Effects of seasonal water level changes on the chemical and biological limnology of Lake Murray, Papua New Guinea

Abstract

Lake Murray, with a surface area of 647 km² and a high-water convoluted shoreline 2038 km long, is the largest lake in Papua New Guinea and exhibits marked seasonal fluctuations in water level. The fall in water level of 4 m between April and December 1982 was accompanied by a marked rise in pH (from 5.3 to 9.6), conductivity (from 12 to 100 µS cm^-1), total hardness (from 80 to 400µM) and filterable residue (from 11 to 45 mg l^-1). In November 1982, maximum production of phyto-planktonic oxygen was 1120 mg O₂ m^-3 h^-1 at the surface but declined sharply with depth because of light attenuation by suspended solids. It was much higher than that recorded in April 1982 (250 mg O₂ m^-3 h^-1). The long shoreline and the shallowness of the lake result in a very large littoral zone. Diurnal variation in oxygen concentrations during periods of high water level indicated that the littoral zone is a very productive area of the lake. However, when the water level is low, the lake is surrounded by a wide expanse of barren mud.