STREAMBED THERMAL GRADIENTS IN THE GROUNDWATER DOMINATED HEADWATERS OF THE WHITE RIVER, MANISTEE NATIONAL FOREST, MICHIGAN

Using temperature as a tracer is a relatively new approach for determining volumetric flux of ground water and surface water interactions within a streambed. We deployed six thermal loggers at various depths including surface water and up to a half meter within the streambed of the White River in Manistee National Forest of Central Michigan. The White River, an important trout and salmon resource, is dominated by its groundwater baseflow component of stream discharge. Stream discharge remains relatively constant over time, few tributary streams are observed, and pronounced, discrete, and long-lived sand boils are observed in the streambed. Over the course of two days in early October, 2011, four loggers were placed in the littoral zone of the White River and two data loggers were placed near the middle of the stream at a point of active and focused groundwater discharge. The littoral site remained deployed for the following three months. Surface water temperatures varied diurnally by as much as 5° C, whereas streambed groundwater temperature varied generally less than 0.5° C. In the littoral zone, ground water temperatures were nearly a full degree higher than groundwater temperatures near the middle of the stream. Also, the littoral zone groundwater showed diurnal variations that the other site did not display in thermograph data. Data revealed that the half meter locations were generally cooler and more stable than the surface locations. Streambed groundwater fluxes determined from measured temperature gradients, and compared with spatially variable head gradients measured through the streambed, might assist in the development of a conceptual model that illustrates the mechanisms and heterogeneity of groundwater flux into the headwaters of the White River.