Distinguishing Between Biogenic and Lithogenic Processes Controlling Mineral Nutrients In Soils

Spatial and temporal variations in pore water compositions are characterized for a deep regolith profile developed on a marine terrace chronosequence near Santa Cruz California. Variations are resolved in terms of the dominance of either a lithogenic process, i. e. chemical weathering, or a biogenic process, i. e. plant nutrient cycling. The concept of elemental fractionation is introduced which describes the extent that specific elements are mobilized and cycled as a result of these processes.

The ability to uniquely resolve these solute variations is attributed in part to specific characteristics of the Santa Cruz site, e. g., the development of a prominent argillic horizon which spatially isolates the lithogenic and biogenic processes and to the strong season control on hydrology and plant growth. Although both processes occur in most soil environments, resolution comparable to that obtained in this study may be more difficult. The ongoing development and use of other parameters, including Sr, Ca, N and Si isotopes and Ge/Si ratios further our ability to distinguish between biogenic and lithogenic processes in such soils.