SEDIMENTS OF LAKE ROTORUA AS SOURCES AND SINKS FOR PLANT NUTRIENTS

Lake Rotorua, on the Central Volcanic Plateau of the North Island of New Zealand, is a third‐class lake of 81km2 and 10.7 m average depth. The lake is eutrophic and in recent years has produced blue‐green algal blooms of potential nuisance proportions. By a mass balance approach, nutrient exchanges between lake sediments and the water above were quantified. Phosphorus released from temporarily deoxygenated sediments was estimated at 20–40 mg.m‐2.d−1 and nitrogen at 250–530 mg.m−2.d−1. Phosphorus sedimentation was less than 1 mg.m−2d−1 when the sediment surface was oxidised. A massive net loss of nitrogenous material from lakewater to sediments and/or the atmosphere, equivalent to 20 mg.m−2.d−l, may contribute to the shortage of nitrogen exhibited by the algae of this lake. © 1978 Taylor & Francis Group, LLC.