Gas transfer velocities have been determined for a first-order stream by performing a 3-hour release of the volatile tracer sulfur hexafluoride, SF6, and the nonvolatile tracer tritiated water, 3H20. The average gas transfer velocity for the 292-m reach was 29 cm/h which corresponds to a reaeration coefficient for oxygen at 25øC of 134 day -1 . Groundwater inflow along the stream was corrected for by measuring the downstream dilution of the 3H20 spike. Downstream discharge increased from 0.5 L/s, 2 m downstream of the point of tracer release, to 19.3 L/s at a point 292 m downstream. As an alternative to using (radioactive) 3H20, we investigated the possibility of using natural radon, 222Rn, as a groundwater tag and using the variation of SF 6 and 222Rn along the stream to determine gas exchange rates and groundwater inflow. The method yielded an average transfer velocity of 21 cm/h and underestimated the groundwater inflow by a factor of 3. This large discrepancy is attributed to a doubling of stream discharge between the time the stream was sampled for radon and the tracer experiment and the limited number of radon samples.

Gas transfer velocities across the air‐water interface are correlated with wind speed, friction velocity, and radar backscatter from the surface in a large wind‐wave tank in Delft, the Netherlands. The rates of sulfur hexafluoride and nitrous oxide exchange were measured at wind speeds ranging from 3.5 m/s to 20 m/s, and with mechanically generated waves in the 100 m long, 8 m wide, and 0.7 m deep tank. Gas transfer velocities were related to wind speed with a power law dependence. Gas transfer showed a linear dependence with friction velocity. An exponential relationship between gas transfer and average radar backscatter cross section fits the wind tunnel data well for microwave units operating at 13.5 and 35 GHz in VV and HH polarization. The relative rates of gas exchange of the two gases confirm an inverse square root dependence on the Schmidt number at intermediate wind speeds. A slight enhancement of sulfur hexafluoride exchange compared to nitrous oxide exchange was evident when breaking waves were present.

Radiocarbon measurements suggest that 14C‐free carbon enters from beneath Mono Lake at a rate of about 1 mol/m2/yr. An input of this magnitude should be manifested in the inorganic carbon budget of the lake and with this in mind we have devised a model to reconstruct the evolution of the partial pressure of CO2 (pCO2) over the past 150 years. This encompasses a period (1945 to present) during which major diversions of source waters via the Los Angeles aqueduct have been in effect, significantly increasing the salinity of the lake and hence its pCO2. The model has been constrained by experimental characterization of the carbonate chemistry of the lake water, by the temperature dependence of pCO2 for the lake water, and by pCO2 measurements made on the lake water in 1966, 1969,1981, and 1989. Our calculations suggest that prior to 1945 the pCO2 of Mono Lake water was about 1.3 times the atmospheric value. To produce this excess, an input of CO2 of about 3.3 mol/m2/yr is required. Volcanic activity beneath the lake is a probable source of this input.

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Measurements from scatterometers pointing at wind-waves in three large wave-tanks are examined to study fetch effects and the correlation with wind friction-velocity u•. Time-series measurements were made at 13, 35, and 95m with a K.-band scatterometer aimed upwind at 30· incidence angle and vertical polarization. Average normalized radar cross-section (Jo values from all fetches follow a common trend for (Jo as a function of u" so the fetch dependence is negligible. An empirical power-law model yields a high correlation between (Jo and u" but because systematic anomalies arise, we re-examine a turbulence approach that delineates low and high regimes with a transition at u. of approximately 25cms-l . Using this criteria, the data are well represented by a two-section power-law relationship between (J0 and u •.