Environmental Engineering Reference
In-Depth Information
change the environment. These activities alter the
amount of water going into and out of a given
location. They also may change the local albedo
by in
The rate of reclamation of marshes and par-
ticularly mangrove swamps has accelerated in
recent years in some parts of the tropics due to
the rapid expansion of pond farming of shrimps
for export. About 50 % of the mangrove forests
in the Philippines have been developed into
brackish water
uencing the ground cover and altering the
amount of sunlight that is absorbed. For example,
there is evidence to suggest that the climate of
Greece and other Mediterranean countries was
permanently changed by widespread deforesta-
tion between 700 BC and 1 AD (the wood being
used for ship building, construction and fuel),
with the result that the modern climate in the
region is signi
fl
sh ponds (Saclauso
1989
). The
area converted in Thailand is estimated to be
about 27 % and in Ecuador about 13
14 %. Such
large-scale conversions have aroused consider-
able environmental concern among the public
and development agencies.
The
-
cantly hotter and drier, and the
species of trees that were used for ship building
in the ancient world are no longer be found in the
area.
A controversial hypothesis by William Rud-
diman called the early anthropocene hypothesis
suggests that the rise of agriculture and the
accompanying deforestation led to the increases
in carbon dioxide and methane during the period
5,000
oral spectrum in coastal area has been
largely altered by aquaculture and more speci
fl
-
cally by shrimp culture. Owing to presence of
congenial hydrological parameters in terms of
salinity and nutrient level, mangrove ecosystem
has always attracted the shrimp culturists for
short-term gain without caring much about the
ambient environment. This attitude has consider-
ably affected the mangrove ecosystem. Tabuchi
(
2003
) estimated that on a global scale, the area
under mangroves is shrinking by 100,000 ha
annually due to clear cutting of timber and con-
version into aquaculture projects (Figs.
7.32
and
7.33
). In Thailand, about 65 % of the area of
mangroves was lost during 1976
8,000 years ago. These increases, which
reversed previous declines, may have been
responsible for delaying the onset of the next
glacial period, according to Ruddimann
-
'
s over-
due-glaciation hypothesis.
In modern times, a 2007 Jet Propulsion Lab-
oratory study found that the average temperature
of California has risen about 2
1991 due to an
expansion of shrimp farming in the central, east
coast and south-east regions of the country
(Aksornkoae et al.
1993
; MacKinnon
1997
) esti-
mated that by the early 1990s, Myanmar had lost
almost 75 % of the original extent, Vietnam had
lost 37 % and Thailand 84 %. By the mid of 1980s,
Brunei and Philippines had lost 20 and 67 % of
their original mangrove cover, respectively. Ear-
lier estimates suggested that by early 1980s,
Indonesia had lost 55 % of its mangroves. Chan
et al. (
1993
) estimated that Malaysia had lost 12 %
of its mangrove forests between 1980 and 1990.
According MacKinnon (
1997
), by 1993, about
74 % of mangrove area in Malaysia was lost from
their original extent. In a few regions (i.e. Latin
America and the Caribbean), however, the man-
grove area is increasing as a result of plantation
forestry and natural regeneration. The lack of
adequate data on changes in mangrove for some
south-east Asian countries prevents efforts to
report trends for the region as a whole.
-
over the past
50 years, with a much higher increase in urban
areas. The change was attributed mostly to
extensive human development of the landscape.
In coastal zone and estuarine villages, modi
°
ca-
tion of landscape is done in large scale to pro-
mote aquaculture.
The term aquaculture encompasses the culture
of aquatic species ranging from seaweed to
sh.
Oyster culture, crab culture, mussel culture and
clam culture are all the
components under
aquaculture. The mangrove ecosystem offers a
congenial, natural condition for the growth and
survival of aquacultural species. The nutrient
provided by mangrove litter and detritus pro-
motes the growth of phytoplankton and subse-
quently the zooplankton which are the natural
feed for the cultured species. This is the main
reason why coastal aquaculture farms are con-
structed on salt marshes and intertidal mud
vital
fl
ats of
mangroves.
