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Don’t let your ponds bog you down

Ponds can be restored to glory, with the right touch


June 16, 2021
By Julia Webber

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Cattails surrounding a pond. Shutterstock image. M.V.Photography

We have all seen ponds that are surrounded with cattails to the point where you cannot see if there is a pond in the centre, and thought, “How did it get to that point?” You may even have one of those ponds on your course that you inherited in this state and thought, “Nothing I can do to it except start over.”

But is a pond that is mostly filled in and surrounded by plants a lost cause? I would suggest that in all but the worst cases, with some diligence and the right products, ponds can be restored to their former glory. And for those with ponds not that far gone, the road to recovery is even shorter.

To understand how a pond progresses to this state, let us first look at the progression of a pond in nature. Newly formed ponds often begin life as clear rivers that have been blocked in their progress. The water is clean and clear initially, with little plant life or nutrients. They are quickly colonized by microscopic organisms that set up the most basic of food chains and the foundation for future colonizers.

As the pond matures, larger animals move in and bring with them the seed of plant species. The new pond is still balanced and has little excess nutrients, but this soon changes as more plant life colonizes and grows into larger numbers. Each fall, this plant life dies off and breaks down into organic matter or compost to feed more plants the next year, and so on.

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The leaves from surrounding vegetation also contributes to the organic matter that spurs growth, just as it does in land-based systems. Soon, the pond has an abundance of plants and more nutrients than it needs. This leads to algae blooms that create large swings in oxygen that makes life in the pond precarious.

The buildup of organic matter also makes the pond shallower, so that marginal plants can grow further out from the edge and more densely, and the pond – year over year – becomes less pond and more swamp. The open water is limited to a few areas and the landscape begins to look more like the river that was originally there.

Eventually the pond disappears altogether, and the organic matter that started as pond plants now benefits terrestrial ones.

Very few people plan to have a swamp down the road as they dig their pond, but if we know what maintenance is required on a pond to delay or prevent this natural progression, then the work in years to come is much diminished. But, what if the pond was dug many years back without this knowledge and needs to be restored?

Managing a pond’s organic matter

Knowing how the pond progressed to this stage actually helps to find the path back to the pond envisioned when it was first built. The main difference between these stages of pond maturity is the amount of nutrients (or organic matter) that are present in the system. So, by managing this organic matter through aeration, probiotics and weed control, we can mitigate the filling in and increased maintenance of a pond.

Before we look at these techniques for restoring a pond, I would first like to address the idea of re-digging a pond that is mostly filled in. There are situations where this is going to be the best option for a fast reset and an opportunity to start over. Before going this route, however, there is some information you should be aware of so that you are prepared for what will be in store after the pond is re-dug.

One of the main nutrients that is required for plant growth is phosphorus, or phosphates. Phosphorus is a soil-based nutrient that is absorbed into ecosystems and is not created during the digestive process as waste, such as nitrogen. This means that it is in shorter supply in nature, and this is especially true in aquatic systems where it is often the limiting factor for plant growth.

I say this so that you will realize that as soon as freshly dug soil – say, a new pond – and water come into contac,t the water will have very high levels of phosphorus dissolved into it. This generally results in a problem called “new pond syndrome” where you often encounter frequent and bad algae blooms in cycles.

The fresh start you thought you would have often results in a pond that may temporarily be more problematic than the original pond. To mitigate this problem, setting up a program of aeration, probiotic and/or flocculant can help to bind the phosphorus so that it is less available and breaks the cycle of algae growth.

If re-digging the pond is not the route you choose, I would suggest the following combination to help restore. Firstly, aeration is the best step you can take for your pond and it will have the biggest impact while mitigating a myriad of problems. Aeration will accelerate organic matter breakdown by up to 10 times, reduce smells, reduce mosquito populations, prevent stagnation and reduce algae and weed growth. This is all due the introduction of oxygen into the water column, ideally from the bottom to the top. This is generally accomplished by using an oil-free, continuous-duty air compressor that moves air down to diffusers, or air stones at the bottom of the pond.

Adding oxygen

The air diffuser breaks up the air pushed through it by the compressor into small bubbles that have a large surface area and allow for optimal air transfer. Aeration from the bottom of the pond will benefit all depths while circulating the water as well. This style of system adds oxygen in two ways.

Oxygen is added in the column of bubbles as they rise to the surface through contact-transfer, and they also add oxygen at the surface as the pond is circulated. This will create high oxygen levels throughout the pond with proper air stone placement. These systems have the added benefit of using less hydro compared to the area that they treat and can be located in areas where power is not readily available along the shoreline. While fountains can add both aesthetics and oxygen to a pond, they will only aerate the upper four to six feet of the water column.

Probiotics can be used in ponds to help further accelerate the breakdown of organic matter in a pond and work best in the presence of aeration as they use aerobic (oxygen loving) beneficial bacteria. The probiotics can be designed to do many jobs in a pond, including clarifying the water column, breaking down soluble nutrients in the water and breaking down organic debris at the bottom.

We will focus on the last type as this layer of organic debris on the bottom is a constant source of nutrient to the water in the pond as well as the plants that grow in it. There are many probiotics on the market that target bottom sludge, but when selecting one make sure to compare the dosage rate of each as they can range greatly as well as the climate they are designed to work in. Selecting one that is developed for our climate and produces results across a wide range of water conditions is important and will ensure the best results, and dosage rates can greatly affect the budget you will need for these applications.

The process of breaking down muck with probiotics happens on a microscopic scale, but is fairly simple. Aerobic probiotics use the organic material as a food source if oxygen is present. Just like any other animal with an abundant food source, they will grow and multiply and will also become a food source for other animals in the pond, such as snails, crustaceans and larger microscopic animals.

Organic matter reduction

This results in a reduction of organic matter that will be available to plant life in the pond as well as gradually deepen the pond. This is not an overnight process, but year over year there will be fewer organic debris, which in turn will result in less algae and weed growth. As the pond deepens, there will also be fewer areas for weed and marginal plants, like phragmites, to inhabit as they are limited by water depth.

The final layer to this plan, depending on how far along the pond has progressed, is weed removal. Depending on the type of weed – invasive or native – and the area you are in, there may be different options available to you on this front. Weed removal can be a very labour-intensive job, but it has the benefit of removing not only the plant but all the nutrients that were absorbed by the plant in order to grow. As such, it reduces the organic load of the pond and helps to reduce future problems.

Weed removal is best used as a selective tool to fine tune where plants can grow and how many. I do not want to give the impression that all plants in a pond are bad, but instead it is about balance. Some marginal plants such as cattails are very beneficial as they stabilize the shoreline, remove soluble nutrients for the pond and provide valuable natural habitat, but having the water feature obscured can be problematic. Remove weeds as appropriate to find this balance in your situation.

There are many ponds that we see that have not been maintained and have progressed into a stage of maturity with shallow depth, high organic content and large swaths of marginal plants, but these ponds can be restored. The use of the right combination of tools will be required, as will time, but if you are working on restoring your pond, at least it is not progressing further from its original design.

Julia Webber is president of Fish Farm Supply Co. Inc., which has been serving the lake and pond industry since 1989. www.fishfarmsupply.ca julia@fishfarmsupply.ca