HR: 0800h
AN: H41E-0338 INVITED     [Abstracts]
TI: Retention of Atmospheric and Biogeochemically Cycled Nitrogen in a Mediterranean Climate
AU: * Meixner, T
EM: tmeixner@mail.ucr.edu
AF: Department of Environmental Sciences University of California, Room 2217 Geology, Riverside, CA 92521 United States
AU: Michalski, G
EM: gmichalski@ucsd.edu
AF: University of California, 3975H Miraman St , San Diego, CA 92037 United States
AU: Fenn, M
EM: mfenn@fs.fed.us
AF: USDA Forest Service - Forest Fire Laboratory, 4955 Canyon Crest Drive , Riverside, CA 92507 United States
AU: Wohlgemuth, P
EM: pwohlgemuth@fs.fed.us
AF: USDA Forest Service - Forest Fire Laboratory, 4955 Canyon Crest Drive , Riverside, CA 92507 United States
AU: Riggan, P
EM: priggan@fs.fed.us
AF: USDA Forest Service - Forest Fire Laboratory, 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. 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 Mediterranean ecosystems of southern California. Over the past several decades catchment scale research in southern California by us and by others has shown several causes for the spatial and temporal differences of nitrogen in theses ecosystems. First, interannual variability appears to be due to 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 vadose zone/groundwater system. Taken together these results indicate that seasonal and interannual storage of atmospheric nitrogen in southern California catchments is not small and could have a significant control on water quality.
DE: 1806 Chemistry of fresh water
DE: 1871 Surface water quality
DE: 1615 Biogeochemical processes (4805)
DE: 0322 Constituent sources and sinks
DE: 0400 Biogeosciences
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting