Headwater Stream Processes Revealed by Continuous Ultra-high Resolution Thermal Measurement

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Progress in understanding headwater catchment hydrology is measurement limited. Almost all current measurement techniques are point-based. This is especially problematic for the study of streams, where measurements of flow and components of flow are made at a gauging station--but the processes of interest are distributed longitudinally down the channel. This project proposes exploration of headwater stream processes based on heat and solute transport measured using ultrahigh resolution measurements of in-stream temperatures, multiple micrometeorological stations and hydrologic tracers. Our preliminary research has shown that these new technologies can transform understanding of stream hydrology and stream heat fluxes, revealing heterogeneous groundwater inflows, hyporheic exchange, and microclimatic conditions. We will observe both natural and imposed (heat and solute tracers) variations in temperature, dissolved oxygen, specific conductivity and pH in the stream using multi-parameter data logging sondes, and use a fiber optic Distributed Measurement Systems (DTS) to measure stream temperatures with 0.03oC precision every meter, every hour. 20 autonomous climatic stations will monitor nine variables along the stream in a wireless network. These studies will take place at the HJ Andrews Experimental Forest and LTER site, where stream temperature research has been a focus for the past 20 years. A parallel experiment of the similar design will take place in the Maisbich, Luxembourg in collaboration with TU Delft and the EPFL, where stream temperature studies are ongoing. An invertible numerical model of stream temperature and solute transport will be developed based on the currently operational forward model. This will allow estimation of physical characteristics of the surface and subsurface flow system along the entire length of the stream with resolution to the meter level, testing conceptualization of stream processes.Intellectual MeritHydrologic science has long been forced into the characterization of heterogeneous hydrologic systems using a handful of point measurements (e.g. stream gauges, thermocouples, rain gauges). The combined DTS/data-sonde/networked sensor approach provides over 1000 points of measurement continuously in time, an unprecedented data set, facilitating reexamination of stream-hillslope interactions across three orders of magnitude in scale and testing of process-based conceptualizations of stream function. Since thermal energy is conserved, heat will be used as a tracer, both through observation of natural and imposed signals. The simultaneous tracer detection at hundreds of locations provides an unparalleled broadly-applicable tool for exploring hydrologic processes. The proposed study will both develop and make use of this methodology, expanding our understanding of headwater stream systems, and the range of tools available to the community to carry out further studies. The team is uniquely well qualified to carry out this study, including leaders in hillslope/stream processes (Selker, McDonnell), stream temperature (Johnson), and hydrologic instrumentation (Selker).Broader ImpactThis project has three major thrusts: (1) elucidation of ecologically critical stream processes; (2) development of broadly useful research methodologies; and (3) training of graduate and undergraduate students (nine directly supported by the requested funds). Methodological developments include: application of DTS to stream systems; development of an invertible numerical model to interpret joint DTS and geochemical data; and the development and testing of a thermal heat pulse system. Each is novel and widely useful in understanding the hydrology and ecology of headwater streams. Processes will be studied at scales heretofore unobserved, which will reveal the scales and extents of groundwater/surface water interactions critical to ecological function. This understanding is essential to more effectively protect the many species endangered due to high temperatures of stream waters in summer months during peak consumptive demand. Six undergraduates will be funded to work on the project, in addition to the on-site students from the HJ Andrews REU and field camp programs, giving them both training and incentive to pursue further research and education. The two master's students and the PhD student will be given the opportunity to carry out critical research, as well as taking part in national scientific meetings. The PhD student will also take part in an international collaboration, opening doors for a career of collaborative international exploration.