Swim ponds, koi ponds, and smaller backyard ponds mimic nature. In reality they are closed ecosystems that require a little help with filtration to keep the water clean and the living organisms happy. That’s why every ecosystem pond designed by Splash Supply includes two types of filters. Each of these filters play a critical role in ensuring happy healthy fish and crystal clear water.
The goal of these filters is to help ensure an oligotrophic (Ollie gō-trō′fĭk) environment. This just means an environment or ecosystem that has very little nutrients.
The first pond filter is a mechanical pre-filter such as a pond skimmer. The goal here is to remove the majority of the nutrient source before it has an impact on the ecosystem. Many factors, including size, help us determine whether a molded pond skimmer with a basket and filter mats or a custom wet well or intake bay is the best choice to help remove large organic compounds from the water before it reaches the wetland filter.
If a skimmer is not used, the efficacy of the wetland filter will be greatly reduced. If leaf debris, uneaten fish food, pollen, etc. is not removed, it can overload the sedimentation chamber in the wetland. Additionally, biological filters, including a wetland filter need dissolved oxygen to do the work of keeping your ecosystem happy.
A skimmer pulls water from the surface. That’s where the oxygen levels are the greatest, in part because the water is in direct contact with the atmosphere. A healthy wetland filter consumes oxygen through a variety of biological processes. The greater the fish load, the more critical this becomes. The mixture of sediments, fish waste, dissolved nutrients and oxygen will allow flow into the bottom of the filter.
A properly designed skimmer will help to remove up to 90 percent of physical debris (leaves, twigs, sticks, pollen, solids from fish waste, etc.) from the pond.
Even in the best case scenario, there will still be some fine organic compounds – fish waste, silty clays, etc. – passing through to the biofilter. This is why a Sedimentation Chamber is the first part of the properly designed biofilter. A wetland filter is no exception.
Aquascape designed the Snorkel and Centipede system to create an area that allows the sediments to drop out before the water flows up. The centipede reduces the velocity of the water and has a smooth flat bottom that is sloped towards the Snorkel. Aquablox are placed directly above the centipede to further reduce the speed of the water flowing up through the wetland filter.
After the sedimentation chamber, a traditional molded BioFalls will have filter mats, lava rock, bioballs, bio-ribbon or other material. The role of each of these materials is to provide place for beneficial bacteria and enzymes to colonize and thrive. It is important to ensure the water moves slowly through this area. Ed Beaulieu , the designer of the Aquascape Snorkel and Centipede system explains what happens next:
“As the water continues its path to the surface/top layer of the filter, the water flow will split into smaller and smaller pathways (interstitial spaces). By doing this, we expose the flowing water to the diverse colonies of bacteria, fungi, biofilms and countless aquatic species of copepods, rotifers, tardigrades, etc….
“Every living organism on our planet is competing against other similar organisms for food, a home, sunlight, etc. This competition is fierce! You wouldn’t realize this because it takes place on all trophic levels, from large vertebrates all the way down to the microscopic/nano level.
“Bacteria and fungi compete for space within the filter bed. The reason that I bring this up is that this filter only functions properly when it’s ‘seeded’ with the right strains of bacteria. We use a specific formula that has been developed to consume nitrogenous wastes generated by fish and other aquatic organisms, along with allocthonous organic compounds, such as leaf debris and lawn clippings.
“Without the proper mix of bacteria added to the pond, you are leaving it up to chance that the right beneficial microbes will just happen to show up?!?! That’s not to say that it can’t happen – because it can – but if you want consistent results, then this is the only way to ensure it!
“Aeromonas and Pseudomonas are not a problem if the filter is installed and maintained properly. This is due to the efficient water distribution system, combined with high dissolved oxygen levels … “
To put it a different way, our goal is to create a space where these beneficial bacteria colonies can thrive and multiply. Having more physical space increases the potential for the beneficial bacteria colonies to establish, grow and increase in number. The more bacteria in the filter, the more fish waste, etc. can be processed.
At Splash, we typically design our wetland filters using layers of river rock placed above the Aquablox. The first layer is 5- to 8-inch round river rock (football-size stones). This layer is typically 8 to 10 inches thick.
The next layer is 1- to 3-inch round river rock (large egg-size stones). Again, this layer is typically 8 to 10 inches thick. The different surface area and slowing water velocity in these layers allows for the most diversity of biological activity throughout the wetland filter. Large rock has a lower surface area to volume versus small gravel, which has a higher surface area for its volume. This allows for different levels of colonization to occur within the different river rock layers.
The top of the wetland is typically planted with a wide variety of marginal aquatic plants, which will further aid in the removal of nitrogen from the system. These plants should be cut back and thinned regularly to encourage new plant growth.
Increasing the variety of plants increases the variety of nutrients that are removed. Increasing the quantity of plants increases the quantity of nutrients removed. In northern climates, using tropical plants that die back in the winter prevents aggressive hardy plants from taking over the top of the filter.
The Snorkel part of the wetland filter allows access and visibility to the bottom of the filter. When the lid is removed, you can visually inspect for sediment buildup and remove the sediment by pumping it out with a solids-handling pump.
Typically, we recommend doing this every two to three years, or more frequently, depending on the ecosystem load. The dirty filter water is filled with organic compounds and is a great source of nutrients for the plants.
Move the water around to actively back-flush the gravel bed, sending the fine sediments and water down through the entire filter. Continue pumping the dirty water out of the snorkel until the water being discharged is sufficiently clean.
Here are a few design guidelines we use at Splash:
- A typical constructed wetland on a ecosystem pond would be 15 to 20 percent of the square fo0tage of the pond. In some situations this could be increased to 30 percent.
- Flow rate through each full size centipede should be 2,000 to 3,000 gallons per hour.
Additional cross sectional views of typical Constructed Wetland Filter: