Hydrograph Separation Using Dual Isotopes in Catchments with Minimal Seasonality: A Bayesian Mixing Model Approach
Abstract
Stable isotopes in water have been used extensively over the last several decades for hydrograph separation. The majority of these have been in upland mid-latitude headwater catchments with few studies capturing the dynamics of low-relief lower latitude catchments with minimal seasonal variability in precipitation isotopes. Here, we analyze a long term (~10 years) isotopic and hydrological data collected from three adjacent forested watersheds located at the Savannah River site, South Carolina, USA, to understand streamflow dynamics in a, low-relief sub-tropical system. While seasonality in the precipitation signal is low, streamflow response to rainfall differed markedly for the three catchments (named B, C and R). Baseflow was non-existent in R and was low for catchments B and C. Following rain events, streamflow increased substantially in catchments B and C, however for R, a stream response was generated only after intense rain events. Interestingly, for each of these catchments, we did not observe any difference between their baseflow and storm runoff isotope values. Stream isotope values largely followed these hydrometric patterns. Catchment B streamwater isotope values fell in between the shallow riparian water and deep groundwater end members. For the R catchment, stream isotope values were always similar to the deep groundwater; for the C watershed, stream isotope values were significantly enriched compared to the deep groundwater due to the presence of a shallow wetland. We used a Bayesian mixing model to calculate the contribution of the different sources to streamwater. Whereas the differences between B, C and R stream highlights the control of local topography and soil properties on streamflow for each catchment, the lack of isotopic differences between baseflow and storm runoff for each of these catchments suggests little if any hillslope-riparian-stream connection. Through long-term and continuous monitoring of baseflow, ground and riparian water, combined with event based sampling and analyzing the ensuing data within a Bayesian mixing framework, we have calculated the contributions of different endmembers to the stream. Our framework overcomes the previous limitations of dual isotopes and opens a new window on the applicability of isotopes in catchments with minimal seasonality.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.H41Q1979J
- Keywords:
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- 1041 Stable isotope geochemistry;
- GEOCHEMISTRY;
- 1813 Eco-hydrology;
- HYDROLOGY