news from the waterfront by Tim Matson
THE PONDKEEPER’S SEASONS: WINTER
The advantages of pondkeeping by the season are most dramatic in the winter. The very existence of some ponds depends on it. Across town, tucked behind the town meeting house, sits a small, flat field. For more than forty summers it was Elwin Coburn’s potato patch. And every winter it is transformed. Village firemen spray down sheets of ice and create a skating pond.
It’s the transformation of water into a crystalline platform that makes winter magic for pond keeping. For instance, why measure surface acreage in summer? Throwing soggy lines around the shoreland seems off the mark when it’s so simple to stand on ice and pace the feet in snow.
The sand drop is another well-esteemed pond keeper’s trick that takes advantage of the ice deck. It’s an upkeep technique well suited to older ponds in need of restoration, particularly where aquatic vegetation or mud get unruly. To set up a sand drop, the pond keeper spreads a two-to-four inch layer of sand – not salted road sand! — over the ice. In the spring when the ice thaws, poof! The sand falls in a uniform layer over the basin floor. Sand works like an inorganic mulch, shading out weeds and, like the finings in a beer crock, holding down sediment. In muddy ponds, it’s a good carpet material for the basin floor. One of my neighbors was able to use a sand drop to eliminate the slimy bottom in her family’s pond, along with snakes and leeches. True, the sand drop does fill in the pond to a minute degree, but it’s not often done, and it sure beats herbicides.
The sand drop technique works well for depositing boulders in the pond. Stones falling in the center of the basin can provide a shady retreat for fish. Or they can be arranged to create a diving rock, a foundation for a pier or platform, or an island, welcomed by waterfowl where dogs are a bother.
It seems natural to extend the drop technique to include lime, fertilizer, or precipitating agents, sometimes used by pond keepers as a tonic for ailing waters. Take care that these ingridients are not flushed out of the pond with spring runoff: concentrate the drop upstream, away from the spillway area.
Another benefit of the solid ice sheet is for catching felled trees. If there are trees to clear from a pond shore, I recommend waiting until winter
provides a safe sheet of ice so you don’t have to deal with pulling trees out of the water.
Icing can mean trouble, too. Late in autumn when my pond begins to freeze, I watch the frothy inflow harden into a starry glaze, like a miniature Milky Way. Those stars are bubbles of air caught in the ice, and they signal the start of a spell of lowered oxygen levels in the water, potentially fatal for fish.
The trout here need about five parts per million dissolved oxygen in winter; other fish that winter over under ice have similar requirements. All may be subject to oxygen starvation due to overcrowding, underwater vegetation decay, and lack of light to stimulate photosynthesis. So far I’ve never experienced any winterkills, and my stock has climbed to a winter peak of sixty eight-inch brook trout – not bad for an eighth-acre pond with no supplemental feed. Proper pond construction accounts for most of my successful defense against winter oxygen starvation. At least five feet of water under the ice is recommended in these north-country parts.
Besides, the pond is too young for a massive vegetation die-off. But there’s another reason that ice hasn’t choked the trout: broom hockey. Keeping a patch of ice clear for skating opens up the bottom of the pond to the sunlight necessary for oxygen production in submerged plants.
The pond keeper can also turn to the wind for help with aeration. Given a slight breeze there are several windmill aerators that will oxygenate the water and keep a hole open in the ice for oxygen transfer and a wildlife watering hole (many pond keepers move the diffuser close to shore in winter to prevent animals falling into deep water).
From Earth Ponds: The Country Pond Maker’s Guide
To Building, Maintenance, and Restoration.
January 14, 2010