Measurement of the surface water reaeration coefficient using Kr as a gas tracer

Murphy, J L and Mackinnon, P A and Zhao, Y Q and Kalin, R M and Elliot, T.; Brebbia, C.A., ed. (2001) Measurement of the surface water reaeration coefficient using Kr as a gas tracer. In: Water pollution VI. International Series on Progress in Water Resources . WIT Press, GRC, pp. 505-514. ISBN 1853128783

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Abstract

Details are presented of a system devised to use Krypton (Kr) to quantify the reaeration coefficient in surface waters. The technique is based upon similarities in the gas transport mechanisms of dissolved Kr and oxygen (O-2) in water, and relies on the low natural abundance of Kr in the atmosphere and consequently in surface waters. The experimental protocols used in laboratory tests and preliminary field trials are given. Kr was released into the water bodies, either by introduction of "kryptonated" water (in the laboratory) or by using a fine-pore diffuser (in field tests). In each case, a quantity of the fluorescent dye tracer, Rhodamine WT, was released simultaneously - the latter to identify the progress of the kryptonated water and to act as a conservative tracer (allowing the effects of dispersion and tracer dilution to be quantified and isolated from the gas loss through mass transfer process). Breakthrough curves (BTCs) for the tracers were monitored at predetermined locations downstream of the release point by taking a series of "grab" samples. The samples were taken and stored using predetermined protocols to ensure reliable results. The samples were analysed for Kr in the laboratory by gas chromatograph - mass spectrometry (GC-MS) using headspace analysis, and then for Rhodamine WT by sensitive fluorimetry. Using the BTCs for Kr and Rhodamine WT, the rate at which Kr was released from the water to the atmosphere was calculated from the mass difference between downstream points (areas under BTC) after correction for dispersion/dilution effects. The rate of Kr release was then used to determine a value for the reaeration coefficient. The results of laboratory and river tests show that, with further refinement, the method could provide a viable means for evaluating the reaeration coefficient, and hence the potential for reoxygenation, of surface waters.

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