1.2 Ecological study of Brahmaputra River floodplain
1.2.1 Majuli River Island
Majuli River Island located in the heart of Brahmaputra River in the upper-central Assam, has been designated as one of the world’s largest river island. Majuli has recently been a proposed nomination to world heritage site under UNESCO because of its richness in cultural and ecological values. Majuli is situated in the north of Jorhat
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between 93°30' to 94°35'E longitude and 26°50' to 27°10'N latitude. Majuli extends from north to south direction with an altitude of 85 – 90 m above the mean sea level (Misra, 2013; Dutta et al., 2012). Initially Majuli was a narrow lane known as “Majali”
or “Mojali” between the river Brahmaputra and its tributary Dihing in the early 1600 century. It took a finite shape in the course of time as a result of several geographic changes. Genesis of the river island could not be traced exactly though there are evidences that earthquakes (1661-1696) and frequent floods caused the separation of the landmasses from the main track. The Brahmaputra separates Majuli sub division from the mainland on the northern side of Jorhat district in North Eastern India.
Initially the land area of Majuli was 1246 km2 till 1950, it has now reduced progressively to 925 km2 in 1971 under the stress of regular flooding and bank erosion (Space Application Centre and Brahmaputra Board 1996; Mani et al., 2003; Kotoky et al., 2003; Dutta et al., 2010).
Land area of Majuli has been comprehensively discussed and various statistics were provided by researchers. Based on satellite imagery data, the land area of Majuli has been reported as 706.14 km2, 578.38 km2 and 484.34 km2 in the time period 1966- 1975, 1998 and 2008 respectively (Dutta et al., 2010; Dutta et al., 2012). Total land mass of 50 km2 has been lost in the time period 1969 to 1994 (NBSS and LUP, ICAR, 2006). Out of this, the eroded area due to Subansiri river is 3.91 km2 (0.42% of total area) as against 46.36 km2 (5.43% of total area) eroded by the Brahmaputra river (Singh, 2011). The river island is an isolated and closed system characteristic of fluvial geomorphology. Majuli being an inherent part of the Brahmaputra River system experiences wet monsoon type of climate. The mean annual rainfall is high and more
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than 90% of the rainfall is received in the months of April, May, June, July, August, September and October. Rainfall in December and January is less than 20%. Mean temperature is 24.1°C with a range of 7° to 37°C whereas mean summer temperature is 26.8°C and winter temperature is 7.3°C (NBSS and LUP, ICAR, 2006). Majuli is an agriculture based region depending mostly on paddy cultivation, with a cropping intensity of 102% (NBSS and LUP, ICAR, 2006). Fishing is another practised occupation for livelihood. Flooding is a phenomenal and seasonal process in Majuli strongly linked to bank erosion and submergence of chars and smaller sand bars. Soils of the Jorhat district as well as Majuli vary from sandy loam to clay loam (Singh, 2011).
Majuli is composed of 12 Gram Panchayats covering an area of 37670 .98 hectares. The population of Majuli is 81731 with a density of 2.16 persons per hectare (Majuli Block Development Office, 2011). The land forms of island include seven important geomorphic units- 1) Active Floodplains, 2) Sand Bars with grass covers, 3) Sand Bars, 4) Swamps, 5) Old Floodplains, 6) Channel Fills and 7) Natural Leeves (NBSS and LUP, ICAR, 2006). Majuli is rich is wetland resource. A total of 112 wetlands covering an area of 20.13 km2 were reported in 1917 and 50 wetlands covering an area of 17.88 km2 were reported in 1966 to 1972 (Sarma et al., 2004). 64 wetlands are under Majuli Development Block, 61 wetlands are under Ujani Majuli Development Block, 6 wetlands are under Assam Fisheries development Corporation (AFDC) and 9 wetlands are under Revenue Bils (wetlands) (Nath, 2009). Technically wetlands are classified into six basic types (Keddy, 2010):
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1) Swamp: Dominated by trees rooted in hydric soils, but not in peat. Example:
mangroves
2) Marsh: Dominated by herbaceous plants that are emergent through water and rooted in hydric soils, but not in peat. Example: Marshes around the Great lakes and reed beds around the Baltic Sea
3) Bog: Dominated by mosses, sedges, shrubs or evergreen trees rooted in deep peat of low pH around 5. Example: peatlands
4) Fen: Dominated by sedges and grasses rooted in shallow peat with or without ground water movement with a pH of around 6. Most of them occur on calcareous rocks having brown mosses. Example: peatlands of northern Canada and Russia 5) Wet meadow: Dominated by herbaceous plants rooted in occasionally flooded
soils. Such vegetation during temporary flooding do not include terrestrial plants and swamp plants, but drier growing seasons may produce plant communities typical of moist soils. These wetlands are generally produced due to periodic flooding. Example: wet prairies along floodplains or herbaceous meadows on lakes 6) Shallow water: Dominated by aquatic plants submerged in water upto a level of 25
cm. Example: littoral zones of lakes
Depending on the classification given by Keddy (2010), wetlands studied in Majuli are characterized as marshes, a few wet meadows and shallow water dominated by herbaceous plants and drained by monsoon floods. The wetlands areas in Majuli are vulnerable to exploitation (fishery, agriculture, transportation and recreational activities) and contamination due to huge tourism rush and increasing population density.
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1.2.1.1 Status of work done in Majuli
Classical ecological study is lacking in Majuli, however biodiversity and geophysical properties of the river island as key components of ecological study have been reported by a few researchers (Mani et al., 2003; Kotoky et al., 2003; Sarma et al., 2004;
Sankhua et al., 2005; NBSS and LUP, ICAR, 2006; Singh, 2011; Hazarika, 2012; Nath, 2012; Sarkar et al., 2012; Dutta et al., 2010; Dutta et al., 2012; Bhaskar et al., 2013;
Bhaskar et al., 2007; Barman et al,. 2013). The overall study in Majuli River Island is represented in Table 1.1, most of the findings are available as online articles. Majority of the outcomes at the grass root level may have not been reported, though developmental activities have been conveyed by Block Development reports, Department of agriculture, Brahmaputra boards and local people in Majuli.
Table 1.1 Details of online articles based on different ecological study components in Majuli, Assam, India
Type of online articles
Flood and erosion
Development Demography Cultural
studies Geochemistry Biodiversity Agriculture Research
papers 12 Nil 2 1 2 7 7
Conference
proceedings 3 Nil Nil Nil Nil Nil Nil
Reports 12 11 Nil 2 2 3 3
Majuli is though rich in biodiversity, lack of proper documentation of the available species of flora and fauna has generated a breach between ground level and observatory data. Majuli has a rich floral and faunal diversity. The biodiversity of Majuli is under major threat to natural geophysical processes (Nath, 2011), and to some
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extent anthropogenic activities. As soon as educational institutions have started developing and research and development activities have become centralized, researchers from various places have shown their keen interest in exploring and detailing the biodiversity of Majuli. Among the floral species, the medicinal values and their ethnobotanical importance have been reported (Bora et al., 2012a, 2012b). A survey a total no. of 23 plant species belonging to15 family have been recorded and use of parts of different plants in diverse localities have been informed (Bora et al., 2012).
Study of faunal species involved exploration of fishes and amphibians in Majuli. A thorough study on fish species in Kakarikata beel and Kharjan beel (wetlands) in Majuli enlisted a total number of 82 species belonging to 10 orders, 54 genera of 23 families. Among all, Cyprinidae family was dominant with 32 species followed by Bagridae and Channidae with 7 and 5 species respectively. 6 species were endangered, one critically endangered, 19 species vulnerable, one data deficient and status of 34 species in lower risk category (Das et al., 2012). Fishes were categorized on the basis economic uses into food fish (96.4%), ornamental fish (74.4%) and commercially important fishes (40.3%). 32% of fish species were found in threatened category and 49% of fish species were lotic fishes whereas rest of the species were lentic (Das et al., 2012).
From the articles available online and from local offices, is was observed that a bulk of the research activities has been focussed on flooding, erosion and agricultural activities in Majuli. Flooding, erosion and deposition of sediment are perpetual processes in Majuli River Island. In the flooding history, the most active years
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recounted in Majuli are 1951, 1962, 1966, 1969, 1970, 1974, 1977, 1988, 1991, 1993, 1995, 1998 and 2008 (Nath, 2012).
Under the conditions of extremities of flooding and erosion-deposition, the suitability of soil and its physico chemical properties for paddy cultivation has been finely explained by Bhaskar and Sarkar (2013). Being a flood inundated island, two major components pertaining to ecological balance have been identified in Majuli.
These components are recounted as flooding erosion and sedimentation among the natural drive and crop management activities under man made adaptations.
1.2.1.2 Influence of flooding, erosion and sedimentation
Flooding in general deposits a huge amount of silt and at the same time, strong water currents aggravates the bankline erosion. These processes resulting in erosion are further boosted by the braiding nature of the Brahmaputra River (Akhtar et al. 2011).
Erosion is not only confined to banks in Majuli, surface erosion due to rainfall and land use is inevitable (Barman et al., 2013). Natural and to some extent man induced processes have been extensively studied in the last three decades (Nath, 2012; Akhtar et al., 2011; Singh, 2011; Sarkar et al., 2012; Sarma, 2013; Sankhua et al., 2005; Sarma et al., 2004; Mani et al., 2003; Kotoky et al., 2003). Researchers have explained the root causes of erosion-sedimentation processes, results of such findings have simplified our approach pertaining to the massive loss of land and biodiversity in Majuli. Reports on average annual rate of erosion in the time period 1917 to 2001 gives an account of the extent of bank erosion, loss of area of 1.77 km2 in 1917 to 1972, 1.84 km2 in 1972 to 1996 and 6.42 km2 in 1996 to 2001 was approved (Sarma et al., 2004). Sarkar et al.
(2012) demarcated the range of bankline erosion in selected two reaches of Majuli,
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analyzing satellite images of Indian Remote Sensing (IRS) from 1990 to 2008, they have identified the North Bank and South bank erosion and deposition profiles delineating Majuli (near Bessamora) and upstream Majuli (near Sibsagar). Some other reports indicate total erosion of 32.79 km2 and total deposition of 9.07 km2 in the South bank and total erosion of 64.27 km2 and total deposition of 0.73 km2 in the North Bank of Brahmaputra River (Department of Water Resources Development and Management IIT Roorkee 2012). Satellite imageary revealed that Majuli land area has reduced from initially 1245 km2 till 1950 to 577.65 km2 and finally to 376.93 km2 in 2002 under the strong circumstances of flooding and erosion (Kotoky et al., 2003; Sankhua et al., 2005). Similar data were published by Space Application Centre, Ahmedabad and Brahmaputra Board (SAC), they have reported a reduction of land area from 1250 km2 in to 925 km2 in 1971. Mani et al., 2003 described relevant figures specifying loss of land area in the time period 1991 to 1997, erosion in 1900 ha and deposition of sediment in 700 ha of land respectively. Remote sensing analyses of satellite images by Sankhua et al (2005) showed that the area of Majuli has declined by 39.30 km2 in the time period 1990 to 2002. Barman and researchers (2013) have detailed the loss of soil or surface erosion directly correlated to land use processes or vegetation cover and average rainfall of 2048.62 mm, documented in the time period 1970 to 2008. Remote sensing and model output data quantified the annual loss of soil from 7.53 to 8.39 km m-2 and reduction in vegetation cover from 237.69 m2 to 86.21 m2 in the time period of 1975 to 2008.
Flooding and erosion-deposition processes influence land cover/land use undertakings, alter and disturb normally growing flora and fauna. Submergence of
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small islands and chars has immensely affected the livelihood and economic condition of the inhabitants in Majuli. Huge deposition of silt and fine sand has put the farmers under a bitter experience of loss of assets and economic commodities. Flooding leads to anoxic conditions in submerged soils that deprive plants and microorganisms from oxygen (Unger et al., 2009). Every year flood deposits a layer of silt over land cover and vegetation, the nutrient status of land is disturbed and growth of microorganism in the topsoil and subsurface soil are suppressed due to lack of oxygen and moisture and thereafter rate of transformation and decomposition of organic matter is slowed down (Fifield, 2004). Vegetation is a necessity because it keeps the nutrient content intact in soil and enhances microbial activities. Deposition of silt and fine sand renders the agricultural land productive for a long term (Nath, 2012), from previous information it was found that 116.2 km of fertile agricultural land of have been covered by barren sand leading to loss of productivity of the area (Sarma, 1998). The entire ecosystem of Majuli is distressed and ecological disturbances have a direct link with the biodiversity of the places affected. Several species of plants, migratory birds and river dolphins have diminished in course of time, results were prominent in Bongaon and Kamalabari in the southern part of the island and a few places in the northern eroded part of Subansiri River (Hazarika, 2012).
1.2.1.3 Influence of crop management activities
Agriculture, horticulture, animal husbandry and fishery are the chief practices adopted by local farmers under Majuli Development Block and Ujani Majuli Development Block (Block Development Report, Majuli 2011). Utiliztion of modern techniques and introduction of high yielding varieties and fertilizers in cropping system in Majuli has
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taken a better form in the recent decades. Paddy cultivation is main agricultural practice in Majuli. Wetlands provide a good platform fulfilling the water and nutrient requirement for paddy cultivation. Other crops cultivated in Majuli are mustard potato, lentil, cowpea, vegetable crops and a few cereals. The inclusion of crop management activities has left an influential effect on the microbial communities in the soil.
However the application of weedicides and pesticides has been reported as minimal when surveyed among the local inhabitants. In addition to it literature review on use of weedicides and pesticides showed passive results (ICAR Proceedings, 2011).
The areas cultivated for crops are mostly active floodplains, old floodplains and channel fills (NBSS and LUP, 2006 and Bhaskar et al., 2013). These flood inundated land forms are characterized by deposition of sediments differentiated into silt and fine sand with mineral composition like tourmaline, rutile, zircon, epidote, kyanite, silimanite, staurolite, micas (biotite and chlorite), hornblende, zoisite and opaque minerals and clay content containing mineral as illite, kaolinite and chlorite (Singh, 2011). Deposition of flood driven sediments and its role in cropping activities can be directly correlated to the microbial abundance in the soil (Unger et al., 2009).