Determination of gas exchange rate constants for a small stream on Walker Branch Watershed, Tennessee

The steady state tracer gas method was used to determine gas exchange rate constants (k) for a small stream (annual average flow ≤1 m3/min) draining the West Fork of Walker Branch watershed in eastern Tennessee. Chloride was used as a conservative tracer to account for dilution by lateral inflow, and propane and ethane were used as volatile tracers. Gas exchange rate constants for propane (kp) were about 100 d−1 over a wide range of flow conditions, while those for ethane (ke) were about 117 d1; an equivalent rate constant for O2 (KO2) would be about 118–139 d−1, depending on the method used for its calculation. These rate constants are much larger than those typically found in rivers and large streams. Much lower kp values (about 50d−1) were found during one experiment conducted at low flow with much of the stream surface covered with floating leaves. Nineteen previously published empirical equations were used to predict kO2 values for one 72m stream reach; agreement between the predicted and measured values was generally very poor, underscoring the importance of field-measured gas exchange rates in studies of the transport and fate of volatile compounds. Because ethane and propane have similar gas exchange rates and similar aqueous diffusion coefficients (ke/kp and De/Dp are both close to 1, where D is the compound's diffusion coefficient), accurate determination of the exponent n in the relationship ke/Kp− (De/Dp)n was not possible. The ratio ke/kp (1.17) is much closer to De/Dp (1.24) than to He/Hp (0.82, where H is the compound's Henry's law constant), suggesting that stripping of dissolved volatiles by air bubbles was not a dominant mode of gas exchange for the study stream.

[1]  G. T. Orlob,et al.  Turbulent Diffusion and the Reaeration Coefficient , 1962 .

[2]  B. Jähne,et al.  A New Optical Bubble Measuring Device; A Simple Model for Bubble Contribution to Gas Exchange , 1984 .

[3]  A. F. Gaudy,et al.  Atmospheric Oxygenation in a Simulated Stream , 1968 .

[4]  Stephen J. Kline,et al.  The Purposes of Uncertainty Analysis , 1985 .

[5]  M. Owens,et al.  SOME REAERATION STUDIES IN STREAMS. , 1964, Air and water pollution.

[6]  R. S. Grant,et al.  Comparison of tracer methods and predictive equations for determination of stream-reaeration coefficients on three small streams in Wisconsin. Water-resources investigations (final) , 1980 .

[7]  R. Rathbun,et al.  Determination of stream reaeration coefficients by use of tracers , 1987 .

[8]  W. H. Durum,et al.  The aeration capacity of streams , 1967 .

[9]  G. Parker.  A procedure for estimating reaeration coefficients for Massachusetts streams , 1987 .

[10]  M. Negulescu,et al.  Recent research to determine reaeration coefficient , 1969 .

[11]  J. Bennett,et al.  Reaeration in open-channel flow , 1972 .

[12]  Peter A. Krenkel,et al.  Reaeration Prediction in Natural Streams , 1969 .

[13]  D. A. Stedfast,et al.  AN ASSESSMENT OF STEADY-STATE PROPANE-GAS TRACER METHOD FOR REAERATION COEFFICIENTS COWASELON CREEK, NEW YORK , 1983 .

[14]  P. Witherspoon,et al.  Correlation of diffusion coefficients for paraffin, aromatic, and cycloparaffin hydrocarbons in water. [Châ, CâHâ, CâHâ, butane, pentane, benzene, and cycloalkanes] , 1969 .

[15]  R. A. Buckingham,et al.  The prediction of stream reaeration rates , 1962 .

[16]  D. Himmelblau,et al.  Diffusion Coefficients of CO2,C2H4, C3H6 and C4H8 in Water from 6 to 65 C. , 1964 .

[17]  A. McDonnell,et al.  A multivariate analysis of reaeration data , 1969 .

[18]  M. K. Bansal.  Atmospheric reaeration in natural streams , 1973 .

[19]  H. Hemond,et al.  Naturally Occurring Radon 222 as a Tracer for Streamflow Generation: Steady State Methodology and Field Example , 1990 .

[20]  H. Hemond,et al.  Dichlorodifluoromethane (Freon-12) as a Tracer for Nitrous Oxide Release from a Nitrogen-Enriched River , 1984 .

[21]  L. Merlivat,et al.  Gas exchange across an air‐water interface: Experimental results and modeling of bubble contribution to transfer , 1983 .

[22]  P. Mulholland,et al.  Use of radon-222 and calcium as tracers in a three-end-member mixing model for streamflow generation on the West Fork of Walker Branch Watershed , 1993 .

[23]  Harold F. Hemond,et al.  Spatial and temporal variability in streamflow generation on the West Fork of Walker Branch Watershed , 1993 .

[24]  R. Rathbun,et al.  Laboratory Studies of Gas Tracers for Reaeration , 1978 .

[25]  M. Baird,et al.  Annular jets—II: Gas absorption , 1962 .

[26]  L. Merlivat,et al.  The Contribution of Bubbles to Gas Transfer Across an Air-Water Interface , 1984 .

[27]  D. Wise,et al.  The diffusion coefficients of ten slightly soluble gases in water at 10–60°C , 1966 .

[28]  J. Elwood,et al.  Gas exchange rates for a first‐order stream determined with deliberate and natural tracers , 1990 .