Oxygen content of the mud water

 The 'Oxygen transect'
A 30 m transect was laid out stretching from within the mangrove stand out into the salt marsh and a series of holes 100 mm in diameter and about 500 mm deep were bored along the line of the transect, using a post hole digger.

Hole filling with water
If the hole does not intersect with a crab hole (if it does another hole must be dug), it will fill slowly with water. As long as the water is not stirred, then the oxygen content of the water at the bottom of the hole will be the same as that of the ground water.

Oxygen content of Mud water (mol 02.m-3)

(Air saturated sea water contains 0.23 mol O2 per m3 at 20o C)



On Salt Marsh


Site 1 - 0m

Site 2 - 5m
Site 3 - 15m

Site 4 - 30m

Oxygen conc.
(mol 02.m-3)





As we move from the mangroves out to the salt marsh, the oxygen content of the soil water increases from close to zero to almost half the air saturated value. The soil colour also changes from grey within the mangrove stand to red-brown under the salt marsh. This may be related to the change in the oxidation state of the iron in the soil (from Fe++ to Fe+++).