New Zealand Journal of Marine and Freshwater Research abstracts

---

Conditions stimulating planktonic N₂-fixation in Lake Rotongaio

A. B. VINER

Taupo Research Laboratory
Division of Marine and Freshwater Science
Department of Scientific and Industrial Research
P. O. Box 415, Taupo
New Zealand

Abstract Measurements of acetylene reduction by the plankton of Lake Rotongaio (New Zealand) were carried out approximately monthly from November 1979 through 1980, and were calculated in terms of N,-fixation. Parallel photosynthetic ¹⁴C-fixation assays were also made. As well as the seasonal cycle of N₂-fixation dependent upon the summertime presence of the heterocystous cyano-phyte Anabaena oscillarioides there were other fluctuations in fixation rate. For each assay occasion the N₂-fixation rates through the water column were strongly correlated with light attenuation and less so with heterocyst numbers. Inorganic nutrient nitrogen and temperature had little influence. The relationship between N₂-fixation, light, and heter-ocysts was variable with time, and was interpreted as being influenced by small scale vertical changes in physiological environment, particularly of the light field. Approximate estimations suggested that N_:-fixation was not a major contributor to the lake's daily nitrogen requirement (0.03-2.0%) nor to the total annual nitrogen budget (23-24% of the supply from the surface influent), in spite of the occasional occurrence of high fixation rates at some water depths.

Keywords N,-fixation; lake plankton nitrogen; acetylene reduction; nitrogen budgets; Lake Rotongaio; plankton

New Zealand Journal of Marine and Freshwater Research, 1985, Vol. 19: 139-150 Received 26 July 1984; accepted 15 October 1984

PDF file of entire paper: medium quality (888K); (scanned from paper original: notes about this process)

---

This year's abstracts | Journal home page | All abstracts | Publishing home page