Nesbitt, Ian M.; Smith, Sean MC; Koffman, Bess; Campbell, Seth; Arcone, Steven
Geological Society of America Abstracts with Programs (2019)doi: 10.1130/abs/2019NE-328587
Sediment core retrieval and analysis in freshwater lakes shallower than 20 m is a fundamental tool for a wide variety of studies in lacustrine and fluvial sciences focused on investigations of historical landscape and river corridor changes, including damming. Yet, many cores are collected and analyzed without complete understanding of the local stratigraphic setting that lends to their architecture. Core interpretations themselves are used as context for models of spatially variable geomorphic change. Knowledge, tools, and techniques to understand the stratigraphic context associated with coring locations have improved and become more widely accessible in recent years. Delineation of the limits of a sediment deposit and specification of the number of measurements necessary to quantify sedimentation rates accurately are examples of problems confronting lake sedimentation analyses. The problems are particularly difficult in post-glacial settings where sedimentation rates are low and pond morphometry is complicated by features resulting from a combination of glacial and anthropogenic processes. We propose that ground-penetrating radar (GPR) allows for portable, low cost-of-mobilization shallow subsurface geophysical investigations that can provide measurements to guide selection of informative coring locations. GPR transects are easy to integrate with core results, and are useful for non-destructive, reproducible sub-aqueous geological data collection. Moreover, the method we propose for subsurface profiling of shallow, freshwater lakes in river corridors of the Northeast is far more portable and can resolve layering within and below gas- and organic-rich overburden far better than traditionally used shallow seismic reflection (SSR) profiling. We provide examples of how GPR can be a valuable decision-making tool for core extraction field campaigns important to watershed, river, and lake assessments to guide modern watershed and river management strategies.
Sediment cores from shallow, freshwater lakes are important tools for understanding landscape change. Yet many cores are collected and analyzed without complete understanding of the surrounding sedimentary context from which they are taken. Cores are used as models of spatially variable landscape change. The tools and techniques used to understand the sedimentary context of core locations have improved and become more widely available recently. Finding the spatial limits of sediment layers is a problem that point-source measurements like cores are not well suited for. This problem is particularly difficult in post-glacial settings where the sedimentation rates are low and the pond shapes are often complex. We propose that ground-penetrating radar (GPR) allows for easy investigation of the subsurface that can both guide the selection of coring locations and aid in the interpretation of core results. GPR transects are reproducible and non-desctructive. GPR can also resolve fine layering in materials that competing seismic methods cannot. We provide examples of how GPR can be a valuable decision-making tool for core extraction studies of various kinds, and how it can guide modern watershed management strategies.