An Introduction to Environmental Chemistry

O HORIZON

SURFACE LITTER:

fallen leaves and

organic debris

Litter

L

F

Partially

decomposed

litter

A HORIZON

TOP SOIL:

organic matter (humus),

living organisms,

inorganic minerals

E HORIZON

ZONE OF LEACHING

(ELUVAL HORIZON):

dissolved or suspended

materials move

downward

B HORIZON

SUBSOIL:

accumulation of iron,

aluminium, humic

compounds and clay in

illuval horizons leached

down from the A and E

horizons; more altered

material than in C horizon

C HORIZON

WEATHERED PARENT

MATERIAL:

partially broken-down

inorganic minerals

R HORIZON

BEDROCK:

impenetrable layer

Fresh

M

Fig. 4.21Idealized soil profile showing master soil horizons and horizon abbreviations. The
O, A, E and B master horizons can be further subdivided into subordinate horizons depending
on composition (see Figs 4.23–4.25). Note that the O horizon is composed of fresh (L) and
partially decomposed (F) organic litter. Soil profiles are typically 0.5–1.0 m thick such that
master horizons are typically centimetres to tens of centimetres thick. SOM, soil organic
matter; CEC, cation exchange capacity.