THE LIMNOLOGY OF AN ABANDONED GRANITE QUARRY IN SINGAPORE

Abstract

A limnological study was carried out at Hindhede Quarry, Singapore where a lake has formed within the abandoned quarry pit. This site was chosen due to its tropical equatorial setting and also because lake water levels have been rising continuously. The objectives and aims of this thesis included a study of the water budget, spatial variations, physico-chemical structure, diurnal variations and a comparison between pan and lake evaporation in Hindhede lake. These were achieved by making daily visits in January 1997 and carrying out a lake survey at two sampling points in the lake. Results obtained indicated a new discovery in that lake evaporation was about two to three times greater than pan evaporation. This result questions the applicability of using the Class A pan coefficient values of 0.7 or values less than one in Hindhede lake and other lakes in the tropical region. In addition, the water budget showed a net positive increase in January 1997. Calculated annual rates of water levels rise are 0.624 m yr-1 , 0.876 m yr-1 and 1.8 m yr-1. These values were calculated from data collected during an exceptionally dry month. Horizontal differences between sampling locations were found to be negligible. Vertical variation in the form of weak physico-chemical stratification was observed. A thermocline was observed at the depths of 15-20 metres with a rapid temperature drop of 0.21 °C. The water column is stratified into the epilimnium (0.6-15 metres), metalimnium (15-20 metres) and hypolimnium (20 metres onwards). Diurnal variations were slight and the water chemistry of Hindhede lake indicate that it is an oligotrophic lake. The short duration and exceptionally dry conditions experienced during data collection implies that the data collected can at best provide results that aid in the preliminary understanding of the limnological processes at work in Hindhede lake.