MAPPING AND STRATIGRAPHIC INVESTIGATIONS OF PLAYA BASINS ON THE HIGH PLAINS OF KANSAS

Small, internally drained, ephemeral lakes, referred to as playas, are ubiquitous features on the High Plains. Playas are important features on the High Plains because they focus recharge to the heavily utilized Ogallala Aquifer and provide a valuable wetland resource. Although playas are a vital element of the landscape, an accurate inventory does not currently exist for Kansas. In addition, little is known about the origin of playa lakes or the processes involved in playa evolution. This research develops new methods of playa identification and mapping utilizing geographic information system (GIS) data coupled with field verification as well as detailed soils investigations of select playas. GIS data include National Agriculture Inventory Program (NAIP) color aerial photography with 2-meter resolution for the years 2003, 2004, 2005, and 2006, digital raster graphics (DRGs), Soil Survey Geographic Database (SSURGO) data, and political boundary data. Playas are mapped at the county level by “heads-up” digitizing; each county database includes playa area, absence or presence on each year of NAIP photography, absence or presence of a depression on associated DRGs, and absence or presence of hydric soils based on SSURGO data. Stratigraphic investigations involve collecting soil cores using a hydraulic coring rig along transects parallel and perpendicular to the playa long axis and the downwind ridge of sediment accumulation, termed a lunette. Soil cores are analyzed for a host of properties including magnetic susceptibility, δ¹³C, chloride concentration, CaCO₃ equivalence, and radiocarbon analysis when possible. Playas and lunettes exhibit complex sequence stratigraphies that can be correlated, and soil properties provide proxy evidence of paleoclimate, which when coupled with ¹⁴C age control identify periods of climate change, paleohydrology, and playa expansion. Comparing playa, lunette, and upland paleovegetation and paleohydrology with age control indicates if soil and playa formation was contemporaneous or if playa formation and expansion pre-date or post-date soil formation on uplands. Also, since buried soils represent periods of increased moisture and landscape stability, playa formation stages dominated by infiltration can be discerned from those dominated by wind deflation.