Effects of herbicide application on carbon dioxide, dissolved oxygen, pH, and RpH in paddy-field ponded water(Soil Physics)

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Herbicide application may affect dissolved oxygen (DO), dissolved carbon dioxide (CO_2), pH, and RpH in ponded water, and RpH of the water which is the water pH aerated with the atmosphere. In the present study, DO concentration did not reach supersaturated state after herbicide application, and variation in DO decreased. The herbicide application reduced the diurnal variation in dissolved CO_2 and increased the overall concentration. During the day, before the herbicide application, variations in pH and RpH were large, with pH higher than RpH, allowing absorption of CO_2 from the air, whereas at night, the relationship between pH and RpH was inverted. Application of the herbicide caused a reduction in pH and RpH, and RpH exceeded pH throughout the remainder of the day. After the herbicide application, average CO_2 concentration in ponded water increased, and RpH was greater than pH, which caused CO_2 emission to the air throughout the day. Moreover, the ponded water absorbed oxygen (O_2) from the air during the day because DO in the ponded water did not reach saturated concentrations. These facts indicated that the ponded water absorbed O_2 from the air and emitted CO_2 to the air throughout the day after the herbicide application. Thus, herbicide application affects not only ponded water, but also the surrounding atmosphere.