Saturday, October 1, 2005

What was that stuff floating on the river?

Jane Moorman News-Bulletin Staff Writer; jmoorman@news-bulletin.com

What was that stuff floating down the river? Was it soap suds?

The lumps of sandy foam floating down the Rio Grande on Friday were apparently a natural occurrence after a rainstorm that produced a large run-off, the experts say.

There are two theories as to the cause — one from a hydrologist, the other from a biologist. Each admits that it could be a combination of both theories — or neither — but here are their thoughts on what caused the floating river foam.

David Gensler, hydrologist for the Middle Rio Grande Conservancy District, said frothing occurs naturally when fast-flowing water stirs up silt in the water.

"It happens when the fine suspended organic material in the water is whipped up into a froth," Gensler said. "I see it develop in the Rio Grande when the tributaries rush water into the main stream after a heavy rainfall like we received on Thursday."

The National Weather Bureau recorded over the course of the storm rainfall ranging from 2.59 inches in Las Vegas to 2.46 inches at Sedillos Hill in the Sandia Mountains and 1.9 inches in Angel Fire to 1.25 in Albuquerque and 1.12 inches in Taos. Belen recorded about .9 of an inch Wednesday and Thursday. This above-average rainfall generated runoff into the Rio Grande.

"It's just like the sea foam that forms on beaches when the waves hit the sand," Gensler said. "I've even seen the river foam float off sandbars when the water has percolated through the sand, bubbling up and making a sandy foam.

Gensler said he's not sure why it lumps together but expects it has to do with natural surface tension.

Another observation he has made over the years is that the foam does not form in clear water. "It seems like you have to have a fine, suspended silt of sand or salt to make the foam," he said.

Biologist Sterling Grogan, also with the Middle Rio Grande Conservancy, went into more detail about why he things the suds form.

"I've also wondered about this occurrence, and then I remembered learning about it during my soil science classes," Grogan said. "It is the result of a natural surfactant, or detergent, called saponins that is in plants and therefore is in the water as organic matter."

Plants containing saponins include alfalfa, yucca, soapwart, broomweed, soybeans, common beans, peas and other legumes and many varieties of ivy, foxglove and soap lily.

"Alfalfa is high in saponins in the summer," Grogan said. "Farmers will tell you that, if animals get into an alfalfa field and overgraze, they will bloat. This is from the saponins in the plant."

Another plant common to New Mexico is yucca.

"Native Americans have used the root of yucca plants for centuries for soap. They used the soapy leaves from yucca for numerous conditions," he said.

Grogan said the chemical gets into the water during runoff and foaming is caused by the combination of the nonpolar sapogenin and the water-soluble side of the chemical chain.

While saponins are a natural detergent, many people fear the Rio Grande foam is man-made.

A New Mexico Environment Department study of the river's water quality has not found significant amounts of detergents in the water, according to Grogan

"It's important to put it into context. The New Mexico Environment Department conducts a study of the quality of the Rio Grande's water every three years. They are currently completing such a study," Grogan said. "In the report from 2002, they found the only serious pollutant is animal waste, with the major source of it being wildlife and wild birds."

One last thought about saponins is that they are commonly used in cough remedies and diuretics. Saponins are used in toothpaste as well, and in shampoo or for foaming agents in drinks, such as root beer, and to improve the head in beer.

Industries also use the natural chemical in fire extinguishers as a foam producer and in photographic emulsions.

There are current studies regarding health benefits of saponins, particularly that saponins inhibit growth of cancer cells.

Recent studies at the University of Toronto in Canada have indicated that dietary sources of saponins offer preferential chemo-preventive strategies in lowering the risk of human cancers.

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