While the dredged soil is a nice dark color with about 3 percent organic matter, it is high in salt, metals and nitrate concentrations, Hons said. The company tried planting seed on it, but little would grow.
Hons started his project in October 2010. He began lab and greenhouse work to look at the dredged material's chemistry and how it affected plant growth. After reviewing techniques used to successfully revegetate surrounding soils, he then came up with treatments to help render the metal in the Milltown sediments less soluble, making them unavailable for plant uptake and thus less damaging.
"We developed large greenhouse trials to look at both the top and the root growth and uptake of metals by the plants," Hons said. "We were trying to devise methods to make the soil more amenable to plant growth. If the metals dissolve, the plants can take it up and don't thrive. Increasing rooting depth is important because this is a semi-arid environment where water is often limited and deeper rooting is needed for long-term survival."
The solutions they laid out for Atlantic Richfield are a combination of influencing the pH, salinity and organic matter of the soil, he said. Elevating the pH is critical to successful revegetation as it generally reduces the solubility of the heavy metals. Heavy metal uptake is damaging to plants.
Hons' team continued with Atlantic Richfield's practice of beneficially reusing waste products where possible. They chose a cement production byproduct lime kiln dust to raise the pH of Milltown sediment. It directly decreases the water solubility of metals or creates new minerals through the process and the metals adhere to the surface of those minerals and are less soluble, he said.
Plowing this byproduct into the soils creates a more oxygenated environment and produced some favorable chemical changes also, Hons said.
|Contact: Dr. Frank Hons|
Texas A&M AgriLife Communications