WATER CHEMISTRY IN AND AROUND THE SUNDARBANS MANGROVE FOREST, SOUTHWEST BANGLADESH

Abstract

The study presents the spatial and temporal patterns of river water chemistry at 25 sites in and around the Sundarbans. Conductivity, TDS, major cations, major anions, alkalinity, pH and hardness were determined during September 2008 to July 2009 in four seasons at Sarankhola, Chandpai, Nalian and Burigualiny from Bhola, Passur, Sipsa and Khulpatua rivers respectively. There is wide temporal variation in conductivity (from 201 µS/cm to 43.7 mS/cm) and TDS (0.13 to 31.2 g/L) from the eastern to western Sundarbans suggests low flow of fresh water into the western Sundarbans. Variation in major cations Na+ (9225 to 25 mg/L), K+ (4 to 510 mg/L), Ca+2 (26 to 273 mg/l) and Mg+2 (5 to 869) and major anions Cl- (13 to 13471 mg/L), HCO3- (102 to 180 mg/L) and SO4-2 (9 to 1414 mg/L) were also observed. Alkalinity, pH and hardness were 90 to 224 mg CaCO3/L, 6.5 to 8.3 and 85 to 4235 mg CaCO3/L respectively. Data on DO, BOD, COD, nutrients and heavy metals during 2001-2009 were collected from secondary sources. Dissolved oxygen (4.9 to 6.9 mg/L) is within the Environmental Quality Standard (EQS) of Bangladesh. BOD and COD are higher in coast than the inner part of the Sundarbans. Ammonium (0.04 to 6.74 mg/L), nitrate (0.1 to 1.4mg/L) and phosphate (0.026 to 0.252 mg/L) are present in sufficient quantity for aquatic life to survive. Heavy metal concentrations are exceeded in some areas. The study reveals that water chemistry of the Sundarbans Mangrove Forest are approaching critical value for the survival of organism.