The Complex Ecosystem of Ponds

A pond can be a wonderful addition to any property.

They can be functional by providing a reservoir of water for irrigation, offer fire control, and more. Ponds also provide a multitude of recreational opportunities including fishing, swimming, skating and boating. Or they can just be appreciated for the natural beauty and wildlife they attract, from dragonflies to migratory birds.

Ponds, like any other outdoor feature such as a garden, lawn or swimming pool, require a bit of care and maintenance to keep them looking great. Unfortunately, however, ponds are often neglected until problems arise – at which point owners seek a magical cure to rid the pond of algae and weeds and the accompanying smells, quickly and inexpensively. Unfortunately that’s not possible. Ponds are complex ecosystems that require a thorough understanding of biology to fix.

Think of it like a garden, which has to be watered regularly and weeded often, otherwise the weeds overtake the garden and your tomatoes and onions are lost. Similarly, excessive algal and weed growth can overtake an uncared for pond.

When a pond is first dug, they look wonderful. They appear to be a nice Bermuda blue with crystal clear water. Over time a pond starts accumulating nutrients. These can be in the form of leaves, agricultural runoff, septic tank leaching and many other possible food sources. Nutrients are broken down to Nitrogen and Phosphorus, the two elements plants need to grow, along with water and sunlight. Add an increase in temperature and you’ll get a significant increase in the growth rate of aquatic plants, including algae, weeds, duckweed and chara.

Pond owners often find their ponds are fine for years as the pond’s ability to deal with incoming nutrients is sufficient. But those nutrients (in the form of plant growth) if not removed, are recycled annually and nutrient levels increase over time. With the increase, however, the water clarity may diminish, it may become a bit green once in a while, but it recovers. All is OK until something called the nutrient threshold is reached.

Once this happens the algae starts growing really fast. If the pond dynamic is not reversed quickly and brought back into balance, aquatic weeds start growing and cattail may start encroaching from the shoreline. When this happens, the pond is going through eutrophication and this is when, rather than a few preventative ounces of pond cure, you need a pound of it to fix the problem. Much like the vegetable garden analogy, there is no magic blue pill that fixes it all instantly and inexpensively.

To have your pond looking great, you’ll need to work with nature.

Herbicides are banned now, though they only provided a band aid solution anyway as the nutrients were never redirected, they just sank to the bottom of the pond awaiting the killing effect of the herbicide to subside and ta-da multiple rounds were needed to get rid of that unwanted pond plant growth.

Winter kills all the aquatic pond vegetation for free, providing a new opportunity to deal with available nutrients each spring. Unfortunately, it is summer and we want to enjoy the here and now.

Introducing some various nutrient uptaking plants at the pond’s edge can help. Plants that are easy to control, such as blue and yellow irises, forget-me-nots, arrowhead, pickerel weed and water cress are good first steps to help stop or slow the incoming nutrient sources that are feeding your pond. If you can identify the sources, great. If not, you’ll need a pond consultation.

Sunlight, which increases in water temperature, can accelerate aquatic plant growth tremendously. When looking at the sunlight portion of a pond’s balance you can change it in two ways.

Firstly, sunlight is best reduced with a good, high-volume surface fountain. The surface ripples created by the fountain’s spray deflect a great deal of sunlight from reaching the pond bottom, where the nutrients that feed the unwanted aquatic plants are found and are at their highest concentration. Algae, duckweed and other aquatic plants grow at the bottom, then float to the surface.

A fountain should be properly sized to your pond. I am not a big fan of bubblers, which add heat and churn the colder nutrient rich waters to the surface, warming up the whole pond. Warming an entire pond, especially a small pond, can lead to more aquatic plant growth and eliminates the cooler summer refuge the bottom of your pond offers.

You can also use a pond colourant called True Blue. When used at the proper concentration, it acts like a pair of dark sunglasses for the pond to reduce sunlight penetration. But by virtue of being a dark colour, it attracts and retains heat, warming up the pond and inadvertently accelerating the growth of many aquatic plants. True Blue is useful tool when the pond bottom is inundated with weeds and is best applied at spring ice off.

Nutrient reduction and diversion is the real battleground, which is why you need to know where the nutrients are coming from so you can stop, or at least slow, nutrient introduction into the pond.

A good aerating fountain will provide sufficient oxygen throughout the pond water to initiate the chemical breaking down of Nitrogen and Phosphorus by natural oxidation. Biological breakdown of these nutrients is achieved by re-introducing in high numbers naturally occurring bacteria or enzymes.

I prefer a live product, like Natures Pond Conditioner, over freeze dried bacteria products because live is faster acting and more effective. In the presence of ample oxygen provided by the fountain, these bacteria and enzymes quickly break down the nutrients, depriving the unwanted algae and weeds of the food they need to grow. Furthermore, the bacteria/enzymes re-direct these nutrients to other more productive natural pathways.

If you build it, all sorts of aquatic life still come. Including many biting insects, such as mosquitoes and blackflies, leeches may be carried in by wading birds, as can the eggs of many minnow species, and crayfish can over take a pond if allowed to be the pre-dominant species.

Often pond owners want to add fish that can reproduce, without calculating what may occur when reproduction goes unchecked. Add 10 gold fish and in a few years there are 50-100,000 and the pond’s water clarity is destroyed.

Pond owners frequently want to add bass, which are extremely successful pond breeders. Unfortunately and instinctively, they have to chase something to eat it. Ten bass become a 1,000, which quickly become 10,000 or more, and they’ve eaten all the other life in the pond, including aquatic insects and worms that would normally address bottom nutrients, leaving it sterilized so algae and weeds become problematic.

Trout, which reproduce poorly in a pond, grow in size and not numbers, making them a better pond choice. Speckled trout (Char) are the most temperature sensitive, preferring temperatures below 65 degrees Fahrenheit, which can still be found at the bottom of a deep pond. Rainbow trout are a customer favourite as they grow well and can take temperatures up to 75 degrees Fahrenheit.

Brown trout, the fresh water cousin of the Atlantic Salmon, can tolerate worse water quality and warmer temperatures – up to 80 degrees Fahrenheit if ample oxygen is provided.

If your pond is shallow and you think trout and other fish may not survive the summer heat, add fish in the fall, when water is colder and oxygen levels are high – they should be good until next July.

A pond is fairly easy to maintain if it’s given a little TLC when required. It’s much easier, in fact, than a pool or garden.

Think of a pendulum: When the pond was first dug the pendulum is far left and the pond is looking great. Over time, the pond accumulates nutrients, then the pendulum is now in the middle, the pond is in a balanced state, nutrients in are being dealt with by the ecosystem. If the pond continues to accumulate nutrients, the pendulum swings more to the right and the pond now has serious algae and weed issues that will worsen every year if nothing is done.

Sometimes a pond needs extensive work like re-excavation and sometimes a good aerating fountain, a bit of shoreline work and good biologicals will make a huge difference. Changing the paradigm of the pond’s ecosystem so that the pendulum spends most of its time in the middle, back in ecological balance, will achieve the desired results. Every pond is different, with varying challenges, but once on the right track, having small success will add up and before you know it the pond is a very appreciated feature of your landscape.

Lou Maieron is a Fisheries Biologist who owns and operates Silver Creek Aquaculture Inc. in Erin, Ont. The farm produces quality pond raised fish, as well as a range of equipment, plants and consultation services. For more information about Silver Creek Aquaculture Inc. go to

Author: LivingSpaces

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