Variability of Meteoric Water Isotopes in the Great Lakes Region

2021 Pamela J. Mackintosh Undergraduate Research Awards, Multi-term, 3rd PlaceThe hydrological processes that govern water balance in the Great Lakes region are undergoing significant change as shifting climatic conditions continue to impact the area. Meteoric water isotopes (δ18O and δ2H) are an efficient tool for studying these changes, but little work has been done to describe the baseline isotopic variability of meteoric waters in the Great Lakes region. Here I analyze precipitation, river, lake, and groundwater samples collected from the University of Michigan Central Campus (UMCC) andUniversity of Michigan Biological Station (UMBS) from April 2017 to February 2020 to understand how their isotopic compositions vary seasonally, between sampling sites, and by water type. The precipitation, river, and lake water samples collected from both the UMCC and UMBS show seasonal patterns in isotopic composition that are consistent with previously established predictions for isotopic seasonality in the mid to high latitudes. Precipitation samples collected from each sampling location show little variation between sampling sites, demonstrating the pervasiveness of the regional isotopic signal produced by Lake Michigan evaporation. δ18O and d-excess values of the precipitation, lake, and groundwater samples collected from the UMBS indicate hydrologic mixing between each water source and demonstrate the usefulness of sampling multiple water types when studying hydrologically connected groundwater and surface water systems. Precipitation samples from the UMCC and UMBS demonstrated high d-excess values ranging from3.1 to25.0‰ and -3.2 to 25.2‰ respectively, which indicates the input of recycled moisture from LakeMichigan. In addition to investigating isotopic variability, I assess the usefulness of downwind precipitation d-excess values as a proxy for tracing changes in evaporation on the Great Lakes with a simple isotopic mixing model and conclude that climate-induced changes in evaporation may be difficult to identify over small time scales. With rapidly changing climatic conditions threatening to alter the hydrologic processes that govern water balance in the Great Lakes region, this work serves as an important baseline for tracing future hydrologic change using meteoric water isotopes.http://deepblue.lib.umich.edu/bitstream/2027.42/168407/1/Pelletier2020_seniorthesis.pdff4ff7577-2bc3-41bf-b9b3-048dca20629fDescription of Pelletier2020_seniorthesis.pdf : ProjectSEL