47
D. Kar, Wetlands and Lakes of the World,
DOI 10.1007/978-81-322-1023-8_4, © Springer India 2013
4.1
Wetland Soils: Morphology:
Soil Types—Types
and Definitions
4.1.1 Morphology: Soil Types—
Types and Definitions
4.1.1.1 Types and Definitions
Wetland soils are important media, in which,
many of the wetland chemical transformations
take place (Jackson 1973). They are also regarded
as permanent storage systems of available chemicals for most wetland plants. They are often
designated as ‘hydric soils’ as defined by the
Natural Resources Conservation Service of the
US Department of Agriculture (NRCS 1998).
Further, soils, which are formed under conditions
of saturation, flooding or standing long enough
during the growing season, may develop anaerobic
conditions in the upper part. Nevertheless, wetland
soils are broadly of two types, namely, (a) mineral soils and (b) organic soils. It is important to
note here that nearly all soils have some amount
of organic material. However, a soil is generally
designated as ‘mineral soil’ when the soil has
<20–35 % organic matter.
For an estimate of the organic carbon (OC),
when organic matter (OM) content is known,
estimation of organic carbon (OC) could be
done by:
%
%
/
C
O M
org =
2
where,
% C org = % of OC
% OM = % of OM
Contrary to the above, mineral soils occur in
wetlands, such as in some FW marshes or riparian forests. They generally have a soil profile
made up of horizons or layers. The upper layer of
wetland mineral soils is often organic peat composed of partially decayed plant materials.
Organic soils are different from mineral soils
in a number of physico-chemical features other
than the % of OC. Further, organic soils have
lower bulk densities (BD) and higher waterholding capacities than do mineral soils.
Incidentally, BD may be defined as the dry weight
of soil material per unit volume. However, both
organic and mineral soils have wide ranges of
possible hydraulic conductivities which depend
on their degree of decomposition. Moreover,
more minerals are usually tied up in organic forms
in organic soils. However, it may not mean that
organic soils have more total nutrients. Rather, it
may often be the other way round in wetland soils.
For example, organic soils may contain very low
quantity of bioavailable P and Fe, which may be
enough to limit plant productivity. Nevertheless,
organic soils have a greater cation-exchange
capacity. It may be defined as the sum of exchangeable cations which a soil can hold. On the other
hand, cation-exchange capacity of mineral soils is
dominated by the major metal cations (Ca
++
,
Mg
++
, K
+
, Na
+
). It is pertinent to note here that
4
Lentic Soil or Mud (Physicochemical Characteristics of Soil)
D. Kar, Wetlands and Lakes of the World,
DOI 10.1007/978-81-322-1023-8_4, © Springer India 2013
4.1
Wetland Soils: Morphology:
Soil Types—Types
and Definitions
4.1.1 Morphology: Soil Types—
Types and Definitions
4.1.1.1 Types and Definitions
Wetland soils are important media, in which,
many of the wetland chemical transformations
take place (Jackson 1973). They are also regarded
as permanent storage systems of available chemicals for most wetland plants. They are often
designated as ‘hydric soils’ as defined by the
Natural Resources Conservation Service of the
US Department of Agriculture (NRCS 1998).
Further, soils, which are formed under conditions
of saturation, flooding or standing long enough
during the growing season, may develop anaerobic
conditions in the upper part. Nevertheless, wetland
soils are broadly of two types, namely, (a) mineral soils and (b) organic soils. It is important to
note here that nearly all soils have some amount
of organic material. However, a soil is generally
designated as ‘mineral soil’ when the soil has
<20–35 % organic matter.
For an estimate of the organic carbon (OC),
when organic matter (OM) content is known,
estimation of organic carbon (OC) could be
done by:
%
%
/
C
O M
org =
2
where,
% C org = % of OC
% OM = % of OM
Contrary to the above, mineral soils occur in
wetlands, such as in some FW marshes or riparian forests. They generally have a soil profile
made up of horizons or layers. The upper layer of
wetland mineral soils is often organic peat composed of partially decayed plant materials.
Organic soils are different from mineral soils
in a number of physico-chemical features other
than the % of OC. Further, organic soils have
lower bulk densities (BD) and higher waterholding capacities than do mineral soils.
Incidentally, BD may be defined as the dry weight
of soil material per unit volume. However, both
organic and mineral soils have wide ranges of
possible hydraulic conductivities which depend
on their degree of decomposition. Moreover,
more minerals are usually tied up in organic forms
in organic soils. However, it may not mean that
organic soils have more total nutrients. Rather, it
may often be the other way round in wetland soils.
For example, organic soils may contain very low
quantity of bioavailable P and Fe, which may be
enough to limit plant productivity. Nevertheless,
organic soils have a greater cation-exchange
capacity. It may be defined as the sum of exchangeable cations which a soil can hold. On the other
hand, cation-exchange capacity of mineral soils is
dominated by the major metal cations (Ca
++
,
Mg
++
, K
+
, Na
+
). It is pertinent to note here that
4
Lentic Soil or Mud (Physicochemical Characteristics of Soil)