In the zone of illuviation (B Horizon), what happens to dissolved constituents?

• A. They are leached out from this zone
• B. They are deposited within this horizon
• C. They are formed by weathering
• D. They are preserved in place

Answer: (C)

In the zone of illuviation, dissolved constituents are moved downward by infiltrating water and become deposited within that horizon. This is the process of illuviation, where materials leached from above accumulate in the B horizon, often forming layers rich in clays, iron/aluminum oxides, carbonates, or organic matter. So the dissolved materials don’t stay in place or form there from weathering; they are transported downward and are deposited here. This deposition within the B horizon is what characterizes illuviation, distinguishing it from eluviation (removal from a horizon) or in-place weathering (formation of new material at the surface or within the same layer).