PRELIMINARY RESULTS OF BACK-TRAJECTORY ANALYSIS USING HYSPLIT AND ISOTOPIC VARIABILITY OF PRECIPITATION, NORTHWEST, ARKANSAS, USA

Analysis of moisture-source origins and intra-event water isotopic variability during precipitation events are often uncharacterized and no studies of dual identification have been conducted at Bella Vista, Arkansas. This presents an otherwise well-characterized site for investigation of δ²H and δ¹⁸O variability and moisture source origin. During March 2012, 13 samples of intra-event water from precipitation were collected (Kniermin et al. 2014). To assess moisture origins, NOAA’s HYSPLIT model was used to analyze air parcel trajectories for precipitation events. Individual trajectories were modeled for individual sampling periods. Median d-excess for all events (excluding one outlier consistent with another trajectory) was 11.9‰. During the AM hours of March 22, the d-value shows a 20‰ positive shift and coincides with source trajectories, likely revealing a different moisture source origin from early to late event; trajectory area shifted from the Gulf of Mexico to southwestern United States. Several factors could contribute to the considerable spike in precipitation d-excess, including: humidity, air-parcel velocity, amount of moisture cycling, and surface temperature along air parcel pathways. Overall, median d-values are similar to those observed for local surface waters (Kniermin et al. 2014) potentially indicating moisture trajectories from the Gulf of Mexico (GM) to be predominantly responsible for groundwater recharge. Deviations in d-excess for precipitation and other waters (e.g. surface waters, groundwater) may be attributed to air parcel trajectories other than GM. A much larger observations set and HYSPLIT simulations are needed to test this hypothesis. By analyzing precipitation event and HYPSLIT backward trajectories, our research illustrates utilizing isotopic variability and HYSPLIT for determining precipitation source and, potentially developing isotopic ‘fingerprints’ for moisture sources of surface water and groundwater in Northwest Arkansas.