Light attenuation in a small tropical reservoir (Solomon Dam, North Queensland): seasonal changes and the effects of artificial aeration

Abstract

Seasonal changes in light attenuation are described for a small tropical reservoir (Solomon Dam) at Palm Island, north Queensland, and the attenuation characteristics are compared with those reported for other Australian water bodies. The major components of the water column that affect attenuation of photosynthetically available radiation (PAR) were studied over a 4-year period, including 16 months when the reservoir was artificially aerated. The pattern of light attenuation varied at different times of the year, depending largely on the stratification conditions and on the dominant phytoplankton species. The vertical attenuation coefficient for PAR varied on a seasonal basis, the major peaks being related to periods of high phytoplankton densities. The only time tripton contributed significantly to attenuation of PAR was coincident with the start of artificial aeration. Gilvin concentrations in Solomon Dam were moderately high, especially in the hypolimnion of the strongly stratified reservoir. Artificial aeration moderated the range of seasonal fluctuations in light attenuation, by reducing the density of phytoplankton in the surface layers.