HR: 0800h
AN: H41D-0332    [Abstracts]
TI: A Survey of \delta$^{18}$O and \delta$^{15}$N Ratios in Ground Water from an Agricultural Community in the San Joaquin Valley, California
AU: * Glowacki, S D
EM: o2lavalady@aol.com
AF: California State University, Fresno, Dept of Earth and Environmental Sciences, M/S MH24, Fresno, CA 93720 United States
AU: Suen, C J
EM: john_suen@csufresno.edu
AF: California State University, Fresno, Dept of Earth and Environmental Sciences, M/S MH24, Fresno, CA 93720 United States
AU: Suen, C J
EM: john_suen@csufresno.edu
AF: California Water Institute, 6014 North Cedar Avenue, Fresno, CA 93710 United States
AB: We studied ground water samples from domestic and monitoring wells in an agricultural community in the eastern side of the San Joaquin Valley, California. The study area is rich in alluvial soils creating an extremely fertile farmland. Livestock farms and agricultural fields are abundant in the area. Fifty-four ground water samples were analyzed for \delta$^{18}$O and \delta$^{15}$N in dissolved nitrate, in addition to nutrients and major minerals. Nitrate concentration levels in groundwater are elevated and affected by agricultural and other activities. Possible sources of nutrients include: a municipal waste-water treatment facility, a raisin processing plant, a meat processing plant, a turkey farm, diary operations, and agricultural fields. However, except for the turkey farm and a diary, we found no statistical significant contribution of nitrate from the other facilities as compared to the rest of the area. The \delta$^{18}$O versus \delta$^{15}$N ratios plot of dissolved ground water nitrate shows most samples clustered around an area consistent with soil organic nitrogen. In addition, the rest of the samples show a trend that is indicative of denitrification process. Generally, high \delta$^{15}$N values are associated with low nitrate concentrations. The isotopic signal of denitrification is particularly pronounced in samples in the vicinity of the waste water treatment facility, where the highest values of \delta$^{15}$N and the lowest nitrate concentrations are observed. However, these samples also have elevated chloride concentrations indicating a waste-water source. These data suggest that the denitrification in the subsurface may have been enhanced by bacteria species introduced by the effluence of the plant. [This study was performed with the collaboration of Steven R Silva of USGS, Menlo Park, and Iris Yamagata and Holly Jo Ferrin of California Department of Water Resources.]
DE: 1806 Chemistry of fresh water
DE: 1831 Groundwater quality
DE: 1040 Isotopic composition/chemistry
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting