Bayly--Net-seston from Lake Taupo to the Waikato River

New Zealand Journal of Marine and Freshwater Research abstracts

Nature and quantity of net-seston exported from Lake Taupo to the Waikato River, New Zealand

IAN A. E.BAYLY

Department of Zoology Monash University Clayton, Victoria 3168 Australia

Abstract Over a diel cycle, the concentration in Waikato River water of negatively buoyant seston and of some animals from the littoral of Lake Taupo was significantly correlated with the velocity of wind over the lake. Riverine abundance of several littoral, lacustrine animals was significantly correlated with the weight of negatively buoyant seston. A significant negative correlation existed between the densities of negatively buoyant and positively buoyant seston in the river. In qualitative comparisons, eulimnetic species were sometimes over-represented and sometimes under-represented in river water, with no consistent pattern. Concentrations of eulimnetic species in river water were usually greatly less (down to 10~²) than those in the lake. The range of densities of zooplankters (> 160 Jim in size) in the river was c. 20-2000 ind. nr³. Significant differences in thedensity of eulimnetic species in the river occurred at different times of the day, but on only 1 occasion was this probably linked to diel vertical migration in the lake. An increased rate of discharge from the lake may cause an increase in the density of some taxa in the river. The mean daily export of Botryococcus from the lake was at least 230 kg dry weight Forty-five animal taxa derived from the littoral region of the lake were collected from the river including many not hitherto recorded from Lake Taupo.

Keywords seston; outwash; zooplankton; Botryococcus; Lake Taupo; Waikato River

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