KAWAI NUI MARSH

Water Quality ~ DO
A general introduction to Water Quality specifically written for Kawai Nui Marsh is presented in KOOLAU.NET. Basic information on measuring dissolved oxygen or DO can be found in CPIE. DO values reported here were obtained with a field DO probe (membrane electrode method), a standard technique for this measurement.

The means of nine measurements of DO in Maunawili Stream at the old highway bridge (Sta. KBAC001) and in Kahanaiki Stream beneath the Hwy bridge (Sta. KBAC002) were 5.05 and 3.53 mg/l respectively. These values represent a saturation of around 50%. While this is a low value, the sample station locations are at the very low end of the streams just above where each enters the marsh. In fact, for Kahanaiki, the station is within the marsh with respect to gradient. Saturation approached 80% in some samples from Sta. KBAC001.

Six samples from Sta. KBAC005 in the marsh had a mean value of 0.20 mg/l (and a range of 0.12 to 0.31 mg/l), about 2-3% of saturation. It is apparent that although stream water input DO is low, little or no oxygen remains in the water after it enters Kawai Nui Marsh. The DO is actually higher at the two stations located further into the marsh: 0.66 mg/l (mean of 8) at Sta. KBAC006 and 4.3 mg/l (mean of 8) at Sta. 007. The differences presumably reflect local conditions. For example, Sta. KBAC006 is located on one of the ponds opened up at Na Pohaku o Hauwhine. A pond can develop phytoplankton (microscopic algae) that produce oxygen during the daylight, with a result that the DO is more typical of a pond than a marsh per se. Because various processes can add or take oxygen away from the water, it is a non-conservative parameter, and may not follow any pattern anticipated by flow.

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