Due largely to human activities associated with food and energy production, the world is experiencing an un-precedented mobilization of bio-active nutrients such as nitrogen (N) and phosphorus (P). A substantial portion of mobilized N and P flows into streams and rivers, and eventually down to coastal waters, where nutrient over-enrichment has been associated with a host of environmental impacts, including increased frequency and severity of low-oxygen events, increased frequency and severity of harmful algal blooms (e.g. red and brown tides), and loss of biodiversity. En route to the ocean, these nutrients can strongly affect ecosystem function as well as the balance of atmospheric greenhouse gases.
My research group uses experimental, remote sensing, and spatially explicit modeling approaches to elucidate processes governing the mobilization, transport, transformation and ecosystem/biogeochemical impacts of land-based N, P, and other bio-active elements. Current and past projects focus on regional nutrient and greenhouse gas dynamics in Mexico's Yaqui Valley, California's Central Valley, and in watersheds of the Pacific Northwest. We also work at the global scale, and have developed spatially explicit, global models of nutrient and organic matter export as part of a UNESCO-IOC-funded research project called Global Nutrient Export from Watersheds (Global NEWS).