Cycling of Beryllium and Carbon through hillslope soils in Iowa

Isotopes of Be and C were used to reconstruct loess accumulation,hillslope evolution, and agricultural modification in soils of western Iowa.While both elements are derived from additions by the atmosphere (via plants inthe case of carbon), the differences in element cycling allow erosional anddepositional processes to be separated from biochemical processing. Based on¹⁰Be, loess accumulation likely occurred simultaneously withhillslope degradation. Rates of loess accumulation declined five-fold betweenearly stages (late Pleistocene and early Holocene) and later stages (lateHolocene) of accumulation, but the absolute timing of accumulation requiresindependent dating methods. Based on ¹⁴C measurements, plant inputsand decomposition are significant near the surface, but below1–1.5 m carbon inputs are minimal and decompositionisnearly arrested. The amount of carbon below 1.5 m isconstant (0.1%) and is composed of soil organic matter that was buried byloess.Agricultural modification results in a dramatic redistribution of¹⁰Be through soil erosion and deposition. By contrast, theredistribution of soil organic matter is masked by the rapid cycling of Cthrough the topsoil as it continually decomposes and is replaced by plantinputs.