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2.2 MATERIALS AND METHODS
2.2.1 Description of study area .1 Majuli River Island
Majuli River Island is located in the heart of Brahmaputra River in the upper middle stretch of Assam in North East India. It has been designated as one of the world’s largest river island (Figure 2.1). Majuli is situated in the north of Jorhat between 93°30' E to 94°35' E longitude and 26°50' N to 27°10' N latitude, extending from north to south direction with an altitude of 84.50 m above the mean sea level (Phukan, 2005;
Dutta et al., 2012). Majuli subdivision is separated from the mainland on northern side of Jorhat district by the Brahmaputra. The land area of Majuli was initially 1246 km2 till 1950 which reduced to 925 km2 in 1971 due to flooding and bank erosion (Space Application Centre and Brahmaputra Board 1996; Mani et al. 2003; Kotoky et al. 2003 and Dutta et al. 2010). Total land mass of 50 km2 has been lost in the time period of 1969 to 1994 (NBSS and LUP, ICAR, 2006). Activities of Brahmaputra River and Subansiri River collectively led to bank erosion in large scales. The eroded area due to Subansiri River is 3.91 km2 (0.42% of total area) and due to Brahmaputra River is 46.36 km2 (Singh, 2011). Majuli represents a unique fluvial geomorphology and experiences a tropical wet monsoon climate. Mean annual rainfall is more than 90%,
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received in the months of April, May, June, July, August, September and October.
Winter rainfall is observed in December and January which is less than 20% of the mean annual rainfall. The mean temperature is 24.1°C where mean summer temperature is 26.8°C and mean winter temperature is 7.3°C (NBSS and LUP, ICAR, 2006). Majuli is an agriculture dominated region mostly practising paddy cultivation and has a cropping intensity of 102% (NBSS and LUP, ICAR, 2006). The land area in Majuli experiences regular flood inundation in the banks. Most of the smaller islands or sand bars known as chars get submerged during the monsoon floods. The lithogenic composition varies from sandy loam to clay loam (Singh, 2011). The unique land form in Majuli is differentiated into seven significant 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 has a huge wetland resource. A total of 112 wetlands covering an area of 20.13 km2 was reported in 1917 and 50 wetlands covering an area of 17.88 km2 was 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). Water sampling was carried out in 14 wetlands, out of which 2 wetlands are not named [Table A 2.1 (A), (B), Appendix 2].
Water and soil sampling were performed in the wetlands areas in Majuli River Island [Table A 2.1 (A), (B), Appendix 2].
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Among the wetlands studied, Kharjan (Kharjan Morisuti), Daria (Doria), Bhereki (Bherek), Sarala (Charala), Tuni (Tuninodi Balichat) and Gakhajuwa (Ga- khojuwa) wetlands are under Majuli Development Block; Kakarikata (Kakarikota) and Bhereki (Vereki) are under AFDC; and Daria (Doria dubi), Kharkhari (Kharkhori), Barbil (Dakhipat Borbil), Tuni (Tuni fishery) and Magurmara are under Revenue Bils.
Theses wetlands are open wetlands connected to Brahmaputra and Subansiri during the monsoon floods. The details of all the wetlands studied are described in Table A 2.1 (A), (B), Appendix 2.
Figure 2.1 Map of Majuli River Island showing sampling sites
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2.2.1.2 Kamrup: Amingaon and Umananda River Island
Kamrup is located between 25°46'0"N to 26°49'0"N latitude and 90°48'0"E to 91°50'0"E longitude in Assam, North Eastern India (Figure 2.2). The study sites in Kamrup are Amingaon situated on the mainland near the bank of Brahmaputra River in the north of Guwahati and Umananda River Island or Peacock Island lying on the north east of Guwahati (Figure 2.2). Kamrup is a large district in lower Assam occupying an area of around 4345 km2. The topographic features consist of a combination of hilly landscape of undulant nature. The hills are scanty at places and dispersed with plain landmass. The hilly terrain extends upto Meghalaya on the southern part that gradually converge into a flat terrain towards Brahmaputra River. These areas are characterized by presence of small hills and residual hillocks. A major part of Kamrup district is occupied by the Brahmaputra River in the heart of Guwahati city. Adjoining smaller tributaries include Puthimari, Bornoi, Nona, Kulshi, Pagladia and Kalajal. Flooding events are observed in the months of May to August every year in low lying areas. Late floods occasionally occur in September and October. Flash floods are common in rainy season (State Level Nodal Agency, IWMP, Guwahati, 2014).
Kamrup has been experiencing an average annual rainfall of approximately 1738 mm since last ten years. According to metrological data, approximately 90% of rainfall occurs between April and September with maximum incidence in June, July and August. January is observed as driest month of the year with scanty rainfall of around 5.46 mm, during the last ten years. Highest temperature is recorded at 33°C in the month of July and August and minimum temperature is recorded at 10.82°C in the
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month of January. Relative humidity is as high as 90% that creates a hot and humid climate in Kamrup. Maximum humidity is witnessed in the month of January. Kamrup is an earthquake sensitive zone and included in High Risk Zone-V of earthquake incidents, where a maximum intensity of IX can be expected (Guwahati City Disaster Management & Response Plan, 2014). Soil type varies between sandy loam, loam, sandy clay and clay loam depending on the lithogenic composition. River flow, steepness and gradient determine fertility of the alluvia in downstream areas of Kamrup (State Level Nodal Agency, IWMP, Guwahati, 2014).
Figure 2.2 Map of Kamrup showing sampling sites in Amingaon and Umananda River Island
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The research area is focussed on Amingaon and Umananda Island or Peacock Island, two economically important sites in Kamrup. Amingaon and Umananda experience a tropical wet monsoon climate in the district of Kamrup lying at an altitude of 31-55 m above mean sea level, depending on the terrain. Amingaon is known for its industrial activities in the core area. It is located between 26°11′0.5″N latitude and 91°40′1.2″E longitude in the north of Kamrup district. Umananda is a highly visited pilgrimage site, located between 26°11′47.76″N latitude and 91°44′43.44″E longitude.
Umananda is also popularized due the occurrence of endemic species of Golden langur (Trachypithecus geei), exclusively in Kamrup.
Geomorphology of the study area represents an alluvial form of soil occurring in the family of Aquic Udifluvents (Vadivelu et al., 2004), desirable for agricultural activities. Soil in Amingaon and Umananda are of sandy clay loam nature and the pH ranges from slightly acidic to slightly alkaline in nature. The vegetation profile includes large trees, herbs and shrubs of great ethnobotanical importance. Flooding is witnessed by the inhabitants residing on the banks of Brahmaputra River. Increasing population density and industrial activities in Amingaon and concurrence of huge pilgrimage mass in Umananda appears to be a daunting challenge to the ecological entities in their natural habitat. Soil samples were collected from Amingaon and Umananda River Island in pre-monsoon and monsoon seasons.