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Excessive supersaturation of dissolved gases, primarily nitrogen and oxygen, can cause gas bubble disease, and eventual mortality, in fish. This potential threat is currently a concern in efforts to aid anadromous fish survival in the northwestern United States. In an effort to better understand dissolved gas supersaturation and assist in its mitigation, physically based relationships have been expanded and developed to predict dissolved gas supersaturation below spillways. This paper discusses the predictive technique as applied to the dissolved gas supersaturation that occurs because of the stilling basin and the river reaches immediately downstream of the structure. Gas transfer across both the water surface and the bubble interface are considered. Extensive field data from three spillways on the Columbia and Snake Rivers is used to fit coefficients that the predictive relationships require. The inclusion of more physically based parameters will allow for the evaluation of the operation and design of the structures and may provide insight for efforts to mitigate high dissolved gas concentrations downstream of such structures.

A mass balance model was developed and applied to the Sacramento River in northern California during the July 1991 Sacramento River metam-sodium spill. The transport and reactions of metam-sodium, a soil fumigant, and the volatile and toxic methyl isothiocyanate (MITC) were simulated during the two-and-a-half days of movement along a 68-km stretch of river. Results from modeling were compared with field data for MITC, which is the only product measured downriver after the spill. Agreement between the simulated and measured values of MITC concentrations were found at Doney Creek (65.9 km downstream). Results illuminated the complexities and unique characteristics associated with the multiple kinetic processes of the chemical plume in the river. In particular, the photolysis of metam-sodium followed zero-order kinetics for high concentrations and first-order kinetics for low concentrations, a unique phenomenon consistent with the finding reported in a laboratory study. Concentrations of metam-sodium for transition from zero- to first-order, obtained by calibration and model sensitivity analyses, were in the same range as those in the reported laboratory results.

The European Commission has launched a research project designed to combat what could be Europe's most dangerous source of pollution, the accidental release into the environment of 5,000 tonnes/yr of biologically active chemicals. The commission became alarmed about the release of these chemicals because of the danger that they could result in bacteria developing a resistance to antibiotics, and that this resistance could then be passed on to bacteria that is present in the human body.