Water has very unique density qualities.
Most liquids become denser as they become cooler.
Water, however, gets denser as it cools
until it reaches a temperature of approximately 39ºF.
The denser the water becomes the more oxygen it can hold.
50º is a common earth subsurface temperature necessary to stimulate germnation.
As Water cools below 39º,
it becomes lighter until it freezes (32ºF).
As ice develops,
water increases in volume by 11 percent.
The increase in volume allows ice to float rather than sink,
a characteristic that prevents ponds from freezing solid.
Dissolved gases are those which are in a water solution.
An example of gas dissolved in solution is soda water
which has large quantities of dissolved carbon dioxide.
The most common gases are oxygen,
carbon dioxide, nitrogen, and ammonia.
Concentrations are measured in parts per million (ppm)
or milligrams per liter (mg/1), both units of measure are the same.
At sea level and zero salinity,
(that means no nutes),
68ºF water can hold 9.2 ppm DO,
while at 86.0F,
saturation is at 7.6 ppm DO,
and unable to support "any useful life".