AIRBORNE GEOPHYSICAL SURVEYS IN HYDROGEOLOGIC FRAMEWORK MAPPING FOR CLIMATE CHANGE STUDIES, SAND HILLS OF WESTERN NEBRASKA

The Sand Hills are the largest dune sea in the western hemisphere and represent a sentinel ecosystem because climate change impacts can lead to the possible mobilization of the dunes, dramatic effects on ecosystems, and changes to recharge of the underlying high plains aquifer. Airborne electromagnetic (AEM) resistivity surveys were performed in the area of Crescent Lakes National Wildlife Refuge (2009), Gudmunsen Sandhills Laboratory and Jumbo Valley (2008) as part of climate change studies.

AEM surveys map shallow and deep (< 300 m) subsurface hydrogeologic features that can be interpreted to provide hydrogeologic frameworks that are critical inputs for coupled hydrologic and climate models. Time domain AEM surveys in the Gudmunsen and Jumbo Valley areas in conjunction with ground time domain electrical soundings and audio magnetotelluric soundings were designed to map the base of high plains aquifer. Ground-water flow paths controlled by buried topography interpreted from new geophysical surveys are important in predicting how ground-water resources can be impacted from climate change.

A frequency domain AEM survey performed along three flight lines from a dune dam south of Crescent Lake and north to Hackberry and Gimlet lakes. The objective was to the map shallow hydrogeologic features of the southwestern part of the Sand Hills that contain a mix of fresh to saline lakes. The dune dam is defined by a resistive zone that has a depth of 45 meters suggesting that it influence modern ground-water flow paths and surface-water features. The lakes are defined by low resistivity which in the case of Gimlet Lake extends to depth. The saline waters may be following a buried paleo-channel of ancestral Blue Creek.

Understanding how the climate history of dunes currently influences ground water quality and flow will be essential in assessing impacts from possible climate changes. Modeling of coupled deep and shallow ground-water flow can be dramatically improved with input from AEM surveys combined with ground data. These hydrogeologic models placed in the context of climate change models are critical to understanding past climates and thresholds for future climate impacts on water use and availability to ecosystems.