Narrator: This is Science Today. Wetlands are increasingly used to treat sewage around the world. They're cheap, simple and reliable. So how can a bunch of reeds and plants work to break down sewage? Ecologist Alex Horne of the University of California, Berkeley says, it's simple.

Horne: The way to look at this is to think, how many living, breathing so to speak organisms you find in a cubic foot of sediment or wetland versus a lake or soil or anything else. And if you think how many organisms you could strain out of a lake, there wouldn't be very many.

Narrator: But a wetland has millions of microorganisms per quart of water.

Horne: So why we can treat wastewater with wetlands is there's so many more living organisms already naturally there to carry out the transformations. On top of that they have free unlimited power...

Narrator: In the form of sunlight heating a broad expanse of shallow water.

Horne: So given this vast amount of energy, the vast amount of organisms, it's not surprising that a vast amount of chemical transformations can occur.

Narrator: For Science Today, I'm Steve Tokar.