Wetland vindication: Pasture wetlands help filter runoff

Short of potty training cattle, maintaining wetlands is best, says research

Don Curlee
For the Capital Press

January 25, 2008

What a relief! Researchers at the University of California have found that wetlands have some benefits for the farmers and ranchers on whose land they are found.

The finding comes after two decades of incessant drumming by environmentalists claiming that something good can come from the bogs and swamps that dot the land.

Endless regulations to protect and preserve them have been developed, particularly at the federal level.

Even with the stimulating news that the overgrown puddles provide more than shelter for weeds, frogs, salamanders, mosquitoes, algae and several other insects and assorted wildlife, many farmers with unsightly year-around mud holes are still likely to think of them as unproductive nuisances.

But the researchers have found that levels of E. coli, for example, in streams draining some of California 's range country are reduced by an average of 74 percent when they run through a wetland.

In other words, the bacteria level of water draining out of a wetland is lower than it is in the stream that feeds it.

Before encountering the wetland, a typical stream is likely to pick up any number of bacteria from cattle, wild animal and bird feces or other sources along its meandering way.

Reporting in the October-December issue of California Agriculture, the university's research magazine, researchers Kate Knox, Kenneth W. Tate, Randy A. Dahlgren and Edward R. Atwill said the filtering effect of a wetland is one of three steps that can be taken to reduce the amount of bacteria in streams that drain irrigated pastures.

The other two preventive measures are reduction of the runoff rate and resting the pasture from grazing(clearing out all the animals) for a week before irrigation water is applied. Doing so allows manure patties to dry and be less likely to pollute the streams.

The latter preventive procedure, of course, depends on having an alternate site where the cattle can be moved.

Not surprisingly, the research team found that a combination of all three preventive measures was the most effective.

The study by the four Davis researchers was done on a 12-acre flood-irrigated pasture in the northern Sierra Nevada foothills, somewhat typical of what the authors described as "a patchwork of irrigated perennial grass and clover pastures interspersed with annual grassland and oak woodland."

Such sites make up about 800,000 acres of California 's pastureland. The pasture was irrigated six times in 2004, and six times in 2005 as the study was undertaken. "Results from this study," the authors said, "indicate that passing tailwater through relatively small wetlands can significantly reduce E. coli from irrigated pastures."

In another part of the same publication, two other forms of tailwater filtration were pictured: a portable wetland on a trailer - you have to see it to believe it - parked at a nursery, and a series of 5- to 10-foot vertical pipes filled with sand. Logically enough, they are called sand filtration columns.

Short of potty training the cattle and other species that roam foothill pasturelands, or letting the pastures dry up altogether, maintaining the wetlands seems to provide multiple benefits. And if tadpoles are among your favorite things, locate your friendly neighborhood wetland and offer your congratulations.

Don Curlee is a veteran ag publications editor and ag freelancer in Clovis , Calif. E-mail: agwriter1@sbcglobal.net. 

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