Eutrophication Is World Wide Environmental Issue Environmental Sciences Essay

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1st Jan 1970 Environmental Sciences Reference this


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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

Coldwater fishery

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:

nutrient dispersion,

phytoplankton growth

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:

• Aquaculture development: Expansion of aquaculture contributes to eutrophication by the discharge of unused animal food and excreta of fish into the water;

• 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;

• 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

of eutrophication

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

become eutrophic.

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

of eutrophication

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: • 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.

• 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.

Eutrophication Management

Establishment of eutrophication

management goals

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

management goals.

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

for growth.

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

or implemented.

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)

control measures

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.

Post-treatment monitoring

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

planning purposes.

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:

• Prevention eutrophication.

• To take necessity precautions before the crucial results that can be described as ‘early warning purposes’.

• To get information about the situation of the water quality for handling the problems.

• Research.


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:

• 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.

• 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

with nutrients.

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


• 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.

• Regular soil nutrients analysis, fertilization plans and

registers at plot level.

• Sufficient manure storage capacities, for spreading

of manure at appropriate periods.

• Green cover of soils during winter, use of “catchcrops”

in crop rotations.

• Unfertilized grass buffer strips (or broad hedges)

along watercourses and ditches.

• Promotion of permanent grassland, rather than temporary

forage crops.

• Prevention of erosion of sloping soils.

• 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


• 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.

• Copper chelates such as copper


These can be used in hard and alkaline

waters, where copper sulphate is less


• Oxidants such as chlorine or

potassium permanganate.

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

several days.

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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