SEASONALITY OF RAINFALL ISOTOPES IN A SOUTHERN APPALACHIAN WATERSHED

Understanding the variability of precipitation is key to assessing runoff generation and other hydrological processes in headwater catchments of the Southern Appalachians. The ruggedness of the Southern Appalachian terrain makes precipitation difficult to study and even more difficult to monitor at spatial and temporal scales of relevance to understanding hydrological flowpaths and runoff generation in headwater catchments. Stable isotopes of precipitation water can be sampled relatively easily, and they can be used to trace the transformation of precipitation into surface and subsurface flow. Currently, there is a lack of precipitation isotope monitoring within this region. We established a network of stations to examine the variability of precipitation isotopes in a Southern Appalachian watershed from the start of June 2011 through July 2012. Weekly rainfall samples were collected from 13 rain gauges located within the Little Tennessee River Basin in southwestern North Carolina. Rain gauges were located across a range of elevations, aspects and forest canopy conditions. Rainfall samples were analyzed for ∂²H and ∂¹⁸O (referenced to VSMOW) with an accuracy of ±0.05 ∂¹⁸O, ±0.5 ∂²H using Cavity Ring Down Spectroscopy. We analyzed resulting data to assess isotopic characteristics of precipitation across the landscape and to determine whether the isotopic signature of precipitation varied spatially and temporally in the mountain range. The local meteoric water line had a slope of 8.09 and an intercept of 16.71. Analysis of covariance suggested that local meteoric water lines were not statistically different among individual stations. By studying precipitation isotopes in the Southern Appalachians, not only can we trace the precipitation back to the source, but also track its movement within the watershed and what can alter the precipitation’s isotopic signature during this time.