HR: 11:15h
AN: H22A-04    [Abstracts]
TI: Asynchrony Controls on Biogeochemical Fluxes in a Mediterranean Climate
AU: * Meixner, T
EM: tmeixner@hwr.arizona.edu
AF: University of Arizona, Dept. of Hydrology and Water Resources, Tucson, AZ 85721 United States
AU: Fenn, M
AF: USFS-PSW Forest Fire Lab, 4955 Canyon Crest Drive, Riverside, CA 92507 United States
AU: Allen, E
AF: UC-Riverside, Dept. of Botany and Plant Sciences, Riverside, CA 92521 United States
AU: Wood, Y
AF: UC-Riverside, Dept. of Environmental Sciences, Riverside, CA 92521 United States
AU: Sirulnik, A
AF: UC-Riverside, Dept. of Botany and Plant Sciences, Riverside, CA 92521 United States
AU: Michalski, G
AF: UC-San Diego, Dept. of Chemistry and Biochemistry, La Jolla, CA 92095 United States
AU: Wohlgemuth, P
AF: USFS-PSW Forest Fire Lab, 4955 Canyon Crest Drive, Riverside, CA 92507 United States
AU: Riggan, P
AF: USFS-PSW Forest Fire Lab, 4955 Canyon Crest Drive, Riverside, CA 92507 United States
AB: Southern California has some of the highest rates of atmospheric nitrogen deposition recorded in the world. These high rates of atmospheric deposition have resulted in elevated levels of dissolved nitrogen in some streams in southern California and may have contributed to landscape level changes in vegetative communities. The levels of nitrogen (overwhelmingly as nitrate) in streams correlate with atmospheric deposition in the region but there is also considerable spatial and temporal variability. The variability in space and time appears to be due to differences in hydrologic flowpath and biogeochemical cycling and how they affect the fate, storage and transport of nitrogen in the environment of the dominant semi-arid Mediterranean ecosystems of southern California. Catchment scale research in southern California has shown several causes for the spatial and temporal differences in nitrogen in theses ecosystems. First, interannual variability appears to be due to some level of nitrate storage within these catchments since wet years following dry years have elevated nitrate concentrations with the reverse also being true. Second, isotopic results recently published indicate that 10% of the nitrate observed at baseflow is direct throughput of atmospherically derived nitrate and during storm events nearly 40% of exported nitrate is throughput of atmospheric nitrate. These high fractions during storm events are likely due in part to direct throughfall into streams. Third, nitrate is well correlated with discharge in any stream in southern California with a significant groundwater flow component, which indicates groundwater storage of nitrate. Fourth, since the water in storm event flows bears a groundwater signature the nitrate observed in stormflows must have undergone some level of storage within the catchments vadose zone/groundwater system. Taken together the interannual variability, correlation with discharge, isotopic data and mixture modeling results indicate that the common temporal disconnect (asynchrony) between when and where nitrogen is physically available and when and where biological processes demand this nitrogen play a leading control in the export and processing of nitrogen in seasonally dry ecosystems. Additionally the increased fertility offered by the within landscape storage of nitrogen appears to contribute to a positive feedback encouraging the extirpation of coastal sage scrub and their replacement with exotic annual grasslands.
DE: 0400 Biogeosciences
DE: 1806 Chemistry of fresh water
DE: 1809 Desertification
DE: 1875 Unsaturated zone
DE: 4805 Biogeochemical cycles (1615)
SC: Hydrology [H]
MN: 2005 Joint Assembly