Remote Sensing Application for Exploring Land Use and Land Cover Dynamics in and Around Chatra Wetland, English Bazar, West Bengal

Received: January 25, 2021 Revised: April 23, 2021 Accepted: May 28, 2021 Published Online: July 06, 2021 Wetlands are often called as biological “supermarket” and “kidneys of the landscape” due to their multiple functions, including water purification, water storage, processing of carbon and other nutrients, stabilization of shorelines and support of aquatic lives. Unfortunately, although being dynamic and productive ecosystem, these wetlands have been affected by human induced land use changes. India is losing wetlands at the rate of 2 to 3 per cent each year due to over-population, direct deforestation, urban encroachment, over fishing, irrigation and agriculture etc (Prasher, 2018). The present study tries to investigate the nature and degree of land use/land cover transformation, their causes and resultant effects on Chatra Wetland. To fulfil the purpose of the study, GIS and remote sensing techniques have been employed. Satellite imageries have been used from United States Geological Survey (USGS) Landsat 7 Enhanced Thematic Mapper plus and Landsat 8 Operational Land Imager for the year 2003 and 2018. Cloud free imageries of 2003 and 2018 have been downloaded from USGS (https://glovis. usgs.gov/) for the month of March and April respectively. Image processing, supervised classification has been done in ArcGis 10.5 and ERDAS IMAGINE 14. The study reveals that the settlement has increased by about 90.43 per cent in the last 15 years around the Chatra wetland within the buffer zone of 2 Sq km. Similarly agriculture, vegetation, water body, swamp and wasteland witnessed a significant decrease by 5.94 per cent, 57.69 per cent, 26.64 per cent 4.52 per cent and 55.27 per cent respectively from 2003 to 2018.


Introduction
Land use/land cover is an important phenomenon that reflects the intricate and multiplex interaction between the environmental factors and induced human activities, which brings land transformation. The impact of land transformation and land conversion degraded the quality of water and threatened wetland ecosystem (Fazal et al., 2011). The land transformations brought changes in morphometry, hydrology and biodiversity of a place besides validating a concurrent change in socioeconomic patterns of the local population (Jamal et al., 2019;Papa et al., 2011). Geospatial tools like ERDAS, Arc-GIS are employed for computing these changes in the geographical extent of vulnerable ecosystems (Jamal and Ajmal, 2020). Wetlands are biologically diverse and economically productive as well as an integral part of the ecosystem of the earth but are often undervalued and their conservation is neglected (Halls, 1997;Ganaie et al., 2020. "Wetlands are the areas of marsh, fen, peat-lands or water, whether natural or artificial, permanent or temporary, with water that is static or flowing fresh or brackish or salt, including areas of marine water, the depth of which at low tide does not exceed meters" (Ramsar convention bureau, 2013). Wetlands are of immense value providing an innumerable supply of goods and services to humans, still they are threatened ecosystem in a region (Mitsch & Gosselink, 2000). Wetlands perform multifarious ecological functions in water purification, flood protection, shoreline stabilization, groundwater recharge etc. and it also provides shelter and feeds thousands of different plants and animals (Boyer & Polasky, 2004;Shafiq et al., 2019). Many of the functions and values often go unnoticed. Thus, being one of the valuable components of the ecosystem, providing diverse functions, wetlands are often narrated as "biological supermarket" and "kidneys of the landscape" (Mitsch & Gosselink, 1993;Barbier et al., 1997). It also provides supporting services to the human society like ground-water recharging, flood control, water purification, water supply, soil protection but the agony is that these wetlands are also losing their overall qualities by the human interventions day by day (Wondefrash, 2003).
Unfortunately, being such dynamic and productive ecosystem, these wetlands have been affected by humaninduced land-use changes (Chen et al., 2018). The changes in land use not only change the morphology of the area but also bring changes in average temperature and humidity regimes, thereby endorsing a concurrent change in socio-economic patterns of the inhabiting local community. The disintegration and degradation of wetlands are greatly attributed to agricultural and settlement reclamations, resulting in negative ecological consequences like flooding, declining of biodiversity and extinction of several endemic species. Consequently, qualities of water in most wetlands have also been heavily deteriorated, due to waste water and effluent discharges, causing widespread eutrophication (Zhao et al., 2005).
Malda district is gifted with magnificent wetlands and water bodies. These wetlands in the district are both perennial and seasonal in nature; most of them are connected with the major rivers like Ganga, Mahananda, Kalindri, Tangon, Pagla, Punarbhaba and other small streams that flow through the district. Among these wetlands some are very old and originated naturally and some are artificial in nature (Chowdhury, 2009). According to National Wetland Atlas 2010, the district has 4939 wetlands out of which 502 wetlands are more than 2.25 hectare while 4437 are less than 2.25 hectare. Out of 502 wetlands, 382 are natural and the remaining 120 are artificial in nature. The district records the maximum number of wetlands because of its low lying surface in the state. This low-lying topography favours the formation of numerous ox bow lakes by the Kalindri River (Das, 2016). Seasonal variation of water spreading is the normal phenomenon in the district. In post-monsoon the area covered by the wetlands is 19384 hectares which decrease up to 15295 hectares in pre monsoon (NWIA, 2010). Owing to the location and significance, Chatra wetland has been chosen to conduct the present study. This wetland also experiences seasonal variation such as approx 142-hectare area is occupied by the water in post-monsoon and only 65 hectares in pre-monsoon (Kar, 2014). The Chatra wetland is an artificial wetland formed due to the construction of NH34, embankment of railways, afflux embankment (after Farakka barrage 1974). These embankments have shut off the natural drainage line and thus stagnant water started accumulating in the low land. The wetland also considered as the lung of the town (Kar, 2018). It provides numerous services to the local people living around it, including fishing, gorgon cultivation, agriculture, irrigation, medicinal plants, fodder, recreation and aesthetic values. The present research work inquires the general pattern of urban expansion and land transformation in and around Chatra wetland. The study aims to focus on the impact of these land transformations on Chatra wetland.

Study Area
The study has been conducted on Chatra wetland located in the Malda district of West Bengal. This is one of the largest artificial wetlands in the district (Kar, 2018). The latitudinal and longitudinal extent of the wetland lies between 24°58'56"N to 25°00'09"N and 88°06'38"E to 88°08'10"E. The wetland is located at the elevation of 29 metres above mean sea level in the south-west part of the district. The Chatra wetland has an area of about 142 hectares (Director of Fisheries, Malda District, 2009). The entire district constitutes of three physiographic divisions i.e. Tal, Diara and Barind region. The particular wetland lies in the Diara region and stretching from the north-west to the south-east direction in the English Bazar block. It has been found that the surrounding area of the wetland has a significant LULC change by different categories. Being the only functional town, people are attracted to settle here. The settlement is only increasing in the north-eastern side of the wetland due to its suitable location. The other side of the municipality has low built-up due to the presence of the river Mahananda. The municipality population has increased from 161,456 (census 2001) to 205,521 (Census 2011) and this expansion of population requires more land to settlement and agriculture. To fulfil their requirement they started land reclamation along the wetland. Remarkable LULC change has been seen along the wetland. For indepth analysis, the study area was demarcated by 2 Sq. km buffer around the Chatra wetland.

Contribution of Chatra Wetland Resources to the Household Economy
Throughout the globe, all the people living in and around wetlands are getting benefited by the wetland resources directly or indirectly (Das et al., 2015). Similarly, a field survey reveals that the community living around the Chatra wetland are blessed by many natural resources available in the wetland, which contributed significantly to the household economy. Products from the wetland kalmi (water spinach), sushni (dwarf water clove), hingcha (water cress), kulkhera (swampweeds), thankuni (Indian pennywort) etc, are used for medicinal purposes by the locals (Kar, 2014). People collect many items from the wetland like food, fodder, fuel, building material and plants. Some wetland dependent communities sell these products in local market and earn up to 55.02 USD per month individually (field survey, 2018). Fishing has been reported as the main occupation for some people to sustain their lives. Another important aspect is the cultivation of gorgon nut, which has a significant demand in the international market throughout the world. Now, this crop has been accepted for "International commercial crop" (Kar, 2018). The people, who are living around the wetland, get a high amount of economic support from gorgon cultivation, chest-nut and lotus for their market demand (Dutta et al., 2015). It is also observed that another commercial crop jute has a significant demand in the region. Cultivation and production of jute in the area has an important role in the household's economy. The farmers use the wetland water for jute retting (the process of extracting fibres from the long-lasting life stem or bast fibre plants) because of slow water motion which is favourable for jute retting.

Wetland Degradation
Wetlands are being destroyed and degraded; we have lost more than 50 per cent of the total wetland since 1900AD (Davidson, 2014). India is losing wetlands at the rate of 2 to 3 per cent each year due to overpopulation, direct deforestation, urban encroachment, over fishing, irrigation . Migration also plays a vital role in decreasing the wetland area; people choose the wetland area to practice land reclamation for making their residential zone and economic land (Demnati et al., 2012). Wetlands are used as a dumping site by filling domestic materials and other garbage Islam et al., 2010). Apart from these, rapid construction of residential buildings and filling up the wetland played a vital role in reduction of the wetland area (Leisangthem et al., 2012). Unscientific application of toxic materials like fertilizer, pesticides and insecticides in the agricultural fields located around the wetland area is constantly polluting the wetland ecosystem (Byomkesh et al., 2009). The Chatra wetland became a dumping site for the occupants and as well as for the residents of the town. The sewerage system of the whole town connected with the wetland. Both solid and liquid wastes dumped from the households in the wetland resulted in surface water exploitation (Kar, 2018). The increasing human population in wetland area is threatening the wetland species and migratory birds (Turner et al., 2000). Another threatening aspect for the wetland species and migratory bird is human intervention in the wetland. Locals are trapping and hunting birds for food, resulting into serious decline of bird population in the wetland, which is the major loss for the wetland habitat.
It has been noticed that, gorgon (fox nut) cultivation is a dominant tradition in the wetland as well as in the district. The cultivation of gorgon nut in the wetland needs removal of many aquatic plants, weeds, herbs, shrubs, fishes, crabs, earthworms and snakes etc (Khatun et al., 2012), which directly disturbs the wetland ecosystem. The wetland is suitable for gorgon cultivation. Gorgon nut (Euryale Ferox Salisb) has less economic input and high return output. Along with this the gorgon nut supports local population in their household economy but on the other hand threatens the aquatic plants and diversity. The cultivation needs the elimination of plants and species from the water which directly damage the wetland habitats.
The field survey of the study area reveals that the Chatra wetland of Malda district is also declining at a faster rate, due to urban encroachment and different types of land uses.

Material and Methods
To fulfil the objectives of the study, Remote Sensing and Geographical Information System (GIS) techniques have been used. Satellite imageries Landsat-7 Enhanced Thematic Mapper plus and Landsat-8 Operational Land Imager have been downloaded from USGS for the year 2003 and 2018. Satellite imageries of 2003 and 2018 were downloaded for the month of March and April respectively. The months were chosen for the clear atmosphere and cloud free sky. Spatial resolutions of both the images were 30m. For image classification band 2, 3, 4, 5, 7 and panchromatic bands were used. Image processing followed by supervised classification (with maximum likelihood classifier) was done in ArcGis 10.5 and ERDAS IMAGINE 14., to get the desired output and to calculate the area of the water body, settlement, swamp, wasteland, agriculture and vegetation. The change detection of LULC has been calculated for the time period 2003 and 2018. Moreover, for gaining an intuitive knowledge of the study area, field visit has been done.

Result & Discussion
The study involved mapping of about 31.58 Sq. Km in and around the Chatra wetland of English Bazar to detect the change in different classes from 2003 to 2018. A total of six classes has been identified in the study area i.e. settlement, agriculture, vegetation, water body, swamp and wasteland. The analysis of the LULC dataset of 2003 reveals that about 7.63 Sq. Km area have been lying under the settlement. The settlement increased along the south-western boundary as compared to the north-eastern boundary of the municipality due to the presence of the Mahananda River. It has been found that the area under agriculture is one of the main activities, about 9.43 Sq. Km. Water bodies act as the life-line to the surrounding area, which constitutes an area of about 2.89 Sq. Km i.e. 9.15 per cent of the study area, swamps cover about 1.99 Sq. Km. As per the dataset, wasteland (which includes fallow lands, barren lands, open spaces, land under airport authority) class is considered, which occupies the area of 2.37 Sq. Km while the vegetation (including orchards and mango trees) covers an area of 9.43 Sq. Km of the study area (Table 1 and Figure 2). Dataset of 2003 reveals that the study area was having ample distribution of water bodies. But the area under water bodies significantly decreased in 2018 which affects the household's economy of the community living around the wetland.      Similarly, the area under water body and swamp also decreased during the assessment period. A remarkable change of the wasteland category has been found which lost more than 50 per cent of its total area in 2018 (Figure 7).

LULC in 2018
The statistics of raster classified maps of the study area revealed that area under settlement, agriculture, vegetation, water body, swamp and the wasteland was 14.53 Sq. Km, 8.87 Sq. Km, 3.08 Sq. Km, 2.12 Sq. Km, 1.90 Sq. Km and 1.08 Sq. Km respectively in the study period 2018. Thus, it is clear that settlement occupies the maximum share in the study area, and wasteland with the least area. The probable cause for the maximum area under settlement in the study area can be associated to increase in growth rate of the population which in turn requires the increase in demand for infrastructural facilities like housing. The water body which is the basis for sustenance of life, has lost its area hence, depicts that this natural resource is under anthropogenic stress.

LULC Transformation in the Study Area
In the present study a notable change of LULC has been found in the study area. Table 4, shows LULC transformation matrix, which revealed that both the positive and the negative growth rate of different classes of land use in the study area, has taken place from 2003 to 2018. Figure 8, shows LULC change from 2003 to 2018 in the study area. In one and half decade, built-up has increased around the wetland in a significant manner; negative growth has been seen in the five classes out of six. Out of the six classes, settlement revealed a positive growth rate and the remaining five classes, agriculture, vegetation, water body swamp and wasteland depicted negative growth rate.

Settlement
The analysis of our study reveals that a remarkable change in built-up category has been seen in the poststudy. In 2003 the share of built-up was 24.16 per cent which increased up-to 46.01 per cent in 2018 (Table 3). Thus, registering an increasing rate of change in the settlement category is +90.43 per cent from 2003 to 2018. Escalating population pressure in the study area is considered as the major reason for a notable change in built-up category. The remarkable increase in rate of settlement class was significant around the wetland on its North-Eastern part.

Agriculture
Agriculture is the main activity in the district where most of the population is depending on agricultural activities to feed their dependent ones.  Figure 8). The loss of the water body in the study area is directly related to human intervention and encroachment. Construction of residential buildings, roads, farms and disposing sites in and around the water body are the main causes for declining its area. Similarly, other classes of land use/land cover depicts a noteworthy change in their respective areas like agriculture (-5.94 per cent), waterbodies (-26.94 per cent), swamp areas (-4.52 per cent). The heavy population pressures, haphazard encroachment, loss of vegetation, horticulture and gorgon nut cultivation have emerged as important factors that enhance the LULC change of the study area. The intrusion of municipal waste-water through drains into the wetland ecosystem has reinforced its degradation. This pathetic situation of the wetland under investigation demand immediate planning measures and attention of governmental and NGO'S for its sustainability before it is too late. Further it also requires operational sewage treatment plants so that no untreated sewage is disposed off to the wetland as it acts as a life-line for the town and also provides livelihood to a large number of local population. To control the built-up encroachment and human intervention in and around the wetland, there is an urgent need to pay attention to these unplanned concrete jungles for the maintained and ecological balance of these fragile ecosystems of nature.
To bring these steps in action in reality, strong will and mass awareness regarding the benefits of such ecosystem among the local people is prerequisite.