L. K. Lautz, State University of New York, College of Environmental Science and Forestry
Stream-groundwater (SW-GW) interaction is a critical component of a variety of water quality and quantity issues. It has proven difficult to accurately characterize SW-GW interactions, particularly in streams, and they are often ignored due to the challenges of spatial and temporal generalization of point-in-space or -time measurements. There has been a renewed interest in the use of heat as a tracer in hydrologic systems because heat transport has a number of advantages over traditional methods of characterizing SW-GW interaction. Despite recent technological and analytical developments in the application of heat as a tracer in hydrologic systems, much remains to be learned. The major objective of this proposal is to integrate research and teaching to advance the application of heat transport theory to characterize water flux between streams and groundwater and to relate those fluxes to changes in water quality over a variety of spatial and temporal scales. Proposed work includes: (1) Linking field observations of temperature with modeling to quantify SW-GW flux rates over different scales and (2) linking SW-GW interaction to geochemical variability. Research innovations in this proposal include scaling-up observations while maintaining fine-scale spatial resolution by using fiber optic distributed temperature sensor technology and thermal remote sensing. Innovations also include quantifying SW-GW fluxes over a range of temporal and spatial scales and developing procedures for integrating observations across scales into process-based models.
The techniques developed and tested through this proposal will be of broad interest to a spectrum of researchers and professionals to inform stream restoration, contaminant remediation, nutrient dynamics and solute transport in streams. The results of this work will also have broad applicability for collaborators from industry and from non-profit organizations. This work will establish the foundation for a sustained and strengthened program to integrate the study of heat as a tracer of SW-GW interaction with educational opportunities for students enrolled in undergraduate, community college and graduate programs across a number of institutions. Mentoring relationships between undergraduate students, graduate students, faculty members, industry professionals and representatives of non-profit agencies will be formally developed to support the recruitment and success of underrepresented minority groups, including Native Americans, and women.
Start Date: March 1st, 2008
Exchange of water across the streambed interface is a critical component of a number of water quality and quantity issues, including water yield, solute and contaminant transport, natural attenuation of water contaminants, ecological diversity, and biogeochemical cycling. Despite the critical importance of quantifying stream-groundwater exchange rates, it has proven difficult to accurately characterize fluxes between streams and groundwater and they are often ignored due to the challenges of spatial and temporal generalization of point-in-space or -time measurements. Heat tracing has been the subject of renewed interest over the past decade because it has a number of advantages over traditional methods of measuring stream-groundwater exchange. Research for this project was aimed at exploring the limitations of heat tracing of stream-groundwater exchange and to provide guidance on best practices for applying heat tracing methods in field studies across a range of scientific disciplines, including hydrology, ecological engineering, ecology, and biogeochemistry. Results of controlled modeling and laboratory experiments have demonstrated the limitations of using one-dimensional (1D) heat tracing of stream-groundwater exchange under conditions that violate simplifying model assumptions, including non-vertical flow directions, irregular temperature signals in the stream, and changing flux rates through time. Although method limitations have been clearly demonstrated and quantified through this project, the overall findings indicate heat tracing is a powerful tool for field measurements of stream-groundwater exchange rates and is reliable, inexpensive, and simply to implement, relative to other methods. Through this project, new and refined methods have been developed that are now being routinely used in field studies of stream-groundwater exchange. We piloted the use of high-resolution temperature sensors (HRTS) that use fiber optic distributed temperature sensing to collect detailed temperature observations through space and time in streambeds. This novel field tool is now being used by the U.S. Geological Survey to make field measurements of fluid exchange across the streambed interface. We also developed a widely used computer model, the Vertical Fluid Heat Transfer Solver (VFLUX), which facilitates interpretation of temperature time series to derive vertical fluid exchange rates. VFLUX incorporates several advanced components of heat tracing, including time series analysis/signal filtering, sensitivity analysis, Monte Carlo error analysis, and integration of multiple heat tracing models, facilitating its adoption as a standard tool for interpreting temperature time series data. In addition to advances in 1D heat transport modeling, we have shown how point measurements of stream-groundwater exchange made using 1D heat tracing can be scaled-up to the reach scale by integrating high-resolution streambed temperature maps with point measurements of water flux inferred from 1D temperature profiles. The effectiveness and potential errors of this methodology have been explored through numerical groundwater flow and heat transport modeling. Overall, our results demonstrate the enormous potential for using heat tracing to quantify spatial and temporal changes in water flux across the bed interface at high resolution. The methods presented take advantage of inexpensive temperature sensors and user-friendly modeling methods, such as VFLUX, making heat tracing a good option for field practitioners interested in observing spatial and temporal heterogeneity of water flux at the bed interface. This project has contributed to the professional development of several graduate students, undergraduate students, postdoctoral research associates, and collaborators. Research for this project was integrated into the curriculum at the University of Missouri’s Branson Geology Field Camp and into courses at Syracuse University. Several community college students and a collaborating faculty member at Central Wyoming College (a community college with a high percentage of Native American students) collaborated on this project. Mentoring relationships were established through this project between undergraduate students, community college students, graduate students, faculty members, and industry professionals, contributing to the professional development of Native American and women students.
