Aeolian Landforms on Loess Tablelands of the Great Plains Limit Connectivity of Surface Runoff and Sediment Transport to Surrounding Stream Networks, Potentially Enhancing Long-Term Sediment and Carbon Storage

Loess tablelands of the central Great Plains, USA, are mesa-like landforms underlain by thick loess and surrounded by intensely dissected terrain. Preservation of thick Quaternary loess and paleosols that still contain substantial soil organic carbon (SOC) is much greater beneath tableland summits than in surrounding landscapes. We hypothesize that aeolian topography on tablelands contributes to their preservation, by creating internal drainage into closed depressions, thus disconnecting summits from the dense drainage network across the surrounding landscape. This lack of connectivity in surface runoff and sediment transport retains in storage substantial amounts of loess that would otherwise become sediment in the Missouri-Mississippi river system, as well as SOC from paleosols that could otherwise enter the fluvial system and be oxidized.

Aeolian erosional features observed on tablelands include oval depressions (called playas in the Great Plains) and linear troughs up to 10 km long, often with closed depressions on the floor of the trough. Many of these features likely formed through deflation during or after deposition of thick Late Pleistocene Peoria Loess, but some may have formed earlier on underlying bedrock or sediment surfaces and are reflected at the modern surface through a uniform loess mantle. High rates of Late Pleistocene loess accumulation in the central Great Plains generated substantial new local relief from loess mantled uplands to river valleys, which combined with highly erodible loess and intense summer rainfall has produced an extremely dense stream network apart from the tableland summits. However, flow path analysis using 2-m LiDAR-based DEMs confirms internal surface drainage on many tableland summits, separated from the surrounding network by a drainage divides at distinct rims at the summit margins. The hypothesized effect of this disconnection on tableland preservation can be reproduced under some conditions by landscape evolution simulations with the Landlab toolkit (Hobley et al., 2017, Earth Surf. Dyn. 5:21-46). We are investigating whether accumulative soil development on tableland summits enhances vegetation resilience and tableland preservation, and quantifying landscape-scale effects of tableland preservation on sediment and SOC storage.