Response of mangroves to the change in tidal and fresh water flow – A case study in Pichavaram, South India

Mangroves grow in intertidal zone of tropical coasts and nourished by the influence of freshwater and tidal water added to local rainfall. This study attempts to spatially analyse such hydrological influence on the mangrove area over seven decades in Pichavaram, a wetland of South Indian East coast. Analysis of local rainfall, freshwater and tidal flow and spatial maps derived using Geographic Information System was carried out to interpret the influence of hydrological parameters on the extent of mangroves. The analysis shows that mangrove area has a positive correlation of 0.98 with amount of freshwater and 0.66 with tidal flow in terms of estuarine dimensions till 1991. After 1991, mangrove area is increased even with reduced amount of freshwater. Major reason for the increase in mangrove forest cover was the restoration of the wetland by avoiding stagnation of tidal water in degraded area and thereby reducing soil to support mangrove regeneration. However, this manipulation of local hydrological condition supported only one species of mangroves Avicennia marina, which is tolerant to high salinity. As indicated in this study freshwater inflow is one of the main factors that determine species diversity of mangrove plants since most of the mangrove species requires moderate saline condition for their optimal growth and biomass production. However, due to increased demand for freshwater upstream, amount of freshwater reaching mangroves are reduced. It is suggested that in order to at sustain mangrove wetlands suitable management procedures need to be evolved and applied to ensure required quantity of freshwater flow into mangrove ecosystem for required duration.