Bangladesh Sundarbans, is divided into four ranges namely Sarankhola, Chandpai, Nalianala and Burigoalini for its management. Water samples were collected near Sarankhola, Chandpai, Nalian and Burigualiny stations situated in upstream of four major river-sytems Bhola-Bolesware, Passur, Sibsa, and Khulpatua-Arpangasia during 2008-2009 in four seasons (dry: December to February; pre-monsoon: March to May; monsoon: June to August; and post-monsoon: September to November). In situ measurements for EC/TDS and pH were carried out by applying a portable EC meter with temperature sensor (Lutron CD 4301), a portable pH meter with accuracy ± 0.1 pH units (Hanna HI 98106). Quadruplicate surface water samples were collected from each of the rivers in upstream covering main rivers and creeks. Water samples for dissolved metal concentrations, calcium (Ca2+), magnesium (Mg2+), sodium (Na+), and potassium (K+) were acidified to pH<2 with HNO3 (65% conc.). Sodium and potassium were determined by flame photometer (Jenoy, England). Alkalinity, hardness, calcium, magnesium, chloride, bicarbonate and sulphate were determined in laboratory following standard methods (APHA, 1992). All sites were sampled during day time covering high and low tide.
Water chemistry data from 25 locations between 2001 and 2009 were collected from different sources such as FMRTD (2001), JOECLA (2002), IWM (2003), Rahaman et. al. (2003), Rahaman (2006) and Ara et. al.,(2009). The parameters are conductivity, TDS, pH, alkalinity, hardness, dissolved oxygen (DO), biochemical oxygen demand (BOD), chemical oxygen demand (COD), major cations (Na,+ K,+ Ca2+, and Mg2+), major anions (Cl-, SO4 2-, HCO3-), nutrients (NH4 + , NO3 - and PO4 3-), and heavy metals (Cr, Mn, Fe, Co, Ni, Cu, Zn, Pb). Tidal context was excluded in this analysis.