Stable isotopic fingerprint of a hyporheic–hypolentic boundary in a reservoir

Stable isotopes of H₂O are used to define the hyporheic–hypolentic boundary in Ledbetter Creek as it discharges to Kentucky Lake, a constructed reservoir in western Kentucky, USA. High-resolution (centimeter-scale) sample collection and analysis were utilized to determine one-dimensional variations in δ²H and δ¹⁸O of H₂O and chloride (Cl⁻) across the boundary. During reservoir low stand in winter, the hyporheic–hypolentic zone contains water from Ledbetter Creek and groundwater separated by an interface at ~10 cm below the channel bottom. Following reservoir-stage increase in spring and summer, water from Kentucky Lake infiltrates into the hyporheic–hypolentic zone to a depth of at least 18 cm below the channel bottom. Reservoir-stage decline in autumn causes source-water mixing, largely obscuring the hyporheic–hypolentic boundary. Stable isotopes provide an effective complement to conventional tracers for delineation of water masses within the hyporheic–hypolentic zone.