QUANTIFYING SEASONAL GROUNDWATER RECHARGE UNDER CHANGING CLIMATE IN DAYTON, OH: AN ISOTOPE MASS BALANCE APPROACH

Groundwater is an essential resource in the Dayton region, and is likely to experience changes with global warming. Assessing its sustainability under the changing climate regime is of great importance for the region’s social and economic development. We use stable isotope ratios of oxygen (δ¹⁸O) in precipitation to track large-scale atmospheric processes, local controlling factors and establish moisture source for the Dayton region. Precipitation samples were collected at the University of Dayton precipitation collection station on a daily, weekly and monthly basis between March 2015 and March 2016 for a total of 120 samples. A total of 37 groundwater samples were also collected from monitoring and public supply wells across the Buried Valley Aquifer. Seasonal precipitation isotopic end-member values of -4.26 ± 2.3‰ for warm season (δ¹⁸O_ws), -9.10± 3.3‰ for cool season (δ¹⁸O_cs) precipitation were established by averaging the δ¹⁸O values for the months March through August and September through February, respectively. The average isotope value for groundwater (δ¹⁸O_gw) was determined to be -7.42±0.2‰. We use an isotope mass balance approach, δ¹⁸O_gw(1)=δ¹⁸O_ws(1-x)+δ¹⁸O_cs(x), to determine the relative contribution of precipitation to seasonal recharge of the Buried Miami Aquifer. Our results indicate that warm season precipitation contributed approximately 36% to groundwater recharge, while cool season precipitation comprised the majority of recharge at 64%. Based on climate change predictions, winters in the Dayton region will become increasingly milder and will lead to more prevalent rain events in the cool season rather than snow events. As a result, cool seasonal groundwater recharge amount could be negatively impacted. The outcome of this study, would help to inform local and state water resource management on impact of climate change on the quantity and quality of the aquifer system that supplies water to nearly 2 million people.

 Key words: groundwater, isotope, climate change, sustainability, recharge