Constructing a ~100 Year Record of 15N in the California Bay Area Utilizing Foliar Tissue of Four Sp
Social Sciences
ENVS Individual Senior Thesis
Anthropogenic nitrogen (N) deposition has been increasing, and will likely continue to increase as it has done over the last century. Ecosystem functioning and composition are affected by high N deposition rates due to the resulting increase in biologically available nutrients. The cumulative effects of N deposition can also modify the carbon (C) cycle and sequestration. Human-induced changes to both the C and N cycle are not fully understood, and are dependent on site-specific factors. There is limited knowledge of the historical record of increasing N inputs to many ecosystems, and to what of the degree to which they are affected. The purpose of this study is to gain knowledge about N accumulation in the Bay Area from 1900 to 2010. Archived specimens of four dominant species were sampled across functional groups to serve as indicators of N accumulation: the woody species Quercus agrifolia, annual grass Vulpia microstachys, forb Lasthenia Californica, and moss Grimma trichophylla were studied to assess historical N deposition in the Bay Area by gathering data on leaf 15N, %N, and 13C. There were significant differences in foliar 15N, %N, 13C for all species. Trends of 15N, %N, and 13C across time were declining except Q. agrifolia. Based on the different responses between species, there is a benefit of using multiple species when reconstructing historical records of N cycling. Specifically, mosses are especially valuable for analyzing atmospheric conditions of N because they are reliant on nutrients from the air. These results provide valuable information regarding the influence of anthropogenic N deposition on sensitive ecosystems, such as serpentine grasslands, and the subsequent effects on listed and endangered plant species that have yet to be addressed by current regulations.
