A UMD researcher, Dr. Martin Rabenhorst of the Department of Environmental Science and Technology, has invented a new method for measuring the quality of wetland soils which is easier to use, more accurate, and more environmentally friendly. The new method eliminates problems by using reusable plastic tubes to insert oxide-coated plastic films into the ground for analysis, and 2D images can then be analyzed with the latest image processing and computing software. This tool helps identify essential wetland ecosystems and ensure long-term protection. Rabenhorst’s invention was nominated for UMD Invention of the Year, one of nine inventions recognized with a nomination in a field of over 170 new inventions disclosed during 2017. This invention has the potential to be widely used as the primary technique for wetland soil assessment, which is required and regulated by federal and local authorities.
The technology of using oxide coatings on plastic is called IRIS (indicator of reduction in soils), and the current method applies an iron-oxide paint to PVC pipes that are pushed into the soil and left for a month so the soil can react with the paint. As these reactions occur, the paint is partially dissolved from the tube. If 30 percent or more of the paint is stripped off, the soil is behaving like typical wetland soil. This method, however, is problematic for many reasons. “Some of the paint can rub off the tube as it is transported and when it is pushed into the ground, so that is one source of error,” says Rabenhorst. “The tube is also a 3D cylinder, which makes it difficult to accurately estimate the amount of paint that has actually been removed. You want to be able to scan the surface for analysis, but scanning a 3D tube requires specialized custom-made equipment, so that is a problem.” The current tube system also produces a lot of plastic waste. “I have used 5,000 PVC tubes over the last 10 years or so, and they can’t be reused. It’s a real problem, and it doesn’t feel very ‘green’,” says Rabenhorst.
Out of these issues came Rabenhorst’s new invention. Instead of coating PVC pipes with the iron-oxide paint, Rabenhorst has developed a method to coat thin vinyl films with the paint. These are relatively flexible and can be rolled and dropped directly into a reusable plastic delivery tube. The tube provides protection and is used to push the film into the ground, leaving the paint undisturbed. Then, the tube is removed and the film stays in the soil to react. When it is retrieved, assessors have a 2D film that is easily scanned and analyzed and provides a much more accurate assessment of soil reactivity. And, the films are small, flat, and easy to store, producing much less waste. “This is less than 5 percent of the storage volume and only 13 percent of the weight, so we end up using far less plastic,” says Rabenhorst. “And, the plastic tubes used to deploy the films are reusable, so you only need a few.”
Only in the last 40 years or so have people begun to realize the importance of wetland ecosystems. They are valued for their diversity in wildlife, as well as their natural ability to prevent floods, filter water, mediate carbon emissions, and create healthier ecosystems, waterways, and atmosphere. However, before this was known, more than 50 percent of wetlands across the United States and 70 percent across Maryland were lost over the past 200 years.
“There are three major parameters needed to classify an area as a wetland: hydrology or water, the plant community, and soil properties,” explains Rabenhorst. “These are all critical because wetlands are highly regulated and protected ecosystems. The soil is perhaps the most complicated piece of the puzzle because you have to confirm that certain biogeochemical processes are actually happening below ground where they are not easily seen. That is why having an easy-to-use tool for assessors is so important. Properly protecting these wetlands and promoting restoration is essential, but we also want to make sure not to over delineate or over regulate. Our goal is to be scientifically and environmentally responsible.”
Rabenhorst joined UMD in 1983 as a soil scientist, and his study of wetlands has been the dominant focus of his work. Rabenhorst also helps coach the soil judging team at UMD that competes and consistently places nationally, including a 2017 national championship. The wetland soils class that he established in 1991 was probably the first ever full credit college class of its kind in the country. He has dedicated himself to the study of these complex ecosystems, with the ultimate goal of bringing good science to the table in difficult regulatory settings. This means always looking for better ways to analyze and collect the data needed to make these tough calls.
“With the Chesapeake Bay as a priority, Maryland is a pretty environmentally enlightened place, and we value these ecosystems,” says Rabenhorst. “This tool gives those of us working in wetlands an easier way to do a better job, and that is exciting.”