Director, Institute of Ocean Management, Anna University, Chennai
Email: [email protected]
Coordinator, Indo British Integrated Coastal Zone Management Training Programme
Institute of Ocean Management, Anna University, Chennai
Email: [email protected]
A comprehensive database, including the information on distribution and extent of mangrove areas and species composition is a prerequisite for mangrove management.
Mangroves are considered as one of the important and critical resources for various ecological, environmental and socio-economic resources, which has been used by coastal communities for thousands of years. They act as a barrier against cyclonic storms and act as a buffer against floods, there by averting soil erosion in the coastal zone. Deltaic environments of India’s east coast support extensive mangrove formations due to general intertidal slope and heavy siltation. The largest stretch of mangroves in the country lies in the West Bengal and in Andaman and Nicobar Islands located in the Northeast of Indian Ocean. The degradation of mangroves directly reflects on the shoreline erosion and more adversely by the sea level rise. The recent estimate of areal extent of mangroves indicates considerable loss of mangrove resources in India. Conversion of mangrove forest cover has been witnessed in mainland coastal states rather than in islands coast. Based on remote sensing mapping and previous literature it was estimated that nearly 40 percent of mangrove forest has been reduced during the last three decades. Apart from human induced causes, the various biophysical factors are affecting mangrove wetlands considerably.
The Institute for Ocean Management at Anna University has undertaken a number of studies on mangrove wetlands during the last six years especially mapping and monitoring mangrove wetlands, analysis of different satellite sensor data to demarcate mangrove zonation, degradation sites, spectral studies on mangroves using ground-based instruments, development of GIS based mangrove wetland database and Critical Habitat Information System.
Good vegetation of mangroves occurs mainly in Kutch islands of Gujarat and it is less exploited by man. Whereas, the mangroves in Maharashtra coast was highly in degraded condition due to human exploitation and industrial developments. Mangrove wetlands act as a dynamic ecotone between the land and sea, are controlled by several interacting factors such as tides, quality, quantity and periodicity of freshwater and sediment influx, topography, soil and water quality and sedimentation pattern. These factors are very much related to the land and water use and agriculture practices in the adjacent areas of the mangroves. The studies carried out by M. S. Swaminathan Research Foundation in Pichavaram area shows the degradation of mangroves due to the changes in topography and tidal water flow pattern. The studies carried out in Micronesia also claims that the biophysical factors such as geomorphology, soil and water quality, tidal level and even the microtopography of mangrove forests are controlling the formation of strand structures.
Remote Sensing Application
The important aspects in the study of mangroves are mapping and change-detection, identification of species/plant communities and biomass estimation. A comprehensive database, including the information on distribution and extent of mangrove areas and species composition is a prerequisite for mangrove management. As a first step towards this, the Institute for Ocean Management has carried out visual and digital analysis of TM, IRS and ERS data of Pichavaram mangroves in Tamil Nadu. This work has provided the status of wetlands primarily the level-I and level-II categories. The total area of mangroves has been estimated to be about 4 sq. km. Based on the analysis of TM data, the exact mangrove area alone was demarcated and the Major zonation of mangrove has been demarcated based on the ratio of TM bands 4 and 7. It is noteworthy to mention that the demarcation of mangrove areas from agricultural lands becomes more difficult in ERS-1 SAR imagery. Due to the influence of mangrove canopy structure on microwave backscattering the demarcation of dense and less dense mangroves is extremely difficult in SAR imagery. As a first attempt, the Maximum Likelihood and Fuzzy classification were attempted using IRS and TM to estimate the classification accuracy. It was observed that the Fuzzy classifier classifies the entire mangrove pixels but the MLC classifies only 88.57 % of the mangrove pixels. Considerable attempts have been made to study the spectral properties of mangroves in Tamil Nadu coast. The qualitative study on spectral response (grey level variations) of mangrove areas i.e., at-satellite reflectance were analysed using TM and LISS-II digital data. A five-meter height stand was used to acquire spectral reflectance measurements of mangrove canopy. The above experiments were conducted at Ennore, Adyar, Pichavaram and Muthupet mangrove areas during May 1994 and February 1995. Ennore mangroves are very much affected by industrial pollution. Adyar mangroves situated in main part of Madras city, which received lot of sewage. Spectral properties of twelve mangrove species were studied using ground-based spectroradiometers having MSS, IRS and TM bands. The reflectance curves have a crest at 0.52 – 0.60 mm (corresponds to band 2 in IRS and TM) and followed by a trough at 0.62 – 0.69mm. The amplitude of spectral reflectance varies in different mangrove species. Also in this study the spectral properties of mangroves were compared with various plant parameters like leaf chlorophyll and water content, leaf pattern, canopy structure and leaf adaxial surface morphology to understand its influence on spectral reflectance. The validation of spectral properties of mangrove species with plant parameters is found to be useful in studying the plant health, biomass, etc.
GIS is increasingly used in order to assist in the process of capturing spatial data, storing and retrieving them, processing relevant information from them and making this information available as required. GIS also encourages the development and use of standards of coastal data definition, collection and storage therby maintaining data integrity. Moreover, GIS in addition to providing efficient data storage and retrieval facilities, also offers the ability to model, test and compare alternative management scenarios. The development of Critical Habitat Information Systems (CHIS) based on GIS in being carried out at the Institute for Ocean Management for all the major mangrove sites in east and west coast of India. Optical remote sensing data is being used to derive most of the thematic information upto the scale of 1:25,000. For specific sites the spectral merge of LISS-III and PAN are being used to derive detailed information on vegetation cover and infrastructure availability. The external database like Oracle is being used to store the non-spatial data on physio-chemical parameters, flora, fauna, microbiological parameters, biodiversity data, etc. Finally, spatial data derived from satellite data and non-spatial data stored in the external database were integrated in the GIS and a systematic analysis is possible. In this study the Decision Support System is being developed using the CHIS to prepare management plan for the mangrove areas.
|Fig.1a:Landuse map of Pichavaram-1987||Fig.1b:Landuse map of Pichavaram-1998|
|Fig. 2: TM digital data analysis to demarcate mangrove areas in Pichavaram|