Soil Scientists Strike Pay Dirt

In a wooden shed tucked away in the Angeles National Forest, history is stored in a bottle. Or, to be more precise, in almost 1,000 Mason jars filled with 65-year-old dirt.

The byproducts of a failed science project concluded long ago, the jars, and the quart of mountain soil each one holds, are the leading characters in a tale of how serendipity sometimes shapes science.

The setting is the 17,153-acre San Dimas Experimental Forest, a portion of the larger Angeles National Forest set aside during the presidency of Franklin D. Roosevelt to conduct scientific research.

Projects conducted at the experimental forest usually represent the ecological concerns of their time: Current studies often focus on how man has changed the environment.

But in the forest’s early days, the mid-1930s, some scientists were bent on controlling nature. One plan: Replant the San Gabriel foothills with less-thirsty vegetation so that the forest would yield more water for the communities below.

With the help of the Civilian Conservation Corps, scientists embarked on an ambitious project in 1935 to test their theories. In a vast clearing within the forest, they built a series of lysimeters, complicated, oversized planters, that would measure how vegetation took in and processed water.

The lysimeter project was so elaborate and labor-intensive that it probably never would be duplicated today. It took nearly two years for the scientists, working with the CCC, to construct 32 lysimeters, most of them 11 feet wide, 21 feet long and 6 feet deep.

It was, according to the Journal of Forestry, “one of the largest lysimeter installations in existence.” Five types of native vegetation were planted: scrub oak, Coulter pine, buckwheat and the evergreen shrubs chamise and ceanothus.

A concrete bunker below the planters housed an elaborate system of tanks--massive contraptions manufactured by Republic Steel in Youngstown, Ohio--to measure rainfall, runoff and the amount of water that percolated within the lysimeters’ soil.

For almost 30 years, scientists regularly descended a set of concrete steps into the narrow, chilly bunker, often scribbling mathematical equations in pencil on the outside of the tanks.

But, the scientists learned, the lysimeters did not sufficiently reproduce the natural environment of the forest to supply meaningful data.

Among other things, the soil in the planters, like soil in a flower pot, pulled away from the planter walls, allowing water to rush in through the cracks--something that would not happen in the open forest.

“It was a great chalkboard idea that didn’t pan out,” said Pete Wohlgemuth, a hydrologist with the U.S. Forest Service, who serves as the experimental forest’s manager.

Scientists used their data with trepidation, publishing a few papers on the project but, for the most part, allowing the research to peter out. After a fire swept through the San Dimas Experimental Forest in 1960, burning most of the plants in the lysimeters, the study concluded for good.

That is, until the late 1980s, when Robert Graham, a professor newly arrived at UC Riverside, was given what he calls a gift.

Graham was just starting to teach soil science at Riverside in 1986 when he got a call from Hutch Wood, a research scientist at the experimental forest.

“There’s something really interesting out here that I want you to see,” Wood told Graham. He took the professor to a pyramid-shaped building only a few hundred feet from the lysimeters.

Graham and Wood climbed down a ladder through the building’s only entrance. Inside, Graham first glimpsed the Mason jars that would become the focus of his research for the next 20 years. Each contained a sample of 1930s soil, a sort of dusty, dirty historical archive.

“Hutch showed me the shed with all the samples labeled in fountain pen,” Graham said recently. “I thought, this is an opportunity--there’s nothing like it in the world.”

The shed resembled the storage cellar of someone with a serious jam-making bent. For Graham, Wood and other researchers, each one of those airtight jars was, in essence, a time capsule, an authentic version of the soil that once was.

When the lysimeters were built, the original researchers had taken samples of soil every two inches down in the planters and had labeled the jars accordingly.

On a recent visit to the forest, Wohlgemuth acted as a tour guide to the treasure hidden within the pyramid. He climbed down into the building and brought out a jar: Lysimeter 13, Layer 11, its fading label read. The 13th lysimeter from the left--one of the ceanothus planters--22 inches down.

“It’s mind-boggling to see this level of intense commitment to a project of this nature,” said Wohlgemuth of the scientists and CCC volunteers who assembled the jars.

At first, UC Riverside’s Graham was curious whether the passage of half a century would actually be enough to show measurable changes in soil. “I thought, this could be good,” he said of his first feelings about the project. “But I also thought, there hasn’t been enough time.”

The lysimeters proved otherwise.

Graham began comparing the soil in the jars with the equivalent layers still in the lysimeters. “We measured [acidity], the percent of sand, silt and clay--performed a number of chemical extractions. We even dissolved the soil completely with hydrofluoric acid and analyzed the complete composition of the soil.”

And what he found was that the soil had, indeed, changed. And drastically.

Levels of zinc and lead in soil that had been exposed to the current environment were highly elevated compared to the soil in the jars.

“We expected to find the lead increase, because of leaded gasoline,” said Graham. “The zinc was a surprise to us. At first, we didn’t know the probable cause. But it probably was related to tires, like steel-belted tires.”

Graham suggested that as automobile tires wear down, particles dispersed into the atmosphere find their way into the upper levels of the forest soil. “We aren’t certain of that,” he said, “but that’s what we can interpret.”

Graham also discovered that a soil layer known as an argillic horizon develops much faster than had been believed. The argillic horizon is the thin layer of clay that accumulates in soil as clay particles leach downward. Soil scientists had thought that thousands of years were required for such a layer to develop.

Using the soil in the jars--noting that in some of the lysimeters argillic horizons now exist that clearly were not there when soil was placed in the jars--Graham and his team could demonstrate that the process takes not centuries, but decades.

Most of the research Graham has conducted so far has focused on just four of the 32 lysimeters, and he says he has tested only a fraction of the jars housed in the dark shed.

“I don’t know that we need to analyze every one of those jars,” he said. “But as more and more people find out about them, more people step forward with interesting questions to study.”

Other studies are planned, including a controlled burn at the lysimeters to assess how the soil responds to fire.

Wohlgemuth, who has worked in the San Dimas Experimental Forest for more than 20 years, said that for a long time, the lysimeter site was little more than an expensive museum piece.

“But subsequent soil scientists have justified its existence,” he said. “It’s still a site where people want to come to work. I’m always in awe when I see it.”