A study of pigment and diatoms in a core from Lake Rotorua, North Island, New Zealand, with emphasis on recent history

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Abstract
Sedimentary pigment and diatom distribution were determined in a 104 cm core representing over 120 years of the history of Lake Rotorua. The sediment immediately above the debris from a nearby volcanic eruption in 1886, and that deposited over the last 20 years, was subsampled in greater detail. Sedimentary pigment (biomass) increased gradually over the post-eruptive period, with occasional peaks but no obvious evidence of any increase in biomass resulting directly from the eruption. The main species in the sedimentary diatom flora were Melosira granulata Ehr., Asterionella formosa Hassall, Melosira distans (Ehr.) Kütz., Stephanodiscus rotula var. minutula (Kütz) Ross et Sims and Melosira granulata v. angustissima Müll. Melosira distans and Asterionella formosa have entered the flora at different times since AD 1900. The populations of both increased sharply for a brief period, followed by an extensive interval in which the population of A. formosa remained very small. Populations of both species have waxed and waned a number of times over the last 20 (A. formosa) to 40 (M. distans) years. The Shannon-Wiener Diversity Index, and data on relative abundance and biomass show increasing instability over recent years, coinciding with a period of well documented increases in sewage discharge to the lake.

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