HR: 1330h
AN: H33B-01    [Abstracts]
TI: Isotopic Fingerprint of a Hyporheic-Hypolentic Boundary
AU: * Aseltyne, T A
EM: taasel2@uky.edu
AF: University of Kentucky, Dept. of Geological Sciences 101 Slone Research Bldg., Lexington, KY 40506-0053 United States
AU: Fryar, A E
EM: afryar1@uky.edu
AF: University of Kentucky, Dept. of Geological Sciences 101 Slone Research Bldg., Lexington, KY 40506-0053 United States
AU: Rowe, H D
EM: hrowe@uky.edu
AF: University of Kentucky, Dept. of Geological Sciences 101 Slone Research Bldg., Lexington, KY 40506-0053 United States
AB: Kentucky Lake is located in western Kentucky (USA) and is the largest reservoir on the Tennessee River. Current management practices by the Tennessee Valley Authority (TVA) dictate that water level is raised 1.5 m in March and lowered 1.5 m over a three-month period beginning in August. Ledbetter Creek, a third-order tributary to Kentucky Lake, is located on the western side of the reservoir. The mouth of Ledbetter Creek spreads out across a mudflat before discharging to an embayment attached to Kentucky Lake. The mudflat is inundated following reservoir-stage increase in the spring, and is drained in the autumn. Stable isotopes of H₂O and conservative solutes, such as chloride (Cl^-), were used to define the hyporheic-hypolentic boundary at the mouth of Ledbetter Creek and trace water movement associated with reservoir-stage manipulation. Three water sources were defined in the Ledbetter Creek watershed, based on isotopic composition and Cl^- concentration: ground water, stream water from Ledbetter Creek, and embayment water from Kentucky Lake. At winter pool, δ²H and δ¹⁸O values decreased across the hyporheic-hypolentic boundary from -36.8 to -42.5 per mil and -6.04 to 7.24 per mil, respectively. Cl^- concentrations decreased across the boundary from 3.2 to 1.3 mg/l. The profile indicates that Ledbetter Creek infiltrated into the substrate to a depth of 10 cm near the confluence with the embayment. Below this depth, isotopic values and Cl^- concentrations were indicative of ground water within the Ledbetter Creek watershed. Following reservoir-stage increase, δ²H and δ¹⁸O values shifted from -24.5 to -42.5 per mil and -4.87 to -7.46 per mil, respectively. Cl^- concentrations shifted from 5.7 to 1.6 mg/l across the hyporheic-hypolentic boundary. At this time, surface water from the embayment infiltrated into the hyporheic-hypolentic zone to a depth of at least 16 cm below the channel bottom. Reservoir-stage decline in the autumn caused source-water mixing, largely obscuring the hyporheic-hypolentic boundary. However, based on these findings, stable isotopes provide a suitable alternative to conventional tracers for delineation of water masses within the hyporheic-hypolentic zone.
DE: 1040 Isotopic composition/chemistry
DE: 1045 Low-temperature geochemistry
DE: 1857 Reservoirs (surface)
SC: Hydrology [H]
MN: 2005 Joint Assembly