For many pond owners a time will come to improve water quality. A growing number of people meet this challenge with aeration. Aeration can be especially useful when you're raising fish, particularly in the wintertime north where oxygen levels under the ice can be fatally low without that extra dose of air bubbles, otherwise known as dissolved oxygen. But there's a downside to winter aeration you don't hear about much: animals falling through the ice.
Not long ago I heard a CBC story about a moose falling through the ice, and a dramatic rescue. But what really caught my attention was the reason for the near drowning. An Alberta pond owner had been running an aeration system, which created a hole in the ice above the diffuser, and that's where the moose fell in.
I see a lot of ponds every year, and hear about even more, but it's my impression that this sort of mishap is a rarity. Or is it?
Here's what happened. Buck Olsen raises rainbow trout in a small pond outside of Edmunton, Alberta. For a decade or so he's been using a windmill powered compressor to aerate his pond. Air is first delivered into the pond depths, where the water would otherwise be low in dissolved oxygen. In winter the rising bubbles open the ice and create another oxygen rich area. Result, healthy fish.
Enter the moose. Around the hole the ice is thick enough to support the animal until it gets near the opening, then down it crashes. Now this is not the first moose that ever fell through the ice, even without an aerator, but in my experience most animals have an uncanny sense about when the ice is safe enough to tread. But you'd have to admit that a man-made hole in the ice would constitute an unnatural surprise to a wild creature. Was the moose just an unlucky passerby? Maybe the open water looked like a rare unfrozen water fountain, which would make it even more treacherous.
Luckily one of Olsen's neighbors saw the thrashing moose and called the pond owner. Using a sheet of plywood and a chain saw, they were able to get out on the ice and cut a channel for the moose to get to shore and escape.
I talked to Buck Olsen about his adventure, and found out that a similar incident happened about eight years ago, but that time no one saw the moose, and it wasn't so lucky. I didn't ask him what happened to the moose carcass.
I asked Buck what he would do to prevent more moose mishaps. "The moose got caught up in the air line and the line's out of the water now, so it's not going to happen again this winter." As for the future? He said he was giving it some thought, but he did have one suggestion for the windmill company. "Maybe the windmill could have a noisemaker attached to scare off animals." But windmills depend on the vagaries of the weather, and there will be times when the blades stop turning, a noisemaker goes silent, and better precautions are needed. Buck did say that he always has the option to shut the windmill down and eliminate the hole completely. How the trout would then fare is uncertain.
Perhaps most ominous of all is the situation when the wind stops and the hole refreezes with just a shell of ice. How easy it would be for an animal, or human, to misread it as being as thick as the ice around it — especially with a light coat of snow to disguise it – and fall through.
I suppose it might be possible to stand a temporary fence around the aerator hole, but getting it up and removing it in spring would require some caution, or you'd find yourself in the same predicament as the moose. Besides, at least in this part of Vermont, moose don't often let a fence stop them. For people, a sign would warn those old enough to read.
Depite the potential pitfalls, I'm a big fan of windmill powered aeration. After all, the energy is clean, renewable and free. And they're great for the many ponds that aren't near an electric line. You'll just have to adjust to the shortcomings on windless days.
Pond owners with electricity near the pond will have an easier time. They could run a motorized aerator to keep the hole from stop-and-go freezing. They could also use a plug-in noisemaker.
But if you depend on the wind, one safety option might mean moving the diffuser to a location closer to shore in winter. If an animal fell in, the water would be shallow enough to climb out. Of course the ultimate solution would be to turn off the aerator during the winter, and hope to avoid downturns in water quality and fish survival.
There's no doubt that aerators are becoming increasingly popular as more people build ponds, encounter water quality problems, and raise fish. I'd like to hear from any pond keepers with thoughts on the aerator ice problem.
Photo: Actual moose from story. Credit Garth Helland.