The process of doing research on ecosystems often generates as many questions as it answers. This certainly has been the case with the IES research on the effects of air pollution on the forests and streams of the Catskill Mountains, involving a team of researchers led by Drs. Gary Lovett and Kathleen Weathers of IES and Dr. Mary Arthur of the University of Kentucky. The work has focused on the fate of atmospheric nitrogen oxide pollutants that are emitted by fossil fuel combustion, primarily in power plants and automobiles. The nitrogen in these pollutants can cause acidification of soils and streams, excessive growth of algae in estuaries, and nutrient imbalances in forests. Forests are known to retain large amounts of the nitrogen pollution that reaches them, but the ability of many forests to do so is thought to be nearing capacity. In this case, forests may switch rapidly from being nitrogen-absorbers to nitrogen conduits, and harmful levels in groundwater, streams, rivers and estuaries can be reached in quick order.

Early on in this project, the researchers learned that most of the deposited nitrogen that was retained in the Catskill Mountain forests was trapped in the soil, attached to substances derived from the decay of leaves, wood and other organic matter. This raised the question of whether nitrogen retention was primarily a biological process, mediated by soil microbes, or a purely physical process. Knowing the process involved is critical to understanding what limits the capacity for nitrogen retention in forest soils, which in turn is key to predicting the consequences of continued emissions of these pollutants.

To tackle this problem, Lovett, Weathers and Arthur hired a Postdoctoral Associate, Dr. Ross Fitzhugh. Fitzhugh's experience lay primarily in soil and water chemistry and hydrology, expertise that complements the more biological focus of the others. Like most postdoctoral appointments, the collaboration is mutually beneficial: the project gains breadth from Fitzhugh's expertise in chemical and physical sciences and also gains a bright young scientist with time to focus on a particular issue. At the same time, Fitzhugh gains valuable research experience while learning more about biological aspects of forest ecosystems.

Soon after Fitzhugh arrived at IES in July 2000, he and the research team designed an experiment to test which of the several forms of nitrogen present in the soil was most efficiently retained by the soil, and whether the process was microbially mediated or abiotic (i.e., physical). The experiment involved adding a non-radioactive, isotopically labeled form of nitrogen to trace the fate of nitrogen added to a soil sample. Nitrogen movement is being compared in a treatment where some soils were sterilized temporarily to eliminate microbial activity while other soils remained untreated, as a control. This large study, completed in the summer of 2001, produced hundreds of samples requiring careful analysis that (as of fall 2001) is still underway. Preliminary results indicate that different forest types in the Catskill Mountains vary substantially in their capacity to retain added nitrogen. The researchers hypothesize that a large fraction of the nitrogen retention they observed is abiotic.