A PRELIMINARY STUDY OF THE PHYSICAL, CHEMICAL AND BIOLOGICAL CONDITIONS OF TWO FRESH-WATER FISHPONDS IN SINGAPORE

Abstract

The investigation has been conducted to determine the general characteristics of two Chinese carp ponds referred to as pond A and pond B. The seasonal and diurnal variations of plankton in relation to the physical and chemical factors are discussed. The bottom flora and fauna are studied and their seasonal changes traced. The seasonal fluctuations of the physical and chemical conditions of the water showed no definite patterns. However, their relationships were drawn where possible. The fluctuations of algae were not periodic and their trend was related to rainfall and albuminoid ammonia. A positive correlation between the total algae and the pigment -----was found. A comparison of the two ponds shows that pond A, being richer in nutrients, supported a higher population of algae than pond B, though the total zooplankton counts did not differ much. The bloom of Ruglena spp. occurred when values of albuminoid ammonia organic matter and nitrate were slightly higher than when Microcystis aeruginosa started to appear. Before Microcystis aeruginosa started to bloom, there was a general fall in total algae number followed by a reduction of the nutrients of the water. Chlorococcales as a group dominated the algae population in both ponds. Rotifers dominated the zooplankton population almost to the exclusion of the others. The seasonal changes in the bottom flora and fauna were not obvious. The bottom flora and fauna were generally sparse and were dominated respectively by Soenedesmus spp. and Difflugia accumulate in pond A and by Navicula spp. and Difflugia accumulate in pond B. Regarding the diurnal variation, the classical relationship of dissolved oxygen. Dissolved CO2 and pH found elsewhere in the world is also prevalent here. Dissolved ammonia was found to vary directly with albuminiod ammonia and inversely with nitrate. Phosphate and nitrite showed slight diurnal fluctuations. In both ponds, the diurnal variations of dominant forms such as Sohroederia sppm--- Proton--- Eygkeba soo and Microcyatis aeruginosa showed more or less the same trend and this determines the trend of the total algae. The algae rose to the surface during the day and this rise could be due to active multiplication and decrease at night due to feeding by zooplankton and by sinking. Rotifers showed diurnal movements which might correspond to light and algae number.