INSITU MEASUREMENTS OF DISSOLVED-OXYGEN (DO) IN SPRING WATERS WITH A PORTABLE DO METER

Concentrations of dissolved oxygen (DO) in natural spring waters and r iver waters in the Kusatsu-shirane volcano area, Gunma, were measured in situ with a portable DO meter. In advance of the field study, a ser ies of laboratory experiments were carried out to examine the applicab ility of the DO meter to the field use. It was found that the DO meter was usable beyond the temperature range of 0-40-degrees-C in which th e reading of the meter was guaranteed, if appropriate correction was m ade ; the meter can be used to measure DO concentrations of hot spring waters with temperatures of 40-90-degrees-C. Importance of in situ me asurements at water outlets was also pointed out, when measuring sprin g waters. As for the natural spring waters examined, the degrees of DO saturation varied from spring water to spring water, ranging from 0 t o 100%, which indicated the variety of history of the waters. For some spring waters, correlation was observed between their DO concentratio ns and residence times underground. That is, the longer the residence time was, the lower the DO concentration was, and this showed the unde rground strata were reductive. The river waters examined generally sho wed high degrees of DO saturation (over 79%) as is usually the case wi th river waters.