| Summary: | The nature of carbon (C) cycling in the vadose zone where groundwater is in contact with abundant gas-filled voids is poorly understood. The objective of this study was to trace C cycling in a karst landscape using stable-C isotopes, with emphasis on a shallow groundwater flow path through the soil, to an underlying cave, and to the spring outlet of a cave stream in the Ozark Plateaus of northwestern Arkansas. Blowing Spring Cave (BSC) occurs in the Springfield Plateau of the Ozark Plateaus. The cave passage is relatively horizontal, the entrance to BSC is a spring outlet, and no other human-sized entrances into the cave are known to occur. Soils generally are less than 2 to 3 meters thick above the cave and dominated by the Clarksville soil series (loamy-skeletal, siliceous, semiactive, mesic Typic Paleudults). Gas samples for carbon dioxide (CO₂) concentration and isotopic composition (δ¹³C-CO₂) and water samples for dissolved inorganic carbon (DIC) concentration and isotopic composition (δ¹³C-DIC) were collected from two suction-cup soil samplers above the cave (L1 and L2) and from within the cave. Cave-sampling locations included a drip-water pool fed by a waterfall in a side-passage of the cave (BS06), two locations along the main passage of the cave stream (BS07 and BS03), and at the spring outlet of the cave stream (BS01). Preliminary, intermittent sampling began in June 2011 and regular, bi-monthly sampling continued from March 2012 to May 2013, including storm-event sampling during high-flow conditions when discharge generally exceeded 0.5 cubic meters per second. This dataset includes inorganic carbon species concentrations and isotopic compositions (CO₂, δ¹³C-CO₂, DIC, δ¹³C-DIC, bicarbonate, carbonate, carbonic acid, and aqueous CO₂), physical water parameters (pH, specific conductance, temperature), calcium, calcite saturation, and stable C isotope equilibrium values (∆DIC-CO₂, εDIC-CO₂(g)) for samples collected at the BSC study site. For a complete description of sampling methods, laboratory analysis, and data analysis, see: Knierim, K.J., 2015. Stable Isotopes as a Tool to Characterize Carbon Cycling and Develop Hydrologic Budgets in Mantled Karst Settings (Dissertation). University of Arkansas, Fayetteville, Arkansas.
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