Isotopic study of sulfate sources and residence times in a subalpine watershed |
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| Authors: | Cynthia L Kester Jill S Baron John T Turk |
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| Institution: | 1.US Geological Survey, Box 25046, Denver, Colorado 80225, USA,;2.Natural Resource Ecology Laboratory, US Geological Survey, Colorado State University, Fort Collins, Colorado 80523, USA, |
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| Abstract: | Stable sulfur and oxygen isotope ratios and naturally occurring 35SSO4 activities were used to examine sulfate sources, address the role of sulfur dynamics, and estimate residence times of atmospherically derived sulfate in Loch Vale Watershed, Colorado. In 1996, surface water samples from small streams flowing through talus, forest, and wetland areas had '34SSO4 values ranging from 1.8 to 3.7. Values of '18OSO4 at the three sites ranged from -1.3 to 3.7. Average '34SSO4 and '18OSO4 values in Loch Vale precipitation (1991-1999) are higher (5.2 and 13.6, respectively) than surface water values, indicating that some of the deposited sulfate is transformed and/or mixed with other sulfur sources in the watershed (e.g. mineral and organic sulfur). Sulfate ages determined by 35SSO4 activities support this and show that deposited sulfate may be stored on a timescale of 1 year or more prior to being released to surface waters. |
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