247
contain enormous intercellular spaces. These
often form regularly arranged chambers.
Physiologists now refer to such tissues as aerenchyma. This term was originally coined to
describe a rather specialised porous tissue
arising secondarily from an epidermal or cortical layer. The airspace formation is environmentally inducible.
3. Some wetland plants, particularly those of
oligotrophic soils, are apparently xeromorphic. This was originally interpreted as a
response to ‘physiological drought’. This
concept has long been abandoned. But there
is some experimental support now for the
suggestion that a reduced transpiration rate
will show the movement of reduced toxins to
the root surface and permit more effective
oxidative detoxifi cation of Fe
2+ .
4. Nutrient availability in wetlands differs very
widely. Rainfed pits are probably the world’s
most mineral-defi cient biotope. Some
groundwater fens and reed swamps receive
continuously replenished mineral supply.
They also maintain conditions which are
very favourable for nitrogen fi xation.
5. Concomitant to above, wetlands are commonly affected by both drought and fl oods.
However, the ombrotrophic mires are rarely
affected by drought, but their mineral nutrition is dependent on wind-blown dust, solutes in precipitation.
6. AM was found to exhibit a heterogeneous
assemblage of 23 species in Sone Beel.
Association of different species of AM,
forming phyto-social units, is generally
encountered in the wetlands. AM biomass
was found to vary from 0.58 to 21.90 kg/m
2
(average 2.48 ± 0.82) having the maximum in
December and the minimum in May. Further,
23 species of AM could be recorded, till date,
in the 1,600 ha (at FSL) Chatla Haor in
Assam. Also, 16 species of AM have been
recorded in the 39.2 ha (at FSL) Baskandi
Anua in Assam.
7. ‘Plankton’, the living fraction of material
found in water and moving passively by
wind or current, is composed of bewildering
varieties of microscopic organisms. Fortyseven different forms of phytoplankton were
recorded in Sone Beel. The Chrysophyta
included the maximum number and
Pyrrophyta, the least. The phytoplankton
density in the Beel varied from 48 to 5,308
(average 1,027) units/l. Nineteen different
forms of zooplankton, belonging to fi ve
groups, have been recorded in Sone Beel.
Further, studies conducted in c 1,600 ha
Chatla Haor revealed the occurrence of 18
species of zooplankton.
8. Lentic bodies could be productive or unproductive in almost the same way as agricultural land. When the input of nutrients in a
lentic body increases (either through natural
processes or by human activities), changes
which occur in the lentic body are known as
eutrophication . Conversely, lakes which
have a naturally low supply of nutrients are
called oligotrophic . Nutrients are generally
carried into wetlands by the hydrologic
inputs of precipitation, river fl ooding, tides,
surface and groundwater infl ows, etc.
Productivity refers to the amount of new living matters formed in a certain period of
time. Net primary production (NPP) is conventionally defi ned as the difference between
gross photosynthetic production and overall
respiratory loss of dry matter.
9. There is necessity of sink to take care of the
pollutants. And wetlands have considerable
ability to ‘sink’ pollutants of all kinds,
including nitrogen and phosphorus, from
sewage and agricultural drainage.
10. In addition to above, many animals live in
the wetlands. Small invertebrates inhabit
the water fi lm between soil particles. Hence,
there is an overlap of species composition
between open water and soil. These animals
include mainly the protozoans, porifers and
nematodes. They occur in both organically
rich water and in wet soil litter. Similar
overlaps are found amongst the larger invertebrates also. Further, wetlands support a
variety of blood-sucking insects whose larvae inhabit water, wet moss and litter. Many
vertebrates inhabit wetlands from the surrounding land. The swamp-dwelling catfi shes
15.6 Aquaculture
contain enormous intercellular spaces. These
often form regularly arranged chambers.
Physiologists now refer to such tissues as aerenchyma. This term was originally coined to
describe a rather specialised porous tissue
arising secondarily from an epidermal or cortical layer. The airspace formation is environmentally inducible.
3. Some wetland plants, particularly those of
oligotrophic soils, are apparently xeromorphic. This was originally interpreted as a
response to ‘physiological drought’. This
concept has long been abandoned. But there
is some experimental support now for the
suggestion that a reduced transpiration rate
will show the movement of reduced toxins to
the root surface and permit more effective
oxidative detoxifi cation of Fe
2+ .
4. Nutrient availability in wetlands differs very
widely. Rainfed pits are probably the world’s
most mineral-defi cient biotope. Some
groundwater fens and reed swamps receive
continuously replenished mineral supply.
They also maintain conditions which are
very favourable for nitrogen fi xation.
5. Concomitant to above, wetlands are commonly affected by both drought and fl oods.
However, the ombrotrophic mires are rarely
affected by drought, but their mineral nutrition is dependent on wind-blown dust, solutes in precipitation.
6. AM was found to exhibit a heterogeneous
assemblage of 23 species in Sone Beel.
Association of different species of AM,
forming phyto-social units, is generally
encountered in the wetlands. AM biomass
was found to vary from 0.58 to 21.90 kg/m
2
(average 2.48 ± 0.82) having the maximum in
December and the minimum in May. Further,
23 species of AM could be recorded, till date,
in the 1,600 ha (at FSL) Chatla Haor in
Assam. Also, 16 species of AM have been
recorded in the 39.2 ha (at FSL) Baskandi
Anua in Assam.
7. ‘Plankton’, the living fraction of material
found in water and moving passively by
wind or current, is composed of bewildering
varieties of microscopic organisms. Fortyseven different forms of phytoplankton were
recorded in Sone Beel. The Chrysophyta
included the maximum number and
Pyrrophyta, the least. The phytoplankton
density in the Beel varied from 48 to 5,308
(average 1,027) units/l. Nineteen different
forms of zooplankton, belonging to fi ve
groups, have been recorded in Sone Beel.
Further, studies conducted in c 1,600 ha
Chatla Haor revealed the occurrence of 18
species of zooplankton.
8. Lentic bodies could be productive or unproductive in almost the same way as agricultural land. When the input of nutrients in a
lentic body increases (either through natural
processes or by human activities), changes
which occur in the lentic body are known as
eutrophication . Conversely, lakes which
have a naturally low supply of nutrients are
called oligotrophic . Nutrients are generally
carried into wetlands by the hydrologic
inputs of precipitation, river fl ooding, tides,
surface and groundwater infl ows, etc.
Productivity refers to the amount of new living matters formed in a certain period of
time. Net primary production (NPP) is conventionally defi ned as the difference between
gross photosynthetic production and overall
respiratory loss of dry matter.
9. There is necessity of sink to take care of the
pollutants. And wetlands have considerable
ability to ‘sink’ pollutants of all kinds,
including nitrogen and phosphorus, from
sewage and agricultural drainage.
10. In addition to above, many animals live in
the wetlands. Small invertebrates inhabit
the water fi lm between soil particles. Hence,
there is an overlap of species composition
between open water and soil. These animals
include mainly the protozoans, porifers and
nematodes. They occur in both organically
rich water and in wet soil litter. Similar
overlaps are found amongst the larger invertebrates also. Further, wetlands support a
variety of blood-sucking insects whose larvae inhabit water, wet moss and litter. Many
vertebrates inhabit wetlands from the surrounding land. The swamp-dwelling catfi shes
15.6 Aquaculture