Re: [gardeners] Winter storm in Rochester
Kay Lancaster (gardeners@globalgarden.com)
Mon, 18 Jan 1999 15:18:14 -0800 (PST)
On Sat, 16 Jan 1999, penny x stamm wrote:
> Kay, I ask in innocence: what happens when a lake gets a thick
> enough crust of ice to allow ice fishing, and the erection of
> protective "huts" on top...? When this breaks up, doesn't it have
> the very same potential of screwing up the oxygen content within
> the lake..?
Yes, it does, but the huts are not covering most of the ice surface the
way 10 ft of snow dumped from shore does.
Here's what happens normally in a lake in winter:
With cooling temperatures, some of the vegetation in the lake dies back,
and that starts a slight oxygen deficit as the vegetation decomposes.
(That's one reason folks who are out after fish like walleye look for
lakes with a lot of "green weeds" and not many "brown weeds"... walleye
need lots of oxygen, and they won't survive in a lake that has much
decomposing vegetation).
At the same time, the cooling waters make the lake animals demand for
oxygen go down a little. Usually, there's enough oxygen dissolved in
the water to carry the animals through most of the winter before the lake
completely ices over.
The first ice that forms is "black ice" -- frozen lake water. It appears
black to us because light isn't being reflected back to us... it's going
through the ice and into the lake water, where it's still being used for
photosynthesis by plants and planktonic forms. The next ice, the white
stuff, is formed by snow and slush on the surface of the black ice; the
black ice often cracks under the burden of extra weight, and the lake
water soaks the snow, making an icy slush that refreezes hard. That
ice is white because it's reflecting back almost all the light that
hits it... very little is getting through for photosynthesis.
When a snowstorm hits, the snow does pile up on the lake, but it also
tends to blow off the ice fairly well.... so the small amount of
photosynthesis that's going on, together with the dissolved oxygen in
the cold lake water, is usually enough to carry most of the lake
population through the winter. Sometimes, though, you'll notice
a fishkill in the spring, as the lake thaws, generally because the
lake stayed white too long for the amount of available oxygen.
When you dump roadscrapings on the ice, they're not likely to blow
off the way natural snow will (as anyone who's tried to shovel out
the end of the driveway after the snowplow's been through can attest!)
And you set up a couple more problems for the natural system:
1) the heavy snowpack further decreases the amount of light hitting the
lake water, decreasing the amount of oxygen available
2) the extra snow (and ice) acts like extra insulation, making it less
likely that the lake will thaw "on time" the next spring... which means
a greater likelihood of fishkills.
Kay Lancaster kay@fern.com