Identification of major acidic and basic species in surface water at Semenyih Dam (semi-urban area) / Norhafiza Abu Bakar

Acid deposition was first identified by R.A Smith in England in 19th century. Acid deposition appear to be an ecological issue in the late 1960s and early 1970s with acid precipitation and surface water acidification both in Sweden and around Scandavia. Over 30 years scientists have gain greater insight into the ways in which acid deposition has altered ecosystem. East Asia is receiving considerable international attention with respect to potential threats to acid deposition. East Asia already accounts for one-third of total air pollutants worldwide resulted from increasing of energy consumption. The objective of this study is to determine the presence and extent of surface water acidification of Semenyih Dam (semi-urban area) using the pH, alkalinity and also acid-neutralizing capacity (ANC) calculations. The study was conducted for three months from July 2007 to September 2007. Samplings were conducted at four points which are located along the middle of Semenyih Dam. Water samples were analyzed in-situ and in the laboratory for parameters of temperature, pH, and electrical conductivity (EC). The alkalinity and ion measurement analysis were done in the laboratory only. The concentration of base cations (Na+, Ca2+, K+, Mg2+ except NH4+) was analyzed using the Induced Coupled Plasma Optical Emission Spectroscopy (ICP-OES) and the acidic anion concentration (F־, Cl־, NO3־ and SO42-) and NH4+ was analyzed with ion chromatography (IC). The results of the concentration major ionic species in the water are as followed: Na+ > Ca2+ > K+ > SO42־ > Cl־ > Mg2+ > NO3־ > NH4+ . The base cations are the predominant species in the water. The pH values of water at four (4) sampling points were around 7 and the alkalinity values were 0.21 meq/L (above 0.002 meq/L), which indicate that the dam was not acidic. The high alkalinity and high ANC values (above 0.200 meq/L) indicate the high buffering capacity of the dam. Therefore, the values of pH, alkalinity and ANC indicate that the Semenyih Dam water resource is currently insensitive to acid deposition and safe for general human consumption and ecosystem.