SPATIAL DISTRIBUTION AND GEOMORPHIC EVOLUTION OF PLAYA-LUNETTE SYSTEMS ON THE KANSAS HIGH PLAINS

Geographically and hydrologically isolated, ephemeral playa wetlands are ubiquitous features of the High Plains. Lunettes are dune-like features that form downwind of some larger playas. Although playas are important landscape elements, few systematic inventories have been conducted, and little is known about their evolutionary history. A comprehensive Geographic Information Systems database was created for Kansas utilizing several geospatial data sources, including aerial imagery, digital raster graphics, and SSURGO soils data. In addition, two playa-lunette systems (PLSs) were investigated to reconstruct paleoenvironment during PLS evolution.

Mapping results indicate there are >22,000 playas in Kansas, ranging in size from 0.03 ha to 188 ha, with a mean area of 1.65 ha. More than 80% are smaller than 2 ha and only about 400 playas are larger than 10 ha. Results indicate that previous inventories failed to identify most playas smaller than 2 ha because data sources were not of sufficient resolution. Additionally, playa identification criteria have not been consistent for all inventories, making it difficult to compare results and establish trends for various playa attributes across the entire High Plains.

Stratigraphic investigations of the two PLSs indicate they are composed of sediment spanning >40 kyrs, which began accumulating during at least Marine Isotope Stage (MIS) 3. Climate during MIS 3 was similar to modern: warm temperatures, low effective moisture, and playa floors exposed long enough to allow pedogenesis. During MIS 2, climate was relatively cool with higher effective moisture, and playas were inundated for longer periods. During the Pleistocene-Holocene transition, climate warmed, yet moisture availability remained relatively high. Several distinct shifts in δ¹³C identify rapid climate changes associated with the Bølling-Allerød/Younger Dryas climate sequence. Warming continued into the Holocene, though moisture availability was highly variable; Holocene soils are common. Thus, PLSs represents a continuum of the uplands High Plains loess sequence, though deposits are altered by playa hydrology. Geomorphic processes alternated between fluvial- and eolian-driven as climate changed, and detailed records of environmental change throughout their evolution are preserved.