Southern high plains cyclical wetlands: Precipitation, flooding, infiltration, clay mineralogy, and iron and manganese nodules

Abstract

Southern High Plains (SHP) playa wetlands act as flood control, native plant refugia, wildlife habitat, and recharge underlying Ogallala aquifer. To understand climate and soil property roles in playa soil hydrologic functioning, soil profiles were described and soil samples collected from basin center to edge in typical SHP playa (mean annual precipitation [MAP] 478 mm). Soils were inner-basin Randall (very fine, smectitic, thermic Ustic Epiaquerts) and outer-basin Lofton (fine, mixed, superactive, thermic, Vertic Argiustolls). Soil samples were analyzed for physical, chemical, and mineralogical properties. Playa soils had greater fine clay contents, but clays were mineralogically similar to SHP upland soils. Playa soil clays contain tetrahedrally charged disordered vermiculite, illite, and kaolin. Aerial imagery observed 1996–2013 playa conditions. Inner-basin was flooded 10 of 18 years and outer-basin only 3 of 18 years. Double-ring water infiltration rates increased from playa center to upland rim paralleling decreases in clay content. Lower outer-basin clay contents and greater infiltration rates favor aquifer recharge, but outer-basin soils rarely flood. Oxidizing conditions were measured in 2000–2001 in playa without flooding. Iron (Fe) and manganese (Mn) nodules are persistent playa wetland features. Playa nodules were compared to Texas Gulf Coast (TGC) Vertisol nodule Fe values linearly correlated with MAP (predicts likely redox oscillation frequency) and Fe/(Fe + Mn) nodule ratios. Playa soil Fe–Mn nodule Fe was much lower, but Fe/(Fe + Mn) ratios were comparable to TGC Vertisols with MAPs > 1000 mm. The Fe–Mn nodules (and likely aquifer recharge) in SHP playas might sporadically form in wet years when precipitation and runoff equal two to three times MAP.