Seasonal Changes in Water Quality as Affected by Water Level Fluctuations in Lake Tonle Sap, Cambodia

Lake Tonle Sap has the largest surface area of any lake in Southeast Asia. The lake’s water level varied by 8 m between seasons in 2005, which resulted in dramatic seasonal changes in the surface area. The quality of the lake water can be divided into two contrasting types in the lowand high-water-level periods. Measurements of water quality were made during the low-water-level period. Na-HCO3 type water was a characteristic feature of the water quality in the foreshore areas from March to May of 2005. Of particular interest during the low-water-level period is the ratio of chloride ions to total dissolved solids. Changes in the quality of the lake water during low-water-level periods are caused in part by an increase in the influence of discharge from inflowing tributaries as the volume of lake water decreases. In addition, seasonal changes are caused by anthropogenic contamination from mobile villages of floating and folding houses situated around the lake margin. In contrast to the low-water-level period, the dominant composition during the high-water-level period was Ca-HCO3 type water. The water quality of the lake during the rainy season does not appear to be affected by human activity but is significantly affected by reverse inflow from the Mekong River to Lake Tonle Sap.