Landscaping features such as stone walls and sandy beaches are common enhancements to a natural swimming pool.
PLANTS AND BACTERIA
In an NSP regeneration zone, water is cleaned via a three-step biological process where 1) plants and algae produce food for plankton, 2) bacteria turn the waste from the plankton into nitrate, and 3) this nitrate is absorbed by the plants.
The heavy lifting takes place in step two. There, in a chemical process called the nitrogen cycle, bacteria transform one nitrogen-containing compound into another. First, heterotrophic bacteria consume the plankton waste (or detritus) along with pollutants from bathers, bugs, animals, and plants, and turn it into ammonia. Nitrosomonus bacteria consume the ammonia and turn it into nitrite. The nitrite is then consumed by nitrobacter bacteria and released into the water as nitrate. The nitrate, the primary ingredient used in fertilizer, is then absorbed by the plants.
The process works best if the regeneration zone has just the right number and type of plants, a blend that depends on factors that include geographical location, pool size, the expected number of bathers, and whether the pool is shaded. Because the plants compete with the algae for those nitrates, the goal is to keep them hungry so they work harder. How do you know you got it right? “The plants will look fine to the untrained eye,” says Robyn,” but a horticulturist will say that they could use some fertilizer.”
Ecological Relationships in an NSP
Producers Plants,
Algae, Phytoplankton
Consumers
Herbivore & Zooplankton
Reducers
Fungi & Bacteria
Nitrogen Cycle of an NSP
“Nature’s Waste Management System”
1. Heterotrophic bacteria consume organic material in the water, oxidizing it and breaking it down into water, CO2 and ammonia.
2. Nitrosomonas bacteria convert ammonia to nitrites.
3. Nitrobacter bacteria convert nitrites to nitrates.
4. Nitrates are taken up by plants as fertilizer, thus making use of the once-harmful compounds in a beneficial way.
Smaller pools can work, but they’re more expensive to build and pose more of an engineering challenge. “The larger ones get biological momentum,” says Mick Hilleary of Total Habitat, a pool builder and consultant from Bonner Springs, Kan. He says that with a smaller water area, he tends to supplement the natural filtration with a carbon filter.
Overcoming Objections
When people first hear about this technology they almost always raise health concerns. To address this, Morgan Brown, president of Whole Water Systems, a Seattle company that builds NSPs and water features for eco-resorts, encourages people to think of the NSP the same way they would a small lake or pond. “Natural bodies of water are eff ectively cleaned by wetlands, and it’s the same with an NSP.”
He says that an NSP is better equipped to handle a sudden increase in bacteria, as when a toddler goes in the pool and soils his diaper. In a conventional pool, the usual response is to shock it with toxic levels of chlorine, but with an NSP that’s not necessary. “The bacteria say ‘Whoopee—a bit more food,’ and quickly clean it up themselves, just like in a natural lake,” says Brown. He adds that NSPs typically have half the E. colilevels considered safe for lake swimming, and that long experience in Europe proves their safety. “There’s never been an incident of anyone going over the limit of E. coli in Europe. Why? Because the water is constantly circulated through a wetland.”
Some people also worry about algae that can appear on the surface of an NSP right after installation and in the early spring. This is nothing to worry about, Robyn says. “A week later, the plants will start doing their thing and clean it all up.”
29
03.2011
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