Air and water temperatures were higher in April than in

March but at most stations dissolved oxygen reached higher

levels in March. In March pH was lower, especially at night,

possibly the result of higher metabolic activity associated

with the higher water temperatures. Diurnal oxygen curves,

although markedly different among stations, were similar

at each site on both occasions.

 These pictures of the diurnal changes in dissolved

oxygen are useful in assessing the health and productivity

of an area.

 Under purely physical forces, dissolved oxygen in sur-

face waters tends to equilibrate at 100 per cent of satura-

tion. The analysis of diurnal oxygen curves for their fluc-

tuation around the saturation point can be used to assess

the metabolic activity of an area and to estimate changes

in photosynthesis and respiration and the relative balance

between the two. Dissolved oxygen levels beyond saturation

indicate net photosynthetic activity while concentrations

below saturation reflect relatively greater respiration than

photosynthesis and, therefore, a net consumption of oxygen.

 Station 2 (Figure 9) was the deepest of the diurnal

stations and on both occasions maintained supersaturated oxy-

gen levels well into the night. Dissolved oxygen never fell

far below saturation. The surface water here is well mixed,


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