Each of the four seasons create dramatic changes in the dynamics of your pond. Some of the changes cause good effects and others bad effects. It is important to understand the why your pond reacts to the changing temperatures the way it does.
Spring thaw: coldest water
is on top (32-33 degrees F); the bottom water is 39 degrees F.
Water is heaviest at 39 degrees F. As the pond surface warms the
top water gets heavier and sinks into the colder water below.
The sun heats the water while the wind mixes and circulates. The
warming continues until all depths are 39 degrees F.
Once all depths reach 39 degrees F, the wind will circulate the whole pond for a short period of time. The excessive nutrients and gases are brought to the surface where oxygen replaces the gases that escape into the air. The pond is now oxygenated from the top to the bottom.
As the days get longer with intense sunshine and calmer winds,
your pond rapidly warms and thermal resistance develops as the
warmer water floats on top of the cooler water. The warmer layer
seals off the cooler layer from air and wind. Circulation is limited
to warm surface waters. Average temperatures on surface are from
about 72 degrees F - 85 degrees F . The warmer layer will usually
be 4-6’ deep. Oxygen is lost in the deeper water, especially
in the sediment. The lower layer has a rapid temperature drop
from 72 degrees F - 55 degrees F, the bottom waters accumulate
gases and sludge is formed from the black decaying materials.
Gases such as methane, carbon dioxide, ammonia, and hydrogen sulfide
replace the oxygen that was in the water and bad odors occur.
As the nights begin to cool and the winds begin to pick up, the
surface water begins to cool. The heavier water sinks and the
wind mixes cooler water deeper. The cooling and mixing continues
until the entire pond reaches a uniform temperature. The water
color may change, cloudiness and odors may appear as water from
the bottom is brought to the surface. The pond is reoxygenated
from top to bottom. As the top water cools below 39 degrees F
it becomes lighter and stays on the surface.
As ice forms on the surface of the pond it seals the water from the air and there is not any circulation. Ice and snow cover reduces or stops photosynthesis (oxygenation). With snow cover, all plants die and begin to decompose using the minimal amount of oxygen that the pond had. Little or no oxygen is produced and oxygen depletion slowly occurs and gases accumulate. As spring returns, the annual temperature cycle is repeated.