Environmental problems that are related to high concentration nutrients. It is the process due to increment of algae productivity which affects adversely aquatic life and also human and animal health. It is mainly influenced by humankind activities that include agriculture and sewage effluent due to creating high amount of nutrients.
Although the increased production may increase the rate of lake filling, it is incorrect to define eutrophication as lake aging. A lake does not die with it reaches a state of high productivity, but when it no longer exists (is filled in). Lake filling results both from production that occurs in the lake, which may increase with eutrophication, and from organic and inorganic material deposited from outside the lake, which has no relationship with lake
Stormwater runoff from these developed land areas is the major source ofnutrients for most lakes. Other activities that contribute to eutrophication are lawn and gardenfertilizers, faulty septic systems, washing with soap in or near the lake, erosion into the lake,dumping or burning leaves in or near a lake, and feeding ducks.
The trophic state of a lake is a hybrid concept with no precise definition. Originally, trophic
referred to nutrient status. Eutrophic water was water with high concentrations of nutrients and, by extension, a eutrophic lake was a lake that contained eutrophic water. Later the concept of trophic state was applied to lakes rather than water, and its precise definition was lost. Now trophic state not only refers to the nutrient status of the water, but also to the biological production that occurs in the water and to morphological characteristics of the lake basin itself.
Now a eutrophic lake may not only be a lake with high levels of nutrients, but also a very
shallow pond, full of rooted aquatic plants, that may or may not have high levels of nutrients.Lakes are divided into three trophic categories: oligotrophic, mesotrophic, and eutrophic. The prototypic oligotrophic lake is a large deep lake with crystal clear waters and a rocky or sandy shoreline. Both planktonic and rooted plant growth are sparse, and the lake can support a coldwater fishery. A eutrophic lake is typically shallow with a soft and mucky bottom. Rooted plant growth is abundant along the shore and out into the lake, and algal blooms are not unusual. Water clarity is not good and the water often has a tea color. If deep enough to thermally stratify, the bottom waters are devoid of oxygen. Mesotrophic is an intermediate trophic state with characteristics between the other two.
Steep shoreline and bottom gradient
Low nutrient enrichment
Little planktonic growth
Few aquatic plants
Sand or rock along most of shoreline
High dissolved oxygen content
Moderate nutrient enrichment
Moderate planktonic growth
Some sediment accumulation over
The mechanism of eutrophication is briefly described in Figure 1. Large amount of nutrient input to the water body is the main effect and high level of phytoplankton biomass results that lead to algal bloom. Consumption of oxygen close the bottom of the water body is the result. The other effects of the process can be divided two categories that are related to:
The main steps of the eutrophication process can be observed in Figure 2.
Nitrogen and phosphorus are two main nutrients for aquatic life. In addition, A silica is also necessary for the diatoms. Nutrient concentration in the water body changes during eutrophication. The nutrient is the limiting factor, if it is not be available for algae develop.
The sufficient factor to determine limiting factor is the ratio of nitrogen to phosphorus compounds in the water body is an important factor for control mechanism. (Table 1). Phosphorus is generally limiting factor for phytoplankton in fresh waters. For large marine areas frequently have nitrogen as the limiting nutrient, especially in summer. Intermediate areas such as river plumes are often phosphorus-limited during spring,but may turn to silica or nitrogen limitation in summer.
Eutrophication providing factor and its reasons
Increasing amount of the substances in the water is mostly raised by man made activities and partly also natural issues. This situation can be generalized on the whole of the world. On this stage, some main sources of anthropic nutrient input occurs, such as
Leaching (from used or agricultured era and sewer from urban area)
Athmospheric Nitrogen (combustion gases and animal breeding)
According to the Europian Environment Agency (EEA), ‘the main source of nitrogen pollutants is run-off from agricultured land, whereas most phosphorus pollution comes from households and industry, including phosphorus- based detergents. The rapid increase in industrial production and in in-house consumption during the 20th century has resulted in greater volumes of nutrient-rich wastewater. Although there has been recently a better management of nitrogen and phosphorus in agricultural practices, saturation of soils with phosphorus can be noted in some areas where spreading of excessive manure from animal husbandry occurs. Nutrient removal in sewage treatment plants and promotion of phosphorus-free detergents are vital to minimize the impact of nitrogen and phosphorus pollution on Europe’s water bodies.”
Some activities can lead to an increase in adverse eutrophication and, although they are very specific, they should be noted:
â€¢ Aquaculture development: Expansion of aquaculture contributes to eutrophication by the discharge of unused animal food and excreta of fish into the water;
â€¢ The transportation of exotic species: Mainly via the ballasts of big ships, toxic algae, cyanobacteria and nuisance weeds can be carried from endemic areas to uncontaminated ones. In these new environments they may find a favourable habitat for their diffusion and overgrowth, stimulated by nutrients availability;
â€¢ Reservoirs in arid lands: The construction of large reservoirs to store and manage water has been
taking place all over the world. These dams are built
in order to allow the collection of drainage waters
through huge hydrographic basins. Erosion leads to
the enrichment of the waters of these reservoirs by
nutrients such as phosphorus and nitrogen
Factors supporting the development
Besides nutrient inputs, the first condition supporting
eutrophication development is purely physical – it is
the containment (time of renewal) of the water. The
containment of water can be physical, such as in a
lake or even in a slow river that works as a batch
(upstream waters do not mix with downstream
waters), or it can be dynamic.
The notion of dynamic containment is mostly relevant
for marine areas. Geological features such as the
shape of the bottom of the sea, the shape of the
shores, physical conditions such as streams, or large
turbulent areas, and tidal movements, allow some
large marine areas to be really “contained”, exhibiting
very little water renewal. This is known as dynamic
containment. In other cases, due to tidal effects, and/or streams,
some areas that would seem to be prone to containment
see their waters regularly renewed and are not
contained at all and are therefore very unlikely to
Other physical factors influence eutrophication of
water bodies. Thermal stratification of stagnant water
bodies (such as lakes and reservoirs), temperature
and light influence the development of aquatic algae.
Increased light and temperature conditions during
spring and summer explain why eutrophication is a
phenomenon that occurs mainly during these seasons.
Eutrophication itself affects the penetration of
light through the water body because of the shadow
effect coming from the development of algae and
other living organisms and this reduces photosynthesis8
in deep water layers, and aquatic grass and
weeds bottom development. Main consequences
The major consequence of eutrophication concerns
the availability of oxygen. Plants, through photosynthesis,
produce oxygen in daylight. On the contrary, in
darkness all animals and plants, as well as aerobic
microorganisms and decomposing dead organisms,
respire and consume oxygen. These two competitive
processes are dependent on the development of the
biomass. In the case of severe biomass accumulation,
the process of oxidation of the organic matter that has
formed into sediment at the bottom of the water body
will consume all the available oxygen. Even the oxygen
contained in sulphates (SO4
2-) will be used by
some specific bacteria. This will lead to the release of
sulphur (S2-) that will immediately capture the free oxygen
still present in the upper layers. Thus, the water
body will loose all its oxygen and all life will disappear.
This is when the very specific smell of rotten eggs, originating
mainly from sulphur, will appear.
In parallel with these changes in oxygen concentration
other changes in the water environment occur: â€¢ Changes in algal population: During eutrophication,
macroalgae, phytoplankton (diatoms, dinoflagellates,
chlorophytes) and cyanobacteria9, which
depend upon nutrients, light, temperature and water
movement, will experience excessive growth. From
a public health point of view, the fact that some of
these organisms can release toxins into the water or
be toxic themselves is important.
â€¢ Changes in zooplankton11, fish and shellfish population:
Where eutrophication occurs, this part of the
ecosystem is the first to demonstrate changes. Being
most sensitive to oxygen availability, these species may die from oxygen limitation or from changes in the
chemical composition of the water such as the excessive
alkalinity that occurs during intense photosynthesis12.
Ammonia toxicity in fish for example is much
higher in alkaline waters.
Establishment of eutrophication
There are several approaches for assigning a priority to alternative eutrophication
control programmes. The programmes can be directed either toward treating
the basic causes or the symptoms (e.g. reducing aquatic plant nutrient inputs
from the drainage basin versus periodic harvesting of excessive aquatic
plant growths). In some cases, a combination of the two will be most useful.
In a given
case, the basic approach should be tied as closely as possible to the overall eutrophication
Where possible, it usually is most effective to attempt to treat the underlying
and most readily-controllable causes of eutrophication, rather than attempt
merely to alleviate the symptoms. In most cases, this means reduction or elimination
of the excessive nutrient inputs that stimulate the excessive growths of
aquatic plants in the first place. This approach will work to eliminate the basic
problem, and usually is the most effective strategy over the long term.
Reduction of nutrient Inputs
The first control priority usually is to limit or reduce nutrient inputs to the waterbody
from the sources in the drainage basin that contribute the largest quantities
of the ‘biologically available’ forms of the nutrients (Rast and Lee, 1978,1983;
Lee et al. 1980, Sonzogni et al. 1982). The control effort can be directed to both
the point (‘pipeline’) and/or non-point (diffuse) nutrient sources in the drainage
basin. For example, human and animal wastewaters contain large quantities of
phosphorus and nitrogen, in chemical forms easily used by algae and other aquatic
plants. Treatment to reduce the level of the nutrients in these wastewaters
usually is a cost-effective approach to keep them from reaching surface waters
O f course,
the costs can vary, dependent upon such factors as the age of the plant, the degree
of treatment and the population served
sphorus and nitrogen are not the only nutrients needed by aquatic plants
Further, reduction of the quantities of
phosphorus in phosphate-containing detergents can be an effective supplemental
measure, especially in areas where the removal of phosphorus at municipal
wastewater treatment plants is not practised, or where there are a large number
of septic tank disposal systems in a drainage basin.
Another method of reducing nutrient inputs to a waterbody is to divert m u nicipal
sewage wastewaters from the drainage basin of concern into a downstream
basin. This latter method can be effective for the affected waterbody.
However, it does not eliminate the basic problem; it merely shifts it to another
waterbody which may or may not be more capable of handling it. There also are
obvious social and political problems associated with this type of ‘solution’.
A large number of nutrient control options also exist for non-point sources
of nutrients in the drainage basin. These various measures exhibit a wide range
of costs and effectiveness ( P L U A R G 1978a, Monaghan Ltd 1978, Skimin et al.
1978, Monteith et al. 1981, Ryding and Rast 1989).
In-Lake control measures
Some treatment measures can be applied directly in a lake or reservoir to attempt
to alleviate the symptoms of eutrophication (Table 6). They also can be
used to augment other treatment methods, or to provide temporary relief from
eutrophication symptoms while a long-term control strategy is being formulated
Examples of in-lake methods include the harvesting of aquatic plants, the use
of algicides, in-lake nutrient inactivation or neutralization, artificial oxygenation
of bottom waters, dredging or covering of bottom sediments, increasing the
water flushing or circulation rates, and ‘biomanipulation’ (Cooke et al. 1986,
Ryding and Rast 1989). Although such measures usually are less effective over
the long term than external nutrient control programmes, they do offer an effective
means of combatting, at least temporarily, the negative impacts of eutrophication.
simple approach for selecting
a eutrophication control programme
A logical sequence of decisions to be made by a water manager was outlined
previously in Figure 1. It is pointed out here that the final decision on an appropriate
control strategy should be a ‘multi-judgement’, based on the relevant social,
technical, economical and ecological aspects. It is also very important to
set up a responsive monitoring programme both for defining the necessary pretreatment
condition of the waterbody and for properly evaluating the final outcome
of the remedial measures enacted.
Assess eutrophication problem,
define eutrophication goals
One must first determine the nature of the eutrophication problem and decide
on the goals of a control programme. The eutrophication problem in a given
situation may be excessive growths of algae and/or macrophytes, decreased
water transparency, hypolimnetic oxygen depletion and related fish kills, nutrient
regeneration or water quality deterioration due to the regeneration of reduced
chemicals, taste and odour problems in drinking water supply reservoirs,
or a combination of these types of problems.
Assess limiting nutrient
If a eutrophication control programme is necessary to achieve the desired water
quality goals for a lake or reservoir, one can then assess the logical measures to
take in a given situation.
. Since an effective, long-term control measure is
usually to control the external nutrient load, the next step is to determine the
likely nutrient to be controlled.
The trophic state of the waterbody must be considered in order to make a realistic
estimate of the role of nitrogen and phosphorus as potential algal growthlimiting
nutrients. The absolute concentrations of the biologically available nutrients
are especially important in this assessment. As a rough rule-of-thumb, if
the biologically available nitrogen and phosphorus concentrations decrease
below approximately 20 ng N/1 or 5 p.g P/l, respectively, during an algal bloom
peak, that nutrient is likely the limiting one. If both nutrients decrease below
this value, both may be limiting.
The simple stoichiometric atomic ratio between C : N : P of 106:16:1 in plankton
cells (which corresponds to a mass ratio of approximately 40:7:1) has also
proved to be useful in deciding whether nitrogen and/or phosphorus is the nutrient
most limiting to algal growth. Under the assumption that the ratio in algal
cells reflects the relative proportion needed by algae for growth and reproduction,
measurement of the quantities of these nutrients in the water column can
be used to determine which nutrient is not present in the needed proportions.
Ryding and Rast (1990) provide further information on this topic.
Assess need for control of nitrogen
Even if nitrogen is not the limiting nutrient, it may be necessary to take measures
to control nitrogen, if the critical concentration for drinking water supply is exceeded.
Since drinking water supply is one of the principal uses of lakes and
reservoirs, excess nitrate levels require a high priority in the context of the management
of lakes and reservoirs. Control measures should be implemented as
far as possible from the water treatment plant, and as close as possible to the nitrate
sources. Obviously, the successful application of preventive measures
presupposes that the principal sources in the drainage basin have been correctly
Assess alternative phosphorus control option.
Assess need for further (In-lake)
If the expected improvement in water quality and/or trophic conditions from external
phosphorus control measures will not be sufficient (based on model predictions
or post-treatment monitoring) to achieve the eutrophication control
goals, one can also consider in-lake control methods as supplemental measures.
The expected water quality improvement, for example, following a phosphorus
load reduction of 75-90 percent may still represent eutrophic conditions in some
cases, especially in shallow waterbodies. Shallow waterbodies can be especially
sensitive because their water mass is more susceptible to mixing by wind action,
their algae biomass is more frequently present in the euphotic zone, etc.
In such cases, one may consider such options as alterations in the lake basin
morphometry (e.g. dredging) or initiation of in-lake nutrient control measures.
Such measures can be very useful when the primary method of external nutrient
control alone is either inadequate to achieve the goals, or is too expensive to be
implemented in a given situation. In-lake controls (Table 9) include such
measures as nutrient inactivation, hypolimnetic aeration, harvesting of macrophytes,
application of algicides, etc. Biological controls (e.g. enhancement of
certain food chain pathways by introduction or replacement of specific food
chain organisms) may also be considered, although the long-term, ecological
effects of this approach are largely unknown at present. sess effectiveness of control programme
In most of the cases studied so far, economic optimization with respect to water
quality is primarily concerned with control measures in three major areas: (1)
nutrient source control in the watershed (external control); (2) temporal detention
in the waterbody (internal control); and (3) treatment plants (off-line control),
in the case of water used as a water supply.
In order to obtain sufficient information for a judicious selection of eutrophication
control measures, extensive studies of the chemical and biological conditions
of the waterbody of concern and its tributaries are usually required. Upon
completion of such studies, after control measures have been planned and carried
out, one may then conclude that further studies are not necessary. Such a
conclusion is false. Even after eutrophication control programmes have been initiated
(e.g. reducing the nutrient influx), post-treatment studies should be continued
for at least several more years. This should be done to compare the condition
of the waterbody before and after the start of eutrophication control
measures, and to ascertain whether or not the results expected from model calculations
have actually been achieved. Only then can one be certain whether or
not (or to what degree) the corrective action taken was correct, and whether or
not the monetary investment was a financially responsible one.
This will also work to decrease the uncertainty of model predictions for future
Post-treatment monitoring and evaluation also provide valuable information
to others concerned with similar eutrophication management problems, and help
guide future efforts
Monitoring of eutrophication
Monitoring is useful if it is performed for a purpose.
The monitoring objectives of ‘water body’ for monitoring a water body are:
â€¢ Prevention eutrophication.
â€¢ To take necessity precautions before the crucial results that can be described as ‘early warning purposes’.
â€¢ To get information about the situation of the water quality for handling the problems.
The causes that drive eutrophication are multiple and
the mechanisms involved are complex. Several elements
should be considered in order to assess the
possible actions aimed at counteracting nutrient
enrichment of water supplies. The use of computerised
models now allows a better understanding of the
role of each factor, and forecasting the efficiency of
various curative and preventive measures. The best
way to avoid eutrophication is to try to disrupt those
mechanisms that are under human control; this clearly
means to reduce the input of nutrients into the water
basins. Such a control unfortunately does not have a
linear effect on the eutrophication intensity. Integrated
management should comprise:
â€¢ Identification of all nutrient sources. Such information
can be acquired by studies of the catchment
area of the water supply. Knowledge of industrial
activities, discharge practices and localization, as
well as agricultural practices (fertilizer
contribution/plant use and localization of crops) is
necessary in order to plan and implement actions
aiming at limiting the nutrient enrichment of water.
The identification of sewage discharge points, agricultural
practices, the nature of the soil, the vegetation,
and the interaction between the soil and the
water can be of great help in knowing which areas
should be targeted.
â€¢ Knowledge of the hydrodynamics of the water
body, particularly the way nutrients are transported,
and of the vulnerability of the aquifer, will allow determination
of the ways by which the water is enriched
Anthropogenic nutrient point sources such as nontreated
industrial and domestic wastewater discharge
can be minimized by systematic use of wastewater
treatments. In sensitive aeras, industries and local
authorities should control the level of nutrients in the
treated wastewater by the use of specific denitrification
or phosphorus removal treatments.
Diffuse anthropogenic nutrient sources can be controlled
by soil conservation techniques and fertilizer restrictions.
Knowledge of the agronomic balance (ratio of
fertilizer contribution to plant use) is very relevant to
optimize the fertilization practice and to limit the loss of
nutrients. Diffuse nutrient losses will be reduced by
implementation at farm level of good practices such
â€¢ Fertilization balance, for nitrogen and phosphorus,
e.g. adequation of nutrients supply to the needs of
the crop with reasonable expected yields, taking into
account soil and atmospheric N supply.
â€¢ Regular soil nutrients analysis, fertilization plans and
registers at plot level.
â€¢ Sufficient manure storage capacities, for spreading
of manure at appropriate periods.
â€¢ Green cover of soils during winter, use of “catchcrops”
in crop rotations.
â€¢ Unfertilized grass buffer strips (or broad hedges)
along watercourses and ditches.
â€¢ Promotion of permanent grassland, rather than temporary
â€¢ Prevention of erosion of sloping soils.
â€¢ Precise irrigation management (e.g. drip irrigation,
fertilisation, soil moisture control).
In coastal areas, improvement in the dispersion of
nutrients, either through the multiplication of discharge
points or through the changing of their localization,
can help to avoid localized high levels of nutrients.
Reuse and recycling, in aquaculture and agriculture,
of waters rich in nutrients can be optimized in order to
avoid discharge into the water body and direct
consumption of the nutrients by the local flora and
Treatment of water bodies
affected by blooms
When a bloom affects a water body,
preventative measures can be taken
either to limit its spread over unaffected
areas or to treat the contaminated
When the regulations of countries
permit it, algicides can be used if no
other solutions are available or efficient.
Several algicides such as copper
sulphate, chlorine and citrate copper
are capable of killing algal and
cyanobacterial cells. This will result in
the release of their intracellular charge,
including the undesirable toxin. This
approach is radical and should be
undertaken with caution. Algicide
treatment of water bodies may result in
adverse taste and odour of the affected
water. Moreover, some of the algicides
have undesirable environmental
impacts which can lead to the selection
of resistant species of algae or
cyanobacteria. The efficiency of the
algicide depends on the features of the
water and especially the quality of the
contact made between the product and
the target. Examples of algicides
â€¢ Copper sulphate
This has been frequently used due to its
efficiency and low cost. Copper, which
is not biodegradable, can accumulate in
sediments and could in turn affect
phytoplankton, macro-invertebrates or
even fish directly or indirectly by
depleting the available oxygen.
â€¢ Copper chelates such as copper
These can be used in hard and alkaline
waters, where copper sulphate is less
â€¢ Oxidants such as chlorine or
In many countries the use of algicides is
prohibited or strictly limited. Where they
are permitted care should be taken not
to allow the use of the water supply for
drinking water production, for animal
watering or as a recreational site during
the treatment and until the toxins are
degraded. This can take several weeks.
Algicides should be applied when the
cell density is low to avoid a massive
release of toxins, which generally
appears between three and 24 hours
after the treatment.
If the bloom is well established,
algicides could be the last option.
These should only be used if the
reservoir can be disconnected for
Reservoirs which frequently receive
water from lakes have their intake
system equipped with a possibility of a
catchment at different depths, allowing
an intake from uncontaminated areas of
the water column.
The Role Of Public Awareness
Public involvement in developing an effective petrifaction, where it is feasible.
Where it is feasible, public participation in developing an effective eutrophication
control programme can be important, particularly with regard to lakes and
reservoirs used extensively for recreational purposes. Many individuals may
have experienced eutrophication-related problems in such waterbodies in the
past, or else may have been exposed to media coverage of such problems. The
result can be a ‘collective memory’ of poor water quality conditions in certain
waterbodies, which can lead to a certain degree of public curiosity about
lake/reservoir management problems. Greater public awareness of water-related
issues usually can be developed by making details of new eutrophication
control programmes, and expected improvements
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