New Zealand Journal of Marine and Freshwater Research abstracts

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Seasonal dynamics of epilithic periphyton in oligotrophic Lake Taupo, New Zealand

IAN HAWES
ROB SMITH

NIWA - Freshwater
National Institute of Water and Atmospheric
Research Ltd
P. O. Box 8602
Christchurch, New Zealand

Abstract  The biomass and species composition of epilithic periphyton in oligotrophic Lake Taupo was measured over a full year. Measurements of photosynthetic carbon uptake were made during summer and early winter. The lake supported a high biomass of epilithic periphyton throughout the year, averaging 100-600 mg m-2 over the 0-35 m water depth and peaking in early summer. Periphyton extended to at least 40 m depth. Depth-integrated carbon fixation rates of 242-362 mg m-2 h-1 were measured. Periphyton constituted more than 90% of the algal biomass and carbon fixation within the littoral zone, but less than 2% of production on a whole-lake basis. Based on taxonomic composition, periphyton could be divided into three zones, surface (0-2 m), mid water (2-20 m) and deep (> 20 m). The diatoms Aulacosira granulata, Rhopalodia novae zealandiae, Epithemia sorex, and Fragilaria spp. dominated the deep assemblage, Tolypothrix tenuis and Mastogloia elliptica the mid water, and Scytonema, Dichothrix, and filamentous chlorophytes the shallow zone. Indicator pigments, analysed by high-performance liquid chromatography, confirmed these groupings. Biomass-specific rates of photosynthesis were low in shallow water (assimilation number <= 1 at 1 m depth) and at depths of 20 m and below, photosynthesis was light-limited. We hypothesise that the periphyton community was slow-growing and that the high biomass seen at all depths resulted from gradual accrual with low rates of loss.

Keywords  Lake Taupo; periphyton; benthic biomass; benthic productivity; species composition

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