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1. Environmental Chemistry
Assignment no 4:
“Eutrophication”
Semester 3rd
The University of Lahore

2. EUTROPHICATION
Eutrophication may be defined as the inorganic nutrient enrichment of natural waters, leading to
an increased production of algae and macrophytes. Many lakes are naturally eutrophic, and in
some cases there is a progressive eutrophication as the lake matures eutrophication is more
widely known in relation to human activities, where the artificial introduction of plant
nutrients(particularly phosphorus and nitrogen) Has lead to community changes and a
deterioration of water quality in many freshwater systems. This aspect has become increasingly
important with increases in human population and more extensive development of agriculture,
and eutrophication now ranks with otherma or anthropogenic effects such as deforestation,
global warming, and large scale environmental disturbance in relation to its potentially harmful
effect on natural ecosystems. And terms of aquatic microbiology, eutrophication resulting
changes in the biomass and composition of all groups of microorganisms present in fresh water
system. This assignment about the origins of eutrophication, the algal response to increased
nutrient levels, and measures that can be taken to control the growth of deleterious microbial
populations.
These issues are discussed particularly in relation to standing waters (lentic systems) where high
nutrient levels can lead to the development of intense algal blooms and the resulting
environmental deterioration. Eutrophication of rivers and streams is also an important aspect of
freshwater microbiology, but environmental effects are generally less acute than in lentic
systems lakes and reservoirs are generally less effective at diluting pollutants than streams are,
for two reasons. First, deep lakes and reservoirs often contain stratified layers. That undergo little
vertical mixing. Second, they have little or no flow. The flushing and changing of water in lakes
and large artificial reservoirs can take from 1 to 100 years, compared with several days to several
weeks for streams. as a result, lakes and reservoirs are more vulnerable than streams are to
contamination by runoff or discharge of plant nutrients, oil, pesticides, and non-degradable toxic
substances such as lead, mercury, and arsenic. Many toxic chemicals and acids also enter lakes
and reservoirs from the atmosphere.
Origin of Eutrophication:
The origin of Eutrophication can be natural as well as result of human activities i.e.
artificially.

3. Natural Eutrophication
The three inorganic nutrients of major importance in freshwater systems are nitrates, phosphates,
and silicates. 4igh concentrations of these nutrients in lake water promote the active growth of
phytoplankton, leading to the massive development of algal biomass (high primary productivity).
And the resulting growth (high secondary productivity) Of all other lake organisms including
bacteria, zoo plankton, and fish. The twin aspects of nutrient concentration and productivity have
been used to provide a trophic classification of lakes in temperate climates. Two major categories
can be recognized as:
Eutrophic lakes
High concentrations of nitrates and phosphates, high primary and secondary productivity
Oligotrophic lakes
Low concentrations of either nitrates or phosphates (or both) low primary and secondary
productivity. These two major categories are part of a continuum in terms of water quality, and it
is convenient to recognize five main groups hypertrophic, eutrophic, mesotrophic, oligotrophic,
and ultra oligotrophic in descending order of enrichment and productivity. Attempts have been
made to define these terms in relation to fixed “boundary” values for both nutrient and
productivity water quality parameters. One particular scheme, developed by the organization for
Economic cooperation and development (OECD), provides specific criteria for temperate lakes
in terms of the mean annual values of total phosphorus, chlorophyll a, and Secchi depth
Although this scheme provides a useful conceptual framework for defining trophic categories,
there are limitations in its practical use for classifying particular lakes. Because of variability
within eco systems, some water bodies can be classified in one or another trophic category,
depending on which parameter issued. In an attempt to alleviate this, a more flexible ‘open
boundary’ system has been developed (OECD 1982), where the status of individual water bodies
is determined by statistical fit to more open ranges of the above parameters. The connection
between nutrient status and algal productivity implied in this system is not absolute.
Artificial Eutrophication
Artificial eutrophication is the eutrophication due to human activities. Human activities have
been a major cause of eutrophication of freshwater systems either by direct discharge of
contaminating nutrients into the aquatic system or indirectly, by such processes as deforestation
or alteration of drainage patterns. Direct contamination of water sources involves three main

4. types of pollutant domestic discharges (particularly sewage), industrial effluent, and agricultural
waste. The sources of nutrient entry into the fresh water system are of two main types as follows.
Point Source: where inflow into the lake or stream is localized. This is typical of sewage and
industrial effluent, and is also characteristic of some types of agricultural pollution.
Following are some of the point sources
 Waste water effluent (municipal and industrial)
 Run off and leachate from waste disposal systems
 runoff and infiltration from animal feedlots
 runoff from mines, oil fields, unsewered industrial sites
 7verflows of combined storm and sanitary sewers
 Run off from construction sites less than 20,000 m2
(220,000 ft2
)
 Untreated sewage
Diffuse source: where entry of organic pollutants occurs over a wide area and includes
agricultural seepage, run off from road systems, and aerial pollution.
Following are some of the diffuse sources
 Run off from agriculture/irrigation
 Run off from pasture and range
 Urban runoff from unsewered areas
 Septic tank leachate
 Run off from construction sites 20,000 m2
 Run off from abandoned mines
 Atmospheric deposition over a water surface
 7ther land activities generating contaminants
Ecological effect of Eutrophication in standing
waters:
 Increased biomass of phytoplankton
 Toxic or inedible phytoplankton species
 Increases in blooms of gelatinous Zooplankton

5.  Increased biomass of benthic and epiphytic algae
 Changes in macrophytes species composition and biomass
 Decreases in water transparency (increased turbidity)
 Colour, smell, and water treatment problems
 Dissolved oxygen depletion
 Increased incidences of fish kills
 Loss of desirable fish species
 Reductions in harvestable fish and shellfish.
 Decreases in perceived aesthetic value of the water body.
Algal blooms & Eutrophication:
Algal blooms are simply dense populations of planktonic algae which develop in aquatic
systems. They may occur in a wide range of environments, including lakes and rivers, exposed
mudflats, and snowpack and are part of the normal seasonal development in many ecosystems.
in all of these environments, the development of algal blooms can be seen as a balance between
the processes of population increase (high growth rate, ability to out compete other algae) And
population loss (effects of grazing, parasitic attack). Increased levels of inorganic nutrients lead
to a general increase in primary productivity (see previously) But may also promote algal blooms
at different times of the year. In lentic environments, these blooms include the spring diatoms
bloom, late spring blooms of green algae, and summer blooms of dinoflagellates and blue green
algae. Most of these blooms have no adverse effects on the environment, and the increased algal
biomass is transferred to other lake biomass via the normal food web. The major problems of
eutrophication come with anthropogenic enrichment of the environment and the formation of
dense blooms of toxic dinoflagel lates and colonial blue green algae.
Production of toxins due to blue green algae:
In the freshwater environment, toxins are produced and secreted in quantity by one major group
of algae 5 the blue greens. These toxins are part of a wide range of bioactive secondary
metabolites produced by these organisms, including poly ketones, alkaloids, and peptides.
Toxins reach particularly high concentrations under conditions of bloom formation, when they
contaminate the water supplies of wild and domestic animals and can also harm humans. Toxin
production by other algae may occur in some situations. Toxic populations of the eukaryote alga
Prymnesium Parvum (prymnesiophyceae), for example, may develop in the brackish waters of
tidal or coastal freshwater systems causing dramatic changes in fish communities. In the marine

6. environment, toxin production by dinoflagellates assumes greatest significance contaminating
sea water, but also causing shellfish to become poisonous due to ingestion and bio concentration
by these organisms. Major categories of toxins include Neurotoxins including Anatoxina and
Saxitoxin & Hepatxins including microcystins and nodularians.