CHAPTER - II
REVIEW OF LITERATURE
Wetlands are probably the earth’s most important freshwater resources and are also the
most threatened ones. Wetlands influence the surrounding environment where these exist and
also play a vital role in the socioeconomic lives of the people along its vicinities. There is no
single, formal definition of wetlands among ecologist, managers or government regulators
(Dennison, 1993; Mitsch and Gosselink, 1993). Due to the complex nature of wetlands,
ecologist, managers and government agencies have struggled to identify a formal regulatory
definition of wetlands. The regulatory definitions are often different from the ecological
definition identified in the scientific literature, as there is no universally accepted definition
of wetlands because of the large number of characteristics that describe wetlands and their
somewhat arbitrary boundaries. In USA, the state of Washington as well as most other states
and local governments have accepted the regulatory definition developed by the U.S. Army
Crops of Engineers and the U.S. Environmental Protection Agency. This definition ascertains
that wetlands are those areas that are inundately surface or ground water with a frequency
sufficient to support plants and animals that depends on saturated or seasonally saturated soil
conditions for the growth and reproduction (Cowardin et. al. 1979).
The National Research Council of U.S.A in 1992 simply identifies wetlands as transitional
areas between terrestrial and open water system, whereas in 1995 the NRC defines them as
“an ecosystem that depend on constant or recurrent, shallow inundation or saturation at or
near the surface of the substrate (NRC, 1995).
Other wetland scientist ecologically define a wetland as an ecosystem that “ arises when
inundation by water produces soils dominated by aerobic processes and forces the biota,
particularly rooted plant, to exhibit adaptation to tolerate flooding (Keddy, 2000).
Marshes, swamps, and bogs have been well-known terms for the common people, but
during the mid-1970s an attempt has been made to group these landscape units under the
single term “wetlands”. According to Lefor and Kennard (1977) wetland definition may
focus on particular attributes of inland wetland definitions. A botanist’s definition of
wetlands would emphasize the occurrence of certain plant species and certain plant
communities and the wetness conditions promoting their colonization. A multiple definition
and criteria have been developed for classification of the wetlands for different purposes. The
primary purpose of this classification is to identify and describe wet habitats to aid in their
inventory, assessment, and management.
The International Conference on Wetlands and Waterfowl held at Ramsar, Iran in 1971
emphasized on the protection and conservation of wetlands worldwide. The most significant
aspect of modern efforts for environmental protection has been the realization that
conservation and development must go hand in hand. This sustainable development has been
placed high on the political agenda, both internationally and nationally. Giving continued
high priority to implementation of the ‘wise use’ concept should therefore be an important
part of a strategy to strengthen and give more political weight both to the Ramsar Convention
and to wetland conservation in general. The Ramsar definition of wetland is quite broad,
extending the water ward depth of wetlands to 6m, thereby including many “deepwater
habitats” of the U.S. definition in the concept of wetland. The definition also recognizes that
wetland ecosystem may contain other habitats i.e. riparian habitats and deep open water areas
as vital components that are virtually inseparable from the wetland itself. Although not
explicit in the definition, it also includes “human-made wetlands” (Ramsar Information
Bureau, 1998). On the other hand, the classification of wetlands is extremely problematic.
Although considerable effort has gone into the development of national and regional wetland
classification, the only attempt at establishing a global system has been under the auspicious
of the Ramsar Convention on wetlands of International Importance. In view of the fact that
the Ramsar convention has now 168 contracting parties worldwide, it is suggested that the
convention’s definition and classification system should be adopted generally for
international purpose.
In this chapter a review of existing literatures on wetlands especially on the degradation of
the wetlands, resources utilization, wetland aquatic macrophytes and their phytosociological
characteristics, physico-chemical properties of water and soil, productivity of aquatic
macrophytes have been discussed relating to the objectives of the present study.
According to Croft et. al. (1989) the majority of information on research work on
wetlands of India come from Keoladeo National Park, Point Calimer, Chilka Lake and the
Sunderbans or from specific regions such as Gujarat and Ladakh. Wetlands result
generally from interactions between the land and open water and often lie sand witched
between the two systems. These interactions form a key factor in wetland management
according to Gopal (1990). Studies on one of the biggest wetland in the northern region
of India, the Harike wetland and its management were carried out by Singh (1990).
Chatrath and Acharya (1990) also conducted management studies on Chilka Lake and arrived
on the concept of optimal sustained utilization of resources of the lake as the key to the
management strategy.
Most of the wetlands of the world are at the verge of degradation due to the rampant growth
of invasive aquatic weed i.e. Eichhornia crassipes. In a balanced ecosystem aquatic plant
population is kept in check through interaction of several physical, chemical, and biological
factors operating both within and outside the water body. But when for some reason this
balance is disturbed, rapid changes in the entire web of life are inevitable, including the
luxuriant growth of aquatic plants. There are three major reasons for the occurrence of
aquatic weeds in water bodies in the country and elsewhere (i) Overenrichment of water
bodies with plant nutrients reaching there through run-off from agricultural lands, as well as
through release of town sewage loads in them. (ii) Heavy silting of water bodies from eroded
soils of catchment areas usually caused by felling of trees and non-adoption of land capability
classification norms. (iii) Introduction of extraneous aquatic plant species from distant
continents. The first two causes lead to accelerated ageing of water bodies which then
become increasingly shallow and polluted with essential plant nutrients and are congenial to
the growth of masses of aquatic plants as weeds. When this phenomenon continues over
years, the ponds and lakes may turn into marshes and eventually, into dry places. The third
reason for occurrence of aquatic weeds are the absence of their natural enemies, chiefly
arthropods and plant pathogens which they escaped while they were transported deliberately
or accidentally from their places of origin to new continents (Gupta, 2001).
Now almost every state in India has aquatic weed problems but in certain states these are
particularly serious. This noxious aquatic vegetation is a serious concern to the freshwater
wetlands, irrigation systems, fishereies and flooded rice fields. The destruction of both
Brahmaputra and Barak valley wetland system of Assam has started with the arrival of the
water hyacinth from Central America more than a century ago (Gupta, 2001).
Wetlands in India are facing tremendous anthropogenic pressures such as rapidly
expanding human population, large scale changes in land use and cover and improper use of
watersheds, which in turn greatly influence the aquatic biodiversity as well ( Prasad et. al.,
2002; Kumar and Gupta, 2009; Ramachandra, 2010; John and Francis, 2010 ).
The wetland resources can be collected for a number of purposes such as food, fodder,
vegetables, medicines, bio-fertilizers, small scale industries and other miscellaneous
purposes. Besides, many terrestrial weeds are also found in the ecotone region of wetlands
that possess several medicinal properties. The study of such weeds having medicinal
properties from the crop fields have already been reported by Bhattacharjya and Bora (2008),
many of which grow in the ecotone region of wetlands of Nalbari district of Assam as well.
Studies on medicinal plants which also grow in the same ecotone region and are used by
Bodo tribe of Nalbari district of Assam, traditional use of such type of weeds used as herbal
medicine by Madahi tribe of Nalbari district of Assam, and ethnomedicinal uses of plant
species which also grow well in the ecotone region of wetlands and terrestrial habitats, used
by the Sarania tribe of Nalbari district of Assam have already been reported by Bhattacharjya
et. al. (2001, 2002, 2006) The study on herbal medicines obtained from the plant species
growing in the marshy habitats of wetlands are used by the common people in Barpeta
district of Assam situated in the adjacent area of the present study site was also carried out by
Bhattacharjya et. al. (2008).
Wetlands with their diverse aquatic macrophytes have attracted the attention of botanists
since early 20th century. Macrophytes play an important ecological as well as economic role
in aquatic ecosystem. They are also known as producer of aquatic ecosystem. They produce
enormous biomass and play a dynamic role in the productivity and nutrient status of the
wetlands. They contribute significantly to the productivity of water bodies, mobilize mineral
elements from the bottom sediments and provide shelter to fishes and other wildlife animals.
Macrophytes are also known as hydrophytes or aquatic plants as they are growing in water.
Most wetland plants do not grow strictly in water or very wet soils, but grow in terrestrial
habitats also, especially under mesic soil conditions (Curtis, 1959). Aquatic plants are the
best adapted and most specialized of the wetland plants, since they spend their entire lives in
water. Such an existence necessitated development of a host of adaptations ranging from
morphological structures for support, waterproofing, and buoyancy to reproductive
adaptations for pollination and germination to physiological mechanisms. Many aquatic
species are stimulated by flooding and send their shoots above the flood level (Jackson and
Drew, 1984; Ridge and Amarsinghe, 1981; Blom et. al., 1996). The adaptations of aquatic
plants for their life in water are well documented by various workers (Arber, 1920;
Sculthorpe, 1967; Hutchinson, 1975). To aid in using plants to identify wetlands, a national
list of vascular plant species that occur in wetlands has been prepared by the federal
government viz. U.S. Fish and Wildlife Service with cooperation from the Army Crops of
Engineers, Environmental Protection Agency, and Natural Resources Conservation Service
(Reed, 1997). In reviewing the scientific literature, nearly 7000 species of plants were
reported growing in United States wetlands. The 1988 U.S. national list of wetland plants
contains 6728 species out of a total of approximately 22,500 vascular plant species that exist
within all habitats in the United States and its territories and possessions (Reed, 1988).
Although the list is lengthy, it does not contain the majority of U.S. plant species, which are
virtually intolerant of flooding or prolonged soil saturation during the growing season.
Roughly one quarter (27%) of the species on the national wetland plant list is represented by
obligate wetland species i.e. more than 99% of the time of occurrence of plant species in the
wetlands under natural conditions (Tiner, 1991). Harshberger (1909) studied the vegetation of
salt marshes and of the salt and fresh water ponds of northern coastal New Jersey. Wells
(1928) studied plant communities of the coastal plain of North Carolina and their
successional relations. Kantrud et. al. (1989) studied the vegetation of wetlands of the Praire
Pothale region in Northern Praire wetlands. Hogland and Jones (1992) recorded the wetland
and riparian flora of the upper Green river basin, south central Kentucky.
Several works relating to aquatic and wetland flora have been carried out by many workers
throughout the world including various parts of India. Earlier works on floral diversity in the
Indian subcontinent were carried out by J. D. Hooker during 1872-1897. Considerable
literatures on aquatic plants of India were contributed by Biswas and Calder (1936,
revised in 1954), Mirashi (1954), Bhadri et. al. (1961), Subramanyam (1962), Chauhan
(1971), Gupta (1979), Kachroo (1983), Srivastava (1987) and Singh (2006).
Majumdar (1965) studied aquatic and semiaquatic flora of Calcutta and adjacent localities,
Rao (1971) studied the ecological study of the three freshwater ponds of Hyderabad, Kaul
(1971) studied the production and ecology of some macrophytes of Kashmir lake, Gopal
(1973) carried out a survey of Indian studies on ecology and production of wetland and
shallow water communities, Thomas (1976) made some ecological survey of aquatic plants
of Kerala. Literature on new taxa of certain hydrophytes from Kerala had been reported by
Sivarajan (1976), Chitranshi and Bilgrami (1986) studied a comparative ecological studies
on two ox-bow lakes of the river Burhi Gandak. Swarnalatha and Narasingarao (1998)
studied the ecological studies of Banjora lake with reference to water pollution. Parihar et. al.
(2000) studied the macrophytic and planktonic components of two contrasting wetlands in
Midnapore district,
The literatures published on aquatic macrophysics are very scanty to northern and central
parts of India. Significant works of aquatic macrophytes were carried out by several workers
including Kachroo (1959), Majumdar (l965), Deb (1975), Ghosh et. al. (1993) in Bengal;
Jha (1965) in Bihar; Maheshwari (1960), Seerwani (1962), Unni (1967), Srivasthava and
Kumar (1987) in Madhya Pradesh; Mirashi (1954), Karthikeyan et. al. (1982), Dhore et.
al. (2013) in Maharashtra; Singh (1990), Devi (1998), Devi (2000), Devi (2001), Devi
(2002), Usha (2002) in Manipur; Patnaik and Patnaik (1956), Hora et. al. (1955) in Kashmir;
Maheshwari and Singh (1973), Nair and Kannodia (1959) and Singh (1978) in Rajasthan;
Singh and Singh(1972), Singh and Tomar(1982) and Maheshwari and Tomar (1983),
Maliya and Singh (2004), Misra and Narain (2010) in Uttar Pradesh; Sukumaran and Raj
(2009), Udayakumar and Ajithadoss (2010), Sukumaran and Jeeva (2011) in Tamil Nadu.
Prasad (1988) and Prasad et. al. (1996) studied the flora and wetland angiosperms of
Keoladeo National Park in detail. Ghosh et. al. (1993) investigated the phonological studies
in aquatic macrophytic plants of Lower Gangentic Deltas, West Bengal. Significant work on
Subansiri river ecosystem of North east India was carried out by Dutta et. al. (2010). Dutta et.
al. (2010) investigated the pre impact studies of the 2000 MW Lower Subansiri Dam on
certain aquatic environmental aspects of downstream of the river Subansiri with special
reference to plankton and fishes. Dutta et. al. (2011) carried out an investigation on the
influence of riparian flora on the river bank health of a Himalayan river before being
regulated by a large dam in North East India.
In Assam some researchers have reported about the wetlands and the aquatic plant of the
state. Some important contribution was carried out by Kar and Barbhuiya (2000). Rao and
Rabha (1966) studied the contribution to the Botany of South Kamrup district. Acharjee
(1997) carried out an ecological studies and productivity of some beel in lower Brahmaputra
Basin. The works regarding the ecological studies of wetlands of different parts of Assam
were done by the few workers including Verma (1971), Malakar (1995), Dutta (2005), Saikia
(2007), Deka and Sarma (2014), Sarma and Borah (2014), Hazarika and Borthakur (2014).
Borah and Sarma (2012) carried out the phytosociological investigation visa vis human
impact on two wetlands of Sonitpur district of Assam. More recently, Deka and Sarma (2014)
carried out the present status of aquatic macrophytes of the wetlands of Nalbari district of
Assam. The quantative analysis of mycrophytes and physicochemical properties of water of
the two wetlands were also reported from the Nalbari district by Sarma and Deka (2014).
There are various parameters that operate in the freshwater wetland ecosystem and
determine the health of the ecosystem. Basically the parameters cover physical, chemical and
biological components and a detail study on these parameters will help in understanding the
appropriate structural and functional aspects of an ecosystem and to devise suitable
mechanism for sustainable development of the ecosystem.
A number of studies and various physicochemical and biological aspects of water of
wetlands were done in all over the world including different parts of lndia. Important
contributions were made by Hutchinson (1937), Gonzalves and Joshi (1946), Sarup
(1961), Khan and Siddiqui (1970), Mahajan (1980), Singh et. al. (1982), Handoo and Kaul
(1982), Kulshreshtha and Gopal (1982), Seshavathararn and Chandramohan (1982), Vyas
(1984), Khatri (1984) and Ramalingam and Jayaraman (1985).
Munawar (1970) studied the limnological studies of freshwater ponds of Hyderabad,
Puttaiah and Somashekhar (1987) studied the limnological studies on certain freshwater
bodies of Mysore district of Karnataka, Upadhyay (1988) studied the physicochemical
characteristics of the Mahanadi estuarine ecosystem in East coast of India, Sarwar and Wazir
(1991) studied the physicochemical characteristics of freshwater ponds of Srinagar
(Kashmir), Kumar et. al (2011) recorded an assessment of seasonal variation and water
quality index of Sabarmati River and Kharicut canal at Ahmedabad, Gujarat.
Reid (1961) stated that solubility of oxygen in water is increased by lowering the
temperature. Other important contributions include those by Sheshavatharam (1990), in
Kolleru lake, Andra Pradesh and Sheshavatharam et. al. (1990) in lake Kodakaria, near
Visakapatnam. Goswami et. al. (2010) carried out investigation on studies on
physicochemical characteristics, macrophytic diversity, and their economic prospect in
Rajmata Dighi of Cooch Behar district of West Bengal.
Bhuyan (1970) studied the physicochemical qualities of water of some ancient tanks in
Sibsagar district of Assam. Lal and Bhattacharya (1989) reported a short term study on the
pollution status of the Bharalu river. Acharjee et. al. (1990) carried out investigation on the
role of physico-chemical parameters in the evaluation of productivity of Dighali beel of
Nagaon district of Assam. Baruah et. al. (1997) investigated the study on the water quality of
Elenga beel at Jagi road in central Assam. Dutta et. al. (2010) studied a statistical overview of
certain physicochemical parameters of river Subansiri in North East India.
The occurrence and distribution of aquatic vascular macrophytes depends on water depth,
transparency, regime, chemical composition, pH and salinity (Madsen et. al., 2006; Vis et.
al., 2007). The presence of certain macrophytic species in aquatic ecosystems also depends
on composition and properties of sediments (Halgard et. al., 2001; Barendregt Bio, 2003;
Makela et. al., 2004). Owing to their high rate of biomass production, macrophytes have
primarily been characterized as an important food resource for aquatic organisms, providing
both living (grazing food webs) and dead organic matter (detritivorous food webs). On the
other hand, the process of eutrophication may get accelerated due to high productivity of
aquatic macrophytes creating large problems, particularly at the time of decomposition of
their biomass (Nikolic et. al., 2007). It has been emphasized that there is a direct relationship
between the primary production dynamics of macrophytes and light regime, temperature,
water depth, sediment composition and the amount of available nutrients (Shilla & Dativa,
2008; Zhu et. al., 2008).
The autotrophs trap the solar energy and convert radient energy into chemical energy. That
is why autotrophs are considered as convertors, transforme and transducer. The amount of
biological material present at a particular time in a unit area is called standing crop biomass
which is used to estimating the Net Primary Productivity (NPP). The energy is stored in
biomass as potential energy from where the organisms obtained their required energy in the
form of food.The total amount of solar energy fixed as chemical energy by green plant is
termed as Gross primary productivity (GPP). The primary productivity provides quantative
information of the amount of energy available for supporting life in a particular ecosystem.
The estimation of primary productivity of aquatic ecosystem is of great importance for
aquaculture management and helps to understand the food chain and food web relationship
that prevails in the ecosystem.
Several works relating to primary productivity of aquatic macrophytes have been carried
out in several workers throughout the world including different parts of India. Ambasht
(1971) investigated the ecosystem study of a tropical pond in relation to primary production
of different vegetational zones. Unni (1976) studied the production of submerged aquatic
plant communities of Doodhadhari lake of Raipur of Madhya Pradesh. Yadava et. al. (1987)
reported that primary productivity was found correlated to temperature, higher light intensity,
and vice- versa and estimated to be more in summer and monsoon months than winter.
Acharjee (1997) investigated the ecological studied and productivity of some beel in lower
Brahmaputra basin, Assam. He recorded that monthly variation in standing crop of
macrophytes in Dora beel showed maximum proliferation during winter and minimum during
monsoon. Seasonal variations in the standing crop of the macrophytes showed maximum
growth during retreating monsoon in Dora beel and Ghorjan beel, while minimum biomass
was observed in winter. Dora beel exhibited a gradual decline in biomass from the month of
January onwards and minimum in June and July. Thereafter, from August onwards it showed
fast improvement upto January. He also further added that primary productivity fluctuation in
accordance with rise and fall of phytoplankton density, temperature and transperancy were
not distinct in the three beels of lower Brahmaputra basin. However primary production
showed direct correlation with temperature, dissolved oxygen and PH and inverse correlation
with free carbondioxide, nitrate and phosphate. Devi (2000) recorded the phytosociology and
primary production of the macrophytes in the freshwater ecosystem of Canchipur of Manipur.
Devi (2001) studied variation in species distribution and primary production of the
macrophyte in Sanapat lake of Manipur. Devi (2002) studied vegetational structure and
primary production of the macrophytes of Ikop lake of Manipur. Pathak et. al. (2004) studied
on hydrological features of eighteen wetlands of Uttar Pradesh indicated their good
productive nature. They recorded that the decomposition of organic matter after death and
decay of macrophytes, contributed significantly to the richness of bottom soil. The organic
carbon, available nitrogen and available phosphorus were high in soil, but the same was not
reflected in the water phase, which was always found to be deficient in nutrients. The
variation in the rate of energy transformation might be due to variations in hydrological
characteristics of the wetlands. Studies showed that almost 60-70% of the gross energy fixed
by producers was actually stored by them as net energy. Nikolic et. al. (2009) studied the
primary production dynamics of dominant hydrophytes in Lake Provala. Bharali et. al. (2010)
reported on a study on primary productivity of the wetlands of Kaziranga National Park of
Assam.
The above mentioned literatures revealed some informations on the structural and
functional aspects of wetland ecosystems. There are no sufficient integrated work covering
the ecological aspect of wetlands in this part of the country to draw and effective action plan
for sustainable development of the wetlands.