(3) Oxygen Content
Winkler's method was used for estimating oxygen and pool 4 was selected for intensive study. Unless otherwise stated, all observations were made on pool 4.
(b) Daily change.
The oxygen content rose during the daytime in the same way as did temperature and pH. The maximum value recorded was 13·1 c.c. of oxygen per litre on June 30, 1946, at 4 p.m., whilst the minimum value was 7·16 c.c. O2 per litre at 2 p.m. on November 14. It would seem, therefore, that the water of the pools must on occasion be
supersaturated. Pool 3, on the headland, with its rather scanty population, showed, on the one occasion investigated (February 23), a much lower value than pool 4, which contained a denser algal population; this low oxygen value corresponds with the lower pH values for the same pool.
The maximum depth in pool 4 is 20 inches, but no significant difference could be detected at any time between the oxygen content of the surface and bottom layers.