Complex disturbance-driven reactivation of near-surface sediments in the largest dunefield in North America during the last 200 years

Abstract

Understanding the historical activity of desert dune systems is important for identifying both the palaeoenvironmental drivers of change and the likelihood of future reactivation. Dating dune sediments in the Nebraska Sandhills has identified regional-scale dune activity over centennial and millennial timescales during the Holocene, occurring at 9.6–6.5, 3.8 and 2.5 ka, and most recently spanning the Medieval Climatic Anomaly 1050–650 years BP. These periods have been interpreted as palaeoclimatic evidence of intense aridity lasting decadal and centennial timescales. A detailed record of dune activity in the historical period, since EuroAmerican arrival, is lacking however, yet important for interpreting the role of human agency amongst the factors influencing disturbance. Without a high-resolution record of short-term, historical, local sediment mobilization, it is not possible to distinguish the environmental factor(s) responsible for local reactivation. In this paper, the individual drivers of vegetation disturbance are reviewed and presented alongside a luminescence-dated reconstruction of dune sediment deposition ages. This allows an integrated assessment of the relationship between drivers and environmental response over a recorded period. We focused our investigation on the aeolian reactivations of surface dune sediments and blowout features around the Niobrara Valley Preserve in the northern limits of the Nebraska Sandhills. Results show a near-continuous (within uncertainties) timeline of local reactivation across the sites studied, with variation between the individual features indicating that both regional (i.e. climatic) and local (i.e. land use) forcings contribute to surface disturbance. © 2019 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd. © 2019 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd.