Threats to Mangrove Forests

Abstract

The chapter presents a comparative account of trace metal distribution, their accumulation in sediments as well as in biota across the Indian and Bangladesh estuarine-mangrove complex through published literature. The study shows that trace metals like Fe and Cd show high contamination in most of Indian and Bangladesh mangrove ecosystem whereas other trace metals like Al, As, Cr, Co, Cu, Mn, Ni, Pb and Zn, show variable contamination in different mangrove settings with ‘low’ to ‘moderate’ value. Tsunamigenic sediment shows higher concentration of almost all trace metals due to waste and discharge brought by tsunami wave or sediment from deep shore of ocean. Speciation of trace metals show dominance of Fe, Cd, Cu, Ni, Pb and Zn mostly in residual fraction, thus making it unavailable in prevalent environments. Whereas, Mn can be found in exchangeable fractions that are readily available and potential risks. Trace metals accumulation in fishes shows the following order Cd>As>Ni>Cu>Pb>Cr, with highest accumulation of Cd; pelagic fishes exhibit lower values of heavy metals than the bottom dwelling fishes. Bioaccumulation of Cu and Zn in both gastropods and bivalves was higher than bioavailability. So, due to increased risk of trace metals pollution in the estuarine-mangrove complex and loss of mangrove biodiversity, there is dire need of in-depth study and better management practices in the tropical mangrove ecosystem of India and Bangladesh.