Oxygen Rescues

In a well-balanced pond, the oxygen content of the water is seldom an issue. But if things move off course, notes Mike Gannon, it’s essential to find the cause — and then apply one of three possible remedies tailored to the urgency of the need and the extent of the budget.

Without question, a pond can be a tremendous asset for just about any property, anywhere on the planet. It may serve as a wonderful, safe home for fish and plants of many sizes and types; it can be beneficial to local populations of birds, amphibians, insects and mammals; and it has an opportunity to enhance the quality of life of its owners, their family and guests.

The key point to be made here is that a pond can do all this and more – but only if it’s healthy.

Numerous factors go into the assessment of a pond’s health, some of them apparent on a simple visual level. Is the water clear? Are the fish and plants thriving? Does the system carry away debris and capture it for easy disposal? But there are other issues here, and the one I’ll discuss here is generally invisible until things reach a point where water quality is far off the mark and both fish and plant health are at risk.

This very basic component of pond health is the level of oxygen present in the water. Let’s take a look at why this is such an important factor – and define what can be done to address the situation if the oxygen level starts to decline.

BALANCING ACT

The first point to be made is that some ponds may need no help at all to maintain a good oxygen level. By design or by luck, these ponds are balanced and stay that way, adjusting more or less automatically to minor changes in water temperature, fish and plant populations and fluctuations in debris or nutrient loads.

Other ponds, however, require intervention – either in the form of rethinking the planting program; adding new equipment to the mix; or perhaps adding a stream or waterfall as a means of injecting much-needed oxygen into the water.

In most cases where direct action is needed, a pond’s oxygen supply becomes depleted because the water is too still: Nutrient-rich material (both fish waste and plant debris) settles in the still areas, and the aerobic bacteria that feed on that material consume the available oxygen in those lower layers of the water column to keep themselves going.

This situation can slide out of balance with relative ease: If the water column continues in a layered, unmixed state, the aerobic bacteria will completely exhaust the oxygen supply. They will die off, and anaerobic bacteria will take over in the dead zones. Soon, the water will become murky as the grime at the bottom steadily spreads and the afflicted water will support neither fish nor plant life. This is the point at which the problem manifests itself clearly: Indeed, if things are allowed to get this far, the pond will not only look horrible, but it will start to smell bad as well.

What’s needed here is good, effective circulation: By keeping the water moving with no dead spots, oxygen is a constantly renewed part of the entire water column, rising and falling steadily between the surface and the deepest, darkest recesses of the pond.

RESTORING ORDER

We’ll look at the options available to help such a pond just below. Before we get to the remedy, however, a good first step with these ponds involves determining the proximate cause of the problem, assessing its severity and figuring out how much time there is to find a lasting solution before the ecosystem effectively dies.

In some cases, a pond’s problems are intermittent or seasonal – perhaps via the intrusion of fertilizer-laden runoff from nearby turf and planting beds as a result of heavy Spring rains. Or maybe the pond was configured in a less-than-ideal way that encouraged debris collection in certain areas by virtue of an inadequate circulation pattern. Whatever the cause, it’s advisable to spend some time figuring things out so the solution you settle on has the greatest chance of long-term success.

[ ] Adding plants

Generally speaking, introducing oxygenating plants to a pond is the most economical way to raise a pond’s oxygen levels – and offers the side benefit of beautifying the setting at the same time, especially if you increase the level of shoreline planting. The drawback of this approach to oxygenation is that it takes quite a while for the new plants to establish their root systems and start restoring the water to good condition.

[ ] Inserting an aerator

If faster results are required, an investment in an aerating system is a great approach. These systems come in two forms: One floats on top of the pond, drawing water up from its afflicted depths and adding oxygen by pelting the surface with oxygen-rich water droplets; the other is submerged in the pond’s lowest point and doses the water with oxygen-rich air drawn from beyond the pond, breaking the flow down into tiny bubbles by emitting them through an air stone (as in an aquarium).

Both options do a great job of bringing oxygen to the water, with a surface aerator contributing an aesthetic element by adding the sight and sound of a fountain feature to the system, while a submerged aerator preserves the pond’s original look, doing little more visually than sometimes adding a flow of small bubbles to the water’s surface.

These systems can evidence their positive, oxygenating effects on a sickly pond within hours. They cost a bit, but they’re relatively easy to install and start working immediately. Generally speaking, however, a submerged system is better at agitating the nutrient-overburdened water at the bottom of the pond, has a more pronounced effect on the water column and does a better job of spreading oxygen evenly throughout a pond.

A floating system gets the job done, too, but usually less immediately and a bit less thoroughly. And there’s a big plus here: They do put on a show, after all, and they can be lit from within at night to enhance the after-hours pond experience.

[ ] Insert a stream and/or waterfall

If immediacy isn’t a factor and the budget tends toward greater generosity, there’s no better oxygenating solution than a well-designed, well-installed stream or waterfall. The upsides here are wonderful, with the most obvious being the visual and aural punch that water cascading over rocks brings to a setting.

As for oxygenating efficiency, a well-considered waterfall or stream can’t be beat, especially if the circulation system’s skimmer or suction points are set up in such a way that water flowing down from the cascade moves directly and easily across to an intake at the far edge of the pond. To be sure, this is not an inexpensive option, nor will its beneficial effects kick in quite as immediately as would be the case with an aerator; aesthetically, however, this solution wins the day.

The important point to consider when confronted by an unhealthy, oxygen-starved pond is that there are three good options for addressing the situation, three relative price points and three timelines for effective action. Knowing with some certainty what’s gone wrong is important, but there’s also great value in knowing that there are multiple, worthy approaches to the problem that bring some flexibility to working through what can, left unaddressed, become a deadly serious problem.

Mike Gannon is owner and lead designer at Full Service Aquatics, a pond installation and service specialist based in Summit, N.J. A certified Aquascape contractor, he may be reached at [email protected].