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American Society of Landscape Architects

 

July 2007 Issue

Microbes Rule!
Landscape architects who understand the relationships between microbes and nutrients in water can create water features that will stay clean without artificial treatment.

By Bruce Kania

Microbes Rule! Floating Island International

For a long time, Iíve studied a small lake that formed long ago in a natural bowl in northern Wisconsin. It has about 20 acres of surface area and is now surrounded by a cow pasture and a cornfield.

Holsteins graze right up to the waterís edge and at times step into the lake to drink. Sometimes, cows being cows, their waste ends up in the water as well. On the opposite shore, the cornfield has an unusual configuration, with its furrows running straight down the slope and into the lake. When it rains or the fields are irrigated, some fertilizer inevitably washes into the lake.

The stage is set for aquatic misery: Viscous, pea-soup mats of green algae and foul odors are the common results of this sort of nutrient loading. Indeed, few life forms other than algae survive in such water, and such situations are far from uncommon. Almost any waterway connected in these ways with human activity can experience profound nutrient surges, and the results tend not to be pretty.

While common sense would tell us its water should be a mess, the fact of the matter is, beyond a slight tannic tinge, the water in this Wisconsin lake is crystal clear. And when you scoop up a sample in a clear glass, you see itís teeming with lifeótiny critters enjoying a swim in water that smells fresh and doesnít have anything more than the slightest trace of algae.

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