1.1 Introduction

Eutrophication is commonly considered as one major
aspect of global environment degradation (Nixon, 1995). Eutrophication is
today, both in the developed and in the developing world, one of our most
pressing environmental problems. In recent years, in one form or another, it
has received considerable media attention, mainly because of the increasingly
pressing need to maintain supplies of fresh water. However, amongst natural
scientists in general (and therefore amongst the environmental managers that
many of their students nowadays become), appreciation of the theoretical basis
of scientific understanding of the nature and causes of eutrophication as a
process (and therefore of its ultimate solutions as a practical problem) is
poor, and based on many misconceptions.

Eutrophication, which comes from the
Greek eutrophos, “well-nourished”,
has become a major environmental problem. Nitrates and phosphates, especially from
lawn fertilizers, run off the land into rivers and lakes, promoting the growth
of algae and other plant life, which take oxygen from the water, causing the
death of fish and mollusks. Cow manure, agriculture fertilizer, detergents, and
human waste are often to blame as well. In the 1960s and ’70s, the
eutrophication of Lake Erie advanced so extremely that it became known as the “dead
lake”. And many areas of the oceans worldwide ——
some more than 20,000 square miles in extent —
have become “dead zones”, where almost no life of any kind exists.


1.2 What is eutrophication?

“Eutrophication is an enrichment of water by nutrient
salts that causes structural changes to the ecosystem such as: increased
production of algae and aquatic plants, depletion of fish species, general
deterioration of water quality and other effects that reduce and preclude use. This
is one of the first definitions given to the eutrophic process by the OECD
(Organization for Economic Cooperation and Development) in the 70s. Eutrophication
is a serious environmental problem since it results in a deterioration of water
quality and is one of the major impediments to achieving the quality objectives
established by the Water Framework Directive (2000/60/EC) at the European
level. According to the Survey of the State of the World’s Lakes, a project
promoted by the International Lake Environment Committee, eutrophication
affects 54% of Asian lakes, 53% of those in Europe, 48% of those in North America,
41% of those in South America and 28% of those in Africa. All water bodies are
subject to a natural and slow eutrophication process, which in recent decades
has undergone a very rapid progression due to the presence of man and his
activities (so called cultural eutrophication). The cultural eutrophication
process consists of a continuous increase in the contribution of nutrients, nutrients,
mainly nitrogen and phosphorus (organic load) until it exceeds the capacity of
the water body (i.e. the capacity of a lake, river or sea to purify itself),
triggering structural changes in the waters.


1.3 Types of

Eutrophication is mainly of two types:

1. Natural Eutrophication, and

2. Cultural Eutrophication.


Natural Eutrophication

The process of lake aging characterized by nutrient enrichment
is called natural eutrophication. During this process oligotrophic lake is
converted into an eutrophic lake. It permits the production of phytoplankton,
algal blooms and aquatic vegetation including water hyacinth, aquatic weeds,
water fern and water lettuce which in turn provide ample food for herbivorous zooplankton
and fish.


Cultural Eutrophication

This process is generally speeded up by human
activities; which are responsible for the addition of 80% nitrogen and 75%
phosphorus to lakes and streams. Lake Mendota and Lake Washington have
undergone rapid eutrophication due to man’s activities is possible.

1.4 Common Causes of Eutrophication

first factor of eutrophication is using of fertilizers. Agricultural practices
and the use of fertilizers in the soil contribute to the accumulation of
nutrients. When these nutrients reach high concentration levels and the ground
is no longer able to assimilate them, they are carried by rain into rivers and
groundwater that flow into lakes or seas. The example refers to (appendix 1.4.A)

discharge of waste water into water bodies also cause eutrophication. (Refer to
appendix 1.4.B). In various parts of the world, and particularly in developing
countries, waste water is discharged directly into water bodies such as rivers,
lakes and seas. The results of this is the release of a high quantity of
nutrients which stimulates the disproportionate growth of algae. In
industrialized countries, on the other hand, waste water can be illegally
discharged directly into water bodies. When instead water is treated by means
of water treatment plants before discharge into the environment, the treatments
applied are not always such as to reduce the organic load, with the consequent
accumulation of nutrients in the ecosystems.

another cause of eutrophication is reduction of self-purification capacity. (Refer
to appendix 1.4.C). Over the years, lakes accumulate large quantities of solid
material transported by the water (sediments). These sediments are such as to
able to absorb large amounts of nutrients and pollutants. Consequently, the
accumulation of sediments starts to fill the basin and, increasing the
interactions between water and sediments, the resuspension of nutrients present
at the bottom of the basin is facilitated (N. Sechi, 1986). This phenomenon
could in fact lead to a further deterioration of water quality, accentuating
the processes connected with eutrophication (V. Tonolli, 2001).

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