The science behind it

by steve beeman

Nitrogen and phosphorus are nutrients that are essential for plant growth. Fertilizers that contain both are used extensively for agriculture and ornamental landscapes. When these nutrients enter the aquatic environment through runoff they can cause pollution problems and contribute to eutrophication.

Phosphorus is the limiting ingredient in natural aquatic ecosystems. When soluble inorganic phosphorus enters the water it is bound by plants and converted to an organic form, which is no longer bioavailable. When those plants die and sink to the bottom, the phosphorus is incorporated into sediments and can be re-converted to its inorganic form by bacterial action. Excess biologically available phosphorus results in algae blooms. Increased algae can lead to lower dissolved oxygen levels due to bacterial activity in the breakdown of that algae.

​Regulatory agencies may soon restrict the use of environmentally harmful chemicals such as copper-sulfate for algae control, and are encouraging the use of planted wetlands, littoral shelves, and floating plant islands for nutrient control. Because higher plants in the aquatic environment store and concentrate nutrients in their tissues, created wetlands have been utilized extensively for bioremediation.

​Most of the treatment of nutrient rich water within a wetland occurs in the thin aerobic layer at the surface of the soils within plant communities. This aerobic biofilm is a result of oxygen leakage from the plant roots at the soil-water interface. In an effort to more efficiently utilize the natural ability of macrophytes to extract and store nutrients from surface water, we have designed a floating mat system to suspend native emergent plants and grasses. By expanding the root zone that is in contact with the water column we can increase the thickness of the aerobic layer, resulting in increased nitrification and accelerating the process in which nitrogen is cycled from the aquatic environment to the atmosphere. The greatly expanded root mass also facilitates increased uptake and storage of inorganic phosphorus in the plant tissues by creating more surface area for beneficial bacterial colonization.

​Through the periodic removal of mature macrophytes from the floating plant mat, we prevent the accumulated nutrients from re-entering the aquatic ecosystem at senescence. Those plants are then composted at an upland location, allowing bacterial decomposition to release some of the organic phosphorus so it can be recycled and used as a fertilizer ingredient for growing soil mixtures. The foam and nylon parts of the floating plant mats are re-used to start a new cycle of plant growth and nutrient uptake.

Floating treatment wetland aided remediation of nitrogen and phosphorus from simulated stormwater runoff

Phosphorus Removal and Accumulation by Swiss Chard Grown In Floating Treatment Wetlands

scientific articles

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