108 TYPICAL QUEENSLAND LAGOON 
until, about the middle of June, the temperature of the water 
is practically the same throughout all depths. About that 
time stagnation once more commences, and continues 
throughout the remainder of the year, until May comes round 
once more, when the process is repeated. (Appendices IV 
and XIII.) 
During the period of circulation the character of the 
water at the various depths is completely changed, the colour 
of the water becomes uniform throughout all depths, conse- 
quently the colour at the surface increases ; indeed I have 
found it on one occasion, viz., 5th June, 1995, to be slightly 
darker at the surface than at the bottom; dissolved oxygen 
is now found at all depths, and the microscopic organisms 
are evenly distributed, whist the food material before 
mentioned is carried to the upper regions where, with light 
and oxygen, the orgarisms are able to utilise it. 
The following figures ilustrate in a striking manner 
the difference between the condition of the water during 
stagnation, and during the period of circulation : 
| DURING THE STAGNATION PERIOD. || DURING THR CIRCULATION PERIOD. 
May 19rH, 1905. ‘May 5TH, 1905|| Jone 5TH, 1905. | Jone 20, 1905 
| : : | Dissolved : Dissolved 
Colour Units. Oxygen. Colour Units. Oxygen. 
ree | | per cent. | per cent. 
|| Red. | Yellow. of Red. | Yellow. | of 
Saturation. | | Saturation. 
| aaa || aaa Petra 
Surface (i ge Be ae Blas 58.5 || 3.0 10.0 103.0 
Thirty Feet || | nil. | 60.8 
Bottom (45ft)} 42.0 | 32.0 |) 2a 8.0 
(Colour determined by Lovibond Tintometer.) 
It will be seen therefore that in this lagoon, containing 
as it does an excessive amount of organic matter, the 
occurence of these phenomena produces no improvement 
in the quality of the water, and is in fact a large factor in 
the process of deterioration. Before leaving this subject, 
liowever, on which one might talk all night and concerning 
which much has been written, I might remark that stagnation 
is productive of no disagreeable effects when the lake 
bottom contains no organic matter, anc that it does not occur 
in shallower lakes such as those only 10 to 15 feet deep, for 
in such lakes thermal stratification hardly exists. 
