Forever Pondering – Philosophies on Nutrient Reduction

Published on January 21, 2008

Floating Islands
Floating Islands

Question:

I’m very interested in your philosophies on nutrient reduction in ponds and wonder if you have any updated information? You previously mentioned work with the University of Maryland. Is there any firm data as a result of your studies?

Answer:

The future of marketing is definitely following a green trend so arming yourself with the most up-to-date facts on new techniques that use plants to improve water quality is critical to ensuring your sales and planning are on track to keep your company in the forefront. The following summary and new information should be helpful to you.

Many, perhaps all, bodies of water are degraded by nutrient overloading, i.e., receiving more nutrients than can be handled without negatively affecting the flora and fauna of the body of water in question. This overloading of nutrients is caused mainly by a burgeoning human population and its activities, domestic, agricultural and industrial. Similarly, the closed system of an ornamental pond becomes overloaded with the addition of high protein feeds and fertilizer.

To cite the Chesapeake Bay, as an example, it receives the storm and wastewater runoff of 64,000 square miles of land in Maryland, Virginia, Delaware, Pennsylvania, and New York states. This watershed has a population of 18 million people and many farm animals. The State of Maryland created 17,700 storm-water retention ponds encompassing 174,000 acres to manage and reduce the nutrient and sedimentary run-off from this watershed into the Chesapeake Bay. This system has failed to control this problem adequately as the Bay continues to be degraded by nutrient overload from storm-water run-off. Most parts of the country experience similar problems with storm water.

The failure of the ponds to do the job may be attributable to their propensity to endlessly accumulate nutrients. While the plants and algae that flourish in the ponds consume and hold nutrients via foliage production and photosynthesis, they release nearly this entire nutrient load back into the ponds when the plants decompose at the end of the growing season or plant life cycle. A goodly percentage of nitrogen is vented to the atmosphere by anaerobic bacteria, but a residual amount builds up year-by-year in the bottom sediments. Thus, the ponds serve as temporary holding reservoirs for nutrients that will eventually make their way into the estuary system or groundwater.

It has been determined that Floating Wetlands or rafted plants are capable of removing 200-500% more nutrients than their rooted-in-soil counterparts. The rafts allow for easy deployment of plants into the ponds and easy retrieval of the same from the ponds. Once retrieved, the vegetative bio-mass created on the raft can be removed for composting, sale or reuse in another application. Removal of the bio-mass ensures permanent removal of the collected nutrients from the pond and hence the Chesapeake Bay (or other estuary system).

Current research indicates that aeration is critical to the increased uptake of nutrients, especially when anoxic conditions exist due to extreme nutrient overloads without any form of natural circulation. Bottom aerators have proven the most successful for de-stratifying the water body, speeding up the aerobic decomposition of organic waste, and circulating the accumulated nutrients (especially nitrate) from the pond bottom to the surface so the Floating Wetlands (rafted plants) can consume the nutrients more efficiently. We refer to this complimentary approach as the Synergy System™. The addition of aeration increases the available nutrient uptake by at least 300%. In a recent study, initial data indicated that up to 20% of the sedimentary nitrogen was converted to removable plant biomass on the floating wetlands. The floating wetlands covered about 4% of the pond’s surface. Bottom aeration also suppresses the release of iron and phosphate from the bottom sediments by reducing anaerobic activity. Both of these nutrients are powerful stimulants to algae growth.

Some plant species have also proven to be more effective than others at consuming nutrients. Hibiscus, Lavender, Musk, Lizard’s Tail and Cattail have shown to be good nutrient uptake plants. Nutrient uptake is also related to the degree of pond pollution. A USDA study in Georgia using wetland rafts in a swine manure pond removed 3 to 4 times the amount of nutrients than was possible in a less polluted storm-water pond. In the case of the swine lagoon, only a few plants could survive its extreme level of pollution. Arundo donax and a variety of St Augustine grass were among the few that could survive such extreme conditions.

The picture accompanying this article depicts a floating wetland located near a ring of bubbles created by a bottom diffuser. It is evident from this picture that the rafted plants are enjoying the association. This system of aeration and floating wetlands generated community pride where before there was only dissatisfaction with the pond in question.

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