Environmental Engineering Reference
In-Depth Information
increased weight of sediments at the top may be
the reasons for the sinking of these structures.
Trenches are long narrow depressions in the
ocean
birds. This is mainly because estuaries are enri-
ched by nutrients that are contributed through
land drainage. Moreover, the nutrient retention
capacity within the estuary is also unique due to
which the
oor that are over 6,100 m deep. The
deepest known trench in the ocean compartment
is the
fl
ora and fauna thriving within such
system never face the scarcity of nutrients.
Several de
fl
Mariana trench
of the western North
Paci
c that is about 11,000 m deep. The Peru
nitions have been forwarded to
depict the features of estuarine compartment,
some of which are highlighted here.
According toCameron and Pritchard (
1963
),
-
Chile Trench extends for over 6,120 km
(3,600 miles) along the coast of South America
and is the longest of the ocean trenches. The Java
Trench extends for a distance of almost 4,760 km
(2,956 miles) along the coast of the islands of
Indonesia. By comparison, the Atlantic has only
two, relatively short trenches, the South Sand-
wich Trench and the Puerto Rico
'
an
estuary is a semi-enclosed coastal body of water
which has a free connection with the open sea and
within which seawater is measurably diluted with
fresh water derived from land drainage
'
.
Cayman
Trench. Trenches are invariably associated with
the systems of active volcanoes and are believed
to be caused by down wrapping of the oceanic
crust beneath the continental crust.
an estuary is a
semi-enclosed coastal body of water which has a
free connectionwith the open sea; it is thus strongly
affected by tidal action and within it seawater is
mixed with fresh water from land drainage
According to Pritchard (
1967
),
'
-
'
.
a semi-
enclosed coastal body of water that extends to the
effective limit of tidal in
Perillo (
1995
)de
ned estuary as
'
Overview of Estuarine Environment
An estuary may be de
ned as a transition zone
between the freshwater and marine water with
unique physico-chemical and biological attri-
butes. According to Odum (
1971
), estuaries
belong to different class of
uence, within which
seawater entering from one or more free con-
nections with the open sea or any other saline
coastal bodies of water is signi
fl
cantly diluted
with fresh water derived from land drainage and
can sustain euryhaline biological species, from
either part or whole of their life cycle
'
fl
uctuating water-
level ecosystems
. Estuaries generally occupy
those areas of the coasts, which are least sub-
jected to marine action and thus are major sites
for development of harbours, recreational activ-
ities and appropriate aquacultural activities. In
estuaries, freshwater collected over vast regions
of the land pours into an ocean, which sends salt
water upstream far beyond the river mouth.
Each estuary has its own physical features that
'
'
.
nitions do not
include the narrowness of the system, neither
these de
Estuaries described by these de
nitions address the situation where
evaporation exceeds the freshwater supply from
rivers and from local rain. Considering all these
gaps, in recent times, estuary has been de
ned as
'
a narrow semi-enclosed coastal body of water
which has a free connection with the open sea at
least intermittently and within which salinity of
the water is measurably different from the salin-
ity in the open ocean
in
uence its ecology. These include the amount
of river discharge, depth and general topography,
speci
fl
c circulation pattern, climatic regime and
vertical tide range. Though the physico-chemical
condition in estuaries is stressful, yet, the food
availability is so favourable that the ecosystem is
packed with life. Organisms living in this habitat
therefore exhibit wide range of tolerances (i.e.,
they are mainly euryhaline). Estuaries rank
'
(
www.es.
fl
inders.edu.au/
*
Classication of Estuary
Estuaries may be of different types (Fig.
1.3
).
Pritchard (
1967
) classi
rst
among the most productive regions of marine
ecosystems as they typically contain high bio-
mass of benthic algae, seagrasses and phyto-
plankton that support large number of
ed estuaries on the
basis of the following four characteristics. They
are (a) salinity (b) geomorphology (c) water cir-
culation and strati
cation and (d)
systems
shes and
energetics.
