Formation of Microaggregates and organo-mineral composite building units: Novel pathways in the soil-parent rock continuum

Formation of Microaggregates and organo-mineral composite building units: Novel pathways in the soil-parent rock continuum

 

Summary

 

Microaggregates and organo-mineral composite building seem to be unique structural features of natural permeable media like soils, rocks and aquifers. Thee develop in response to various aggregation processes and mechanisms that result in a non-random spatial arrangement of the solid phase already at the submicron scale. Soil microaggregates are defined as compound structures smaller <0.25mm, comprising the colloidal-sized and nanoparticulate composite building units and the organo-mineral composites (Totsche et al. 2018). Noteworthy, microaggregates, may be present as suspended or colloidally-dispersed components of the mobile phase. As such, they are prone to transport with the seepage and may affect the surface and pore-space properties. Surface alteration by interactions of seepage components with immobile surfaces is likely an important, yet essentially unexplored pathway triggering formation of microaggregates in the soil-parent rock continuum. In matured soils, the commonly found associations of clays with other, often poorly crystallized but highly reactive minerals and organic matter is the consequence of nucleation in the chemically heterogeneous soil suspension. Both pathways coexist and can be studied in the soil-parent-rock transition zone were weathering and formation/alteration of secondary mineral phases are still in the early stage. The stability of microaggregates and their interactions are dependent on wetting-drying and in turn by hydration-dehydration cycles. Such moisture-related dynamics regularly take place in soils of the temperate regions even down to the soil-parent-rock transition zone and suggests that the hydraulic and osmotic stress and their history results in attachment, detachment, translocation and accumulation. The presentation will We focus on two so far vastly ignored formation pathways of microaggregates and composite building units, i.e., the “geochemical inheritance” and “heteroaggregation from suspension”, thereby considering the role of dynamic relocation of composite building units and microaggregate forming materials from upstream compartments.

 

Totsche K.U., Amelung W., Gerzabek M.H., Guggenberger G., Klumpp E., Knief C., Lehndorff E., Mikutta R., Peth S., Prechtel A., Ray N., Kögel-Knabner I. (2018) Microaggregates in soils. Journal of Plant Nutrition and Soil Science 181(1), 104-136.