SMALL SCALE (<10,000 KM2) ISOSCAPES REVEAL SPATIALLY VARIABLE WATER SOURCES FOR NORTHEASTERN OHIO PRECIPITATION, SURFACE WATER, AND GROUNDWATER

Water isotopes are a long-standing environmental tracer in hydrogeology, but many studies focus on their variations in time rather than space. Isoscapes are an emerging tool to visualize and analyze the variation of water isotopes at large regional scales. Here we hypothesize that varying influences of different air mass source areas, plus lake effects, have the potential to impart variation in water isotopes at much smaller scales. We test this hypothesis in a 10,000 km², low relief study area in northeastern Ohio, which receives moisture from Pacific, Arctic, Gulf of Mexico, and Great Lakes source areas. Across the study area, mean annual precipitation ranges from 900-1100 mm and winter snowfall varies from 800 to 2500 mm. Precipitation was collected at two locations separated by 0.5 degrees latitude: one in the area receiving lake effect precipitation and high snowfall (the “snow belt”). Lake, river, and groundwater samples collected from 120 locations seasonally, and 12 locations sampled biweekly. Water samples were analyzed with the Picarro L2130-I analyzer, and precipitation source areas were calculated using HYSPLIT.

Precipitation samples have high inter-storm isotopic variability associated with different moisture source areas, as well as seasonal variability. There is also a difference between the precipitation isotopes at the two locations, up to +/- 6 ‰ for δ¹⁸O in the winter. At lentic locations, water isotopes are generally more negative in the snow belt, but evaporative effects create additional spatial and temporal variability to the surface water isoscape. Biweekly river samples show both seasonal and spatial variability, with δ¹⁸O ranging from -11.6 to -2 ‰. Rivers in the snow belt have a more negative isotopic ratio than rivers to the south. Groundwater samples show little seasonal variability but there is a gradational variance towards less negative isotopic ratios towards the south of the research area. The northeastern Ohio isoscape illustrates that atmospheric dynamics can impart strong patterns in water isotopes over relatively small spatial scales, suggesting potential applications of small-scale isoscapes for hydrogeologic investigations.