Abstract
The time and geographic sources of streamwater in low-relief watersheds are poorly understood. This is partly due to the difficult combination of low runoff coefficients and often damped streamwater isotopic signals precluding traditional hydrograph separation and convolution integral approaches. Here we present a dual-isotope approach involving O-18 and H-2 of water in a low-angle forested watershed to determine streamwater source components and then build a conceptual model of streamflow generation. We focus on three headwater lowland sub-catchments draining the Savannah River Site in South Carolina, USA. Our results for a 3-year sampling period show that the slopes of the meteoric water lines/evaporation water lines (MWLs/EWLs) of the catchment water sources can be used to extract information on runoff sources in ways not considered before. Our dual-isotope approach was able to identify unique hillslope, riparian and deep groundwater, and streamflow compositions. The streams showed strong evaporative enrichment compared to the local meteoric water line (delta H-2 = 7.15 center dot delta O-18 + 9.28 parts per thousand) with slopes of 2.52, 2.84, and 2.86. Based on the unique and unambiguous slopes of the EWLs of the different water cycle components and the isotopic time series of the individual components, we were able to show how the riparian zone controls baseflow in this system and how the riparian zone "resets" the stable isotope composition of the observed streams in our low-angle, forested watersheds. Although this approach is limited in terms of quantifying mixing percentages between different end-members, our dual-isotope approach enabled the extraction of hydrologically useful information in a region with little change in individual isotope time series.
| Original language | English |
|---|---|
| Pages (from-to) | 125-135 |
| Number of pages | 11 |
| Journal | Hydrology and Earth System Sciences |
| Volume | 19 |
| Issue number | 1 |
| DOIs | |
| Publication status | Published - 8 Jan 2015 |
Bibliographical note
Acknowledgements.We thank John Blake of the USDA Forest Service for his valuable support throughout the study and his knowledge about the SRS. We also thank Ben Morris for the sampling and Tina Garland and Caroline Patrick for their support in the lab. John Gibson is thanked for discussion on the evaporative characteristics of the water cycle components. Laurent Pfister, Sun Chun, and Menberu Bitew are thanked for discussion on the manuscript. Funding was provided for this work by the Department of Energy-Savannah River Operations Office through the US Forest Service Savannah River under Interagency Agreement DE-AI09-00SR22188 and by funding from the US Department of Energy’s Bioenergy Technologies Office to Oak Ridge National Laboratory, the University of Georgia, and Oregon State University. The first author was partly funded during the work by Deutsche Forschungsgemeinschaft (German Research Foundation – DFG Grant KL 2529/1-1 “Development and testing of a new time variant approach for streamwater transit times”). Oak Ridge National Laboratory is managed by UT-Battelle, LLC for the US Department of Energy under contract DE-AC05-00OR22725. Finally, we thank Lysette Munoz-Villers, Kevin Devito, and Markus Hrachowitz for their very helpful reviews and Markus Weiler for handling the manuscript as editor.
Keywords
- CAROLINA COASTAL-PLAIN
- RUNOFF GENERATION
- SURFACE-WATER
- STORM RUNOFF
- HEADWATER CATCHMENT
- CANADIAN SHIELD
- RIPARIAN ZONES
- STABLE-ISOTOPE
- BOREAL PLAIN
- FRESH-WATER