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Coastal wetland and shoreline change mapping of Pichavaram, south east coast of India using Satellite data
Hong Yeon CHO, Lakshumanan.C
Korea Ocean Research and Development Institute
Ansan, P.O Box29, Seoul 425-600. Korea
Usha Natesan
Centre for Environmental Studies
Anna University
Chennai- 600 025, India
Introduction
Most of the human settlements along the Indian coast are located along the estuaries and deltas. In India, mangrove forests are traditionally been used for a variety of purposes like, boat-building, tannin extraction, firewood, stakes for fishing, fodder, fertilizer etc. Anthropogenic activities eliminate the protection provided by mangroves to the coastal and the inland ecosystems, further disturbing wildlife habitat and biodiversity. In south East Asia, there is a severe drive for the conversion of mangrove lands for agricultural and industrial purposes, aquaculture. The factors that severely affect mangrove ecosystems are 1) diminishing fresh water inflow, 2) increasing salinity and, 3) nutrient supply (MOEF, 1987). Prawn culture in the mangroves of Chorao Island (Goa), Chilka lagoon (Orissa) and Pichavaram (Tamil Nadu) is of great concern to different environmental groups in India. In general, the Indian mangroves are considered as degraded (Krishnamoorthy, 1995).
Importace of Wetlands in Ecological Functions
Coastal and inland wetlands play an important role in the ecological functions of wetlands in various ways. They are detailed as follows:
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Wetlands are ecosystems in which multiple natural functions (or processes) occur, and all of them are not functional in all wetlands. Various processes are operational at different times and they act in different ways. Moreover the functions of wetland, just like of any other ecosystem, are highly complex and interactive.
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Many of the wetland functions act as important strainer, and coastal wetlands can actually be regarded as stress-controlled ecosystems.
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The presence of wetlands in a hydrological basin can modify the floods by reducing the total volume of floodwater and retarding flood peaks.
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Wetlands, having dense vegetation, reduce flow velocity, which facilitates sedimentation. Moreover, ecological processes occurring within the wetlands can break up complex chemical substances into smaller ones, and even remove some of them from the system through complex processes.
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During warm period of the year wetlands store heat, this is released during winter. As a consequence air temperature is regulated.
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Wetlands constitute about 6% of the hydrosphere. It has been widely believed that most of natural and anthropogenic carbon dioxide is "trapped" by the hydrosphere, which acts as a main regulator for atmospheric CO2.
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Various autotroph organisms convert solar radiation through photosynthesis, and this net primary productivity is the basis for secondary productivity i.e., the productivity of the heterotroph organisms.
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Wetlands can play a significant role in several important functions of upland and aquatic systems, physical and biological processes, as well as wildlife and human activities.
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Wetland biodiversity is a remarkable part of Earth's biodiversity. Many species of plants and animals that depend on wetlands are also of direct economic importance. Species diversity in a wetland ecosystem is affected by biotic factors especially, the hydrological regime and the physical and chemical properties of water and the substrate.
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Wetlands provide sufficient spawning sites and protected wintering grounds. In addition many wetlands offer rich grazing materials for cattle, sheep and goats during a long period of the year.
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Vegetation from wetlands can provide materials to be used for timber and other purposes (paper, pulp, baskets, mats, etc.).
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Wetland vegetation, among other things, has an erosion control value since it retains soil and disseminates erosional forces of flowing water and waves. In many parts of the world it has been observed that coasts are being eroded to an alarming degree by sea waves following the degradation of coastal wetlands.
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Wetlands have worldwide merit due to their role in trapping atmospheric carbon dioxide.
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Wetlands have increasingly attracted the interest of the scientific community. As a result, the value and functions of wetlands are better documented. Scientific issues such as inventorying, classification, evaluation, monitoring of wetland ecosystems, biodegradation of organic matter, paleoecology, biodiversity, use of wetland habitats etc. comprise important areas in which scientific efforts are being made. With regard to the positive and negative effects of wetlands on other types of ecosystems, the already available information is insufficient. However, interest in wetlands as distinct component of coastal ecosystems, is increasing at a significant rate.
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