UNDERSTANDING GROUNDWATER EXCHANGE WITH LENTIC SYSTEMS: RECENT ADVANCES AND CONTINUING CHALLENGES (Invited Presentation)

Recent technological advancements have led to better quantification of exchange of water, chemicals, and nutrients between groundwater and lakes. Modifications of seepage meters, which provide a direct measurement of flow across the sediment-water interface, result in better repeatability, greater efficiency, and allow use in a broader range of physical settings. Better and cheaper analysis of chemical and isotopic constituents allows greater use of simple mixing models to identify and quantify sources of water in surface water and adjacent groundwater. Temperature-based methods allow both areally extensive reconnaissance for focusing efforts where groundwater flow to a lake or wetland is relatively fast, and the potential for monitoring seepage during extended periods. Nevertheless, the longstanding challenges that have hindered research at the sediment-water interface, identifying and quantifying spatial and temporal variability, remain. Combinations of new and existing measurement methods provide new insights that are directly confronting these challenges. Temperature (infrared) sensed remotely from various platforms can show near-shore distribution of groundwater flow to lakes when groundwater temperature is sufficiently different from that of the lake surface. Fiber-optic distributed temperature sensing can identify areas of focused groundwater discharge on scales from meters to kilometers. Vertical-temperature profiling of bed-sediment temperature is proving ever more useful for quantifying groundwater-surface-water exchange over time using simple models; the accuracy of these models is improved with newly-developed methods to measure thermal parameters of saturated sediments using ambient diurnal signals. Recent improvements in temperature-based analytical tools, such as 1DTempPro and VFLUX, have accelerated the adoption of these methods. Simultaneous implementation of multiple methods provides both improved quantification of flow and improved understanding of the processes that control flow. Combining these physically based advances with improved methods and understanding from the biological and geochemical communities will lead to better understanding of the physical, biological and geochemical linkages that are important to this ecotone.