Thermal and chemical stratification and mixing in a small tropical reservoir, Solomon Dam, Australia

SUMMARY.

• 1 The patterns of distribution of temperature, dissolved oxygen, and filterable iron in the water mass of Solomon Dam were determined at about 30 day intervals over a 2.5 year period (1981–83).
• 2 The thermal stratification, and resultant chemical differentiation of the epilimnion and hypolimnion, was the dominant limnological feature of the reservoir. A pronounced thermoline was present for most of the year and, during the stratified phase, diurnal circulation appeared to be the main mechanism for maxis.
• 3 Evidence for the presence of an internal seiche, a phenomenon commonly associated with stratified water bodies, was also observed.
• 4 An annual overturn in June-July coincided with the minimum in solar radiation. The ‘wet’ season (January-March) caused either partial or complete circulation depending on the volume of the reservoir and the rate of inflow. In 1982 the lake circulated once, fitting the warm monolithic pattern, but in 1983 there were two circulations, the first resulting from flood inflows.
• 5 The study illustrated the inappropriate nature of a thermally derived classification scheme for a small reservoir.