129 Workshop on "Sustainable development and management of ground water in West Bengal and future of irrigation vis-a-ǀis arseŶic coŶtaŵiŶatioŶ iŶ grouŶd ǁater” Central Ground Water Authority & Central Ground Water Board Eastern Region, Kolkata-700 091 19 th February 2013 A CASE STUDY ON THE CHANGING PATTERN OF WETLANDS IN WEST BENGAL AND ITS POSSIBLE IMPACTS ON GROUNDWATER RESOURCES Sayan Sinha, Lipi Kundu Basu, Anindya Halder * and Tapan Chakraborty Geological Studies Unit, Indian statistical Institute, Kolkata-700108 INTRODUCTION Water is the most valuable natural resource and is indispensable for all economic and social development. However, with ever increasing population, industrial growth, water pollution and atmospheric changes, the water availability per capita is shrinking day by day. Growing water scarcity and increasing water demands are expected to reduce diversion of water for agriculture in the future. Efforts are needed to utilize the available limited water resources efficiently. Water resources not only provides water for irrigation but also provide water for a range of other productive uses such as home gardens, livestock, fishing and aquatic products, and micro enterprises such as brick making. In the lower gangetic plain of West Bengal, wetlands are used as multiple systems and have significant impacts on livelihoods of the local people through the most important benefit arising from fisheries as well as wetland cultivation and jute retting. We know that wetlands are the one of most important natural source of water and it maintains the food chain, ecological balance and absorb pollution. Wetlands are known to play important role in ground water recharge, flood control, reduction of soil erosion and detoxifying surface water from many of its toxic and metal ion concentration (Greb et al., 2006)But the wetlands are threatened by the continuous expansion of the urbanization. ROLE OF GROUND WATER IN WETLANDS: Groundwater hydrology is fundamentally important to wetland science. The absence of groundwater beneath a wetland, may prevent the build-up of saturated conditions at the surface and groundwater inflow in many wetlands, and is a critical component of their budget. For most wetlands, the temporal pattern of drainage to and from groundwater storage provides a key control on the water table regime. Where upward groundwater flow occurs, water table can be maintains close to the wetland surface even in times of droughts. In contrast, in the absence of groundwater flow, rapid water table draw down can occur if precipitations fall during times of high evapotranspiration. Alternatively, a reduced flux of water, comprising groundwater recharge from a wetland, can produce a rapid or sustained water table fall. Ground water also tends to be chemically distinct from surface waters with higher concentrations of many elements, particularly K + and Ca2+, and lower concentration of phosphate in comparison with other water sources (Wassen et al. 1990). Ground water fed wetlands therefore tend to be more nutrient rich than those fed by solely surface water and may enable ground water fed wetlands to support distinctive vegetation communities characterized by higher biomass and plant height, in comparison with adjacent areas that do not receive ground water inflow.