Hypolimnetic oxygen consumption in Lake Taupo, New Zealand: A preliminary assessment

Abstract

Abstract The water quality of Lake Taupo is of great national importance to New Zealand, but development pressures in the catchment require attention to prevent organic enrichment of the water. Observations on the lake were made during 1986–87 to relate hypolimnetic oxygen consumption to organic carbon input from the phytoplankton (14C photosynthetic production) and to the amount of sedimenting phytoplankton determined in sediment traps. There is some degree of hypolimnetic oxygen deficit, even at least lake stability, and so no excess supply of oxygen by physical means exists to balance any enhanced organic input. Sedimentation rate varied greatly throughout the year. It was mainly controlled by the onset of stratification which radically affected the heavily frustuled diatoms dominant at this time. The species present also influenced sedimentation at other times but to a lesser extent. Both allochthonous input of organic material and nitrification are significant additions to phytoplanktonic production for oxygen consumption, but both amounts are uncertain at present and could be greater than estimated. Total organic input would probably have to approximately double to start deoxygenation of the sediment at maximum stability and so induce a radical change in the ecosystem.