Stable Isotopes of Oxygen and Natural and Fallout Radionuclides Used for Tracing Runoff During Snowmelt in an Arctic Watershed

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Abstract
Stable isotopes of oxygen, and natural and fallout radionuclides, have been used, respectively, to identify water sources and to quantify watershed fluxes of precipitation‐borne solutes and particles that come in contact with tundra vegetation at Imnavait Creek, Alaska (68° 37′N, 149° 17′W). Oxygen 18/oxygen 16 ratios of water in the snowpack, stream, and unfrozen soil during the peak of snowmelt showed that less than ∼14% of streamwater was derived from sources other than snow. Within a month of snowmelt, 18O/16O ratios in the stream indicated that only negligible amounts of water derived from snow remained in the watershed, in contrast to the low degree of mixing between snow and underlying soil water, greater than 90% of the atmospherically derived 7Be (53‐day half‐life) that was deposited in the snowpack was adsorbed onto the surface 2–3 cm of frozen organic soils and vegetation. A slightly lower degree of absorption (∼2/3) on tundra was observed for atmospherically derived 35S (87‐day half‐life) released during snowmelt. These data indicate that atmospherically derived substances in the snowpack are often retained strongly by sorption or chemical interaction with vegetation and soil during snowmelt. This conclusion is also supported by the vegetation and soil inventories of 137Cs (30.2‐year half‐life), which are similar to values expected as a result of atmospheric deposition over the past 40 years.