"Reel McKoi" wrote in message
...

"George" wrote in message
news:J5M4e.15943$Vx1.13708@attbi_s01...
Starting with autumn, let's see how the pond changed into the winter. The
water
at the surface started out in October at 42°F. The first frost and cold
wind
lowered the surface layer and it sank, while the warm water rose and
replaced it
and was chilled in turn. This circulation process continued until all the
water
reached 39.2°F, at this temperature water is at its heaviest. Normally,
any
cooling beyond 39.2°F does not sink, instead forms a thin layer at the
surface
because of the local geothermal gradient, ...........
============================
This has not been our experience. When our ponds are forming ice at the
surface (coldest place), the bottom can be anywhere from 39 to 42 degrees.
Nothing but a small surface pump (or air stone) runs to keep a hole in the
ice. There is no current to mix the water and disrupt natural
stratification or disturb the hibernating fish.

The wind keeps the convection going, which is why when it is blocked by ice at
the surface, the convection stops. Again, how this affects a body of water
depends largely on its depth. The shallower it is, the less likely it is to
stratify, and the more likely it is to freeze solid. This becomes especially
noticable when the pond is not dug below the frost line where the geothermal
gradient can positively affect the temperature.

"Derek Broughton" wrote in message
...
Reel McKoi wrote:

"George" wrote in message
news:J5M4e.15943$Vx1.13708@attbi_s01...
Starting with autumn, let's see how the pond changed into the winter.
The
water
at the surface started out in October at 42°F. The first frost and cold
wind
lowered the surface layer and it sank, while the warm water rose and
replaced it
and was chilled in turn. This circulation process continued until all the
water
reached 39.2°F, at this temperature water is at its heaviest. Normally,
any
cooling beyond 39.2°F does not sink, instead forms a thin layer at the
surface
because of the local geothermal gradient, ...........
============================
This has not been our experience. When our ponds are forming ice at the
surface (coldest place), the bottom can be anywhere from 39 to 42 degrees.
Nothing but a small surface pump (or air stone) runs to keep a hole in the
ice. There is no current to mix the water and disrupt natural
stratification or disturb the hibernating fish.

That's pretty much what George said :-) If water's densest at 39.2°F, then
(at least in water deep enough to stay liquid and have a noticeable
temperature gradient) the water should never get colder than that but could
be warmer.
--
derek

But when the pond is above the frost line in temperate regions, it is less
likely to stratify significantly, if at all, and will freeze.

"Reel McKoi" wrote in message
...

"George" wrote in message
news:z4T4e.10070$yg7.7550@attbi_s51...
I guess you didn't read my response to Elaine:

## Sometimes my newsreader is behind.

I was waiting for someone to bring this issue up. It was discussed at
length
last fall. In an effort to see how this affects shallow garden ponds, I
conducted a little experiment, measuring the water temperature at the
surface,
and comparing it with water at the bottom (45").

Starting with autumn, let's see how the pond changed into the winter. The
water
at the surface started out in October at 42°F. The first frost and cold
wind
lowered the surface layer and it sank, while the warm water rose and
replaced it
and was chilled in turn. This circulation process (which is typical of
most
temperate bodies of water), continued until all the water reached 39.2°F,
at
this temperature water is at its heaviest. Normally, any cooling beyond
39.2°F
does not sink, instead forms a thin layer at the surface because of the
local
geothermal gradient, which will warm any water that is
below the frost line. However, with shallow ponds, the cold water can
continue
to sink (especially if the pond is not dug below the frost line), and
cause the
pond to continue to cool, and if this process continues (if the air
temperature
remains below freezing for a significant period of time), the pond can
freeze
completely to the bottom.

## Yes. I agree. That's why we try and dig them so at least one part of
the bottom is below the frost line, even here in TN.

The frostline differs from locality to locality. Here in North-Central
Kentucky, the frost line is 22". Although my pond is 45" deep, only 27" of it
is below ground, making the bottom only 5" below the frost line. This is why I
don't see stratification. I recieve just enough warmth from the ground to keep
the pond from freezing solid in the coldest winters (actually, I couldn't dig
any deeper because of a hardpan that exists here below 27", which makes hand
digging exhausting). The pond is also shaded from strong wind because it abutts
a tall wooden privacy fence.

When the weather is cold enough, especially with low wind chill, the
surface
freezes at (32°F). Freezing at the surface helps to stop the circulation,
and
the warmer
water will stay at and below the frost line. Interestingly, when my pond
started to freeze (it only froze slightly on the very ends because I use a
de-icer), the fish didn't stay on the bottom, but hovered just below the
ground
surface (my pond is 18" above ground, and 27" below ground, so they
hovered at
about 18-20" below the water surface). In other words, they stayed about
a
third of the way down in the pond. If it was significantly warmer at the
bottom, and warmth was of great concern to them, one would think that they
would
have stayed at the bottom. This was not the case.

## I was told that aside from warmth the supply of oxygen is also important
to them. But all things being equal they will rest on the bottom and expend
less energy than hovering or fighting a current, any current, all winter.
Mine stay on the bottom barely moving through the winter. In the shallow
pools they stay under the heaters.

Yes, O2 is very important to fish in the winter, especially Koi, or if you have
a lot of fish in the pond. I aerate the pond during the winter. The only fish I
have that goes to the very bottom in winter is my albino channel cat, and he
rarely stays there for long periods of time, even in winter.

Before the ice began to form, but while the air temperature was still
dropping,
the water at the bottom continued to drop until it reached a temperature
of
34-35 degrees, at which time it stabilized. This was about the same
temperature
as the water just below the surface (about 4 inches). It never dropped
below
this temperature range except at the iar/water interface. When the
temperature
was just above freezing, both the surface and the bottom water stayed
around
34-36 degrees. The point is that unless a garden pond is dug well below
the
frost line, you are not likely to see much of the stratification you
normally
would see. This is why ponds that are not dug below the frost line can
and do
freeze solid during a cold winter.

## Gotcha! :-)

--
McKoi.... the frugal ponder...
~~~ }((((o ~~~ }{{{{o ~~~ }(((((o

George wrote:

But when the pond is above the frost line in temperate regions, it is less
likely to stratify significantly, if at all, and will freeze.

Right, I was trying to figure how to quantify "deep enough". Obviously,
below the frost line would be important :-)
--
derek