HR: 14:15h
AN: H43D-04 [Abstracts]
TI: Biogeochemical Processing of N in a Mantled Karst Watershed
AU: * Winston, B A
EM: bwinsto@uark.edu
AF: University of Arkansas, Department of Biological Sciences, SCEN 632, Fayetteville, AR 72701 United States
AU: Laincz, J
EM: jlaincz@uark.edu
AF: University of Arkansas, Department of Geosciences
OZAR-113, Fayetteville, AR 72701 United States
AU: Ziegler, S
EM: susanz@uark.edu
AF: University of Arkansas, Department of Biological Sciences, SCEN 632, Fayetteville, AR 72701 United States
AU: Hays, P D
EM: pdhays@usgs.gov
AF: University of Arkansas, Department of Geosciences
OZAR-113, Fayetteville, AR 72701 United States
AB:
Nitrate (NO3-) contamination of aquatic ecosystems is an increasing threat particularly in karst-dominated
landscapes where agricultural practices are on the rise. The importance of sub-surface NO3- processing in a karst
experimental watershed was assessed by measuring dissolved organic carbon (DOC) bioavailability, geochemical constituents,
nitrate concentration and stable isotopic composition. We used a synoptic sampling method aimed at characterizing nitrate
processing under base and storm flow conditions along a hydrogeologic gradient. Our results, consistent with previous work,
demonstrate the importance of the soil-water interface zone in nutrient processing. However, little is known about the
interflow zone above the epikarst surface. Use of a binary mixing model, with chloride as a conservative tracer, suggests a
>20% change in NO3- and DIC concentration was due to processing and 69% to dilution during storm flow. Ground
water community respiration rate (GWCR)(μ MC h-1) normalized to DOC (mMC) indicate more bioavailable C for
NO3- processing in the interflow zone. Stable nitrogen and oxygen isotopic composition of NO3- should
support the interflow zone as an important site for NO3- transformation in this karst watershed. Results
demonstrate hydrologic flow conditions alter chemical and organic constituents and therefore biological processing in this
karst system.
DE: 0330 Geochemical cycles
DE: 0400 Biogeosciences
DE: 4805 Biogeochemical cycles (1615)
SC: Hydrology [H]
MN: 2005 Joint Assembly