissolved oxygen variations such as the above which
has been responsible for the disappearance of high quality
game fi sh in many of our natural waterways.
CONTROL METHODS TO PREVENT
EUTROPHICATION
There are a number of methods which attempt to limit the
amounts of nutrients in bodies of water once the point of
eutrophy has been reached. Some of these include dredging
and removing bottom sediments with an inert liner, harvesting
the algae, fi sh, aquatic weeds, etc., and diluting the standing
water with a water of lower nutrient concentration. Although
these methods may have their proper application, if eutrophi-
cation is to be decelerated, nutrient removal must start before
wastes are permitted to enter the receiving waters.
Regarding the specifi c nutrients necessary to be removed,
most researchers have placed the blame of eutrophication in
waters to the inorganic forms of phosphorus and nitrogen.
A smaller number of researchers are claiming that the algae–

bacteria symbiosis relationship might be responsible for the
rapid growth of blooms and that the amount of algae pres-
ent in natural waters is in direct balance with the amount of
carbon dioxide and/or bicarbonate ions in the waters. They
further argue that an external supply of the above elements
is necessary for the growth of algae populations. Since nei-
ther theory has been proved conclusively to date, the control
methods given will be for the removal of nitrogen and phos-
phorus since it is these nutrients which most researchers lay
to the blame of eutrophication and which have been there-
fore subsequently studied in detail.
NITROGEN REMOVAL
Land Application
It has been found that nitrogen-bearing waters, when perco-
lated through soil are subjected to physical adsorption and
biological action which removes the nitrogen in the ammo-
nium form. It appears, however, that the nitrate form of
nitrogen remains unaffected. At present this process is only
at the theoretical stage, and to the author’s knowledge no
full-scale application has been attempted. Considerable land
area would be involved which may prove a deterrent.
Anaerobic Denitrification
In this process, the nitrate present in sewage is reduced by
denitrifying bacteria to nitrogen and nitrous oxide gases which
are allowed to escape into the atmosphere. In order to satisfy
the growth and energy requirements of the bacteria, methanol
in excess of 25 to 35% must be added as a source of carbon.
The removal effi ciency ranges from 60 to 95%. The
major advantage to anaerobic denitrifi cation is that there are
no waste products requiring disposal. This process is still

primarily in the experimental stage at this date.
Ammonia Stripping
Ammonia stripping is an aeration process modifi ed by fi rst
raising the pH of the wastewater above 10.0. At this pH the
© 2006 by Taylor & Francis Group, LLC
398 EUTROPHICATION
ammonia nitrogen present is readily liberated as a gas and
is absorbed into the atmosphere. Aeration is usually accom-
plished in a packed tray tower through which air is blown.
This process is suited to raw sewage where most of the
nitrogen is either in the ammonia form or may be readily
converted to that form. In secondary treatment processes
the conversion of ammonia nitrogen to nitrate nitrogen can
be retarded by maintaining a high organic loading rate on the
secondary process.
Effi ciency of nitrogen removal by ammonia stripping is
excellent with 80 to 98% reported. There is also the advantage
that there are no waste materials which must be disposed of.
PHOSPHORUS REMOVAL
Chemical Precipitation
Precipitation of phosphorus in wastewater may be accom-
plished by the addition of such coagulants as lime, alum,
ferric salts and polyelectrolytes either in the primary or sec-
ondary state of treatment, or as a separate operation in ter-
tiary treatment. In general, large doses in the order of 200
to 400 ppm of coagulant are required. However, subsequent
coagulation and sedimentation may reduce total phosphates
to as low as 0.5 ppm, as in the case of lime. Doses of alum
of about 100 to 200 ppm have reportedly reduced orthophos-
phates to less than 1.0 ppm.

Phosphorus removal by chemical coagulation generally
is effi cient with removals in the order of 90 to 95% reported.
Additional benefi ts are gained in the process by a reduction
in B.O.D. to a value of less than 1.0 ppm. Both installation
and chemical costs are high, however, and the sludges pro-
duced are both voluminous and diffi cult to dewater.
Sorption
Sorption is the process of passing wastewater down-
ward through a column of activated alumina whereby the
common form of phosphate are removed by ionic attraction.
Regeneration of the media is accomplished by backwash-
ing with sodium hydroxide followed by acidifi cation with
nitric acid.
Contrary to alum treatment, this process has the advantage
in that sulfate ions are removed and thus the sulfate concentra-
tion is not increased. Since no salts are added, the pH and the
calcium ion concentration remain unchanged. The process is
effi cient with more than 99% removal reported. The process
should be limited to wastewater with a moderate amount of
solids so as not to clog the media.
REMOVAL OF NITROGEN AND PHOSPHORUS
Biological (secondary) Treatment
In the secondary method of sewage treatment, bacteria uti-
lize soluble organic materials and transform them into more
stable and products. In the process nitrogen and phosphorus
are removed from the wastes, utilized to build new cellular
materials, and the excess is stored within the cell for future
use. For each pound of new cellular material produced,
assuming the material to be in the form of C
5

H
7
NO
2
, about
0.13 pounds of nitrogen and about 0.026 pounds of phospho-
rus would be removed from the sewage. In the actual opera-
tion of this process not all of this nitrogen is removed unless
additional energy material in the form of carbohydrates
is added. Although it may be possible to eliminate all the
nitrogen, a considerable amount of soluble phosphorus may
remain, possibly because of the high ratio of phosphorus
to nitrogen in sewage, attributable to synthetic detergents.
Much of this phosphorus can be removed by absorption on
activated sludge fl oc when it is later separated and removed.
This process offers a 30 to 50% removal of nitrogen and
about a 20 to 40% removal of phosphorus without the spe-
cial addition of carbohydrates.
Reverse Osmosis
The process of reverse osmosis consists of passing wastewa-
ter, under pressures as high as 750 psi, through a cellulose
acetate membrane. The result is the separation of water and all
ions dissolved therein. In actual practice the process has been
plagued with diffi culties primarily due to membrane fouling
or premature failure of the membrane. In addition some nitrate
and phosphate ions escape through the membrane.
Removal effi ciency ranges from between 65 to 95% (for
nitrogen).
Electrodialysis
Like reverse osmosis, electrodialysis is a non-selective

demineralization process which removes all ions which
would include the nitrate and phosphate ions. Essentially
an electric current is used in conjunction with a membrane
inserted in the line of current fl ow to separate the cations
and anions.
The problems that have developed in the operation of
this process include membrane clogging and precipitation
of low-solubility salts of the membrane. Acidifi cation of the
water and removal of some of the solids prior to treatment
has been effective in minimizing these problems, although it
adds to the cost.
Removal effi ciency ranges from between 30 to 50% (for
nitrogen).
Ion Exchange
In the ion exchange process wastewater is passed through
a media bed which removes both anionic phosphorus and
anionic nitrogen ions and replaces them with another ion
from the media. Regeneration of ion exchangers is com-
monly accomplished with inexpensive sodium chloride, and
frequently the salt is salvaged by recycling the backwash
water.
Diffi culties in the process may be caused by fouling of
the exchange resin due to organic material and reduction in
© 2006 by Taylor & Francis Group, LLC
EUTROPHICATION 399
the exchange capacity due to sulfates and other ions. The
former may be reduced by removing the organic matter from
the resin with sodium hydroxide, hydrochloric acid, methanol
and bentonite.
The effi ciency and cost of nitrogen and phosphorus

removal by ion exchange depends largely on the degree of
pretreatment and/or the quality of the water to be treated.
Removal of nitrogen ranges from between 80 to 92%.
A number of ions exchange resins are available for nitro-
gen removal alone. These include zeolites, strong base anion
resins (Amberlite IRA-410) and nuclear sulfonic cation
resins (Nalcite HCR and Amberlite IR-120).
Algae Harvesting
A two-phase process which involves (1) growing algae in
special shallow wastewater ponds where they feed on the
absorb nutrients, and (2) removing the algae which then con-
tain the nutrients within their systems. Algal predominance
will depend upon the type of nutrients available and the con-
centrations. Frequently the fl agellates euglena and chlorella
will predominate where the nutrient concentration is high,
and fi lamentous green algae such as spirogyra, vaucheria
and ulothrix will predominate where the nutrient concentra-
tion is more moderate. The most desirable algae would be
those that are large, those that would grow rapidly and those
that would require vast quantities of food for energy, such
as the swimming algae. In addition to removing nutrients,
algae produce oxygen which reduces the B.O.D., and certain
fl agellates which ingest inorganic solids, are able to stabilize
some of the organic material.
One of the major diffi culties experienced with this
process involves the harvesting procedure. A number of
methods have been tried which include screening, settling,
centrifuging and chemical screening. All have been found
to present some form of diffi culty, although it appears from
the standpoint of performance and economy, the screening

method may be the least unsatisfactory. Another problem is
that complete nitrogen removal is seldom achieved unless a
carbon source, such as carbon dioxide or methanol, is sup-
plied. Still another problem is the need for disposing of a
huge, sloppy mass of slimy and odoriferous dead algae.
Pilot studies show that a high-rate continuous-fl ow pro-
cess is feasible when light is not limiting, and that orthophos-
phate concentrations can be reduced 90% to less than 1.0
ppm within 6 to 12 hours. Nitrogen removal is variable with
estimates ranging from 40 to 90% effi ciency depending upon
the feed rate, pond design, and climatic conditions. The major
drawbacks to this process aside from those mentioned, are the
large land requirements needed and the necessity to rely on
climatic conditions. In the latter case, artifi cial illumination
may prove of value depending on power rates in the area.
CONCLUSIONS AND OBSERVATIONS
It might be concluded after examining a vast array of mate-
rial that the bio-physical and bio-chemical factors which
affect algae are extremely complex, and it is diffi cult to pre-
dict, with exacting certainty, future events relating to algal
growth. The complexity is greatly magnifi ed by the interac-
tion which apparently exists between the numerous factors
themselves. When these factors are examined and evaluated,
the conclusions reached by one observer are not always in
complete agreement, or may disagree entirely, with the con-
clusions reached by another observer. Commonly, specifi c
organisms may produce different reactions because of their
phase of life, seasonal changes, or because of other complex
and little understood metabolic functions.
In few areas is there less accord than in the literature

written about algae. (See references—The Physical Nature
of Algae, #1 to 33, at the end of this article.) Authorities
vary sharply in their opinions as to classifi cation, physical
descriptions, toxicity thresholds, etc. When this disagree-
ment is added to the previously expressed uncertainties, it
can be seen that our current knowledge is subject to various
interpretations. Thus it is evident that there is a need for more
work; work to develop new and useful information which
will receive universal acceptance and which will clarify and
expand our present knowledge. Conferences dealing with
unique and local problems involving algae and eutrophica-
tion are ongoing. (See References—Eutrophication, #53, 55,
56 and 57, at the end of this article.)
ACKNOWLEDGMENTS
My sincere appreciation is extended to Mr. Robert G. Wieland
who helped in the preparation of the manuscript and to the
Research Foundation of the Newark College of Engineering
for their aid in the typing of the manuscript.
REFERENCES
THE PHYSICAL NATURE OF ALGAE
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Engineering Center, Cincinnati, Ohio, Public Health Service Pub. No.
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2. Babbitt, H.E. and J.J. Doland, Water Supply Engineering, McGraw-Hill,
N.Y., 1955, p. 457.
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face waters, Jour. of the Amer. Water Works Assn., Jan., 1964, p. 61.
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9. See Reference 1. above, pp. 41 and 42.
10. See Reference 1. above, p. 38.
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26. See Reference 1, above, p. 57.
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29. See Reference 17, above, p. 57.
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31. See Reference 25, above, pp. 112–113.
32. See Reference 1, above, p. 65.
33. See Reference 25, above, p. 111.

EUTROPHICATION
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ROBERT DRESNACK
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