Principal Investigator: Rik Wanninkhof
Collaborating scientist(s):
David Ho (CIMAS) up to 8/95
collaboration with Dr. Jordan Clark, LDEO
Objective: Deploy deliberately injected tracers to study dispersion and air-water gas exchange in inland waters (estuaries and lakes).
Description: Gas exchange and dispersion are two major mechanisms to decrease concentrations of (semi)-volatile pollutants such as PCB's in inland waters. Study of these processes in the field has been hampered by lack of suitable methods. This new method uniquely addresses these processes.
Method: The tracer sulfur hexafluoride (SF6) is injected into a body of water and the tracer patch is followed with time. Since SF6 can be measured down to one part per trillion, it is possible to study these processes on large scales (103 km2) and over long periods of time (months).
Accomplishment: Dispersion and gas transfer in estuaries are of particular interest as they often transect large industrial areas, and the mechanism of mixing is a unique combination of tidal mixing, stream flow, and wind generated surface turbulence. A large scale tracer experiment in the upper Hudson Estuary was led by Dr. Clark of LDEO in which the processes were investigated. Gas exchange wind speed relationships (Figure 1) suggest that tidal mixing has little influence on gas transfer in the upper Hudson. Lateral dispersion determined from the change in the shape of surface concentration profile with time show distinctly lower mixing rates in the first few days when the patch is relatively small (Figure 2)
Key reference:
Clark, J.F., P. Schlosser, R. Weppernig, M. Stute, R. Wanninkhof, and D. Ho, Relationship between gas transfer velocities and wind speeds in the tidal Hudson river determined by the dual tracer technique, in Air-Water Gas Transfer: Selected papers from the Third International Symposium on air-water gas transfer, edited by B. Jaehne, and E. Monahan, pp. 785-800, Aeow Verlag, Hanau, Germany, 1995.

Clark, J.F., R. Wanninkhof, P. Schlosser, and H.J. Simpson, Gas exchange in the tidal Hudson River using a dual tracer technique, Tellus, 46B,pp. 274-285, 1994.

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