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

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. In this paper, 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 findings 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 (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 riparian zonemore » 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:

Klaus, J. ^[1]; McDonnell, J. J. ^[2]; Jackson, C. R. ^[3]; Du, E. ^[4]; Griffiths, N. A. ^[5]

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+ Show Author Affiliations

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:

Thu Jan 08 00:00:00 EST 2015

Research Org.:

USDA Forest Service-Savannah River, New Ellenton, SC (United States); Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)

Sponsoring Org.:

USDOE Office of Environmental Management (EM), Acquisition and Project Management; USDOE Office of Energy Efficiency and Renewable Energy (EERE)

OSTI Identifier:

1167353

Alternate Identifier(s):

OSTI ID: 1265280

Grant/Contract Number:  

AI09-00SR22188; AC05-00OR22725

Resource 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)

Country of Publication:

United States

Language:

English

Subject:

60 APPLIED LIFE SCIENCES; hydrology; low relief forested watershed; dual isotope; 54 ENVIRONMENTAL SCIENCES; 58 GEOSCIENCES; 07 ISOTOPE AND RADIATION SOURCES