Effect of localised nutrient enrichment on the shallow epilithic periphyton of oligotrophic Lake Taupo, New Zealand

A localised increase in nutrient concentrations in the shallow littoral zone of Lake Taupo, New Zealand, resulted from injection of secondary‐treated, nitrified sewage effluent into the groundwater close to the lake. Coincident with this enrichment, there was an increase in periphyton abundance. This increase was restricted to the zone of enrichment and a biomass of up to 1000 mg chlorophyll a m −2 was attained. There was also a change in species composition from a diatom/heterocystous cyano‐bacteria‐dominated assemblage to one dominated by two diatoms, Synedra ulna and Gomphoneis herculeana . Interpretation of the effect of nutrient enrichment on periphyton was complicated by occasional dramatic biomass declines in response to physical variables, notably strong wind events and lake level changes.