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International Journal of Marine Science 2013, Vol.3, No.23, 178-186
http://ijms.sophiapublisher.com
179
which has been widely accepted by the limnologists,
ecologist, policy makers and scientists. This states that
a coastal lagoon is a “
shallow coastal water body
separated from the ocean by a barrier connected,
at least intermittently to the ocean, by one or more
restricted inlets
”. (Phleger, 1969, 1981; Colombo,
1977; Barnes, 1980; Kjerfve, 1986, 1994; Gonenc and
Wolflin, 2004).
2 Classifications of Coastal Lagoons
Coastal lagoons are most dynamic and complex
ecosystems in the coastal zone. The hydrobiology of a
lagoon is dependent upon the geomorphology and
local environmental conditions. Thus, classification of
lagoons on a broad scale is found difficult. Coastal
lagoons, in general have been classified in to different
groups by scientists. Nicholas and Allen (1981)
classified the costal lagoon into four categories
namely (i) estuarine lagoon, (ii) open lagoon, (iii)
partially closed lagoon and (iv) closed lagoon. Later
Kjerfve (1994) had grouped the coastal lagoons into
three types of namely (i) choked, (ii) restricted and (iii)
leaky lagoons. The characteristics of these lagoons as
contemplated by him are as follows.
Choked lagoons: Choked lagoons (Figure 1A) have a
very narrow connection with the nearby sea. It
normally posses tidal oscillations reduced to 5% or
less in comparison to the adjacent coastal tide. They
are also characterized by slow flushing rate of water
and sediment, high wind induced wave action,
dominant wind forcing and irregular stratification of
different environmental parameters due to high solar
radiation and surface runoff from catchment areas.
In arid or semi-arid provinces, the choked coastal
lagoons remain permanently or temporarily hypersaline
in nature (Copeland, 1967; More and Slinn, 1984).
This type of lagoons are found in association with
river deltas or with the nearby by shore line. The
examples of such chocked lagoons in the world are:
Lagoa dos Patos and Lagoa de Araruama Brazil, in
Lake St. Lucia of South Africa, the Coorong of
Australia, and Songkla Lake of Thailand.
(ii) Restricted lagoons: Restricted lagoons (Figure 1B)
are large water bodies commonly found parallel to the
shoreline. They posses two or more inlets connected
with the nearby sea or ocean. Thus, this type of lagoon
generally experiences good tidal circulation amplified
Figure 1 Types of Coastal lagoon
Note: (A) Restricted lagoon; (B) Choaked lagoon; (C) Leaky
lagoon
with wind generated wave action. They represented
well mixed water mass and as such the chance of
vertical stratification is low. Wide range of salinity
from near limnetic to oceanic condition is noticed in
this type of lagoons. Flushing rate is faster as
compared to the chocked lagoons. The examples of
such restricted coastal lagoons are; Laguna de
Terminos of Mexico, and Lake Pontchartrain in USA
and Chilika lagoon of Odisha, India.
Leaky lagoons: Leaky lagoons (Figure 1C) are generally
elongated in nature and found parallel to shore line.
They have many inlet connections to the adjacent sea.
The characteristic features of the Leaky lagoons are
wider channels or inlets, strong tidal currents, strong
littoral drift action, strong wind action and the
salinity is somewhat similar to the nearby sea. They
experience quick flushing rate. Examples of such
lagoons are Mississippi Sound in USA, and Wadden
Zee, the Netherlands.
Another kind of classification i.e. according to the
tidal amplitude was suggested by deferent researchers,
those have been classified in to five types. They are:
(a) Isolated lagoons: Lagoons is found separated from
the nearby sea or riverine mouth region by a barrier of
rock or sediment. Less intrusion of sea water is
possible if it crosses the sand and possesses low life
span due to coastal erosion.
(b) Percolation lagoons: Entry of sea water is possible
by piercing through the sandbar more common during
storm and cyclonic conditions. Thus the lagoon can