HR: 11:35h
AN: B12A-06    [Abstracts]
TI: Biodiversity Risks from Atmospheric Nitrogen Deposition in California
AU: * Weiss, S B
AF: Donald Bren School of Environmental Science and Policy, University of California Santa Barbara, Santa Barbara, CA 93106-5131
AB: Atmospheric nitrogen deposition alters structure and function of terrestrial ecosystems, because nitrogen availability is often limits overall productivity. These alterations can drive losses of biodiversity, as nitrophilous species increase in abundance and outcompete species adapted to more oligotrophic conditions. California is recognized as a "biodiversity hotspot," with a high fraction of endemic taxa with narrow ranges. A state-wide risk screening includes: 1) a 36 x 36 km map of total N-deposition for 2002, developed from the Community Multiscale Air Quality Model (CMAQ); 2) identification of sensitive habitat types from literature and local expertise; 3) overlay of a statewide vegetation map (FRAP); 4) overlay of species occurrence data from the California Natural Diversity Data Base (CNDDB); and 5)species life-history and habitat requirements. The CMAQ model indicates that 55,000 km$^{2}$ (total area 405,205 km$^{2}$) are exposed to $>$5 kg-N ha $^{-1}$ year $^{-1}$, and 10,000 km$^{2}$ are exposed to $>$10 kg-N ha $^{-1}$ year $^{-1}$. Deposition hotspots include coastal urban areas (Los Angeles-San Diego, and the San Francisco Bay Area), the agricultural Central Valley, and parts of the Sierra Nevada foothills. The major known impact of N-deposition in California is increased growth and dominance of invasive annual grasses in low biomass ecosystems, such as coastal sage scrub, serpentine grassland, desert scrub, and vernal pools. For example, 800 km$^{2}$ out of a total 6300 km$^{2}$ of coastal sage scrub are exposed to more than 10 kg-N ha $^{-1}$ year $^{-1}$, primarily in Southern California. Of 225 federal and state "Threatened" and "Endangered" plant taxa, 101 are exposed on average to $>$5 kg-N ha $^{-1}$ year $^{-1}$. Of an additional 1022 plant taxa listed as "rare," 288 are exposed to $>$5 kg-N ha $^{-1}$ year $^{-1}$. Many of these highly exposed taxa are associated with sensitive habitat types and are vulnerable to annual grass invasions. This broad-scale screening outlines potential impacts on California's biodiversity, and paves the way for finer scale analyses using a 4 x 4 km CMAQ deposition map (under development), more complete local data on species occurrences, and establishment of critical N-loads for particular ecosystems.
DE: 3322 Land/atmosphere interactions
DE: 1615 Biogeochemical processes (4805)
DE: 0315 Biosphere/atmosphere interactions
DE: 0345 Pollution--urban and regional (0305)
DE: 0400 Biogeosciences
SC: Biogeosciences [B]
MN: 2004 AGU Fall Meeting