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Title: Where does streamwater come from in low-relief forested watersheds? A dual-isotope approach

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 18O and 2H 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. Thus, the streams showed strong evaporative enrichment compared to the local meteoric water line (δ2H = 7.15 · δ18O +9.28‰) 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 riparianmore » 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.« less
Authors:
 [1] ;  [2] ;  [3] ;  [4] ;  [5]
  1. Luxembourg Institute of Science and Technology, Belvaux (Luxembourg); Univ. of Saskatchewan, Saskatoon, SK (Canada)
  2. Univ. of Saskatchewan, Saskatoon, SK (Canada); Univ. of Aberdeen, Aberdeen (United Kingdom)
  3. Univ. of Georgia, Athens, GA (United States)
  4. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
  5. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Publication Date:
OSTI Identifier:
1167353
Grant/Contract Number:
AI09-00SR22188
Type:
Accepted Manuscript
Journal Name:
Hydrology and Earth System Sciences (Online)
Additional Journal Information:
Journal Name: Hydrology and Earth System Sciences (Online); Journal Volume: 19; Journal Issue: 1; Journal ID: ISSN 1607-7938
Publisher:
European Geosciences Union (EGU)
Research Org:
USDA Forest Service-Savannah River, New Ellenton, SC (United States)
Sponsoring Org:
USDOE Office of Environmental Management (EM), Acquisition and Project Management (EM-50)
Country of Publication:
United States
Language:
English
Subject:
60 APPLIED LIFE SCIENCES hydrology; low relief forested watershed; dual isotope