Managing the lakes of the Rotorua District, New Zealand

In 2005, Burns, McIntosh and Scholes described strategies to manage the Rotorua Lakes using lake monitoring together with designated baseline Trophic Level Index values established for each lake. Continued monitoring has revealed that 9 of the 12 Rotorua Lakes have Trophic Level Index values in excess of their baseline values. Action Plans have been drawn up for the remediation of these damaged lakes that specify the excess nutrient loading to each lake and propose actions for the decrease of these loadings. Nutrient loading to various lakes has been decreased by upgrading waste treatment facilities, dosing tributary streams with alum, diverting an enriched tributary flow directly into the outflow channel of a lake, precipitating in-lake phosphorus with Phoslock (TM) and zeolite additions, and removal of macrophyte biomass from a lake and planting an artificial wetland at the entry point of a tributary to a lake. Where data are available, the results of these actions are explored. The similarities between the management system for the Rotorua lakes with the management systems used for two American and European lakes are described.