HR: 09:25h
AN: H21F-06    [Abstracts]
TI: Tracing Nitrate Sources in a Mixed Land-Use Watershed During Baseflow and Peakflow Conditions
AU: * Buda, A R
EM: arb7@psu.edu
AF: Pennsylvania State University, 136 Land and Water Building, University Park, PA 16802 United States
AU: DeWalle, D R
EM: drdewalle@psu.edu
AF: Pennsylvania State University, 107 Land and Water Building, University Park, PA 16802 United States
AB: Potential sources of stream water nitrate were assessed using a combination of stable isotopic (δ¹⁵N and δ¹⁸O in nitrate), microbiological (bacteria source tracking with E. coli), and inorganic chemical tracers within Spring Creek, a 78 km² mixed land-use watershed located in central Pennsylvania. Four storm events were sampled during the spring and summer of 2005 using a nested sampling design (5 sites) representing a downstream progression of forested, agricultural, urban, and mixed land-uses. Stream samples were collected during antecedent baseflow conditions and at or near peakflow for each event. Precipitation was collected sequentially during storm events and effluent from a sewage treatment plant was sampled during baseflow conditions for each event. Preliminary stable nitrate isotope (δ¹⁵N and δ¹⁸O) results from two spring storms indicated that nitrate changes from baseflow to peakflow shifted slightly towards a varying mix of precipitation and organic sources for the agricultural and mixed land-use catchments. Dilution of nitrate concentrations during storms in these catchments coupled with the subtle changes in δ¹⁵N and δ¹⁸O from baseflow to stormflow may indicate that flushing of nitrate during the two March storms was dominated by existing groundwater sources as opposed to new nitrate sources derived from overland flow. Increases in nitrate concentrations and changes in δ¹⁵N and δ¹⁸O from baseflow to stormflow for the forested catchment indicated that soil nitrate was the most likely important new nitrate source. For the urban catchment, depleted δ¹⁵N and enriched δ¹⁸O in stormflow nitrate clearly indicated that precipitation or urban runoff was the most important new nitrate source. In addition to stable isotope tracing of nitrate sources, chloride and sodium were found to be useful indicators of nitrate from sewage and animal waste sources, especially within the mixed land-use, agricultural, and urban catchments. It is anticipated that information using bacteria source tracing with E. coli coupled with existing stable isotope and inorganic chemistry data will further enhance our ability to identify sources of nitrate in streams with different land-uses.
DE: 0465 Microbiology: ecology, physiology and genomics (4840)
DE: 0469 Nitrogen cycling
DE: 0496 Water quality
DE: 1879 Watershed
DE: 4870 Stable isotopes (0454, 1041)
SC: Hydrology [H]
MN: Fall Meeting 2005