Shoreline changes and its impact on the mangrove ecosystems of some islands of Indian Sundarbans, North-East coast of India

Abstract

This study aims to analyse the shoreline oscillations of three estuarine Islands in Sundarban delta and its impact on mangrove forests around the Islands. Six multi-temporal Landsat images spanning 42 years (1975–2017) have been used in the study. Band ratio was computed to discriminate the water line from the land, which was later digitized. Digital shoreline analysis system (DSAS) was employed for estimation and analysis of the shorelines changes by End point rate (EPR) model and Linear regression rate (LRR) model after laying transects offshore of the baseline. Sea level and topography of the islands have also been analyzed. To assess the mangrove health, time series Normalized Differential Vegetation Index (NDVI) analysis has been performed using the Mann Kendall Tau statistics and Sen’s slope. Mangrove degradation maps were produced from the data and combined with evidences collected from field works. The results point to a very dynamic shoreline ensuing in erosion of mangrove forests while some areas do show encouraging trends due to sustained accretion especially in the southern and eastern parts. Overall erosion is higher than accretion in the Islands. Results show that NDVI has been decreasing along patches that are near to erosion hotspots irrespective of climatic trends. Thus it can be concluded that mangrove forests are under severe stress due to shoreline ingression and sea level rise and not climatic alterations. Going forward this work could provide significant information on the nature of shoreline changes and could assist in sustainable development for Sundarban biodiversity niche management.