Gas exchange on Mono Lake and Crowley Lake, California

Abstract

Gas exchange coefficients have been determined for freshwater Crowley Lake and for saline Mono Lake through the use of a man‐made purposefully injected gas, sulfur hexafluoride (SF 6 ). The concentration decreased from an initial value of 40×10 −12 mol/L to 4×10 −12 mol/L for Mono Lake and from 20×10 −12 mol/L to 1×10 −12 mol/L for Crowley Lake over a period of 6 weeks. Wind speed records from anemometers on the shore of each lake enabled us to determine the relationship between the gas exchange coefficient k and wind speed u. The average wind speed and average exchange coefficient for the experiment were identical for the two lakes (u av =2.9 m/s, k av =2.5 cm/h), despite a large difference in size and chemical composition. From laboratory experiments and theoretical calculations it is estimated that for wind speeds observed over Mono Lake from July until December 1984 the exchange of CO 2 occurred 2–½ times faster than without chemical enhancement. This is a factor of 4 lower than needed to explain the high invasion rate of 14 C produced by nuclear bomb tests.