SLOPE GRADIENT AND ASPECT EFFECTS ON SOILS DEVELOPED FROM SANDSTONE IN PENNSYLVANIA

This study was initiated to determine the basic characteristics and genesis of soils on gentle to very steep slopes on two contrasting slope aspects. Two transects, a southwest (SW) and a northwest (NW) transect, were laid out on a sandstone ridge across the summit and steepest convex shoulder positions. The thickness of the O, A and E horizons was not related to slope gradient across soils on all slope gradients and aspects. This indicates that the present rate of soil formation is greater than erosion, the influence of erosion on steep slopes could be off-set by lateral movement of through-flow water above the B horizon, or the process of tree throw masks slope gradient effects. Solum depth, B horizon thickness, clay, Fe, and Al indexes decreased with increasing slope for both the NW and SW aspects. Organic carbon index decreased with increasing slope for the SW aspect. Decreases in effective precipitation over relatively larger surface areas at steep versus lower slope gradients, a longer influence of periglacial erosion following the Wisconsinan glacial advance, and present slow but significant soil creep could cause these differences in soil development across the slope. Solum depth, B horizon thickness, clay, Fe, and Al indexes showed a smaller decrease across the NW compared to the SW slope. Organic carbon did not decrease across the NW slope. The E horizon was also slightly thicker on the NW compared to the SW slope. These aspect differences were probably caused by less evaporation on "shaded" NW compared to "sunny" SW slopes which produce generally higher moisture levels and more effective eluviation and illuviation on the NW slope.