“Whiting events” or spontaneous precipitation of calcium carbonate in open waters of lakes are well documented, but poorly understood. In Pyramid Lake, a large (438 km2), closed-basin, alkaline lake, some spontaneous precipitation of aragonite occurs annually and major whiting events occur less frequently (ca. every 7- 10 years). Algae associated with late summer blooms have been proposed as nucleation substrates that trigger whiting events, along with increased calcium concentrations and higher water temperatures.
We went to Pyramid Lake in August 1997, when a whiting event was most likely, and studied the lake water in-situ and
in the lab at the Pyramid Lake Research station in Sutcliffe, NV. A whiting event did not occur while we were there, but blue-green algae
(Nodularia spumigena) were observed in the lake. In the laboratory we induced aragonite nucleation by adding
0.1 M CaCl2 solutions dropwise to Pyramid lake waters in stirred flasks. In these reproducible experiments,
a decrease in pH indicated that nucleation had occurred. Levels of supersaturation were quantified in terms of
where
Aragonite = (
Ca2+
CO32-)/KAragonite for a given temperature.
Our results showed that a slightly lower aragonite saturation state was required to induce nucleation in unfiltered (0.1 µm) lake water. Excess algae, collected by filtering waters from fishery ponds at the research station also were added to lake water in another set of nucleation experiments. Waters with excess algae nucleated more readily than filtered lake water.
These results support the theory that the phytoplankton and/or particulates may act as heterogeneous nucleation sites that enhance whiting events in Pyramid Lake.
This poster was presented at the American Geophysical Union (AGU) spring meeting, June 1-4, 1999.
