THE SEASONALITY OF OXYGEN AND HYDROGEN ISOTOPES OF RAIN, STREAM AND GROUNDWATER IN FREDERICKSBURG, VA

Stable isotopes of oxygen and hydrogen, δ¹⁸O and δD, are tracers of climatic changes within the hydrologic cycle, and thus are a potential link in the relationship between climate-influenced changes to the hydrologic cycle and modern and paleoenvironments. The Chesapeake Bay region, located on the boundary between subtropical and subpolar precipitation, is projected to see increased precipitation rates specifically during winter and spring under enhanced levels of greenhouse gases (Najjar et al., 2010). Additionally, paleoclimate archives from the Bay, which are sensitive to freshwater input from rivers, provide a baseline of past natural climate variability, recorded through changes in their δ¹⁸O composition that is a reflection of the δ¹⁸O of the water from which it precipitated (e.g. LeGrande and Schmidt, 2009). Studies have shown that the isotopic content of surface water and groundwater parallel meteoric water (e.g. Dutton et al., 2005); however, there is no previous work connecting δ¹⁸O and δD isotopes from meteoric water with nearby river and groundwater in the vicinity of the Fredericksburg, Virginia region. In this study, the δ¹⁸O and δD content of meteoric and surface water in the Fredericksburg region was analyzed over the course of a year to understand the seasonality of the δ¹⁸O and δD of precipitation, and its relationship between the isotopic values of river water and groundwater. Surface water samples were collected from the Rappahannock River and Hazel Run tributary in Fredericksburg, VA, and precipitation and groundwater samples were collected on the University of Mary Washington campus. We expect that precipitation in winter months are more depleted in heavy isotopes than in warmer months. We also expect to see a correlation between the δ¹⁸O and δD values of precipitation and river water, with river water values reflecting averaged meteoric water values; however, periods of prolonged dryness may result in deviations of this trend due to high rates of evaporation. This work will provide the foundation of using δ¹⁸O and δD of meteoric water to study changing precipitation patterns as climate changes in the local Fredericksburg, VA region, as well as understanding the controls of the δ¹⁸O and δD of surface water for more robust interpretations from proxy records in regional paleoclimate studies.