USING 13C/12C OF DISSOLVED INORGANIC CARBON AND DISSOLVED ORGANIC CARBON AS TRACERS TO CHARACTERIZE KARST SPRING SYSTEMS OF THE SHIVWITS PLATEAU AT GRAND CANYON NATIONAL PARK, ARIZONA, USA

Isotopic analyses for δ¹³C of dissolved inorganic carbon (DIC) and dissolved organic carbon (DOC) can provide insight into the carbon cycling of a groundwater system. Dissolved organic carbon in groundwater is sourced from the leeching of organic acids from terrestrial vegetation and humic matter in soil during infiltration of precipitation. The resulting δ¹³C-DOC of the groundwater retains its terrestrial signature which will vary depending on metabolic pathways in the vegetative cover (C3, C4, or CAM) which can comprise a range in δ¹³C from ca. -33 to -10 ‰. DIC can be sourced from vegetation and humic matter as well although it can be altered in groundwater systems by processes such as microbial activity and carbonate dissolution. Thus, the δ¹³C-DIC of a groundwater system can be used as a tracer in order to characterize spring systems as springs that share a groundwater system will show similar fractionation trends in δ¹³C-DIC resulting from a given flow systems unique microbial biome and preferential dissolution of carbonate strata.

The Shivwits Plateau in western Grand Canyon National Park (GRCA) is relatively unstudied due to difficulty of access and wilderness designation, resulting in difficulty of completing traditional groundwater studies and thus requires a variety of tracer studies to characterize flow patterns. Utilizing δ¹³C of DIC and DOC in a remote karstic system such as the Shivwits Plateau can provide useful parameters for characterizing springs in either low- or high-resolution sampling. δ¹³C-DIC analyses have been completed for samples collected during high flow conditions from 14 springs across the Shivwits Plateau showing variation in δ¹³C-DIC from -13.8 to -6.4 ‰. δ¹³C-DOC results will be compared with δ¹³C-DIC and existing vegetation maps to help characterize water sources and flow paths. These methods could be employed in future studies to improve understanding of flow paths and enhance water management practices in Grand Canyon and elsewhere.