Rick,

The bubbler will keep a hole in the ice for quite a while and is a whole lot
cheaper to run than the electric stock tank heaters. It is true that the
fish don't need much oxygen in their winter stupor, and cold water holds a
lot of oxygen, so the bubbler is probably not necessary for oxygen, but it
does help to drive off other gasses. If the pond does completely freeze
over one night, the stock tank heater can be put in and then will melt a
hole and maintain the hole open until warmer weather returns.
--
RichToyBox
http://www.geocities.com/richtoybox/index.html

"Rick" wrote in message
ink.net...
I have bin told to just put one of those heaters that the farmers use to
keep fresh water for there cattle from freezing in to my pond. They have
a
built in thermostat and only turn on when the water reaches 33 or 34
degrees. I have also bin told that you should not let the pond freeze
over
because of the gas build up and not the lake of oxygen. Are you saying
that
I sill should put in a Bubbler?




"George" wrote in message
.. .

"Ka30P" wrote in message
...
Roark did a bit on water and winter in response to a question and it
makes a
pretty interesting read.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~
From: Roark7
Subject: Bubbling bottoms and super cooling
Date: 1997/10/31

David Swarbrick wrote:

Bubblers are recommended for maintaining an ice free portion of a pond
over winter, and maintaining good oxygen levels. I have also seen it
suggested here that it should not be placed on the bottom of the pond,
but raised so that the circulation it induces does not disturb the
water
at the every bottom because this merely results in the very cold water
by the ice being distributed all over.

I question this.

Yep... And I don't blame you one bit. I had the same doubts and
voiced the
same arguments that you shortly share because it *is*
counter-intuitive...
until you start looking hard.

Actually, if your pond is deep, like mine (45 inches or more), the
circulation,
which goes from bottom to top, will draw the residual warmth in the
ground
below
the frost line to the upper levels of the pond, and moderate the water
temperature. I ran a bubbler from the bottom all winter last year and
only had
ice two days (less than 1/8 inch thick, at that, and only on one end).

First, warm water rises, and cold water sinks. The water at the bottom
will always circulate if there is a temperature difference. Frozen
water
floats. I suppose there must be a point just before water freezes
where
the situation turns on its head, but I assume also that this is only
at
the point very near freezing.

I had major questions about the physics aspect of this whole "winter
pond"
thingy as well. I did some asking and a bit of research and came up
with
three
things which cause the inverse stratification effect. These are, in
ascending
order of importance:

- The native heat of the earth
- The physics of water going from a liquid to a solid
- Surface cooling due to winds and cold air.

I'll rattle through each contributing effect in detail below:

- Heat of the Earth:
It turns out that the earthern bottom of a 4-foot deep pond stays
right
around
34-38 degrees even though the outside air temperature drops much
lower.
The
simple reason for this is the Earth is slightly exothermic.
As you dig down
you hit a point where more heat is being released by the earth than
can
be
pulled-away by wind, night sky, etc. This is why you bury water pipes
below
the "frost line". This heating effect is small in ponds, but it *is*
there.
The earth *is* pumping a bit of heat energy into it all the time. The
other
effects (below) tend to magnify this effect into something useful by
keeping
this slightly warmer water on the bottom.

I will add here that the residual heat of the earth is called the
geothermal
gradient, and varies from place to place, and increases with depth. But
at
shallow depth, it is affected by surface temperatureand wind chill. For
instance, at the latitude where I live (38 degrees), the air in a cave
stays in
the vicinity of 54 degrees F, depending on air currents within the cave,
which
depend on the connectivity of cave passages, and the number of surface
entrances, all of which can affect the transfer the heat to the
surface,and visa
versa. Travel north of this latitude, and the temperature is lower.
Travel
south of this latitude and the temperature is higher. With regard to
ponds, the
surface temperature has an effect on the soil, but only to within a
certain
depth. That depth is called the frost line. Below that depth, the soil
will
not freeze, but will retain it's residual warmth, and increase with
increasing
depth. The frost line varies with latitude. At my latitude, the frost
line is
at 22 inches. In order to keep buried utilities from freezing (such as
water
lines), the local building codes required the utilities to be buried six
inches
below the frost line, at 28 inches. If you live at 38 Degrees north
latitude,
and your pond is 45 inches deep, then the bottom 17 inches will not
freeze
(unless, of course, you have an abnormally cold winter, in which case,
your pond
can actually freeze solid, but this is rare in most cases). Lat year my
pond
only had a small surface crust for two days, and then stayed ice free
the
rest
of the winter.

- Physics of Water:
It turns out that water doesn't move upwards because it is "warm" nor
sink
when
it becomes "cold". A little thought reveals this behavior is strictly
a
function of density. Warmer water *tends* to be less dense so it
rises... but
this isn't gospel. An interesting kink in the water density -vs-
temperature
curve shows-up just prior to 32 degrees F. At the pre-freezing point
(32.8
F), water undergoes a major density change. As it cools it becomes
*less*
dense than water which is just a fraction of a degree warmer. This
difference
is fairly large. Being lighter than the surrounding water,
near-freezing
water
*rises*. (This is one reason frozen pipes tend to burst. The density
of the
water decreases, the mass stays the same, so the result is volumetric
expansion which splits pipes with ease.) The degree of final bouyancy
is
controlled to a large part by the dissolved oxygen content of the
water.
The
more dissolved O2, the greater the expansion once the freezing point
has
been
reached. Since water at the *top* of the pond tends to have a greater
O2
concentration, this further contributes to stratification.
Near-freezing
water moves toward the surface, and then, having reached the surface,
freezes
completely.

Unless, of course, you draw warmer water up from below, which is why I
place the
air stone at the bottom in the winter. Some have suggested that drawing
the
warmer water from the bottom to the top will cause the temperature of
the
water
at the bottom to drop. But that doesn't happen if the pond is below the
frost
line because the surrounding soil will release it's residual heat into
the
water
as the warmer water is drawn towards the surface. Of course, if your
air
supply
is outside, and the temperature gets very cold, pumping that cold air
into
the
water could affect the water temperature. The overall temperture of the
pond
may drop slightly, but usually not enough to adversely affect the fish
unless
the air temperatuere stays below freezing for a long period of time (in
which
case, you might consider keeping your air pump indoors and running the
hose out
to the pond. I know a guy who has installed a buried air hose to his
pond
from
his basement, where his air pump is located. So in the winter, he is
actually
pumping heated air into the pond).

- Surface Cooling Effects
This one is pretty obvious, but its worth restating to put it in
context.
Given a sub-freezing day and a brisk wind, its a simple matter to pull
more
heat from the top layer of water than can be replaced by natural
convection.
Once the top starts to freeze, heat loss to ambient and basic water
physics
insures the top will *stay* cooler than the bottom. If this wasn't
true,
you'd never see a thin coat of ice.... the pond would instead just hit
a
point
where the entire thing suddenly became a solid chunk of ice.

It seems to me that if the air being pumped in is warmer anyway (in my
case, from inside an unheated shed), then the balance will be about
right.

Your idea about pumping warm air into the water isn't a bad one, but
it
will
take a lot of warm air to make a dent in the ponds temperature.... far
more
than you could reasonably produce.

That is true. However, as I stated above, pumping cold air into the
water
can
adversely affect the water temperature. So, the warm air won't heat the
water,
but will simply prevent it from making the water colder than cold air
will.

Pumping a large amount of air in would
also create currents which the fish would need to fight or at least
adjust
for. Hibernating fish are in no position to do this and forcing them
into
this situation uses energy they will need during the rest of the
winter.

For keeping a hole in the ice however, you could likely use this
warm-air idea
to your benefit. Put an airstone a foot under the water and run warm
air to
it. Bear in mind that you will lose lots of heat in just a short run
between
your shed and the airstone.

An alternative would be to purchase an electric deicer for about
$50-$60:

http://www.pondsolutions.com/pond-heaters.htm

Also if the problem with water under ice is the lack of oxygen and
build
up of waste products under the ice, then the more chance the bubbler
has
to oxygenate the water and take away the foul water the better.

Whether you use a de-icer or not, it is always a good idea to add air to
the
pond in the winter time for the reasons you state above.

The oxygen demands of fish near the freezing point are very, very low.
This
is
a good thing because I've got a feeling there isn't much oxygen
available once
you near the peak of winter. Fortunately, decay and decomposition of
wastes
by bacteria has nearly stopped as well which relieves a decent portion
of the
oxygen load. Very little oxygen is needed in a winter pond.

Unless it freezes over, in which case, there is no oxygen exchange, and
the fish
could die.

During a really *cold* winter, I think the idea of a full-blown bubble
system
would tend to upset a natural balance which Nature clearly went out of
her way
to establish. Having said that however, I can see a very definite
*benefit*
to using such a system as the air temp starts to push into the upper
30's and
40's. By introducing additional air and inducing water motion, you'd
be
putting lots of needed oxygen into the water as well as helping the
pond
to
absorb ambient heat. Fish coming out of their winter sleep wouldn't be
oxygen-stressed as well as being thin, worn and badly in need in of a
shower.
From what I'm given to understand, most fish have no problems
during the
actual *wintering*... its the *transition* from hibernation to normal
metabolism which gets them. Your bubbler could be a great tool during
that
transition period.

It is also important to transition your fish to food that is easier to
digest
when preparing the pond for winter as the microbes in their gut that
helps
in
digestion will eventually go dormant.