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Roots under floating mat
Planting a floating wetland
Floating treatment wetland

Floating Treatment Wetlands

Floating treatment wetlands (FTWs) are a useful tool used to increase water quality of ponds and lakes.  FTWs will target excess nutrients in water, which is the main contributor to aquatic weed growth in ponds.  Adding FTWs to a pond can also increase the biodiversity by providing additional wildlife refuge. 


FTWs consist of a buoyant structure, or raft, which supports plants in a growing media over the water column. These plants are perennial, non-invasive emergent plants. FTWs mimic the function of natural wetlands, in that they filter and process nutrients, suspended solids, metals and other pollutants. Opposed to a traditional wetland, the plants will not take root in the soil.  In a FTW the roots will stay suspended in the water column in order for the plants to adjust to any fluctuations in water level without harming the plants.   


The growth of aquatic weeds is promoted by excess nutrients such as nitrates and phosphates.  These nutrients can be picked up when water that does not infiltrate the ground (runoff) comes into contact with potential pollutants such as fertilizers and animal waste.  Once the nutrients enter your pond, an environment that promotes plant growth can be created, increasing your chances of having an aquatic weed and algae problems, and decreases pond biodiversity.  FTWs can help control the amount of nitrates and phosphates in ponds through nutrient uptake by the aquatic plants. 


Even though aquatic plants that naturally grow on the banks of most ponds take up nutrients, the amount of uptake is limited to the banks of the pond. With fluctuating water levels, these plants are not always in the optimal location for nutrient uptake, sometimes being left high and dry. FTW work in deep or shallow water. Due to the FTW's ability to adjust with water levels, the suspended roots are always in contact with the water. The placement of the FTW also allows an increase in nutrient uptake toward the center of the pond opposed to only the banks.


The suspended roots will eventually develop a bacterial or algal biofilm form.  Think of garbage or a boat hull that has been in the water. It doesn't take long before it becomes covered in slime. This slime is biofilm. It's made up of tiny microbes that need nutrients such as phosphorus and nitrogen to thrive. The biofilm will use these nutrients for growth, before algae gets to them. However, this is not he only benefit of FTW's. They can also lower suspended solids. 


Suspended solids are particles that reach the pond and stay suspended in the water columns creating an unhealthy pond environment.   High levels of suspended solids can increase water temperature which can lead to a lowering of dissolved oxygen levels in the water.  Decreasing dissolved oxygen in the water is a threat to most aquatic species and may alter the health of a pond’s biodiversity.  The suspended roots of the FTW traps particles that are suspended in the water column, decreasing the amount of particles suspended in the water. 


Not only can FTWs increase the water quality of your pond, they also provide refuge for birds, macroinvertebrates, and fish.  The more refuge offered for wildlife, the more biologically diverse the pond is going to be.  Biodiversity is important for maintaining a well balance environment, which will help keep your pond healthy.

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