Researchers propose to quantify how sources, transport, and fate of nitrate in storm runoff vary with degree of urbanization in a semi-arid environment. New isotopic tracer techniques of 17O, O, 15N will be refined and used to understand the sources of nitrate in surface water in urbanizing watersheds in Tucson and Phoenix in Arizona and surrounding wildland watersheds impacted by nitrogen deposition. Specifically, three questions will be addressed: 1) How does urbanization impact the processes controlling delivery of nitrate from upland to lowland parts of the desert landscape? 2) What are the dominant nitrate sources in arid urban watersheds? and 3) How does wash substrate type modulate instream/ wash processing of nitrate? Researchers will characterize seasonal patterns of nitrate export from a set of urbanizing watersheds that represent a gradient of land use density in Tucson and Phoenix (CAP LTER). They will perform simultaneous measurement of 17O, O, 15N in nitrate on extracted from precipitation and surface water samples collected in these watersheds. In concert with water isotopes (D,O) and conservative geochemical tracers, the isotopic data will be utilized in conjunction with mixing models and response function representations of nitrate concentration and mass flux. Combined these methods will illuminate the underlying processes and mechanisms controlling nitrogen biogeochemistry along an urbanization gradient. The response functions will also be combined with a decision support system for urban flood hydrology to communicate to decision makers the implications of differing patterns of urban development Intellectual merit of this proposal include highlighting the utility of using what are loosely termed mass independent isotopic anomalies (17O) in the biogeochemical cycling of nitrogen to identify dominant N sources in xeric ecosystems. The proposed research will also identify the mechanisms that account for differences in N sources among alternative urban ecosystem states, and will thereby identify biotic, soil, chemical, and hydrologic conditions that enhance riparian ecosystem capacity to ameliorate contaminating N inputs. Broader impacts of this research lie in the potential to identify sources of surface and water nitrate contamination in arid and semi-arid deserts. Deserts and semi-arid regions occupy more than 30% of the Earth and are under increasing stress due to regional land use change such as urbanization and agricultural development. Water is precious in these regions, yet increasing incidences of contamination of ground and surface waters by nitrate have been observed and threaten this vital resource. The research will be carried out by new investigators who will coordinate local, state and federal resources to focus on a problem that has local, regional and global implications. Four graduate students will be trained in using sophisticated research methods, conducting interdisciplinary research, and communicating their understanding of the urbanization of water resources. At a local level, we will engage citizen scientist volunteers to assist in collection of rainfall and rainfall chemistry. This program and other extension activities will promote a higher level of knowledge exchange.
Supplemental funding is requested to support undergraduate involvement in research on how urbanization modifies hydrological and biogeochemical processes that govern the transformation and movement of nitrogen through ecosystems. Funds will support two outstanding undergraduate students, one a member of an underrepresented group, who have been involved with the laboratory and project through prior summer REU awards, allowing them to continue their research as part of a cohort of undergraduate and graduate researchers. These students will enhance their experience with nearly all aspects of the research enterprise, building upon their initial successes to develop further their research proposal in which hypotheses, predictions, and tests are outlined, to collection and analyses of data, and then to presentations of results at professional meetings and the Arizona State Universitys summer undergraduate research symposium, and publications in peer-reviewed journals. The 20 years of experience in supporting undergraduate research in environmental biology and urban ecology, using REU supplements from the NSF, will ensure that students have meaningful research experiences that will benefit them in their scholarly pursuits.
|Effective start/end date||9/1/09 → 2/28/14|
- NSF: Directorate for Biological Sciences (BIO): $294,769.00