Piece 6 - The Critical Zone
How does the aquifer itself evolve?
The Critical Zone
Groundwater, weathering, vegetation and erosion
The basement aquifer is part of a much larger critical zone, extending from the vegetation canopy to the depth reached by groundwater circulation.
In this system, groundwater is not only stored and transported: it also participates in chemical weathering and the export of dissolved elements.
Key findings
- Although smectites represent only about 4% of the soil volume, their dissolution accounts for approximately 75% of dissolved silica export, while primary silicate dissolution contributes about 15%.
- Vegetation strongly modifies water and solute fluxes. At Mule Hole, evapotranspiration limits runoff, while 80–90% of the annual solute flux exported by the stream passes through vegetation.
The groundwater system is part of a coupled rock–soil–water–vegetation system in which hydrology, weathering and biological processes interact.
