Here are some links you may be interested in...
Great Lakes Water Quality Agreement
Case
Studies on the Great Lakes Water Quality With Regards to Eutrophication
The Phosphorous Cycle (Figure 2.)
The Nitrogen Cycle (Figure 1.)
Page Links to My
Paper:
Introduction
What is Eutrophication?
Causes of Eutrophication
Nitrogen and Phosphorous
Agriculture and Eutrophication
Wastewater and Eutrophication
Effects of Eutrophication
Control Strategies
Engineering Strategies
Management/Legal Aspects
Conclusion
References
Introduction
Eutrophication is the term used to express the ageing of a lake. It occurs naturally in the environment and the associated time span can be measured in the geological timeframe. However in the last few centuries' man has rapidly increased his use of nutrients, especially in agricultural fertilizers and detergents, many of which end up in waterways and accelerate the process of Eutrophication (Hutchinson, 1970). This gives way to the term 'cultural eutrophication', which applies to anthropogenic sources of this process.
As the population continues to increase, a need for more sustainable agricultural practices invokes more technology and fertilization procedures to increase yield. With these fertilizers come nutrients such as phosphate and nitrogen, which can result in the acceleration of the Eutrophication process.
In addition to agricultural processes, wastewater treatment plays a major role as well as phosphate removal from detergents. These sources will be examined as well as controls and management strategies that have been implemented to control the problem of eutrophic lakes.
What is Eutrophication?
Although decreasing water quality can be initiated by a variety of chemical species, the process of eutrophication describes nutrient enrichment of the water body. A series of three categories are used to describe a water bodies tropic status are used. Theses categories are as follows, oligotrophic; mesotrophic and finally eutrophic (Henderson-Sellers, 1987). From an initially nutrient poor (oligotrophic) condition, addition of nutrients such as nitrogen and phosphorous can gradually build up in the lake concentrations in both the water column and sediments (mesotrophic) until a condition of detrimental water quality is achieved (eutrophic) (Henderson-Sellers, 1987).
The immediate consequences of increased nutrient loadings to a lake or reservoir are to encourage plant and subsequently animal growth. Due to the increase in nutrients, mainly phosphorus and nitrogen, that are normally limited, algal growth is stimulated. As this growth proceeds the organisms promote anoxic conditions, using up the oxygen present in the water as they thrive and decay (Klaff, 2002). Light is also restricted to the bottom sections of the water body as the algae tends to form an algal bloom that serves as a "cover" over the surface of the water, which in turn restricts plant productivity deeper in the lake or reservoir. Both of these processes deplete the oxygen need for healthy lakes and in turn become detrimental to fish and wildlife populations, as some of the algae give off toxins as they decompose in the water making it unfit for consumption (Muir, 2001).
Eutrophication is essentially regarded as being a process, which occurs in lenthic or slow moving lakes or reservoirs. There are many causes and indicators for the eutrophic status of lakes but can be grouped into a few main categories discussed below.
Causes of Eutrophication
The main causes of the Eutrophication of water systems can be put into the following categories as follows. Sediments and thermal stratification can be attributed to the causes, with agricultural run-off from fertilizers and manure, containing nitrates and phosphates, and discharge of partially treated or untreated sewage or phosphate containing detergents being the major causes (Henderson-Sellers, 1987).
Other sources can include run-off from erosion and weathering of rocks as can be seen through the phosphate cycle, as well as from the run-off following mining or industrial processes (Cooke, 1973).
SEDIMENTS
Sediments such as sand, silt, and clay, also add to
eutrophication. As
sediments are eroded, the particles are carried in suspension, reducing
light penetration and photosynthesis. Phosphorus make attach onto these
particles and when they become disturbed by erosion are released into the
water making phosphorus a long term problem (Muir, 2001).
Thus, sediments provide a major reservoir of phosphorus, as they can be
transported great distances furthering their role in Eutrophication.
THERMAL STRATIFICATION
Thermal Stratification, or layering, occurs in many lakes.
Whether or not a lake stratifies depends on a number of factors: the shape and depth of
the lake, the amount of wind, and the orientation of the lake (Klaff,
2002). Since the maximum density of water occurs at 4
DISSOLVED OXYGEN
Eutrophication brings about increased dissolved oxygen
consumption in
lakes progressively lowering dissolved oxygen concentrations. Eutrophic
lakes covered with ice and snow, wetlands and northern rivers receiving
large quantities of organic matter from their ice and snow, exhibit
substantial DO losses during the winter (Likens, 1972).
At higher temperatures, water can hold less oxygen when saturated which
results in less oxygen directly available and a lower percentage of the
metabolic demand being satisfied, since the metabolic rate of organisms
increases with increasing temperature (Klaff, 2002).
NUTRIENTS
Nutrients are those materials which organisms use for growth and
reproduction. The nutrient status of any environment is determined by
the supply of nutrients from its catchments, which in turn is affected by
geology (Likens, 1972). Therefore waters will vary in their natural
nutrient status. These changes can be made through changes to the
catchments such as climate, agricultural wastes, which contain man made
sources of nutrients from fertilizers (Henderson-Sellers, 1987).
There are two main sources of nutrients. Point source, for example
wastewater, and non-point sources which contain agricultural sources.
Nutrients can be further split up into organic, which is incorporated in
organic structures and contain carbon, and inorganic, which are
unassociated with carbon compounds in their elemental state (Williams, 1977).
Primary producers assimilate inorganic nutrients and use them in their
life processes, converting them to organic forms. When an organism dies
or is consumed, these nutrients will ultimately revert to their inorganic
form by the process of decomposition and mineralization and will enter
storage until used by another organism (Henderson-Sellers, 1987).
In most aquatic systems it is found to be either phosphorous or to a
lesser extent, nitrogen that is the limiting nutrient.
In a phosphorous limited system, reduction of phosphorous levels
leads to a restriction on plant and algal growth. In this condition the
Eutrophication process can be considered retarded or reversed.
A nitrogen-limited system is often considered to be a greater problem
than a phosphorous limited environment since the sources of this nutrient
are harder to control.
Nitrogen and Phosphorous
Nitrogen and Phosphorus are commonly the elements in greatest demand by
plants and microbes relative to supply and are therefore crucial in
predicting algal blooms in eutrophied waters.
Nitrogen
Nitrogen plays a central role in inland waters and plant life, as it is
needed for growth and the building of proteins (Pidwirny, 2001). Algae
are able to use nitrogen in its molecular form and convert it into forms
that can be utilized by plans such as nitrates (Eckert, 1995). Because
nitrogen, in the form of ammonia and nitrates, acts as a plant nutrient,
it also causes eutrophication.
As aquatic plants and animals die, bacteria break down their large
protein molecules into ammonia. Ammonia is then oxidized, combined with
oxygen, by bacteria to form nitrites and nitrates (Pidwirny, 2001). For
a more detailed look at the nitrogen cycling that occurs to produce these
different forms see figure 1 below.
Figure 1. The Nitrogen Cycle (Pidwirny, 2001)
Nitrogen release rates from catchments to receiving rivers and nitrate
concentrations in the rivers rise with increasing human density (Klaff,
2002). Human density is used as an approximation of organic waste
production, soil quality, and agricultural activity (Klaff, 2002).
However, where the nitrogen plus phosphorous supply rate to
waterways is very high, as in rich agricultural areas, the receiving rivers, lakes,
and estuaries exhibit extreme eutrophication. For example the
intensively farmed drainage basin to the Gulf of Mexico is so high that
the estuary exhibits periodic sediment anoxia, toxic algal blooms, and
the killing of fish populations (Klaff, 2002).
Phosphorous
Phosphorus is one of the top ten elements present in the earth's upper
crust, and has many applications. Phosphate groups are a basic
structural element of nucleic acids, phospholipids and are used as a part
of molecules in photosynthesis, for example adenosine tri-phosphate
(Williams, 1977). It is assimilated from the environment through
decomposition and photosynthesis.
The major anthropogenic sources of phosphorus come from agricultural
practices, wastewater and many other uses including, the manufacture of
soaps and detergents, animal feed, food products and medicines and
electroplating and polishing of metals (Cooke, 1973).
Its cycling in the environment is essentially a one-way flow because
unlike nitrogen, it has no gaseous return phase. When plants and animals
die, bacteria decompose, releasing some of the phosphorus back into the
soil. Once in the soil, phosphorous can be moved 100s to 1,000s of miles
from were they were released by riding through streams and rivers (Cooke,
1973). So the water cycle also plays a key role of moving phosphorus from
ecosystem to ecosystem. Refer to Figure 2. (Below)
Figure 2. The Phosphorus Cycle. (No Author Specified, No Date)
It is now widely recognized that reducing the input of plant nutrients,
especially nitrogen and phosphorus, can control the eutrophication of
fresh water. Of these two elements phosphorus is considered in shortest
supply for algal growth, while the control of nitrogen is more difficult
and more expensive in wastewater treatment and removal (Klaff, 2002).
Agriculture and
Eutrophication
Nutrients from agricultural systems enter natural water systems in
three main ways: through drainage water, in eroded soil and through animal
waste products (Biggar and Corey, 1970).
Drainage plays an important role in agriculture, as the moisture
content of soil is very important in crop propagation techniques, as it is the
nutrient transport medium from the soil to the crop (Biggar and Corey, 1970).
Most of the soluble nutrients that get into lakes and streams from rural
areas are first dissolved in water and then moved in solution to the
waterways (Henderson-Sellers, 1987). This dissolved form comes from the
release of phosphorus from soil and plant material. Some nutrients may
also be suspended in particulate matter and later converted to soluble
forms in the water system, but most dissolved phosphorus is immediately
available for biological uptake (Biggar and Corey, 1970).
In the water that percolates through the soil the soluble phosphorous
concentration is usually very low because the phosphorous precipitates in
the subsoil. Therefore, most of the soluble phosphorous should reach the
waterways via surface runoff (Biggar and Corey, 1970).
Commercial fertilizers provide the major portion of the common plant
nutrients - nitrogen, phosphorus, and potassium, used in crop production.
The remainder is supplied through animal manure and natural sources such
as soil, legumes, which are nitrogen fixating, and precipitation
processes (Van Wazer, 1977).
Nitrogen, particularly in the form of nitrate, is highly soluble in
water, and consequently highly mobile. Application of nitrogen at rates
over and above the ability of the crop to use it results in losses of
that nitrogen, normally by leaching (Eckert, 1995).
Manure or organic wastes from agriculture are a very valuable and
historic resource for improving soil structure and agriculture and can be
considered a fertilizer as well. It must be given the same amount of
care when applied to fields however, because it is more labour intensive
in application giving rise to compaction, which may result in runoff.
The water present also makes them highly mobile (Eckert, 1995).
Good fertilizer practices, including split applications, and delaying
applications when soils are wet, or if heavy rain is forecast, can
prevent excessive leaching of fertilizers (Eckert, 1995). The economic
loss to the farmer and the consequent effect on the environment can then
be predicted.
Wastewater and
Eutrophication
Eutrophication will be enhanced by nutrients contained in wastewater
sources which may be deemed organic, including the food industry, or
inorganic which concerns washing processes and detergents.
Wastewater can be further separated into two main sources, which include
domestic and industrial wastewater. Domestic wastewater, or sewage,
derives the majority of its nutrients from feces and urine, with food
wastes and detergents also contributing significant amounts, although the
composition will vary with regards to geographic location around the
world (Henderson-Sellers, 1987).
For an example of how much phosphorus wastewater contains, the cit of
Toronto can be used as an example. The statistics from their wastewater
treatment plant show that the amount of phosphorus in the plant's
effluent discharged to the lake is no more than 1 mg/L. The average total
phosphorous concentration in wastewater entering this plant is about 6
mg/L. (City of Toronto, 2000).
Industrial wastewater is highly variable in quantity and quality as it
may contain hazardous elements such as heavy metals. Once it is used it
may be disposed of in a variety of ways including re-usage for other
processes, discharge into lakes or reservoirs, for example mine tailing
ponds, and it may go directly to the municipal sewer system (Weibel, 1970).
In Ontario the sewage is "cleaned" at the sewage treatment plant and then
is released into a lake river or the ground. (Kapitain, 2002).
There are five main types of sewage treatment in Ontario. The first
stage or primary treatment involves the screening to remove large solids. In the
secondary treatment aeration tanks are employed and bacteria break down
any organic compounds. This stage also incorporates a metal salt
solution, which removes phosphorus that would otherwise go on to promote
algal growth and potentially, Eutrophication. In the tertiary stage of
treatment sand filtration is used to ensure a higher quality of
effluent. Lagoons and commercial septic systems are also commonly found
in Ontario (Kapitan, 2002).
The ministry of the environment policy 08-04--"Policy to Govern the
Provision, Operation and Assessment of Phosphorus Removal Facilities at
Municipal, Institutional and Private Sewage Treatment Works"--describes
the requirements for the removal of phosphorus from effluents (Kapitain,
2002).
Effects of Eutrophication
Eutrophication can have both temporary and more irreversible effects on
aquatic ecosystems. Significant fluctuations in dissolved oxygen
concentrations between day and night can occur in waters where there is
enhanced plant growth (Muir, 2001). This can cause problems in the early
morning when low oxygen levels, the result of plant respiration, may lead
to the death of invertebrates and fish. This process can be compounded
when algal blooms, through their decay, further reduce the oxygen content
of water. (Klaff, 2002). The growth and/or decay of bottom-dwelling
macro-algae can also lead to the deoxygenating of sediments.
Certain algal species, particularly freshwater blue-green algae, can
produce toxins, which may seriously affect the health of mammals,
including humans, fish and birds (Muir, 2001). This occurs either through
the food chain, through contact with, or ingestion of, the algae. Algal
species also cause fish deaths, for example by physically clogging or
damaging gills, and causing asphyxiation. Eutrophication ultimately
detracts from biodiversity, through the dominance of nutrient-tolerant
plants and algal species. These tend to displace more sensitive species
of higher conservation value, changing the structure of ecological
communities (Muir, 2001).
Eutrophication can also adversely affect a wide variety of water uses
such as water supply (e.g. algae clogging filters in treatment works),
livestock watering, irrigation, fisheries, navigation, water sports,
angling and nature conservation (Hutchinson, 1970). It can give rise to
undesirable aesthetic impacts in the form of increased turbidity,
discolouration, unpleasant odours, slimes and foam formation (Klaff,
2002).
Control Strategies
There are many techniques being used around the world to control
eutrophication processes.
Wastewater treatment plants remove the eutrophic enhancing phosphorous
and sometimes nitrogen before releasing it into the waterways as we have
seen in previous examples.
Agriculture nutrient management techniques can be employed to prevent
runoff and erosion by timing out the deposition of fertilizer, moderating
fertilizer use and maintaining drainage systems (Eckert, 1995). This may
serve to be beneficial to the environment but also economically viable to
the farmer.
Chemicals may also be used to help reduce and control existing
eutrophic conditions. They may be sprayed over the surface of the lake or
injected directly inside, which are intended to precipitate nutrients or
convert them into a form unavailable to aquatic life, such as aluminum's
effect on phosphorus. "Algaecides" may also be used to kill of existing
biomass, such as copper sulfate usage, but have the disadvantage of
having copper remain in the system and the possible health effects on
aquatic life from its deposition (Henderson-Sellers, 1987).
Engineering Srategies
Dredging
As sediments play a big role in the transfer of nutrients to the water
column, their removal often forms an integral part of lake restoration
programs. As well as nutrient removal, dredging may also create further
benefits such as the deepening of lakes. The major disadvantage of this
process however, is the ever-looming costs it creates to implement.
Because lakes become more eutrophic as they age over time sediments
nearest the bottom remain nutrient poor and the surface sediments are
rich in organics (Likens, 1972). Removal of these top sediments through
dredging exposes the nutrient poor layering and curtails the nutrient
cycling capacity (Henderson-Sellers, 1987).
A survey and sample test should be done before any dredging
procedure is done so that an accidental layer of sediments rich in
organic matter is not exposed, and sedimentation rates assessed.
Two main methods are used; hydraulic dredging and bucket dredging.
Through hydraulic dredging a vacuum cleaner principle is employed. The
surface layer of sediment is sucked up, where it is treated and returned
to the lake, the organic material used as a soil additive in some cases.
(Henderson-Sellers, 1987).
The second type, bucket dredging, involves skimming the surface
sediments into a bucket type device, where they proceed to treatment. This method
is more cost efficient than the first but it creates more ecological
disturbance to the system.
Deepening
Sediment stirring can be a problem for eutrophication in shallow lakes,
as it enhances the release of phosphorus held in these sediments. This
gives way to the process of lake deepening. Which may allow for a lesser
degree of stirring by factors such as wind. It may also increase the
amount of oxygen content through volume and reduce the impact of nutrient
inputs.
Deepening can be achieved by increasing the water level or lowering the
lakebed itself, accomplished by dredging methods (Klaff, 2002).
Aeration
Aeration of water bodies can be employed to counter the oxygen depleted
conditions of Eutrophication where sufficient nutrient removal techniques
cannot be employed. Aesthetic conditions may warrant aeration as well to
restore the lake for recreation activity and quality of water may be a
proviso for the costs associated with this system.
There are several techniques used as well as a wide array of machinery
employed. One of the most basic techniques involves the
de-stratification of the lake through circulation or a bubbled air system
placed on the bottom of the lake. The disadvantages of artificial
circulation that can occur contain the homogenization of the water
column, which may impact on certain fish populations that thrive in cold
water regions (Klaff, 2002).
Due to aeration being a relatively new technique for the control and
restoration of aquatic systems, more research needs to be conducted to
assess effects on biota and chemistry of the lake ecosystem.
Lake Bottom Sealing
Lake bottom sealing can also be introduced, although it only covers up
the existing problem. A layer of heavy plastic is laid upon ice covered
waters and covered with sediment that will eventually act as the new lake
floor. In the summer when the ice melts the sediment covered "sheet"
will float to the bottom and cover the existing organic sediments
susceptible to eutrophic conditions (Henderson-Sellers, 1987).
This technique may be complicated on lakes that do not freeze in
wintertime, causing disturbance and uneven deposition.
Management/Legal Aspects
In 1972 Congress passed the Federal Water Pollution Control Act,
commonly known as the Clean Water Act. The goal of the Act was to eliminate the
discharge of pollutants into rivers, lakes, streams and other waterways,
and to attain, wherever possible, waters deemed "fishable and swimmable."
(Environment Canada, 2001). Discharge of pollutants directly into a
river, lake, or stream, is described as point source pollution (as
opposed to indirect, or nonpoint source pollution) and considerable
progress has been made in preventing this type of pollution. According to
the EPA's progress report on the twenty-five year history of the Clean
Water Act, two-thirds of surveyed waters are now safe for fishing and
swimming. Non-point source pollution continues to be a concern in many
areas (Environment Canada, 2001).
Great Lakes Water Quality Agreement
"The Agreement, first signed in 1972 and renewed in 1978, expresses the
commitment of each country to restore and maintain the chemical, physical
and biological integrity of the Great Lakes Basin Ecosystem and includes
a number of objectives and guidelines to achieve these
goals."(International Joint Commission, 2002). "It reaffirms the rights
and obligation of Canada and the United States under the Boundary Waters
Treaty and has become a major focus of Commission activity."
(International Joint Commission, 2002). The Agreement monitored by the
International Joint Commission, covers all the Great Lakes and the
international portion of the St. Lawrence River. Its primary purpose in
1972 was to stem and reverse eutrophication in the lower Great Lakes. In
it's revised (1978) and amended (1987) forms, the Great Lakes Water
Quality Agreement focuses on persistent, toxic, chemicals (International
Joint Commision, 2002).
Table 1. Illustrates the phosphorus loadings present in 1976, and future
loadings that are to be achieved within eighteen months of the agreement
based on recommendations made by the I.JC.
Basin 1976 PhosphorusLoad in Metric TonnesPer Year FuturePhosphorus
Loadin Metric TonnesPer Year
Lake Superior 3600 3400*
Lake Michigan 6700 5600*
Main Lake Huron 3000 2800
Georgian Bay 630 600*
North Channel 550 520*
Saginaw Bay 870 440*
Lake Erie 20000 11000**
Lake Ontario 11000 7000**
Table 1. Phosphorus Loadings in the Great Lakes Including Past and
Future Amounts. (International Joint Commission, 2002).
The Canadian Environmental Protection Act, 1999, also contains
pollution prevention measures and water pollution standards regarding phosphates in
wastewater. More information about this act can be found through
Environment Canada.
According to a study by Environment Canada loadings of municipal
phosphorus to Lakes Erie and Ontario have been reduced by almost 80%.
(Environment Canada, 1999). Reductions in the amount of algae have also
been noted and a great success story can be told of lake Erie.
Conclusion
As our society is now evolving towards a more sustainable way of living
we are incorporating more of an environmentally friendly outlook. There
have been so many technological advances in the past years, and with that
we gained knowledge. Understanding the Eutrophication process was half
the battle and we are already closing in on controlling inputs of
excessive nutrients along with hazardous chemicals. Phosphate reduction
in detergents, policies implemented by the government for sewage
treatment and agricultural progress are all steps in the right
direction. Cultural eutrophication may not be a thing of the past but
with the right ecological mindset we can make it so.
References
Biggar, J.W. and Corey, R.B. 1970. Agricultural Drainage and
Eutrophication.
Eutrophication: Causes, Consequences and Correctives. University of
Wisconson.
City of Toronto. 2000. Ashbridges Bay Treatment Plant.
http://www.city.toronto.on.ca/sewers/mtp.htm Accessed: March 11, 2002
Cooke, G.W. 1973. Sinificange of man-made sources of phosphorous:
fertilizers and
farming. The phosphorus involved in agricultural systems and possabilites
of its
movement into natural water. Phosphorus in Fresh Water and the Marine
Environment. Pergamon Press, New York.
Eckert, D.J. 1995. Nitrates in Surface Water. http://ohioonline.osu.edu/agf-
fact/0204.html. Accessed: March 8, 2002
Environment Canada. 2001. Water Legislation.
http://www.ec.gc.ca/water/index.htm
Accessed March 18, 2002.
Environment Canada. 1999. Measuring Progress.
http://www.on.ec.gc.ca/glimr/data/celebrate-glwqa/progress.html Acessed
March
11, 2002.
Henderson-Sellers, B. 1987. Decaying Lakes. John Wiley & Sons Ltd. Great
Britain.
Hutchinson, G.E. 1970. Eutrophication, Past and Present. Eutrophication:
Causes,
Consequences and Correctives. University of Wisconson.
International Joint Commission. 2002. http://www.ijc.org/ijcweb-e.html
Accessed March
12, 2002.
Kapitain, J. 2002. Ontario's Sewage Treatment Plants and their effect on
the Environment.
http://www.nextcity.com/EnvironmentProbe/pubs/ev527.htm Accessed March
13,
2002.
Klaff, J. 2002. Limnology. Prentice-Hall, Inc. New Jersey
Lewin, H.V. 1973. Phosphates in Sewage and Sewage Treatment. .
Phosphorus in Fresh
Water and the Marine Environment. Pergamon Press, New York.
Likens, G.E. 1972. Eutrophication and aquatic ecosystems. Nutrients and
Eutrophication:
the Limiting nutrient controversy. Allen Press, Inc. Kansas.
Muir, Patricia. 2001. Eutrophication.
http://www.orst.edu/instruction/bi301/eutrophi.htm
Accessed March 13, 2002.
No author specified. No date. The Phosphorus Cycle.
http://www.halfhollowhills.k12.ny.us/Prog/Scie/Apbioweb?phosphoroud_cycle. Acessed March 12, 2002.
Pidwirny, M.J. 2001. The Nitrogen Cycle.
http://www.geog.ouc.bc.ca/physgeog/contents/9s.html Accessed: March 12,
2002.
Van Wazer, J.B. 1977. Phosphorus and Mankind's Problems Today.
Phosphorus in the
Environment: It's Chemistry and Biochemistry. Ciba Foundation Symposium 57.
Williams, R.J.P. 1977. Phosphorus: A General Introduction. Phosphorus in
the
Environment: It's Chemistry and Biochemistry. Ciba Foundation Symposium 57.
Weibel, S.R. 1970. Urban Drainage as a Factor in Eutrophication.
Eutrophication:
Causes, Consequences and Correctives. University of Wisconson.
.
Sediments such as sand, silt, and clay, also add to
eutrophication. As
sediments are eroded, the particles are carried in suspension, reducing
light penetration and photosynthesis. Phosphorus make attach onto these
particles and when they become disturbed by erosion are released into the
water making phosphorus a long term problem (Muir, 2001).
Thus, sediments provide a major reservoir of phosphorus, as they can be
transported great distances furthering their role in Eutrophication.
THERMAL STRATIFICATION
Thermal Stratification, or layering, occurs in many lakes.
Whether or not a lake stratifies depends on a number of factors: the shape and depth of
the lake, the amount of wind, and the orientation of the lake (Klaff,
2002). Since the maximum density of water occurs at 4
DISSOLVED OXYGEN
Eutrophication brings about increased dissolved oxygen
consumption in
lakes progressively lowering dissolved oxygen concentrations. Eutrophic
lakes covered with ice and snow, wetlands and northern rivers receiving
large quantities of organic matter from their ice and snow, exhibit
substantial DO losses during the winter (Likens, 1972).
At higher temperatures, water can hold less oxygen when saturated which
results in less oxygen directly available and a lower percentage of the
metabolic demand being satisfied, since the metabolic rate of organisms
increases with increasing temperature (Klaff, 2002).
NUTRIENTS
Nutrients are those materials which organisms use for growth and
reproduction. The nutrient status of any environment is determined by
the supply of nutrients from its catchments, which in turn is affected by
geology (Likens, 1972). Therefore waters will vary in their natural
nutrient status. These changes can be made through changes to the
catchments such as climate, agricultural wastes, which contain man made
sources of nutrients from fertilizers (Henderson-Sellers, 1987).
There are two main sources of nutrients. Point source, for example
wastewater, and non-point sources which contain agricultural sources.
Nutrients can be further split up into organic, which is incorporated in
organic structures and contain carbon, and inorganic, which are
unassociated with carbon compounds in their elemental state (Williams, 1977).
Primary producers assimilate inorganic nutrients and use them in their
life processes, converting them to organic forms. When an organism dies
or is consumed, these nutrients will ultimately revert to their inorganic
form by the process of decomposition and mineralization and will enter
storage until used by another organism (Henderson-Sellers, 1987).
In most aquatic systems it is found to be either phosphorous or to a
lesser extent, nitrogen that is the limiting nutrient.
In a phosphorous limited system, reduction of phosphorous levels
leads to a restriction on plant and algal growth. In this condition the
Eutrophication process can be considered retarded or reversed.
A nitrogen-limited system is often considered to be a greater problem
than a phosphorous limited environment since the sources of this nutrient
are harder to control.
Nitrogen and Phosphorous
Nitrogen and Phosphorus are commonly the elements in greatest demand by
plants and microbes relative to supply and are therefore crucial in
predicting algal blooms in eutrophied waters.
Nitrogen
Nitrogen plays a central role in inland waters and plant life, as it is
needed for growth and the building of proteins (Pidwirny, 2001). Algae
are able to use nitrogen in its molecular form and convert it into forms
that can be utilized by plans such as nitrates (Eckert, 1995). Because
nitrogen, in the form of ammonia and nitrates, acts as a plant nutrient,
it also causes eutrophication.
As aquatic plants and animals die, bacteria break down their large
protein molecules into ammonia. Ammonia is then oxidized, combined with
oxygen, by bacteria to form nitrites and nitrates (Pidwirny, 2001). For
a more detailed look at the nitrogen cycling that occurs to produce these
different forms see figure 1 below.
Figure 1. The Nitrogen Cycle (Pidwirny, 2001)
Nitrogen release rates from catchments to receiving rivers and nitrate
concentrations in the rivers rise with increasing human density (Klaff,
2002). Human density is used as an approximation of organic waste
production, soil quality, and agricultural activity (Klaff, 2002).
However, where the nitrogen plus phosphorous supply rate to
waterways is very high, as in rich agricultural areas, the receiving rivers, lakes,
and estuaries exhibit extreme eutrophication. For example the
intensively farmed drainage basin to the Gulf of Mexico is so high that
the estuary exhibits periodic sediment anoxia, toxic algal blooms, and
the killing of fish populations (Klaff, 2002).
Phosphorous
Phosphorus is one of the top ten elements present in the earth's upper
crust, and has many applications. Phosphate groups are a basic
structural element of nucleic acids, phospholipids and are used as a part
of molecules in photosynthesis, for example adenosine tri-phosphate
(Williams, 1977). It is assimilated from the environment through
decomposition and photosynthesis.
The major anthropogenic sources of phosphorus come from agricultural
practices, wastewater and many other uses including, the manufacture of
soaps and detergents, animal feed, food products and medicines and
electroplating and polishing of metals (Cooke, 1973).
Its cycling in the environment is essentially a one-way flow because
unlike nitrogen, it has no gaseous return phase. When plants and animals
die, bacteria decompose, releasing some of the phosphorus back into the
soil. Once in the soil, phosphorous can be moved 100s to 1,000s of miles
from were they were released by riding through streams and rivers (Cooke,
1973). So the water cycle also plays a key role of moving phosphorus from
ecosystem to ecosystem. Refer to Figure 2. (Below)
Figure 2. The Phosphorus Cycle. (No Author Specified, No Date)
It is now widely recognized that reducing the input of plant nutrients,
especially nitrogen and phosphorus, can control the eutrophication of
fresh water. Of these two elements phosphorus is considered in shortest
supply for algal growth, while the control of nitrogen is more difficult
and more expensive in wastewater treatment and removal (Klaff, 2002).
Agriculture and
Eutrophication
Nutrients from agricultural systems enter natural water systems in
three main ways: through drainage water, in eroded soil and through animal
waste products (Biggar and Corey, 1970).
Drainage plays an important role in agriculture, as the moisture
content of soil is very important in crop propagation techniques, as it is the
nutrient transport medium from the soil to the crop (Biggar and Corey, 1970).
Most of the soluble nutrients that get into lakes and streams from rural
areas are first dissolved in water and then moved in solution to the
waterways (Henderson-Sellers, 1987). This dissolved form comes from the
release of phosphorus from soil and plant material. Some nutrients may
also be suspended in particulate matter and later converted to soluble
forms in the water system, but most dissolved phosphorus is immediately
available for biological uptake (Biggar and Corey, 1970).
In the water that percolates through the soil the soluble phosphorous
concentration is usually very low because the phosphorous precipitates in
the subsoil. Therefore, most of the soluble phosphorous should reach the
waterways via surface runoff (Biggar and Corey, 1970).
Commercial fertilizers provide the major portion of the common plant
nutrients - nitrogen, phosphorus, and potassium, used in crop production.
The remainder is supplied through animal manure and natural sources such
as soil, legumes, which are nitrogen fixating, and precipitation
processes (Van Wazer, 1977).
Nitrogen, particularly in the form of nitrate, is highly soluble in
water, and consequently highly mobile. Application of nitrogen at rates
over and above the ability of the crop to use it results in losses of
that nitrogen, normally by leaching (Eckert, 1995).
Manure or organic wastes from agriculture are a very valuable and
historic resource for improving soil structure and agriculture and can be
considered a fertilizer as well. It must be given the same amount of
care when applied to fields however, because it is more labour intensive
in application giving rise to compaction, which may result in runoff.
The water present also makes them highly mobile (Eckert, 1995).
Good fertilizer practices, including split applications, and delaying
applications when soils are wet, or if heavy rain is forecast, can
prevent excessive leaching of fertilizers (Eckert, 1995). The economic
loss to the farmer and the consequent effect on the environment can then
be predicted.
Wastewater and
Eutrophication
Eutrophication will be enhanced by nutrients contained in wastewater
sources which may be deemed organic, including the food industry, or
inorganic which concerns washing processes and detergents.
Wastewater can be further separated into two main sources, which include
domestic and industrial wastewater. Domestic wastewater, or sewage,
derives the majority of its nutrients from feces and urine, with food
wastes and detergents also contributing significant amounts, although the
composition will vary with regards to geographic location around the
world (Henderson-Sellers, 1987).
For an example of how much phosphorus wastewater contains, the cit of
Toronto can be used as an example. The statistics from their wastewater
treatment plant show that the amount of phosphorus in the plant's
effluent discharged to the lake is no more than 1 mg/L. The average total
phosphorous concentration in wastewater entering this plant is about 6
mg/L. (City of Toronto, 2000).
Industrial wastewater is highly variable in quantity and quality as it
may contain hazardous elements such as heavy metals. Once it is used it
may be disposed of in a variety of ways including re-usage for other
processes, discharge into lakes or reservoirs, for example mine tailing
ponds, and it may go directly to the municipal sewer system (Weibel, 1970).
In Ontario the sewage is "cleaned" at the sewage treatment plant and then
is released into a lake river or the ground. (Kapitain, 2002).
There are five main types of sewage treatment in Ontario. The first
stage or primary treatment involves the screening to remove large solids. In the
secondary treatment aeration tanks are employed and bacteria break down
any organic compounds. This stage also incorporates a metal salt
solution, which removes phosphorus that would otherwise go on to promote
algal growth and potentially, Eutrophication. In the tertiary stage of
treatment sand filtration is used to ensure a higher quality of
effluent. Lagoons and commercial septic systems are also commonly found
in Ontario (Kapitan, 2002).
The ministry of the environment policy 08-04--"Policy to Govern the
Provision, Operation and Assessment of Phosphorus Removal Facilities at
Municipal, Institutional and Private Sewage Treatment Works"--describes
the requirements for the removal of phosphorus from effluents (Kapitain,
2002).
Effects of Eutrophication
Eutrophication can have both temporary and more irreversible effects on
aquatic ecosystems. Significant fluctuations in dissolved oxygen
concentrations between day and night can occur in waters where there is
enhanced plant growth (Muir, 2001). This can cause problems in the early
morning when low oxygen levels, the result of plant respiration, may lead
to the death of invertebrates and fish. This process can be compounded
when algal blooms, through their decay, further reduce the oxygen content
of water. (Klaff, 2002). The growth and/or decay of bottom-dwelling
macro-algae can also lead to the deoxygenating of sediments.
Certain algal species, particularly freshwater blue-green algae, can
produce toxins, which may seriously affect the health of mammals,
including humans, fish and birds (Muir, 2001). This occurs either through
the food chain, through contact with, or ingestion of, the algae. Algal
species also cause fish deaths, for example by physically clogging or
damaging gills, and causing asphyxiation. Eutrophication ultimately
detracts from biodiversity, through the dominance of nutrient-tolerant
plants and algal species. These tend to displace more sensitive species
of higher conservation value, changing the structure of ecological
communities (Muir, 2001).
Eutrophication can also adversely affect a wide variety of water uses
such as water supply (e.g. algae clogging filters in treatment works),
livestock watering, irrigation, fisheries, navigation, water sports,
angling and nature conservation (Hutchinson, 1970). It can give rise to
undesirable aesthetic impacts in the form of increased turbidity,
discolouration, unpleasant odours, slimes and foam formation (Klaff,
2002).
Control Strategies
There are many techniques being used around the world to control
eutrophication processes.
Wastewater treatment plants remove the eutrophic enhancing phosphorous
and sometimes nitrogen before releasing it into the waterways as we have
seen in previous examples.
Agriculture nutrient management techniques can be employed to prevent
runoff and erosion by timing out the deposition of fertilizer, moderating
fertilizer use and maintaining drainage systems (Eckert, 1995). This may
serve to be beneficial to the environment but also economically viable to
the farmer.
Chemicals may also be used to help reduce and control existing
eutrophic conditions. They may be sprayed over the surface of the lake or
injected directly inside, which are intended to precipitate nutrients or
convert them into a form unavailable to aquatic life, such as aluminum's
effect on phosphorus. "Algaecides" may also be used to kill of existing
biomass, such as copper sulfate usage, but have the disadvantage of
having copper remain in the system and the possible health effects on
aquatic life from its deposition (Henderson-Sellers, 1987).
Engineering Srategies
Dredging
As sediments play a big role in the transfer of nutrients to the water
column, their removal often forms an integral part of lake restoration
programs. As well as nutrient removal, dredging may also create further
benefits such as the deepening of lakes. The major disadvantage of this
process however, is the ever-looming costs it creates to implement.
Because lakes become more eutrophic as they age over time sediments
nearest the bottom remain nutrient poor and the surface sediments are
rich in organics (Likens, 1972). Removal of these top sediments through
dredging exposes the nutrient poor layering and curtails the nutrient
cycling capacity (Henderson-Sellers, 1987).
A survey and sample test should be done before any dredging
procedure is done so that an accidental layer of sediments rich in
organic matter is not exposed, and sedimentation rates assessed.
Two main methods are used; hydraulic dredging and bucket dredging.
Through hydraulic dredging a vacuum cleaner principle is employed. The
surface layer of sediment is sucked up, where it is treated and returned
to the lake, the organic material used as a soil additive in some cases.
(Henderson-Sellers, 1987).
The second type, bucket dredging, involves skimming the surface
sediments into a bucket type device, where they proceed to treatment. This method
is more cost efficient than the first but it creates more ecological
disturbance to the system.
Deepening
Sediment stirring can be a problem for eutrophication in shallow lakes,
as it enhances the release of phosphorus held in these sediments. This
gives way to the process of lake deepening. Which may allow for a lesser
degree of stirring by factors such as wind. It may also increase the
amount of oxygen content through volume and reduce the impact of nutrient
inputs.
Deepening can be achieved by increasing the water level or lowering the
lakebed itself, accomplished by dredging methods (Klaff, 2002).
Aeration
Aeration of water bodies can be employed to counter the oxygen depleted
conditions of Eutrophication where sufficient nutrient removal techniques
cannot be employed. Aesthetic conditions may warrant aeration as well to
restore the lake for recreation activity and quality of water may be a
proviso for the costs associated with this system.
There are several techniques used as well as a wide array of machinery
employed. One of the most basic techniques involves the
de-stratification of the lake through circulation or a bubbled air system
placed on the bottom of the lake. The disadvantages of artificial
circulation that can occur contain the homogenization of the water
column, which may impact on certain fish populations that thrive in cold
water regions (Klaff, 2002).
Due to aeration being a relatively new technique for the control and
restoration of aquatic systems, more research needs to be conducted to
assess effects on biota and chemistry of the lake ecosystem.
Lake Bottom Sealing
Lake bottom sealing can also be introduced, although it only covers up
the existing problem. A layer of heavy plastic is laid upon ice covered
waters and covered with sediment that will eventually act as the new lake
floor. In the summer when the ice melts the sediment covered "sheet"
will float to the bottom and cover the existing organic sediments
susceptible to eutrophic conditions (Henderson-Sellers, 1987).
This technique may be complicated on lakes that do not freeze in
wintertime, causing disturbance and uneven deposition.
Management/Legal Aspects
In 1972 Congress passed the Federal Water Pollution Control Act,
commonly known as the Clean Water Act. The goal of the Act was to eliminate the
discharge of pollutants into rivers, lakes, streams and other waterways,
and to attain, wherever possible, waters deemed "fishable and swimmable."
(Environment Canada, 2001). Discharge of pollutants directly into a
river, lake, or stream, is described as point source pollution (as
opposed to indirect, or nonpoint source pollution) and considerable
progress has been made in preventing this type of pollution. According to
the EPA's progress report on the twenty-five year history of the Clean
Water Act, two-thirds of surveyed waters are now safe for fishing and
swimming. Non-point source pollution continues to be a concern in many
areas (Environment Canada, 2001).
Great Lakes Water Quality Agreement
"The Agreement, first signed in 1972 and renewed in 1978, expresses the
commitment of each country to restore and maintain the chemical, physical
and biological integrity of the Great Lakes Basin Ecosystem and includes
a number of objectives and guidelines to achieve these
goals."(International Joint Commission, 2002). "It reaffirms the rights
and obligation of Canada and the United States under the Boundary Waters
Treaty and has become a major focus of Commission activity."
(International Joint Commission, 2002). The Agreement monitored by the
International Joint Commission, covers all the Great Lakes and the
international portion of the St. Lawrence River. Its primary purpose in
1972 was to stem and reverse eutrophication in the lower Great Lakes. In
it's revised (1978) and amended (1987) forms, the Great Lakes Water
Quality Agreement focuses on persistent, toxic, chemicals (International
Joint Commision, 2002).
Table 1. Illustrates the phosphorus loadings present in 1976, and future
loadings that are to be achieved within eighteen months of the agreement
based on recommendations made by the I.JC.
Basin 1976 PhosphorusLoad in Metric TonnesPer Year FuturePhosphorus
Loadin Metric TonnesPer Year
Lake Superior 3600 3400*
Lake Michigan 6700 5600*
Main Lake Huron 3000 2800
Georgian Bay 630 600*
North Channel 550 520*
Saginaw Bay 870 440*
Lake Erie 20000 11000**
Lake Ontario 11000 7000**
Table 1. Phosphorus Loadings in the Great Lakes Including Past and
Future Amounts. (International Joint Commission, 2002).
The Canadian Environmental Protection Act, 1999, also contains
pollution prevention measures and water pollution standards regarding phosphates in
wastewater. More information about this act can be found through
Environment Canada.
According to a study by Environment Canada loadings of municipal
phosphorus to Lakes Erie and Ontario have been reduced by almost 80%.
(Environment Canada, 1999). Reductions in the amount of algae have also
been noted and a great success story can be told of lake Erie.
Conclusion
As our society is now evolving towards a more sustainable way of living
we are incorporating more of an environmentally friendly outlook. There
have been so many technological advances in the past years, and with that
we gained knowledge. Understanding the Eutrophication process was half
the battle and we are already closing in on controlling inputs of
excessive nutrients along with hazardous chemicals. Phosphate reduction
in detergents, policies implemented by the government for sewage
treatment and agricultural progress are all steps in the right
direction. Cultural eutrophication may not be a thing of the past but
with the right ecological mindset we can make it so.
References
Biggar, J.W. and Corey, R.B. 1970. Agricultural Drainage and
Eutrophication.
Eutrophication: Causes, Consequences and Correctives. University of
Wisconson.
City of Toronto. 2000. Ashbridges Bay Treatment Plant.
http://www.city.toronto.on.ca/sewers/mtp.htm Accessed: March 11, 2002
Cooke, G.W. 1973. Sinificange of man-made sources of phosphorous:
fertilizers and
farming. The phosphorus involved in agricultural systems and possabilites
of its
movement into natural water. Phosphorus in Fresh Water and the Marine
Environment. Pergamon Press, New York.
Eckert, D.J. 1995. Nitrates in Surface Water. http://ohioonline.osu.edu/agf-
fact/0204.html. Accessed: March 8, 2002
Environment Canada. 2001. Water Legislation.
http://www.ec.gc.ca/water/index.htm
Accessed March 18, 2002.
Environment Canada. 1999. Measuring Progress.
http://www.on.ec.gc.ca/glimr/data/celebrate-glwqa/progress.html Acessed
March
11, 2002.
Henderson-Sellers, B. 1987. Decaying Lakes. John Wiley & Sons Ltd. Great
Britain.
Hutchinson, G.E. 1970. Eutrophication, Past and Present. Eutrophication:
Causes,
Consequences and Correctives. University of Wisconson.
International Joint Commission. 2002. http://www.ijc.org/ijcweb-e.html
Accessed March
12, 2002.
Kapitain, J. 2002. Ontario's Sewage Treatment Plants and their effect on
the Environment.
http://www.nextcity.com/EnvironmentProbe/pubs/ev527.htm Accessed March
13,
2002.
Klaff, J. 2002. Limnology. Prentice-Hall, Inc. New Jersey
Lewin, H.V. 1973. Phosphates in Sewage and Sewage Treatment. .
Phosphorus in Fresh
Water and the Marine Environment. Pergamon Press, New York.
Likens, G.E. 1972. Eutrophication and aquatic ecosystems. Nutrients and
Eutrophication:
the Limiting nutrient controversy. Allen Press, Inc. Kansas.
Muir, Patricia. 2001. Eutrophication.
http://www.orst.edu/instruction/bi301/eutrophi.htm
Accessed March 13, 2002.
No author specified. No date. The Phosphorus Cycle.
http://www.halfhollowhills.k12.ny.us/Prog/Scie/Apbioweb?phosphoroud_cycle. Acessed March 12, 2002.
Pidwirny, M.J. 2001. The Nitrogen Cycle.
http://www.geog.ouc.bc.ca/physgeog/contents/9s.html Accessed: March 12,
2002.
Van Wazer, J.B. 1977. Phosphorus and Mankind's Problems Today.
Phosphorus in the
Environment: It's Chemistry and Biochemistry. Ciba Foundation Symposium 57.
Williams, R.J.P. 1977. Phosphorus: A General Introduction. Phosphorus in
the
Environment: It's Chemistry and Biochemistry. Ciba Foundation Symposium 57.
Weibel, S.R. 1970. Urban Drainage as a Factor in Eutrophication.
Eutrophication:
Causes, Consequences and Correctives. University of Wisconson.
.
Thermal Stratification, or layering, occurs in many lakes.
Whether or not a lake stratifies depends on a number of factors: the shape and depth of
the lake, the amount of wind, and the orientation of the lake (Klaff,
2002). Since the maximum density of water occurs at 4
DISSOLVED OXYGEN
Eutrophication brings about increased dissolved oxygen
consumption in
lakes progressively lowering dissolved oxygen concentrations. Eutrophic
lakes covered with ice and snow, wetlands and northern rivers receiving
large quantities of organic matter from their ice and snow, exhibit
substantial DO losses during the winter (Likens, 1972).
At higher temperatures, water can hold less oxygen when saturated which
results in less oxygen directly available and a lower percentage of the
metabolic demand being satisfied, since the metabolic rate of organisms
increases with increasing temperature (Klaff, 2002).
NUTRIENTS
Nutrients are those materials which organisms use for growth and
reproduction. The nutrient status of any environment is determined by
the supply of nutrients from its catchments, which in turn is affected by
geology (Likens, 1972). Therefore waters will vary in their natural
nutrient status. These changes can be made through changes to the
catchments such as climate, agricultural wastes, which contain man made
sources of nutrients from fertilizers (Henderson-Sellers, 1987).
There are two main sources of nutrients. Point source, for example
wastewater, and non-point sources which contain agricultural sources.
Nutrients can be further split up into organic, which is incorporated in
organic structures and contain carbon, and inorganic, which are
unassociated with carbon compounds in their elemental state (Williams, 1977).
Primary producers assimilate inorganic nutrients and use them in their
life processes, converting them to organic forms. When an organism dies
or is consumed, these nutrients will ultimately revert to their inorganic
form by the process of decomposition and mineralization and will enter
storage until used by another organism (Henderson-Sellers, 1987).
In most aquatic systems it is found to be either phosphorous or to a
lesser extent, nitrogen that is the limiting nutrient.
In a phosphorous limited system, reduction of phosphorous levels
leads to a restriction on plant and algal growth. In this condition the
Eutrophication process can be considered retarded or reversed.
A nitrogen-limited system is often considered to be a greater problem
than a phosphorous limited environment since the sources of this nutrient
are harder to control.
Nitrogen and Phosphorous
Nitrogen and Phosphorus are commonly the elements in greatest demand by
plants and microbes relative to supply and are therefore crucial in
predicting algal blooms in eutrophied waters.
Nitrogen
Nitrogen plays a central role in inland waters and plant life, as it is
needed for growth and the building of proteins (Pidwirny, 2001). Algae
are able to use nitrogen in its molecular form and convert it into forms
that can be utilized by plans such as nitrates (Eckert, 1995). Because
nitrogen, in the form of ammonia and nitrates, acts as a plant nutrient,
it also causes eutrophication.
As aquatic plants and animals die, bacteria break down their large
protein molecules into ammonia. Ammonia is then oxidized, combined with
oxygen, by bacteria to form nitrites and nitrates (Pidwirny, 2001). For
a more detailed look at the nitrogen cycling that occurs to produce these
different forms see figure 1 below.
Figure 1. The Nitrogen Cycle (Pidwirny, 2001)
Nitrogen release rates from catchments to receiving rivers and nitrate
concentrations in the rivers rise with increasing human density (Klaff,
2002). Human density is used as an approximation of organic waste
production, soil quality, and agricultural activity (Klaff, 2002).
However, where the nitrogen plus phosphorous supply rate to
waterways is very high, as in rich agricultural areas, the receiving rivers, lakes,
and estuaries exhibit extreme eutrophication. For example the
intensively farmed drainage basin to the Gulf of Mexico is so high that
the estuary exhibits periodic sediment anoxia, toxic algal blooms, and
the killing of fish populations (Klaff, 2002).
Phosphorous
Phosphorus is one of the top ten elements present in the earth's upper
crust, and has many applications. Phosphate groups are a basic
structural element of nucleic acids, phospholipids and are used as a part
of molecules in photosynthesis, for example adenosine tri-phosphate
(Williams, 1977). It is assimilated from the environment through
decomposition and photosynthesis.
The major anthropogenic sources of phosphorus come from agricultural
practices, wastewater and many other uses including, the manufacture of
soaps and detergents, animal feed, food products and medicines and
electroplating and polishing of metals (Cooke, 1973).
Its cycling in the environment is essentially a one-way flow because
unlike nitrogen, it has no gaseous return phase. When plants and animals
die, bacteria decompose, releasing some of the phosphorus back into the
soil. Once in the soil, phosphorous can be moved 100s to 1,000s of miles
from were they were released by riding through streams and rivers (Cooke,
1973). So the water cycle also plays a key role of moving phosphorus from
ecosystem to ecosystem. Refer to Figure 2. (Below)
Figure 2. The Phosphorus Cycle. (No Author Specified, No Date)
It is now widely recognized that reducing the input of plant nutrients,
especially nitrogen and phosphorus, can control the eutrophication of
fresh water. Of these two elements phosphorus is considered in shortest
supply for algal growth, while the control of nitrogen is more difficult
and more expensive in wastewater treatment and removal (Klaff, 2002).
Agriculture and
Eutrophication
Nutrients from agricultural systems enter natural water systems in
three main ways: through drainage water, in eroded soil and through animal
waste products (Biggar and Corey, 1970).
Drainage plays an important role in agriculture, as the moisture
content of soil is very important in crop propagation techniques, as it is the
nutrient transport medium from the soil to the crop (Biggar and Corey, 1970).
Most of the soluble nutrients that get into lakes and streams from rural
areas are first dissolved in water and then moved in solution to the
waterways (Henderson-Sellers, 1987). This dissolved form comes from the
release of phosphorus from soil and plant material. Some nutrients may
also be suspended in particulate matter and later converted to soluble
forms in the water system, but most dissolved phosphorus is immediately
available for biological uptake (Biggar and Corey, 1970).
In the water that percolates through the soil the soluble phosphorous
concentration is usually very low because the phosphorous precipitates in
the subsoil. Therefore, most of the soluble phosphorous should reach the
waterways via surface runoff (Biggar and Corey, 1970).
Commercial fertilizers provide the major portion of the common plant
nutrients - nitrogen, phosphorus, and potassium, used in crop production.
The remainder is supplied through animal manure and natural sources such
as soil, legumes, which are nitrogen fixating, and precipitation
processes (Van Wazer, 1977).
Nitrogen, particularly in the form of nitrate, is highly soluble in
water, and consequently highly mobile. Application of nitrogen at rates
over and above the ability of the crop to use it results in losses of
that nitrogen, normally by leaching (Eckert, 1995).
Manure or organic wastes from agriculture are a very valuable and
historic resource for improving soil structure and agriculture and can be
considered a fertilizer as well. It must be given the same amount of
care when applied to fields however, because it is more labour intensive
in application giving rise to compaction, which may result in runoff.
The water present also makes them highly mobile (Eckert, 1995).
Good fertilizer practices, including split applications, and delaying
applications when soils are wet, or if heavy rain is forecast, can
prevent excessive leaching of fertilizers (Eckert, 1995). The economic
loss to the farmer and the consequent effect on the environment can then
be predicted.
Wastewater and
Eutrophication
Eutrophication will be enhanced by nutrients contained in wastewater
sources which may be deemed organic, including the food industry, or
inorganic which concerns washing processes and detergents.
Wastewater can be further separated into two main sources, which include
domestic and industrial wastewater. Domestic wastewater, or sewage,
derives the majority of its nutrients from feces and urine, with food
wastes and detergents also contributing significant amounts, although the
composition will vary with regards to geographic location around the
world (Henderson-Sellers, 1987).
For an example of how much phosphorus wastewater contains, the cit of
Toronto can be used as an example. The statistics from their wastewater
treatment plant show that the amount of phosphorus in the plant's
effluent discharged to the lake is no more than 1 mg/L. The average total
phosphorous concentration in wastewater entering this plant is about 6
mg/L. (City of Toronto, 2000).
Industrial wastewater is highly variable in quantity and quality as it
may contain hazardous elements such as heavy metals. Once it is used it
may be disposed of in a variety of ways including re-usage for other
processes, discharge into lakes or reservoirs, for example mine tailing
ponds, and it may go directly to the municipal sewer system (Weibel, 1970).
In Ontario the sewage is "cleaned" at the sewage treatment plant and then
is released into a lake river or the ground. (Kapitain, 2002).
There are five main types of sewage treatment in Ontario. The first
stage or primary treatment involves the screening to remove large solids. In the
secondary treatment aeration tanks are employed and bacteria break down
any organic compounds. This stage also incorporates a metal salt
solution, which removes phosphorus that would otherwise go on to promote
algal growth and potentially, Eutrophication. In the tertiary stage of
treatment sand filtration is used to ensure a higher quality of
effluent. Lagoons and commercial septic systems are also commonly found
in Ontario (Kapitan, 2002).
The ministry of the environment policy 08-04--"Policy to Govern the
Provision, Operation and Assessment of Phosphorus Removal Facilities at
Municipal, Institutional and Private Sewage Treatment Works"--describes
the requirements for the removal of phosphorus from effluents (Kapitain,
2002).
Effects of Eutrophication
Eutrophication can have both temporary and more irreversible effects on
aquatic ecosystems. Significant fluctuations in dissolved oxygen
concentrations between day and night can occur in waters where there is
enhanced plant growth (Muir, 2001). This can cause problems in the early
morning when low oxygen levels, the result of plant respiration, may lead
to the death of invertebrates and fish. This process can be compounded
when algal blooms, through their decay, further reduce the oxygen content
of water. (Klaff, 2002). The growth and/or decay of bottom-dwelling
macro-algae can also lead to the deoxygenating of sediments.
Certain algal species, particularly freshwater blue-green algae, can
produce toxins, which may seriously affect the health of mammals,
including humans, fish and birds (Muir, 2001). This occurs either through
the food chain, through contact with, or ingestion of, the algae. Algal
species also cause fish deaths, for example by physically clogging or
damaging gills, and causing asphyxiation. Eutrophication ultimately
detracts from biodiversity, through the dominance of nutrient-tolerant
plants and algal species. These tend to displace more sensitive species
of higher conservation value, changing the structure of ecological
communities (Muir, 2001).
Eutrophication can also adversely affect a wide variety of water uses
such as water supply (e.g. algae clogging filters in treatment works),
livestock watering, irrigation, fisheries, navigation, water sports,
angling and nature conservation (Hutchinson, 1970). It can give rise to
undesirable aesthetic impacts in the form of increased turbidity,
discolouration, unpleasant odours, slimes and foam formation (Klaff,
2002).
Control Strategies
There are many techniques being used around the world to control
eutrophication processes.
Wastewater treatment plants remove the eutrophic enhancing phosphorous
and sometimes nitrogen before releasing it into the waterways as we have
seen in previous examples.
Agriculture nutrient management techniques can be employed to prevent
runoff and erosion by timing out the deposition of fertilizer, moderating
fertilizer use and maintaining drainage systems (Eckert, 1995). This may
serve to be beneficial to the environment but also economically viable to
the farmer.
Chemicals may also be used to help reduce and control existing
eutrophic conditions. They may be sprayed over the surface of the lake or
injected directly inside, which are intended to precipitate nutrients or
convert them into a form unavailable to aquatic life, such as aluminum's
effect on phosphorus. "Algaecides" may also be used to kill of existing
biomass, such as copper sulfate usage, but have the disadvantage of
having copper remain in the system and the possible health effects on
aquatic life from its deposition (Henderson-Sellers, 1987).
Engineering Srategies
Dredging
As sediments play a big role in the transfer of nutrients to the water
column, their removal often forms an integral part of lake restoration
programs. As well as nutrient removal, dredging may also create further
benefits such as the deepening of lakes. The major disadvantage of this
process however, is the ever-looming costs it creates to implement.
Because lakes become more eutrophic as they age over time sediments
nearest the bottom remain nutrient poor and the surface sediments are
rich in organics (Likens, 1972). Removal of these top sediments through
dredging exposes the nutrient poor layering and curtails the nutrient
cycling capacity (Henderson-Sellers, 1987).
A survey and sample test should be done before any dredging
procedure is done so that an accidental layer of sediments rich in
organic matter is not exposed, and sedimentation rates assessed.
Two main methods are used; hydraulic dredging and bucket dredging.
Through hydraulic dredging a vacuum cleaner principle is employed. The
surface layer of sediment is sucked up, where it is treated and returned
to the lake, the organic material used as a soil additive in some cases.
(Henderson-Sellers, 1987).
The second type, bucket dredging, involves skimming the surface
sediments into a bucket type device, where they proceed to treatment. This method
is more cost efficient than the first but it creates more ecological
disturbance to the system.
Deepening
Sediment stirring can be a problem for eutrophication in shallow lakes,
as it enhances the release of phosphorus held in these sediments. This
gives way to the process of lake deepening. Which may allow for a lesser
degree of stirring by factors such as wind. It may also increase the
amount of oxygen content through volume and reduce the impact of nutrient
inputs.
Deepening can be achieved by increasing the water level or lowering the
lakebed itself, accomplished by dredging methods (Klaff, 2002).
Aeration
Aeration of water bodies can be employed to counter the oxygen depleted
conditions of Eutrophication where sufficient nutrient removal techniques
cannot be employed. Aesthetic conditions may warrant aeration as well to
restore the lake for recreation activity and quality of water may be a
proviso for the costs associated with this system.
There are several techniques used as well as a wide array of machinery
employed. One of the most basic techniques involves the
de-stratification of the lake through circulation or a bubbled air system
placed on the bottom of the lake. The disadvantages of artificial
circulation that can occur contain the homogenization of the water
column, which may impact on certain fish populations that thrive in cold
water regions (Klaff, 2002).
Due to aeration being a relatively new technique for the control and
restoration of aquatic systems, more research needs to be conducted to
assess effects on biota and chemistry of the lake ecosystem.
Lake Bottom Sealing
Lake bottom sealing can also be introduced, although it only covers up
the existing problem. A layer of heavy plastic is laid upon ice covered
waters and covered with sediment that will eventually act as the new lake
floor. In the summer when the ice melts the sediment covered "sheet"
will float to the bottom and cover the existing organic sediments
susceptible to eutrophic conditions (Henderson-Sellers, 1987).
This technique may be complicated on lakes that do not freeze in
wintertime, causing disturbance and uneven deposition.
Management/Legal Aspects
In 1972 Congress passed the Federal Water Pollution Control Act,
commonly known as the Clean Water Act. The goal of the Act was to eliminate the
discharge of pollutants into rivers, lakes, streams and other waterways,
and to attain, wherever possible, waters deemed "fishable and swimmable."
(Environment Canada, 2001). Discharge of pollutants directly into a
river, lake, or stream, is described as point source pollution (as
opposed to indirect, or nonpoint source pollution) and considerable
progress has been made in preventing this type of pollution. According to
the EPA's progress report on the twenty-five year history of the Clean
Water Act, two-thirds of surveyed waters are now safe for fishing and
swimming. Non-point source pollution continues to be a concern in many
areas (Environment Canada, 2001).
Great Lakes Water Quality Agreement
"The Agreement, first signed in 1972 and renewed in 1978, expresses the
commitment of each country to restore and maintain the chemical, physical
and biological integrity of the Great Lakes Basin Ecosystem and includes
a number of objectives and guidelines to achieve these
goals."(International Joint Commission, 2002). "It reaffirms the rights
and obligation of Canada and the United States under the Boundary Waters
Treaty and has become a major focus of Commission activity."
(International Joint Commission, 2002). The Agreement monitored by the
International Joint Commission, covers all the Great Lakes and the
international portion of the St. Lawrence River. Its primary purpose in
1972 was to stem and reverse eutrophication in the lower Great Lakes. In
it's revised (1978) and amended (1987) forms, the Great Lakes Water
Quality Agreement focuses on persistent, toxic, chemicals (International
Joint Commision, 2002).
Table 1. Illustrates the phosphorus loadings present in 1976, and future
loadings that are to be achieved within eighteen months of the agreement
based on recommendations made by the I.JC.
Basin 1976 PhosphorusLoad in Metric TonnesPer Year FuturePhosphorus
Loadin Metric TonnesPer Year
Lake Superior 3600 3400*
Lake Michigan 6700 5600*
Main Lake Huron 3000 2800
Georgian Bay 630 600*
North Channel 550 520*
Saginaw Bay 870 440*
Lake Erie 20000 11000**
Lake Ontario 11000 7000**
Table 1. Phosphorus Loadings in the Great Lakes Including Past and
Future Amounts. (International Joint Commission, 2002).
The Canadian Environmental Protection Act, 1999, also contains
pollution prevention measures and water pollution standards regarding phosphates in
wastewater. More information about this act can be found through
Environment Canada.
According to a study by Environment Canada loadings of municipal
phosphorus to Lakes Erie and Ontario have been reduced by almost 80%.
(Environment Canada, 1999). Reductions in the amount of algae have also
been noted and a great success story can be told of lake Erie.
Conclusion
As our society is now evolving towards a more sustainable way of living
we are incorporating more of an environmentally friendly outlook. There
have been so many technological advances in the past years, and with that
we gained knowledge. Understanding the Eutrophication process was half
the battle and we are already closing in on controlling inputs of
excessive nutrients along with hazardous chemicals. Phosphate reduction
in detergents, policies implemented by the government for sewage
treatment and agricultural progress are all steps in the right
direction. Cultural eutrophication may not be a thing of the past but
with the right ecological mindset we can make it so.
References
Biggar, J.W. and Corey, R.B. 1970. Agricultural Drainage and
Eutrophication.
Eutrophication: Causes, Consequences and Correctives. University of
Wisconson.
City of Toronto. 2000. Ashbridges Bay Treatment Plant.
http://www.city.toronto.on.ca/sewers/mtp.htm Accessed: March 11, 2002
Cooke, G.W. 1973. Sinificange of man-made sources of phosphorous:
fertilizers and
farming. The phosphorus involved in agricultural systems and possabilites
of its
movement into natural water. Phosphorus in Fresh Water and the Marine
Environment. Pergamon Press, New York.
Eckert, D.J. 1995. Nitrates in Surface Water. http://ohioonline.osu.edu/agf-
fact/0204.html. Accessed: March 8, 2002
Environment Canada. 2001. Water Legislation.
http://www.ec.gc.ca/water/index.htm
Accessed March 18, 2002.
Environment Canada. 1999. Measuring Progress.
http://www.on.ec.gc.ca/glimr/data/celebrate-glwqa/progress.html Acessed
March
11, 2002.
Henderson-Sellers, B. 1987. Decaying Lakes. John Wiley & Sons Ltd. Great
Britain.
Hutchinson, G.E. 1970. Eutrophication, Past and Present. Eutrophication:
Causes,
Consequences and Correctives. University of Wisconson.
International Joint Commission. 2002. http://www.ijc.org/ijcweb-e.html
Accessed March
12, 2002.
Kapitain, J. 2002. Ontario's Sewage Treatment Plants and their effect on
the Environment.
http://www.nextcity.com/EnvironmentProbe/pubs/ev527.htm Accessed March
13,
2002.
Klaff, J. 2002. Limnology. Prentice-Hall, Inc. New Jersey
Lewin, H.V. 1973. Phosphates in Sewage and Sewage Treatment. .
Phosphorus in Fresh
Water and the Marine Environment. Pergamon Press, New York.
Likens, G.E. 1972. Eutrophication and aquatic ecosystems. Nutrients and
Eutrophication:
the Limiting nutrient controversy. Allen Press, Inc. Kansas.
Muir, Patricia. 2001. Eutrophication.
http://www.orst.edu/instruction/bi301/eutrophi.htm
Accessed March 13, 2002.
No author specified. No date. The Phosphorus Cycle.
http://www.halfhollowhills.k12.ny.us/Prog/Scie/Apbioweb?phosphoroud_cycle. Acessed March 12, 2002.
Pidwirny, M.J. 2001. The Nitrogen Cycle.
http://www.geog.ouc.bc.ca/physgeog/contents/9s.html Accessed: March 12,
2002.
Van Wazer, J.B. 1977. Phosphorus and Mankind's Problems Today.
Phosphorus in the
Environment: It's Chemistry and Biochemistry. Ciba Foundation Symposium 57.
Williams, R.J.P. 1977. Phosphorus: A General Introduction. Phosphorus in
the
Environment: It's Chemistry and Biochemistry. Ciba Foundation Symposium 57.
Weibel, S.R. 1970. Urban Drainage as a Factor in Eutrophication.
Eutrophication:
Causes, Consequences and Correctives. University of Wisconson.
.
Eutrophication brings about increased dissolved oxygen consumption in lakes progressively lowering dissolved oxygen concentrations. Eutrophic lakes covered with ice and snow, wetlands and northern rivers receiving large quantities of organic matter from their ice and snow, exhibit substantial DO losses during the winter (Likens, 1972).
At higher temperatures, water can hold less oxygen when saturated which results in less oxygen directly available and a lower percentage of the metabolic demand being satisfied, since the metabolic rate of organisms increases with increasing temperature (Klaff, 2002).
NUTRIENTS
Nutrients are those materials which organisms use for growth and reproduction. The nutrient status of any environment is determined by the supply of nutrients from its catchments, which in turn is affected by geology (Likens, 1972). Therefore waters will vary in their natural nutrient status. These changes can be made through changes to the catchments such as climate, agricultural wastes, which contain man made sources of nutrients from fertilizers (Henderson-Sellers, 1987).
There are two main sources of nutrients. Point source, for example wastewater, and non-point sources which contain agricultural sources. Nutrients can be further split up into organic, which is incorporated in organic structures and contain carbon, and inorganic, which are unassociated with carbon compounds in their elemental state (Williams, 1977). Primary producers assimilate inorganic nutrients and use them in their life processes, converting them to organic forms. When an organism dies or is consumed, these nutrients will ultimately revert to their inorganic form by the process of decomposition and mineralization and will enter storage until used by another organism (Henderson-Sellers, 1987).
In most aquatic systems it is found to be either phosphorous or to a lesser extent, nitrogen that is the limiting nutrient.
In a phosphorous limited system, reduction of phosphorous levels leads to a restriction on plant and algal growth. In this condition the Eutrophication process can be considered retarded or reversed. A nitrogen-limited system is often considered to be a greater problem than a phosphorous limited environment since the sources of this nutrient are harder to control.
Nitrogen and Phosphorous
Nitrogen and Phosphorus are commonly the elements in greatest demand by plants and microbes relative to supply and are therefore crucial in predicting algal blooms in eutrophied waters.
Nitrogen
Nitrogen plays a central role in inland waters and plant life, as it is needed for growth and the building of proteins (Pidwirny, 2001). Algae are able to use nitrogen in its molecular form and convert it into forms that can be utilized by plans such as nitrates (Eckert, 1995). Because nitrogen, in the form of ammonia and nitrates, acts as a plant nutrient, it also causes eutrophication.
As aquatic plants and animals die, bacteria break down their large protein molecules into ammonia. Ammonia is then oxidized, combined with oxygen, by bacteria to form nitrites and nitrates (Pidwirny, 2001). For a more detailed look at the nitrogen cycling that occurs to produce these different forms see figure 1 below.
Figure 1. The Nitrogen Cycle (Pidwirny, 2001)
Nitrogen release rates from catchments to receiving rivers and nitrate concentrations in the rivers rise with increasing human density (Klaff, 2002). Human density is used as an approximation of organic waste production, soil quality, and agricultural activity (Klaff, 2002).
However, where the nitrogen plus phosphorous supply rate to waterways is very high, as in rich agricultural areas, the receiving rivers, lakes, and estuaries exhibit extreme eutrophication. For example the intensively farmed drainage basin to the Gulf of Mexico is so high that the estuary exhibits periodic sediment anoxia, toxic algal blooms, and the killing of fish populations (Klaff, 2002).
Phosphorous
Phosphorus is one of the top ten elements present in the earth's upper crust, and has many applications. Phosphate groups are a basic structural element of nucleic acids, phospholipids and are used as a part of molecules in photosynthesis, for example adenosine tri-phosphate (Williams, 1977). It is assimilated from the environment through decomposition and photosynthesis.
The major anthropogenic sources of phosphorus come from agricultural practices, wastewater and many other uses including, the manufacture of soaps and detergents, animal feed, food products and medicines and electroplating and polishing of metals (Cooke, 1973).
Its cycling in the environment is essentially a one-way flow because unlike nitrogen, it has no gaseous return phase. When plants and animals die, bacteria decompose, releasing some of the phosphorus back into the soil. Once in the soil, phosphorous can be moved 100s to 1,000s of miles from were they were released by riding through streams and rivers (Cooke, 1973). So the water cycle also plays a key role of moving phosphorus from ecosystem to ecosystem. Refer to Figure 2. (Below)
Figure 2. The Phosphorus Cycle. (No Author Specified, No Date)
It is now widely recognized that reducing the input of plant nutrients, especially nitrogen and phosphorus, can control the eutrophication of fresh water. Of these two elements phosphorus is considered in shortest supply for algal growth, while the control of nitrogen is more difficult and more expensive in wastewater treatment and removal (Klaff, 2002).
Agriculture and Eutrophication
Nutrients from agricultural systems enter natural water systems in three main ways: through drainage water, in eroded soil and through animal waste products (Biggar and Corey, 1970).
Drainage plays an important role in agriculture, as the moisture content of soil is very important in crop propagation techniques, as it is the nutrient transport medium from the soil to the crop (Biggar and Corey, 1970). Most of the soluble nutrients that get into lakes and streams from rural areas are first dissolved in water and then moved in solution to the waterways (Henderson-Sellers, 1987). This dissolved form comes from the release of phosphorus from soil and plant material. Some nutrients may also be suspended in particulate matter and later converted to soluble forms in the water system, but most dissolved phosphorus is immediately available for biological uptake (Biggar and Corey, 1970).
In the water that percolates through the soil the soluble phosphorous concentration is usually very low because the phosphorous precipitates in the subsoil. Therefore, most of the soluble phosphorous should reach the waterways via surface runoff (Biggar and Corey, 1970).
Commercial fertilizers provide the major portion of the common plant nutrients - nitrogen, phosphorus, and potassium, used in crop production. The remainder is supplied through animal manure and natural sources such as soil, legumes, which are nitrogen fixating, and precipitation processes (Van Wazer, 1977).
Nitrogen, particularly in the form of nitrate, is highly soluble in water, and consequently highly mobile. Application of nitrogen at rates over and above the ability of the crop to use it results in losses of that nitrogen, normally by leaching (Eckert, 1995).
Manure or organic wastes from agriculture are a very valuable and historic resource for improving soil structure and agriculture and can be considered a fertilizer as well. It must be given the same amount of care when applied to fields however, because it is more labour intensive in application giving rise to compaction, which may result in runoff. The water present also makes them highly mobile (Eckert, 1995).
Good fertilizer practices, including split applications, and delaying applications when soils are wet, or if heavy rain is forecast, can prevent excessive leaching of fertilizers (Eckert, 1995). The economic loss to the farmer and the consequent effect on the environment can then be predicted.
Wastewater and Eutrophication
Eutrophication will be enhanced by nutrients contained in wastewater sources which may be deemed organic, including the food industry, or inorganic which concerns washing processes and detergents. Wastewater can be further separated into two main sources, which include domestic and industrial wastewater. Domestic wastewater, or sewage, derives the majority of its nutrients from feces and urine, with food wastes and detergents also contributing significant amounts, although the composition will vary with regards to geographic location around the world (Henderson-Sellers, 1987).
For an example of how much phosphorus wastewater contains, the cit of Toronto can be used as an example. The statistics from their wastewater treatment plant show that the amount of phosphorus in the plant's effluent discharged to the lake is no more than 1 mg/L. The average total phosphorous concentration in wastewater entering this plant is about 6 mg/L. (City of Toronto, 2000).
Industrial wastewater is highly variable in quantity and quality as it may contain hazardous elements such as heavy metals. Once it is used it may be disposed of in a variety of ways including re-usage for other processes, discharge into lakes or reservoirs, for example mine tailing ponds, and it may go directly to the municipal sewer system (Weibel, 1970). In Ontario the sewage is "cleaned" at the sewage treatment plant and then is released into a lake river or the ground. (Kapitain, 2002).
There are five main types of sewage treatment in Ontario. The first stage or primary treatment involves the screening to remove large solids. In the secondary treatment aeration tanks are employed and bacteria break down any organic compounds. This stage also incorporates a metal salt solution, which removes phosphorus that would otherwise go on to promote algal growth and potentially, Eutrophication. In the tertiary stage of treatment sand filtration is used to ensure a higher quality of effluent. Lagoons and commercial septic systems are also commonly found in Ontario (Kapitan, 2002).
The ministry of the environment policy 08-04--"Policy to Govern the Provision, Operation and Assessment of Phosphorus Removal Facilities at Municipal, Institutional and Private Sewage Treatment Works"--describes the requirements for the removal of phosphorus from effluents (Kapitain, 2002).
Effects of Eutrophication
Eutrophication can have both temporary and more irreversible effects on aquatic ecosystems. Significant fluctuations in dissolved oxygen concentrations between day and night can occur in waters where there is enhanced plant growth (Muir, 2001). This can cause problems in the early morning when low oxygen levels, the result of plant respiration, may lead to the death of invertebrates and fish. This process can be compounded when algal blooms, through their decay, further reduce the oxygen content of water. (Klaff, 2002). The growth and/or decay of bottom-dwelling macro-algae can also lead to the deoxygenating of sediments. Certain algal species, particularly freshwater blue-green algae, can produce toxins, which may seriously affect the health of mammals, including humans, fish and birds (Muir, 2001). This occurs either through the food chain, through contact with, or ingestion of, the algae. Algal species also cause fish deaths, for example by physically clogging or damaging gills, and causing asphyxiation. Eutrophication ultimately detracts from biodiversity, through the dominance of nutrient-tolerant plants and algal species. These tend to displace more sensitive species of higher conservation value, changing the structure of ecological communities (Muir, 2001).
Eutrophication can also adversely affect a wide variety of water uses such as water supply (e.g. algae clogging filters in treatment works), livestock watering, irrigation, fisheries, navigation, water sports, angling and nature conservation (Hutchinson, 1970). It can give rise to undesirable aesthetic impacts in the form of increased turbidity, discolouration, unpleasant odours, slimes and foam formation (Klaff, 2002).
Control Strategies
There are many techniques being used around the world to control eutrophication processes. Wastewater treatment plants remove the eutrophic enhancing phosphorous and sometimes nitrogen before releasing it into the waterways as we have seen in previous examples.
Agriculture nutrient management techniques can be employed to prevent runoff and erosion by timing out the deposition of fertilizer, moderating fertilizer use and maintaining drainage systems (Eckert, 1995). This may serve to be beneficial to the environment but also economically viable to the farmer.
Chemicals may also be used to help reduce and control existing eutrophic conditions. They may be sprayed over the surface of the lake or injected directly inside, which are intended to precipitate nutrients or convert them into a form unavailable to aquatic life, such as aluminum's effect on phosphorus. "Algaecides" may also be used to kill of existing biomass, such as copper sulfate usage, but have the disadvantage of having copper remain in the system and the possible health effects on aquatic life from its deposition (Henderson-Sellers, 1987).
Engineering Srategies
Dredging
As sediments play a big role in the transfer of nutrients to the water column, their removal often forms an integral part of lake restoration programs. As well as nutrient removal, dredging may also create further benefits such as the deepening of lakes. The major disadvantage of this process however, is the ever-looming costs it creates to implement. Because lakes become more eutrophic as they age over time sediments nearest the bottom remain nutrient poor and the surface sediments are rich in organics (Likens, 1972). Removal of these top sediments through dredging exposes the nutrient poor layering and curtails the nutrient cycling capacity (Henderson-Sellers, 1987).
A survey and sample test should be done before any dredging procedure is done so that an accidental layer of sediments rich in organic matter is not exposed, and sedimentation rates assessed.
Two main methods are used; hydraulic dredging and bucket dredging. Through hydraulic dredging a vacuum cleaner principle is employed. The surface layer of sediment is sucked up, where it is treated and returned to the lake, the organic material used as a soil additive in some cases. (Henderson-Sellers, 1987).
The second type, bucket dredging, involves skimming the surface sediments into a bucket type device, where they proceed to treatment. This method is more cost efficient than the first but it creates more ecological disturbance to the system.
Deepening
Sediment stirring can be a problem for eutrophication in shallow lakes, as it enhances the release of phosphorus held in these sediments. This gives way to the process of lake deepening. Which may allow for a lesser degree of stirring by factors such as wind. It may also increase the amount of oxygen content through volume and reduce the impact of nutrient inputs.
Deepening can be achieved by increasing the water level or lowering the lakebed itself, accomplished by dredging methods (Klaff, 2002).
Aeration
Aeration of water bodies can be employed to counter the oxygen depleted conditions of Eutrophication where sufficient nutrient removal techniques cannot be employed. Aesthetic conditions may warrant aeration as well to restore the lake for recreation activity and quality of water may be a proviso for the costs associated with this system.
There are several techniques used as well as a wide array of machinery employed. One of the most basic techniques involves the de-stratification of the lake through circulation or a bubbled air system placed on the bottom of the lake. The disadvantages of artificial circulation that can occur contain the homogenization of the water column, which may impact on certain fish populations that thrive in cold water regions (Klaff, 2002).
Due to aeration being a relatively new technique for the control and restoration of aquatic systems, more research needs to be conducted to assess effects on biota and chemistry of the lake ecosystem.
Lake Bottom Sealing
Lake bottom sealing can also be introduced, although it only covers up the existing problem. A layer of heavy plastic is laid upon ice covered waters and covered with sediment that will eventually act as the new lake floor. In the summer when the ice melts the sediment covered "sheet" will float to the bottom and cover the existing organic sediments susceptible to eutrophic conditions (Henderson-Sellers, 1987). This technique may be complicated on lakes that do not freeze in wintertime, causing disturbance and uneven deposition.
Management/Legal Aspects
In 1972 Congress passed the Federal Water Pollution Control Act, commonly known as the Clean Water Act. The goal of the Act was to eliminate the discharge of pollutants into rivers, lakes, streams and other waterways, and to attain, wherever possible, waters deemed "fishable and swimmable." (Environment Canada, 2001). Discharge of pollutants directly into a river, lake, or stream, is described as point source pollution (as opposed to indirect, or nonpoint source pollution) and considerable progress has been made in preventing this type of pollution. According to the EPA's progress report on the twenty-five year history of the Clean Water Act, two-thirds of surveyed waters are now safe for fishing and swimming. Non-point source pollution continues to be a concern in many areas (Environment Canada, 2001).
Great Lakes Water Quality Agreement
"The Agreement, first signed in 1972 and renewed in 1978, expresses the commitment of each country to restore and maintain the chemical, physical and biological integrity of the Great Lakes Basin Ecosystem and includes a number of objectives and guidelines to achieve these goals."(International Joint Commission, 2002). "It reaffirms the rights and obligation of Canada and the United States under the Boundary Waters Treaty and has become a major focus of Commission activity." (International Joint Commission, 2002). The Agreement monitored by the International Joint Commission, covers all the Great Lakes and the international portion of the St. Lawrence River. Its primary purpose in 1972 was to stem and reverse eutrophication in the lower Great Lakes. In it's revised (1978) and amended (1987) forms, the Great Lakes Water Quality Agreement focuses on persistent, toxic, chemicals (International Joint Commision, 2002).
Table 1. Illustrates the phosphorus loadings present in 1976, and future loadings that are to be achieved within eighteen months of the agreement based on recommendations made by the I.JC.
Basin 1976 PhosphorusLoad in Metric TonnesPer Year FuturePhosphorus Loadin Metric TonnesPer Year Lake Superior 3600 3400* Lake Michigan 6700 5600* Main Lake Huron 3000 2800 Georgian Bay 630 600* North Channel 550 520* Saginaw Bay 870 440* Lake Erie 20000 11000** Lake Ontario 11000 7000** Table 1. Phosphorus Loadings in the Great Lakes Including Past and Future Amounts. (International Joint Commission, 2002).
The Canadian Environmental Protection Act, 1999, also contains pollution prevention measures and water pollution standards regarding phosphates in wastewater. More information about this act can be found through Environment Canada.
According to a study by Environment Canada loadings of municipal phosphorus to Lakes Erie and Ontario have been reduced by almost 80%. (Environment Canada, 1999). Reductions in the amount of algae have also been noted and a great success story can be told of lake Erie.
Conclusion
As our society is now evolving towards a more sustainable way of living we are incorporating more of an environmentally friendly outlook. There have been so many technological advances in the past years, and with that we gained knowledge. Understanding the Eutrophication process was half the battle and we are already closing in on controlling inputs of excessive nutrients along with hazardous chemicals. Phosphate reduction in detergents, policies implemented by the government for sewage treatment and agricultural progress are all steps in the right direction. Cultural eutrophication may not be a thing of the past but with the right ecological mindset we can make it so.
References
Biggar, J.W. and Corey, R.B. 1970. Agricultural Drainage and Eutrophication. Eutrophication: Causes, Consequences and Correctives. University of Wisconson.
City of Toronto. 2000. Ashbridges Bay Treatment Plant.
http://www.city.toronto.on.ca/sewers/mtp.htm Accessed: March 11, 2002
Cooke, G.W. 1973. Sinificange of man-made sources of phosphorous: fertilizers and farming. The phosphorus involved in agricultural systems and possabilites of its movement into natural water. Phosphorus in Fresh Water and the Marine Environment. Pergamon Press, New York.
Eckert, D.J. 1995. Nitrates in Surface Water. http://ohioonline.osu.edu/agf- fact/0204.html. Accessed: March 8, 2002
Environment Canada. 2001. Water Legislation. http://www.ec.gc.ca/water/index.htm Accessed March 18, 2002.
Environment Canada. 1999. Measuring Progress. http://www.on.ec.gc.ca/glimr/data/celebrate-glwqa/progress.html Acessed March 11, 2002.
Henderson-Sellers, B. 1987. Decaying Lakes. John Wiley & Sons Ltd. Great Britain.
Hutchinson, G.E. 1970. Eutrophication, Past and Present. Eutrophication: Causes, Consequences and Correctives. University of Wisconson.
International Joint Commission. 2002. http://www.ijc.org/ijcweb-e.html Accessed March 12, 2002.
Kapitain, J. 2002. Ontario's Sewage Treatment Plants and their effect on the Environment. http://www.nextcity.com/EnvironmentProbe/pubs/ev527.htm Accessed March 13, 2002.
Klaff, J. 2002. Limnology. Prentice-Hall, Inc. New Jersey
Lewin, H.V. 1973. Phosphates in Sewage and Sewage Treatment. . Phosphorus in Fresh Water and the Marine Environment. Pergamon Press, New York.
Likens, G.E. 1972. Eutrophication and aquatic ecosystems. Nutrients and Eutrophication: the Limiting nutrient controversy. Allen Press, Inc. Kansas.
Muir, Patricia. 2001. Eutrophication. http://www.orst.edu/instruction/bi301/eutrophi.htm Accessed March 13, 2002.
No author specified. No date. The Phosphorus Cycle. http://www.halfhollowhills.k12.ny.us/Prog/Scie/Apbioweb?phosphoroud_cycle. Acessed March 12, 2002.
Pidwirny, M.J. 2001. The Nitrogen Cycle. http://www.geog.ouc.bc.ca/physgeog/contents/9s.html Accessed: March 12, 2002.
Van Wazer, J.B. 1977. Phosphorus and Mankind's Problems Today. Phosphorus in the Environment: It's Chemistry and Biochemistry. Ciba Foundation Symposium 57.
Williams, R.J.P. 1977. Phosphorus: A General Introduction. Phosphorus in the Environment: It's Chemistry and Biochemistry. Ciba Foundation Symposium 57.
Weibel, S.R. 1970. Urban Drainage as a Factor in Eutrophication. Eutrophication: Causes, Consequences and Correctives. University of Wisconson.
.