Brackish water or briny water is water that has more salinity than fresh water, but not as much as seawater. It may result from mixing of seawater with fresh water, as in estuaries, or it may occur in brackish fossil aquifers. The word comes from the Middle Dutch root "brak". Certain human activities can produce brackish water, in particular civil engineering projects such as dikes and the flooding of coastal marshland to produce brackish water pools for freshwater prawn farming. Brackish water is also the primary waste product of the salinity gradient power process. Because brackish water is hostile to the growth of most terrestrial plant species, without appropriate management it is damaging to the environment.

1. Brackish Water :
Brackish waterorbrinywater iswaterthathasmore salinitythan
fresh water, but not as much as seawater. It may result from
mixing of seawater with fresh water, as in estuaries, or it may
occur in brackish fossil aquifers. The word comes from the
MiddleDutch root "brak". Certain human activities can produce
brackish water, in particular civil engineering projects such as
dikes and the flooding of coastal marshland to produce brackish
water poolsfor freshwater prawn farming. Brackish water isalso
the primary waste product of the salinity gradient power
process. Because brackish water is hostile to the growth of most
terrestrial plant species, without appropriate management it is
damaging to the environment.
Technically, brackish water contains between 0.5 and 30 grams
of salt per liter—more often expressed as 0.5 to 30 parts per
thousand (‰), which is a specific gravity of between 1.005 and
1.010. Thus, brackishcovers a range of salinityregimes andisnot
considered a precisely defined condition. It is characteristic of
many brackish surface waters that their salinity can vary
considerably over space and/or time.

2. Mangrove Environment :
A mangrove is a shrub or small tree that grows in coastal saline
or brackish water. The term is also used for tropical coastal
vegetation consisting of such species. Mangroves occur
worldwide in the tropics and subtropics, mainly between
latitudes 25° N and 25° S. The total mangrove forest area of the
world in 2000 was 137,800 square kilometres (53,200 sq mi),
spanning 118 countries and territories.
Mangroves are salt tolerant trees, also called halophytes, and
are adapted to life in harsh coastal conditions. They contain a
complex salt filtration system and complex root system to cope
with salt water immersion and wave action. They are adaptedto
the low oxygen (anoxic) conditions of waterlogged mud.
The word is used in at least three senses:most broadly to refer
to the habitat and entire plant assemblage or mangal for which
the terms mangrove forest biome, and mangrove swamp are
also used, to refer to all trees and large shrubs in the mangrove
swamp, and narrowly to refer to the mangrove family of plants,
the Rhizophoraceae, or even more specifically just to mangrove
trees of the genus Rhizophora.
The mangrove biome, or mangal,is a distinctsaline woodlandor
shrubland habitat characterized by depositional coastal
environments, where fine sediments (often with high organic
content) collect in areas protected from high-energy wave
action. The saline conditions tolerated by various mangrove
species range from brackish water, through pure seawater (3 to
4%), to water concentrated by evaporation to over twice the
salinity of ocean seawater (up to 9%).

3. Mangrove forests are usually found in the tropical and sub-
tropical riverbanks, estuaries and along the coastlines, adapting
to anaerobic conditions of both salt and freshwater
environment.A mangrove communityplaysanimportantrole to
the stabilisation and maintenance of various closely linked
ecosystems, such as seagrass, coralreef andmarine ecosystems.
It represents a unique ecological niche and habitat for a variety
of marine and terrestrial animals. The amount of organic
matter produced by a mangrove community supports not only
the mangrove ecosystem itself but also its related ecosystems.
Apart from providing an important coastal habitat for many
types of species, a mangrove forest forms a community which
helps to stabilise river banks and coastlines. Mangroves
export detritus and nutrients into nearby systems that form a
complex food chain which in turn supports valuable near-shore
fisheries. In general, the mangrove forest of Bangladesh is
divided into three zones, namely the Sunderban (largest
continuous single productive forest of the world with an
area of 577,040 ha), the ChakariaSunderbanin Cox’s Bazar with
an area of 8540 ha, and the planted coastal mangrove forests.
The plantationof mangroves was introduced in the coastal area
of Bangladesh in 1964 and is still carried out in the coastal belt
of Cox’s Bazar, Chittagong, Barisal, Patuakhali and off-shore
islands, and now covers an area of 100,000 ha. Small patches of
mangroves are alsofoundalong the beltof nearlyallcoastalsub-
districts. Different types of mangrove species dominate in
different places of the coastal and estuarine areas of
Bangladesh. Fishing within the mangroves is one of the major
activities in the coastal area. Several species of fish are found;

4. common ones are mullet (Mugil spp.), marine catfish (Mystus
spp.), seabass (Lates calcarifer) and black tiger shrimp (Penaeus
monodon). Other species of shrimps are Metapenaeus
monoceros, M. brevicornis, P. indicus and Macrobrachium
rosenbergii. However, everexpanding traditionalculture of tiger
shrimp has already led to the destruction of mangroves in
Chakaria Sunderban, Moheskhali, Teknaf and Sonadia Island at
the south-east coast of the country. In 2002-3, the destruction
of mangroves for traditionalshrimp culture in the south-eastern
area was much higher than the previous. The environmental
damage and destruction of fishery resources is still unknown in
those areas. The loss of mangrove wetland in Bangladeshduring
the last 25 years is about 50-70%. Similarly, in Sri Lanka an 11-
65% andinThailanda12-25% losswere estimated .However, not
all the blame for mangrove destruction lies in coastal
aquaculture. Depending on the locality, the impact of the
destructive uses is highly variable, though the scale of
impact commonly found elsewhere is similar to that found in
Bangladesh,i.e.from (in descendingorder) clearcut forfirewood
and pool, conversion to agriculture (salt bed and aquaculture),
conversion to humansettlement, and diversionof fresh wateror
water quality changes.

5. CULTURE OPPORTUNITIES :
Brackish water aquaculture is mostly practiced in low-lying
tidal flood plains within Water Development Board (WDB)
polders, that were originally constructed to reclaim land with
potential suitability for agriculture. In many areas, e.g. in
Rampal and several other upazila's in Bagerhat District, the
private farmers have constructed light dykes along the river
banks for dual purpose of agriculture and aquaculture.
Only those areas that are low enough to permit at least 50
cm of inundation by spring tides throughout most of the
year, are normally used for shrimp culture. Excavation of
land for construction of brackish water shrimp farms is not
in practice in Bangladesh. Pumping, to supply water from
the surface or from sub-surface layers, is also not used for
aquafarming. In some places (quite common in Paikgacha,
Rampal, Pirojpur, Patuakhali, and elsewhere) many small
domestic ponds are connected with tidal creeks; these
ponds are used not only for domestic washing, but also for
shrimp and fish culture with various degrees of intensity.

6. Species for culture:
Several species of shrimp, crab and fish may naturally
occur in the brackish water aqua farms. Only two genera of
shrimp, Penaeus (mainly P. monodon)
and Macrobrachium (mainly M. rosenbergii) are deliberately
stocked in the farm ponds. P. monodon is by far the most
desired culture species. M. rosenbergii is stocked only in
areas of low salinity. Although spawning and larval
development of M. rosenbergii occur in the brackish water
region (10–15 ppt salinity), its further development normally
takes place in freshwater. The species may also grow well
in waters of low salinity. Metapenaeus monoceros, a rather
small sized shrimp, is a welcome intruder because of its
export quality; the species abundantly occurs in nature. P.
indicus and P. merguensis occur in small quantities in the
southwest zone of Bangladesh. They are also welcome in
the farms; the two species may grow to a fairly large size
and are well exportable. Metapenaeus brevicornis, a small
shrimp, makes up a substantial contribution to the total
production. This species was more or less considered a
pest in the culture systems, but it has, of late, entered the
export market to a limited extent.
Amongst the fin fishes, mullets Liza and/or Mugil spp.) are
the most desired genera; they are auto stocked. The young
ones of these fishes are occasionally collected from the wild
and stocked along with shrimp.
During the low-saline period, starting with the onset of the
monsoon, some farmers stock freshwater carp

7. (Bangladeshi and Chinese species) and/or tilapia
(Oreochromis nilotica, O. mossambica).
The most bothersome species of fish occurring in the
culture systems include a number of predators, e.g., Lates
calcarifer, Eleutheronema tetradactylum, Glossogobius
giuris, and Mystus menoda.Mudskippers are also quite
common. Congresox eels occur occasionally. Except for
the eels, all other predator fish have high demand and
command a good price in the local markets, but they can
decrease the shrimp harvest substantially.
Seed availability and collection :
Species and numbers collected :
Shrimp farming in Bangladesh still entirely depends on
natural seed supply. P. monodon is the only salt water
shrimp of which postlarvae are collected on commercial
scale for stocking. It is estimated that the number of P.
monodon postlarvae collected in 1985 was in the order of
1–3 billion. M. rosenbergii postlarvae and juveniles are
collected in the Khulna region for stocking in freshwater
ponds or in low salinity brackishwater shrimp farms. No
estimates are available of the number of M.
rosenbergii seed collected annually. Collection of mullet
seed seems to be an occasional practice in the Satkhira and
Khulna districts.
Collection gear :
Basically two types of seed collection gear are
encountered: fixed and mobile. The fixed type is a bag net,
locally called Behundi jal. The net is made of a synthetic
material called velon. The screen has a P-24 quality (24
meshes per 2.5 cm lenght). About 15 m2 material is needed

8. for one net; two guide wings require extra material of the
same quality. The cod end is generally made of second-
hand synthetic cloth. The net is fixed near the shore with a
bamboo pole and can be operated from the shore.
Table 2 - Main collection centres for P. monodon
District Rivers
Satkhira
Ichamoti, Golgasia, Kalindi, Kakshiali,
Chunar,
Chunkuri, Kholpetua, Malancha, Madar,
Aiburi, Betna,
Kapotakshi.
Khulna
Bhadra, Sibsa, Minhaj, Pussur,
Kapotakshi, Koira,
Deluti, Garaikhali.
Bagerhat Mongla, Pussur, Daudkhali.
Cox's
Bazar
Sea beach, Moiscal Channel.
The mobile nets may be triangular or rectangular. They are
made of bamboo or mangrove twig frames and P-24 velon
screen. The gear is operated either by pushing or pulling.
There is a clear scope for improvement of the existing seed
collection gears to achieve more effective seed collection
under varied environmental conditions, such as on the open
sea beach, in tidal areas with mangrove bushes, in rivers
with strong currents or floating trash, on the tidal flats, etc.
Collection season :
The seed collectors report that P. monodon seed occurs in
the main collection centres throughout the year. In the
Khulna region, the period February-May represents the

9. peak seed collection as well as pond stocking season. Later
in the year the seed demand declines, since there will be
not much time for stocked shrimp to grow to good grades
before the monsoon starts freshening the pond and river
waters. In the Cox's Bazar region the peak seed collection
period is April-June.
M. rosenbergii postlarvae are reported to be available in the
Khulna region from April. Its demand peaks in July, when
most of the P. monodon is generally harvested, the water
salinity drops and the large farms are ready for stocking
freshwater species
Seed sorting :
The seed collectors transfer their catch along with floating
mangrove twigs, leaves, etc. to earthen bowls. A group of
small children spreads the collection along with water in
white enamelled flat plates and sorts out the P.
monodon seed with plastic spoons or freshwater mussel
shells, and throws away the rest of the shrimp postlarvae
and fish fry on the shore. This leads to a collossal damage
to the shrimp and fish resources every year.
Detailed quantitative and qualitative analyses of the
collections made during the seed collection efforts have
never been attempted. Rough observations during field
visits suggested, that P. monodon postlarvae constitute at
the most one percent of the total collection; larvae and
postlarvae of miscellaneous shrimp, crabs, mysids, fish,
etc., make up the rest. If one percent of the collection counts
1–3 billion (estimated number of P. monodon postlarvae
collected from the wild), the remaining 99 percent would
count about 99–297 billion animals. This is an enormous
number of organisms, having the potential of producing a

10. large quantity of much needed animal protein for human
consumption.
FARMING PRACTICE :
General farming pattern :
Combination of aquaculture with agriculture is the normal
parctice in the southwest zone. The farming pattern
basically is as follows:
During the high salinity period (January-July):
culture of marine and brackishwater shrimp and fish and
harvesting of the marketable individuals.
During the low salinity period (August-December):
continuation of rearing of the undergrown shrimp and fish
of euryhaline nature in the low-lying areas and ditches in
the fields; culture of freshwater fish and shrimp together
with the euryhaline brackishwater species; cultivation of a
slightly salt-resistant transplanted Aman paddy in the
elevated parts of the fields; harvesting of the residual
shrimp and fish. Most of the shrimp culture activities are
carried out in large dyked areas, called polders. They are
locally known as Ghers, meaning earthen enclosures. The
dyked brackishwater region is suitable normally for one
crop of transplanted Aman paddyduring August-December,
when the water and soil salinities are low. Agricultural crop
production during January-July is difficult. The increase of
the salt content of the top soil in the dry season caused by
capillary rise of the saline ground water, limits the
possibilities for cultivation of a second crop. Freshwater for
irrigation is not available since both surface water and
ground water are saline during the dry months.

11. There is still another problem: the soil is acidic in many
places. When exposed to the sun, the soil acidity increases
further, reducing soil productivity. Instead of keeping the
land fallow during the high salinity period, many farmers find
it rather profitable to utilize the low-lying and adequately
submersible lands for fish and shrimp farming. Thus, many
tidal flood plains are used for agriculture during the wet
months and aquaculture during the dry months (rotation)
Traditional culture techniques :
By mid-December, cropping of paddy is normally
completed. Harvesting of finfish and any residual stock of
marine shrimp is also completed. Macrobrachium
rosenbergii (if stocked at all) may still grow on to a
sufficiently large size; the farmers would therefore prefer
this shrimp to remain in the field. This can be done if there
are suitable ditches or canals that can be used as
sanctuaries. The field itself, along with the paddy stumps, is
normally exposed to the sun until the beginning of February.
Then the P. monodon seed appears in good numbers and
the spring tides are high enough to adequately inundate the
field. The total period of field drying varies from farm to farm
and from place to place.
Until recently, no screens were used in the sluice structures
to prevent entry of predator animals into the farm. Screens
to prevent escape of the autostocked animals were also not
used, based on the belief that autostocked animals (and
particularly P. monodon shrimp) would not leave the farm
with the outgoing tide water before they have grown to a
large size. Sometimes farmers did use coarse bamboo

12. screens in the drainage sluices to retain the stock, but the
screens were too course to serve the purpose effectively.
Selective stocking was unknown until rather recently. A few
farmers started practizing supplementary stocking with P.
monodon and M. rosenbergii postlarvae or juveniles. Seed
collection was limited to Satkhira and Kaliganj areas. A
nursery prctice was not followed. The concept of the need
of liming, fertilization and artificial feeding to enhance
shrimp production was still to be introduced. Unaware of the
ecological needs of the shrimp, the farmers' concern was
only to facilitate entry of as many shrimp seed as possible
into the farm, and not to maintain the required physico-
chemical qualities of the water. By using these traditional
methods, with no or very little efforts for pond preparation,
liming, fertilization, pest control, selective stocking, nursing,
supplementaryfeeding,and water management, the shrimp
production rate was low, probably not exceeding 50 kg/ha
of P. monodon per year.
Present Status of the Bangladesh Sundarbans :
Physical and Chemical Environment:
Climate: The SMF is situated in the warm, humid tropical region
where mean annual minimum and maximum temperatures are 21
and 30 °C, respectively, mean annual relative humidity varies
from 70% to 80% and annual rainfall varies from 1640 and 2000
mm.
Hydrological regimes: Stream flow through Ganges,
Bahmaputra and Surma-Kushiara Rivers. originating from the
Himalayas is the largest component (about 90%) of freshwater
sources in Bangladesh .The rivers flow generally from north to
south. Out of 15.5 million km2 of catchments,Diversity 2015, 7

13. 247 only about 7.5% lie within Bangladesh and are distributed
over most parts of the country
Effect of Farakka Barrage on Salinity: Salinity increase in the
BSMF occurred for two reasons: first, the diversion of freshwater
at Farakka Barrage and second, by oceanic currents. The BSMF
is now facing the two extremes. One immediate effect of the
lower extreme is the increased salinity during the dry
period. The salinity in the northern part of BSMF increased from
7.50‰ in 1968 to 12.50‰ in 1976 for March and to 18.50‰ in
the month of May after two years of operation of the Farakka
Barrage.
Water: A direct relationship of the changed salinity (10.40‰ to
26.2‰ in March) with the TDS (8.03 to > 20 g/L) and
conductivity (16.02 to 34.14 mS/cm) was found in different
locations.Alkalinity ranged from 0.362 to 0.438 meq/L
irrespective of salinity and tides. Similar is the case with pH that
varied from 7.26 to 7.98.
Tide: Depth and duration of tidal inundation is an important
regulator of mangrove productivity. Tides help in mixing vertical
water columns, thereby providing nutrients and enriching water,
providing vertical motion to the groundwater table that may
transport nutrients to the root zones of the mangroves,
transporting oxygen to the root system, etc.Tidal waves vary in
different regions of BSMF
according to the different hydrodynamic characteristics of rivers
and cross channels. Mean tide height in the monsoon is at its
highest (2.00 to 2.86 m) and at its lowest (1.56 to 2.00 m) in the
dry period.
Soil: The forestland soil is grey in color, finely textured and the
subsoil is stratified, compacted at greater depth. At the eastern
part of the soil (having good supply of fresh sediments), the top

14. 15 cm soil layer is soft and fertile, whereas in the western part
(with little fresh sediments), the soil is a hard mass . Na content
of soils varies from 5.7 to 29.8 meq/100g, where the lower value
is found in the eastern part. Mg varies from 4.1 to 9.9 meq/100g.
Chloride is a dominant anion varying from 5.7 to 23.2 meq/100g,
and the high concentration is found in the southern and western
parts. Potassium content varies from 0.3 to 1.3 meq/100g. The
high value of the Na and Mg hampers plant growth. Organic
carbon and nitrogen are 0.62 and 0.05%, respectively. Organic
matter ranges between 4% and 10%. Soils are neutral to mildly
alkaline (6.5 to 8.0 pH). The pH in depressions with high organic
matter ranges from 5.3 to 6.4
Floral Diversity:
Vegetation of the BSMF: A total of 70 species from 34 families
of the entire Sundarbans has been Reported. From the Bangladesh
Sundarbans, 65 species (large trees 10, small trees 20, shrubs 25
and herbs 10 including two ferns) of 37 families have been
reported .Recently, a total of 115 species have been recorded,
where, in addition to more than 10 large trees, seven more
(Avicennia marina, Bruguiera parviflora, B. sexangula, Ceriops
candellana, C. roxburghiana, C. tagal, Rhizophora
apiculata) are added including 10 species of sedges, five species
of grasses, and many species from other
groups.
Phytoplankton: Phytoplankton communities consist of a total of
35 taxa including nano- and picoplankton, the number exceeds
50. Oocystis pussilla, a freshwater phytoplankton, was
recorded as dominant under all salinity conditions.

15. Benthic algae: A total of 35 benthic algae have been recorded
.Most spectacular are species of Catenella, Caloglossa,
Bostrychia and Cladophorella growing on pneumatophores and
on stems submerged during high tide; Enteromorpha intestinalis
as a drifted form, while others grow on
muddy forest floor.
Threats to the Systems:
Natural disasters and man made factors: Cyclonic storms and
tidal surges severely affect the biotic communities of the coast by
uprooting plants, eroding coastal soils, breaking stems and
branches, human settlements and lives. During the 1988 cyclone,
a total of 3,713,655 Heritiera fomes and 4,718,420 Sonneretia
apetala were damaged .Some other natural disasters that affected
the SMF include: flood and tidal surge in 1985, flood in 1987,
cyclone in 1991, flood covering 75% of Bangladesh in 1998,
floods in 2004 and 2007, cyclone Sidr in 2007, Cyclone Aila in
2009, cyclone Mahashen in 2013 destroying a large number of
mangroves, and human settlements at the impact zone.
Oil pollution: Mongla International Shipping Port has a
harboring capacity of over 70 oceangoing ships at a time. Thus,
effects of navigation and the possibility of oil slick to a certain
extent is there, and authorities have taken measures (imposing
fines) to reduce the chance of oil spills. Oil spills will affect
many of the ecological systems. Amongst fungal populations,
species of Aspergillus (75%) and Helminthosporium (about 25%)
are involved in the process of decomposition .

16. Coal-fired power plant: The under construction plant at Rampal,
about 14 km north of the BSMF, has planned to produce 1320
megawatts of electricity, and will require 13,000 metric tons of
coal per day, releasing about 8 million tons of CO2, 0.75 million
tons of fly ash and 0.2 million tons of bottom
ash annually.
Threats to carbon deposits: The growing stock (number of trees
per ha) of the BSMF was reduced to less than 50% by the year
2000
Conservation :
Sundarbans Impact Zone: A 15 to 20 km band to the north and
east of the BSMF has been considered
as an Ecologically Critical Area (Sundarbans Impact Zone) since
1999 under the Bangladesh Environment Conservation Act 1995.
The act is dedicated to the protection and maintenance of
biological diversity to achieve the long-term conservation of
nature with associated ecosystem services and cultural value. The
zone is surrounded by agricultural lands and human settlements
and consists of 154 Unions and 17 Upazilas of Khulna, Satkhira,

17. Bagerhat, Pirojpur and Borguna districts having an estimated
population of 3.5 million. They are also dependent on BSMF for
fishing, harvesting honey, Nypa leaves, etc. A commercial
logging ban is in place until 2015. There is no human
encroachment inthe BSMF
Sanctuaries: There are three wildlife sanctuaries facing the Bay
of Bengal: the Sundarbans East established in 1960, Sundarbans
South and Sundarbans West established in 1977 .Total area
of the sanctuaries is 1397 km2. UNESCO declared these
sanctuaries and the Sundarbans as Natural World Heritage Sites
in 1997.
Restricted fishing areas: There are over 210 species of fish in
the BSMF, and 120 species are harvested. They are also used as
feed for other aquatic animals. For conserving them, Bangladesh
Forest Department identified 18 small rivers in all four ranges. In
addition, measures for selective fishing and protection of brood
areas have been undertaken
National Forest Policy: Environmental policy for conservation
and protection of forest resources including coastal and marine
areas, through Ministry of Environment and Forests, GOB has
been incorporated. To reduce global warming, “Reduced
Emission from Deforestation and forest Degradation” (REDD+)
as per the Copenhagen Accord, has been implemented
Sundarbans, a natural wall: Recently, many of the cyclones that
were supposed to strike Sundarbans changed their routes towards
Chittagong, a phenomenon that is most likely due to buffering of
the atmosphere around the Sundarban Mangrove Forests and
other coastal forests, securing Bangladesh
.The BSMF is also acting against global warming by storing over
56 million metric tons of carbon.

18. Conclusion :
The Sundarbans is a deltaic mangrove forest having freshwater
influence, formed about 7000 years ago by the deposition of
sediments from the foothills of the Himalayas through the Ganges
river system. However, the discharge of sediment-laden
freshwater into the Bay of Bengal through the Bangladesh part
of the Sundarbans Mangrove Forests (BSMF) has been reduced
due to a diversion of water during the dry period from the Farakka
Barrage in India since 1975. The BSMF receives a mean
minimum monthly discharge of 0.00 to 170 m3·s−1 during the
dry period when a minimum of 194.4 m3·s−1 freshwater
discharge is needed to maintain a low saline condition inside the
forests. The zero or very low discharge through the forests allows
seawater intrusion deep inside the BSMF increasing salinity of
water and soil. This affectsthe growth of Heritiera fomes (sundri),
the tallest (at over 15 m) and most commercially important plant
and also affecting growth and distribution of other mangroves and
biota. The high salinity results increase in relatively low-priced
plants Bruguiera sexangula, Excoecaria agallocha and Sonneratia
apetala. The growing stock of 296 plants per ha in 1959 had been
reduced to 144 by 1996. Trend analysis using “Table Curve 2D
Programme,” reveals a decreased number of 109 plants by the
year 2020.