How it Works
To illustrate, let's use a flock of Ibis that are foraging in your yard. Like most birds, they leave behind some waste. The waste falls into the grass and soon gravity will suck it deeper into the canopy until it disappears below the foliage.
The World of Microscopic Life
Below the foliage, the waste enters into a different world - a world that resembles a triple canopy jungle - a dark, wet, sticky, muddy, and windless place - teeming with all sorts of life -but instead of monkeys, birds, and snakes, you have worms, beetles and insects of all kinds - large and small. And there are millions of microscopic single-cell protozoa and bacteria And - simple plant life like fungi, molds, and algae.
A Feeding Frenzy
It is a very crowded jungle - jam-packed with millions of hungry microbes, waiting for what falls from the sky above - leaves, dust, pollen, animal waste, air pollution trapped in rain, and even fertilizers and lawn chemicals - These are the things the microbes feed on.
They attack anything that enters their world. The worms and beetles attack by chewing, scratching, and digging in the waste. The microscopic single-cell protozoa and bacteria cover their prey with an enzyme slime that dissolves the waste, extracting nutrients the microbes can absorb and use for growth and reproduction.
Nothing Left but CO2 and Water
All this insect and microbial activity enriches the soil with nutrients, that the fibrous roots of the turf can completely absorb and use for their own growth and reproduction.
And after the feeding frenzy is over, after the waste has been completely chewed, dissolved, and absorbed, all that remains is water and carbon dioxide. The waste is gone - The lawn is depolluted.
A Lawn Works Constantly
This process happens 24/7/365 days a year to anything that falls into the canopy - including fertilizers and lawn chemicals. This was proven in a seven-year study done by the Fl Depart of Environmental Protection which conclusively showed that fertilizers put on a lawn, never leave the lawn.
It's the Grass
The grass is the jungle - the grass creates the environment. Take away the jungle, and everything stops - the bugs crawl away or fly or burrow to another lawn, the bacteria dry up and die, and the fungi, mold, and algae wither and blow away. It all stops - no more depolluting.
Rock Yards and Xeriscapes are Losers
Do rock yards or xeriscape depollute? - No
Rock yards are the worse - Barren, dry, windswept rock yards support very little insect or microbial life. Whatever falls on a rock yard either blows away, washes away, or percolates down into the soil
The same could be said of unirrigated Grass Lawns - the limited water and thin open canopy have little or no microbial activity. Unirrigated lawns are equal to the rock yard except it needs to be mowed.
Xeriscapes are a little better but not much - the thin sparse planting and limited irrigation, support very little microbial life.
An Irrigated Lawn is Superior
Irrigated grass lawns - are superior to either rock or xeriscape landscapes. A well-watered, tall patch of St Augustine grass can support a diverse and expansive population of beneficial insects, single-cell life forms, and simple plants - all active and thriving to depollute the lawn.
This is not new. A book written in 1945 called Soil and Health by Sir Albert Howard, who many consider the father of organic farming showed the relationship between healthy pastures, and healthy farm animals and farmers. It was the discovery of the microbial breakdown of organic material in a pasture - which he referred to as composting - that lead him to believe that the healthy pastures "depolluted" the land and gave rise to healthy animals and people.
Consider all this when you are thinking about a landscape - lawns don't pollute, they depollute.