224 P. L. Gersper et al. 



Percent Sand 



FIGURE 7-4. Particle 

 size distribution and tex- 

 ture of mineral horizons 

 in soils from A) Aerie 

 Pergelic Cryaquepts on 

 sloping areas marginal to 

 Footprint Creek (10 sam- 

 ples), and B) Histic Per- 

 gelic Cryaquepts and 

 Pergelic Cryohemists in 

 a moist meadow (86 sam- 

 ples). Textural diagram 

 after Soil Survey Staff 

 (1975). 



The very small particles and particle aggregates of sapric soils form a 

 rather dense and relatively impermeable mass that is slow to transmit 

 moisture or oxygen (Figure 7-3). Because of their highly aggregated con- 

 dition, sapric soils have many small pores and retain large quantities of 

 moisture, even in topographic positions that would normally be con- 

 sidered xeric. Further, the porosity of sapric soils may be high, especially 

 in surface horizons, because of repeated ice segregation, which produces 

 lenticular openings. However, vertical permeability is usually very low. 

 In comparison, fibric materials are of low density and have a very large 

 proportion of interconnected, free-draining macropores that permit 

 rapid movement of air and water in all directions. Soils on low topo- 

 graphic positions have fibric surface horizons that remain filled with cir- 

 culating water throughout much of the summer. Horizons containing 

 hemic material have intermediate soil moisture properties. 



Soils with high contents of clay- and silt-sized mineral materials gen- 

 erally tend to have very fine pores and consequently very low permeabil- 

 ity to air and water. Mineral layers in soils of the coastal tundra at Bar- 

 row are generally of this type, although they are often admixed with por- 

 ous organic matter and thus are more permeable. The dominant textures 

 of the mineral horizons (Figure 7-4) are silty clay and silty clay loam, 

 with some clays and a few soils of coarser texture. Mineral fractions of 

 Histosols tend to be finer textured (silty clays) than the Inceptisols, which 

 are silty clay loams, although Cryaquepts of polygon troughs and frost 

 boils commonly have the finest textures. Sandy-textured and loam- 

 textured soils are not common at the Biome research area, and appear to 

 be restricted to alluvial positions and the stream banks along Footprint 

 Creek. 



