ISOTOPIC ENRICHMENT OF SOIL WATER DUE TO DIFFERENTIAL EVAPORATION WITHIN THE ROME SAND PLAINS, NY

Paleoclimate studies are based on the concept that the stable isotopes of oxygen (δ¹⁸O) in soil carbonates are a proxy for those in paleo-rainwater and thus are commonly used in paleoenvironmental reconstructions. However, because of the effect of evaporation on soil water, which increases δ¹⁸O, soil carbonate δ¹⁸O values may represent a proxy for soil water at the time the soil carbonate formed rather than for rainwater. The amount of evaporation and the isotopic composition of soil carbonates change as a function of soil depth. To understand isotopic compositions of soil carbonates, the effect of evaporation on soil moisture δ ¹⁸O at various soil depths and under different amounts of vegetative cover was assessed. This study tested the degree of evaporative enrichment of soil water at two different study sites (Open and Closed canopy) within the Squadrito Farm site located in the Rome Sand Plains near Rome, NY. 38 samples of soil water, 7 rainwater and groundwater samples were collected from May 2014 until November 2014, and were analyzed for their isotopic composition (δ ²H and δ ¹⁸O). Open canopy study site values were enriched in ¹⁸O by ~ 0.8 ‰ over closed canopy study site values. Rainwater had relatively negative isotope values (-4.7 ‰ - -7.9 ‰) and groundwater values were extremely negative (-9.1 ‰ - -9.4 ‰). Isotopic compositions from both sites fall along the same local meteoric water line implying that there was little no change in evaporation between both study sites and that vegetation cover does not significantly affect evaporation rates of soil water. Understanding the role that evaporative enrichment plays in the formation of soil carbonates, can make paleoenvironmental interpretations more accurate especially in regions where shifts in aridity have occurred.