Urbanization dramatically modifies the movement and transformations of nitrogen (N) compounds in semi-arid ecosystems. In particular, nitrate contamination of drinking water is a growing concern in urban areas, especially in arid and semi-arid environments, where urban runoff is actively-managed to recharge groundwater and augment water supplies. Water managers and urban planners, however, lack information on what ecosystem characteristics are most important in controlling the quality of this recharged water, especially its nitrate concentrations. This research will quantify how sources, transport, and fate of nitrate in storm runoff vary with the density and type of urban land use in Tucson and Phoenix (CAP LTER), Arizona watersheds. Seasonal patterns of nitrate export will be characterized, and new isotopic tracer techniques will be used to understand nitrate sources and mechanisms controlling nitrogen transformations along semi-arid urbanization gradients. These mechanisms will be modeled and integrated into interactive visualization products that will aid in decision-making regarding urban development patterns and storm water management approaches.

This research will help identify sources of surface water and groundwater nitrate contamination in arid and semi-arid deserts. Water is precious in these regions, yet increasing incidences of contamination of ground and surface waters threaten this vital resource. This research coordinates local (Tucson, Phoenix), state (Arizona), and federal (National Atmospheric Deposition Program/Environmental Protection Agency) resources to focus on a problem that has local, regional and global implications. The project will engage citizen-scientist volunteers, train graduate and undergraduate students in policy-relevant research, foster interactions between scientists and decision makers, and develop transferable visualization tools.