Relationship Between Sodium Affected Soil Distribution and Relict Patterned Ground On the Loess Covered Illinoian till Plain of South Central Illinois: I.

Sodium affected soils (SAS) or sodium soils are soils that have been adversely affected by sodium salts and/or exchangeable sodium.  They usually occur in arid, semiarid, and subhumid climates where rainfall is insufficient to leach soluble salts from the soils where internal drainage is restricted.  To a much lesser extent SAS occur in humid regions with a mean annual precipitation (MAP) > 100 cm because of factors that restrict leaching of soluble salts from the soil.

High pH, SAS occupy approximately 383,512 ha in south central Illinois.  In general, SAS soils in Illinois occur in areas where the Wisconsinan loess is 1 to 2 meters thick over the leached, less permeable Sangamon Geosol. These soils are much more common and extensive in areas that had dominantly prairie rather than forest vegetation for some time previous to settlement.  The SAS occur in a seemingly unpredictable pattern among normal acidic soils.

The intricate pattern of SAS and non-SAS on level to nearly level uplands indicates differential redistribution of sodium derived from primary minerals in the loess.  Previous research suggests that differential water movement and variations in evapotranspiration, both associated with current and historical soil landscape settings, were the mechanisms responsible for redistribution of sodium in solution.

The recent updating and digitization of Illinois soil surveys revealed that patterns on aerial photos of SAS and non SAS soils on level to nearly level uplands are similar to patterns of ice-wedge polygons in areas of modern permafrost. A model is introduced that proposes that the microtopography responsible for driving the water system resulted, in part, from the formation and degradation of discontinuous permafrost during Wisconsinan glaciation.