Nitrogen fixation in an oligotrophic, saline desert lake: Pyramid Lake, Nevada
High rates of nitrogen fixation by a short-lived but dense unialgal bloom of the planktonic blue-green Nodularia spumigena provided 99.5% of the alga's needs and 81% of Pyramid Lake's annual total combined nitrogen input in 1979. The bloom was spatially very heterogeneous. Bloom size, duration, and presumably N/sub 2/ fixation vary from year to year, but in 1979 about 900 t of nitrogenwere fixed in 2 months in this large deep lake. The annual rate of N/sub 2/ fixation was about 2 g m/sup -2/. In this year of low inflow the Truckee River provided 54 t of inorganic nitrogen and 83 t of organic nitrogen. Planktonic N/sub 2/ fixation has not been measured during high inflow years and may have been small relative to river input. Lakewide average heterocyst to vegetative cell (h:c) ratios followed seasonal trends in N/sub 2/ fixation, but synoptic samples showed only a weak relation between h:c and N/sub 2/ fixation. N/sub 2/ fixation was induced by low epilimnetic levels of inorganic nitrogen and ended before lake overturn in the fall. High rates of N/sub 2/ fixation were confined to the upper 5% of the epilimnetic volume and thus occurred only in calm weather when Nodularia colonies floated to the lake surface. Access to freshly dissolved atmospheric CO/sub 2/ may account for the near-surface dependence, since the lake pH is normally about 9.2. Nodularia will not show the same degree of near-surface dependence in near-neutral lakes or in the ocean.
- Research Organization:
- Univ. of California, Berkeley
- OSTI ID:
- 5418743
- Journal Information:
- Limnol. Oceanogr.; (United States), Vol. 30:6
- Country of Publication:
- United States
- Language:
- English
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