Rijumon Nandy / Earth & Environmental Sciences / Faculty Mentor: Majie Fan
Surface water bodies such as rivers and lakes have shown significant differences in hydrogen (δD) and oxygen (δ18O) isotopic signatures. They dominantly reflect precipitation δD and δ18O values and evaporation. Precipitation δD and δ18O values are further influenced by elevation and local climate as well as the origin and trajectory of the water vapor producing the precipitation events. In this study, we examine the relationship between elevation, vapor trajectory, relative humidity and δD, δ18O and d-excess values from 68 river water samples on each side of the continental divide in Montana. Our data were collected in 2017 and 2021 summers and covered different areas in the two years. Rain vapor trajectory analysis show that moisture in the study area were from several sources. The isotope data from the west in 2017 and east in 2021 show decreases as elevation increases, suggesting the influence of regional topography on precipitation and thus river water isotope values. River waters in eastern Montana have low d-excess, associated with low relative humidity, suggesting significant evaporation. The isotope values from the east in 2017 and west in 2021 do not show statistically significant correlation with elevation, suggesting dominance of snowmelt during the sampling season.
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