Penn State develops a ‘northern rain forest’ to soak up waste water


UNIVERSITY PARK, Pa. – For nearly two decades Penn State has recycled all its waste water by irrigating farm crops and forest areas.

Now, thanks to tree research done in the College of Agricultural Sciences, the system will perform better.

“We have created a sort of northern rain forest,” said Todd Bowersox, professor of silviculture, a branch of forestry dealing with the care and development of forests. In the last seven years he has developed a plant community that can continue to absorb much of the 2 inches of waste water that is sprayed on it every week of the year.

More rain. Normal rainfall in central Pennsylvania is 40-45 inches annually. The university sprays an additional 104 inches onto the waste water recycling area near Toftrees in Patton Township. The irrigation field is part university land and partly owned by the Pennsylvania Game Commission, known as State Game Land 176.

By replacing the typical central Pennsylvania forest community of red oak, black oak, red maple and hickory – trees adapted to normal rainfall and acidic soils – with thirstier species that prefer less acidic soils higher in nutrients, such as bigtooth aspen, quaking aspen, silver maple, sycamore and green ash, Bowersox created a natural demand for waste water.

The waste water is disinfected and most of the nitrogen is removed at the Penn State sewage treatment plant before being pumped 2.5 miles to the 520-acre irrigation area. Overhead sprinklers dispense about 1 billion gallons of waste water annually, which filters down to ground water supplies.

“The level of Penn State’s wells never changes, even during times of drought,” said Bowersox. “All of the water used goes back into the granddaughter system. It has been estimated that Penn State reuses one out of every four gallons.”

The waste water recycling system is critical to operation of the university, which has just a two-to-four-hour storage capacity for waste water, according to Bowersox. “So we must keep spraying,” he said. “We had to develop a plant community that could soak up the water.”

Soil change. The research began in 1995 when Bowersox observed that the existing trees in the irrigation area were deteriorating. There were no new tree seedlings and trees were beginning to die. When he analyzed the soil, he found it had changed since waste water spraying began.

Previously, the soil was acidic and lower in nutrients. Now it was less acidic with more nutrients from the waste water.

“We changed things from conditions of low fertility and low rainfall to high fertility with much greater precipitation,” explains Bowersox. “Clearly, we needed to find some species that would adapt to the new conditions.”

Of course, some undesirable plant species flourish in the wet, nutrient-rich environment. Herbaceous plants such as impatiens, garlic mustard, Canadian thistle and a variety of grasses thrive to the extent they make it difficult for tree seedlings to grow.

So Bowersox developed a protocol to control herbaceous plants with herbicide until the rain forest becomes established.

Trees help. “A tree community is preferred because it creates better conditions for water infiltration in the winter,” he said. “Plus, trees create a more desirable habitat for birds and other wildlife, and they are more aesthetically pleasing to the variety of people who hunt and hike in the area.” The high number of deer in the area also has made it difficult to grow seedlings. Fencing was installed to keep the hungry whitetails at bay and seedlings now grow 10- to 12-feet-tall three years after planting. Growth rates are far beyond “normal” for this latitude.

“Our new tree-dominated community has a better opportunity to maintain a healthy, diverse forest that is necessary to recycle the university’s waste water,” said Bowersox.


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