Nitrogen and phosphorus are necessary to all living things, and we work hard to supply enough of them to crops, gardens, and lawns. These elements, however, can cause health and environmental problems when they get into our water. We'll talk about how research helps us understand where these elements come from, the problems they cause, and ways to reduce those problems. Presented by: Donald Weller Senior Scientist, Ecological Modeling Lab Smithsonian Environmental Research Center Original Airdate: May 16, 2012 You can stay connected with the Smithsonian's upcoming online events and view a full collection of past sessions on a variety of topics.: http://www.smithsonianeducation.org/educators/events/online_events.html With support from Microsoft Partners in Learning.