SEASONAL VARIATIONS OF STABLE ISOTOPE RATIOS OF PRECIPITATION IN DAYTON AREA AND SUSTAINABLE WATER RESOURCES

Understanding the link and interaction between surface water and groundwater, as well as establishing moisture sources and seasonal variability of precipitation is critical to device sustainable use of water resources. The stable isotopes of oxygen (δ¹⁸O) and deuterium (δ²H) in precipitation can be used as tracers in the hydrologic cycle as they track large-scale atmospheric processes, and local controlling factors. In order to use water isotopes in hydrologic studies, the first step is to establish temporal and spatial trends in the isotopic composition of precipitation. Here we present δ¹⁸O and δ²H values of precipitation from a yearlong collection at the University of Dayton in Dayton OH. Precipitation samples were collected on daily, weekly and monthly intervals between March 2014 and April 2015 (n=138). Our initial results indicate that there is a large range of values of δ¹⁸O, δ²H, and d-excess. Daily δ¹⁸O values range from -28.0‰ to 4.22‰, weekly -24.1‰ to -0.84‰, and monthly -15.8‰ to -3.8‰. Daily δ²H values range from -214.2‰ to 28.8‰, weekly -189.3‰ to 2.8‰, and monthly ranged from -114.2‰ to -20.7‰. Daily d-excess values ranged from -22.2‰ to 20.5‰. Both δ¹⁸O and δ²H show seasonal variations where the isotope values are lower in October through March with the lowest daily value recorded in January, and higher in April through September with the highest daily values in May. D-excess, however shows consistent average values, close to the global meteoric water average 10‰., throughout the year except slightly higher values in November and December. Comparing our result with factors that control the isotopic composition precipitation (e.g., temperature, amount of precipitation, and source of moisture), we hypothesized that temperature, source of moisture, and the moisture travel path may be the dominant factors that control the seasonal variation of oxygen and hydrogen isotopes in precipitation in the Dayton area. Precipitation amount on the other hand shows a slight positive correlation with isotope values.