The Spatial Distribution of Isotopic Tracers in Urban Organic Matter: Understanding Multiple and Confounding Effects of Human Activities on Urban Vegetation

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Interactions between plants and the environment have been widely studied in natural ecosystems, but very poorly studied in urban ecosystems. Carbon dioxide concentrations, ozone concentrations, nitrogen deposition, and temperature are all elevated in urban environments, where they may affect physiological processes in plants as well as provide environmental benefits. The overall goal of this project is to improve our understanding of urban plant-environment interactions and ecosystem services. Specifically, this project seeks to: 1) identify the major environmental and geographical factors that affect plant processes and their spatial distribution in the Los Angeles basin; 2) quantify the linkage between plant physiology and urban ecosystem services; and 3) use plant organic material as a proxy for the spatial distribution of atmospheric pollutants, i.e. as a "biomonitor." These issues will be addressed by sampling plant biomass across the study region and estimating plant gas exchange and pollution parameters with isotopic tracers. By analyzing the spatial distribution of stable carbon, radiocarbon, stable nitrogen, and stable oxygen isotope abundance in grass samples, it is possible to estimate plant gas exchange, plant energy balance, the proportion of pollution-derived carbon and nitrogen incorporated into plant material, and the relative amounts of these pollutants in the atmosphere. The Los Angeles Basin was chosen as a study region because extensive datasets of the distribution of land cover, meteorological variables, and atmospheric pollutants are available there. By creating a raster database of these parameters and evaluating spatial correlations with land use, climatic and pollutant variables, linkages between the modified urban environment, plant processes, and ecosystem services can be determined. There is currently a great deal of scientific uncertainty as to how plants in urban and other highly modified environments respond to multiple disturbances. This data gap has limited capabilities for effectively managing urban vegetation in order to maximize its environmental benefits. Several aspects of this study are highly applicable to environmental problem solving and natural resource management. Ecosystem services will be directly estimated by calculating the amount of fossil fuel combustion-derived carbon and nitrogen removed from the atmosphere by plants and by evaluating plant energy balance, which influences the urban heat island effect. The proposed methodology also offers potential for utilizing the isotopic composition of urban biomass to map distributions of atmospheric pollutants that are of concern to human health. This may be a very cost-effective method of estimating atmospheric pollutant concentrations integrated over long time periods. The proposed data collection is local to the University of Califonria-Irvine campus and therefore provides excellent opportunities to engage students and integrate research sites and results into courses and educational activities.