Twenty-Three-year changes in upland and bottomland forest soils of central illinois

Soil formation is a complex process that varies with climate, relief, parent material, organisms, time, and in response to anthropogenic inputs. Time is often difficult to study. Our objective was to determine if the chemistry of two forest soils changed during a 23-year period in response to decreased acidic deposition (upland and bottomland soils) or by periodic sediment inputs (bottomland soils). These sites were sampled by depth in 1986 and 2009 using the same protocols. During an 8-year period in the 1990s, sediment deposition to the floodplain was measured. Soils at all depths and both sites had trends of greater exchangeable Ca, Mg, and K, increased pH, and decreased exchangeable Al and H. However, because of soil variability, increases were only significant in the base rich bottomland soils and were not thought to be biogeochemically important. Soil organic matter was relatively unchanged at both sites, with greater concentrations of C, N, and S in bottomland soils because of sediment deposition. Flooding was estimated to add 37 Mg ha^-1 year ^-1 of organic-rich sediment to the floodplain soils. Sulfate deposition decreased by a total of 3.1 keq ha^-1 during the 24 years^-1 between sampling, whereas base cation pools (0-80 cm) in the bottomland and upland soils increased by 458 and 540 keq ha^-1 (14 and 85% increases), respectively. Therefore, decreased acidic deposition likely had little effect on base cation pools, and the changes observed were thought to be caused by soil variability and possibly through canopy species variation affecting litterfall chemistry.