Human activity has doubled the amount of nitrogen on the landscape, creating a pollution problem and changing the balance among multiple nutrients that limit biological activity in ecosystems. At the same time, other disturbances, such as acidification, interact with nitrogen enrichment in ways that strongly influence the productivity and health of terrestrial and aquatic ecosystems. This project examines the interactions among multiple elements and disturbances (nitrogen, phosphorus, metals, and acidification) along a continuum from the atmosphere through soils to streams. This project takes advantage of two unique experiments in which entire watersheds have been experimentally enriched with nitrogen and acid for nearly two decades. A series of new studies in those watersheds examine how chemical and biological changes in soils alter the ability of streams to take up, use, and retain nitrogen and phosphorus. These nutrient interactions are then related to important biological processes that affect the productivity and health of streams.
This research addresses an important pollution problem that requires an approach that integrates biology and geochemistry along flow paths that link the terrestrial and aquatic ecosystems. This type of integration is a challenge, but needed for effective environmental management, environmental research, and science teaching. Results from this project and interactions between university and US Forest Service researchers will inform effective management of watersheds faced with multiple pollution problems. A series of collaborative workshops in which high school, undergraduate, and graduate students work with researchers and teachers will promote multidisciplinary learning. The collaboration will seek to develop a computer simulation model for use in teaching integrated biology and chemistry in high school and college science curricula.
Atmospheric pollution commonly results in deposition of nitrogen and acidifying chemicals on forested landscapes. This phenomenon changes the chemistry and ecology of both terrestrial and aquatic systems by enhancing availability of a limiting nutrient (nitrogen), while at the same time imposing a stress (acidification). This research project focused on understanding how long term atmospheric pollution changes the interaction of multiple chemicals as they move from soils to streams and the consequences of these interactions for critical ecological processes in stream systems. Research was conducted in two, unique whole-watershed experiment sites in Maine (the Bear Brook Watershed in Maine; https://umaine.edu/bbwm/) and West Virginia (the Fernow Experimental Forest; www.nrs.fs.fed.us/ef/locations/wv/fernow/ ). At both sites experimental watersheds have been subjected to more than 20 years of experimental nitrogen and acid deposition while adjacent reference watersheds have remained untreated. These sites provide a unique opportunity to examine how changes in terrestrial and aquatic systems are interrelated. The increased nitrogen loading to the watersheds led to clear saturation of microbial demand for this typically limiting nutrient. A series of phosphorus addition experiments showed an enhanced role of phosphorus as a limiting nutrient as a consequence of increased nitrogen availabillity. At the same time, acidification of the watersheds has mobilized aluminium from soils into streams where it precipitates and binds to phosphorus, reducing its availability for biological use. These results reveal complex interactions between multiple elements in response to atmospheric pollution and clear linkages between terrestrial and stream processes. There was a strong emphasis on training students and future scientists in this project. Over its duration two postdoctoral fellows and one graduate student conducted research and presented their results to the public and in scientific publications. Eight undergraduates collaborated in research with one going on to publish his results. Research in this project also contributes to a K-12 education initiative (Nitrogen Cycling in Watersheds; http://participatoryscience.org/project/nitrogen-cycling-watersheds) in which students and their teachers engage in research to learn about environmental response to atmospheric pollution.
