Measurement of Dissolved Oxygen in Swamp Waters. Further Modification of the Winkler Method

INTRODUCTION There have been several modifications of the original Winkler method for the estimation of dissolved oxygen (Winkler, 1888) designed to overcome the sources of error due to the presence of oxidizing and reducing substances in natural waters and industrial wastes. In the course of work on tropical swamps we have been interested in the amount of oxygen in water which not only may contain large quantities of organic matter, ferrous or ferric iron, nitrites and other disturbing substances, but may also be deeply coloured or charged with sediment to give anything from a slightly turbid to a densely muddy liquid. For such water none of the modifications so far described is satisfactory. It does not in fact appear that any independent check has been made on the absolute accuracy of any of these modifications, though the reliability of the original method has been proved by Wheatland & Smith (1955) by comparison with gasometric analysis of distilled water and sea water. An attempt is made to assess the absolute accuracy of the method described in this paper.