Pondology
news from the waterfront by Tim Matson

A WIN-WIND SITUATION

Not long ago, Anna Sykas and Fred Crowley bought a retirement house in northern New England with enough land for a garden and firewood, plus an old pond they planned to use for wildlife attraction and swimming. The first year’s garden and firewood harvest went well, but they were shocked to find the pond water so repellant it nixed swimming – especially disappointing for their grandchildren. The summer I visited the pond, the surface scum, submergent vegetation, and algae looked downright toxic.

The pond was two decades old, with minimal fresh water exchange and a lot of shallow areas. It looked ready for a slew of improvements. Perhaps a dredging to remove accumulated nutrients, combined with deepening the shallow edges to discourage plant growth. Maybe an infusion of supplementary water to cool the water and add oxygen and circulation. Those remedies would require a contracting job, or well drilling, or both, at a cost ranging between five and twenty thousand dollars. Ouch.

We started to consider more natural solutions. I suggested stocking the pond with native crawfish, which are great at gobbling up pond bed nutrients and vegetation. I also suggested using aeration to improve water quality. Aeration enhances nutrient decomposition as it adds oxygen; and it circulates and destratifies the water, also a plus for water quality.

Pond owners with water quality problems will often use water tests to determine levels of dissolved oxygen, nitrates, phosphorous, and pH, to help diagnose exactly what’s ailing. The test results can help determine if and how a windmill aerator may be able to improve water quality. Tests for coliform bacteria are also helpful to check safety for swimming.

I recommended a diffusion “bottom up” aerator that pumps air into the bottom of the pond, creating a rising column of oxygen rich water. The concensus seems to be that diffusion systems, as opposed to surface splashers and fountains, are most efficient in a majority of pond setups. There are a number of electric aerators on the market, but I also mentioned that it might be possible to avoid an increased electric bill (and motor noise) if they wanted to experiment with a wind powered compressor. As for sustainability, well, nothing could be greener.

Wind towers can be located close to the body of water, or sited on a nearby hilltop to take advantage of more consistent winds. Low resistant air lines can deliver up to 1,000 feet distant.

I’d been hearing good things about wind powered aeration, and seen a few aeration windmills around New England, but I wasn’t sure about the effectiveness of a system that depended on the vagaries of the wind, especially when hot cloudy weather combines with dead calm to create extreme low oxygen pond conditions. Plus, we had little idea of the wind regime near their pond.

However, it turned out that Fred was game for the experiment. Over the next year or so, he kept me updated on pond progress. First, he bought a second hand windmill aerator and set it up on a rise just north of the pond. The tower was a modest 12 ft high. Mid-way through the second summer on the pond, the water cleared up dramatically and the swimming was great. Fred was so convinced of the windmill’s effectiveness that he added an anti-freeze system for the airline to guarantee aeration all winter. (Up north, condensation in an airline can freeze and block air flow.) “This has worked so well, I don’t want to stop aerating in the winter and get behind the curve on oxygen in the spring,” he told me.

About the same time that Fred’s windmill was clearing the water, the economy was tanking, and fuel and electric prices were soaring. Add environmental damage due to carbon production and other pollution from fossil fuel powered electric generation, and you start to see an even stronger argument for wind powered aeration. Keep in mind that the same windmill that aerates a pond can be switched to pumping water when needed. It’s tempting to say we’ve reached a tipping point in wind powered aeration.

See complete article in July/August 2009 Issue of BackHome Magazine. www.backhomemagazine.com

July 1, 2009

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