APPENDIX I Definition of terms
Introduction
In the concise description of the soils of the Netherlands (chapter 2), a number of
lithological properties - like texture and organic matter content - are introduced to
describe and classify the soil and sediment in the Netherlands. The same classification
and nomenclature is used throughout this thesis. For some of these properties, there is a
worldwide consensus about their definition and terminology (e.g. the sand or clay
fraction), whereas others are typical for the Dutch classification system (e.g. the term
“zavel” for sandy and silty clays). Even within the Netherlands, there is already
considerable discrepancy between the geological and pedological textural nomenclature
(see e.g. fig. I.1, I.2 and I.3). In order to have consistency throughout this thesis, and to
allow for comparison with other classifications, the most important lithological properties
and their terminology are described here. For a more detailed overview, the reader is
refered to De Bakker and Schelling (1989), Van der Sluijs and Locher (1987) and Janssen
et al. (1987).
Texture
The major texture classification is based on the < 2 mm fraction of the mineral
soil/sediment, so on an organic matter and carbonate free and 105 °C dry weight basis.
Herein discerned are the sand fraction (50-2000 µm), silt fraction (2-50 µm) and clay
fraction (< 2 µm), which are classically represented in a texture triangle. The loam
fraction is defined as the weight percentage of all grains <50 um (silt and clay fraction),
but this fraction is not used in the texture classification. The classification of the coarser
material (> 2 mm), like the gravel and pebble fraction, is not discussed here (see e.g. Van
der Sluijs and Locher, 1989).
In the Netherlands, the pedological and geological communities use different
texture classifications. In pedology, different classifications are used for eolian and noneolian sediments (fig. I.1 and I.2). This difference is not made in the geological
classification (fig. I.3). The delineation of the grain size classes is however largely
comparable in both systems, and they basically differ in terms of nomenclature. The sand
fraction can further be described in terms of coarseness, which is based on the median
grain size of the sand fraction and applies to sandy as well as loamy and clayey samples
(table I.1).
For the concise description of the Netherlands and throughout the rest of this thesis,
the pedological texture classification has been followed unless stated. The reason is that
this review is concerned mainly with the soils in the Netherlands. Moreover eolian and
non-eolian sediments do have different ranges in grain size distribution (see chapter 2,
section 2.3.3). Also the terminology used for different clays appears more intuitive. Just
as for the Dutch soil classification system (chapter 2, section 2.6), the texture
classification in the Netherlands is quite different from those used in other parts of the
world (see for example the classification used by US Department of Agriculture in figure
I.4). For the non-eolian sediments (fig. I.2), the Dutch term “zavel” is translated by
“sandy and silty clay” and no further differentiation is made into heavy and light “zavel”.
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Figure I.1 Texture classification used by Stiboka for eolian sediments (e.g. De Bakker and Schelling,
1989). L.P.= loam-poor, S.L. = slightly loamy, V.L. = very loamy, E.L. = extremely loamy (applies to
sand).
Figure I.2 Texture classification used by Stiboka for non-eolian sediments (e.g. De Bakker and Schelling,
1989). The grey line in the fields of sand and silt separate clay-poor and clayey sand and silt. The grey line
in the field of light “zavel” separates very and moderlately light “zavel”. In the text, no differentiation is
used for “zavel”, which is translated as “sandy to silty clay”.
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Figure I.3 Texture classification of sediments according to the Netherlands Normalization Institute (NEN,
1989). L.P.= loam-poor, S.L. = slightly loamy, V.L. = very loamy, E.L. = extremely loamy, CL. = clayey
(applies to sand). S.S.loam = slightly silty loam. Grey lines in the field of sandy clay separate the slightly
sandy, moderately sandy and very sandy clays.
Figure I.4 Texture classification of sediments according to the US Department of Agriculture (Soil Survey
Division Staff, 1993). L.sand = loamy sand.
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Table I.1 Coarseness of the sand fraction (50-2000 µm), which is based on its median grain size (M50; after
De Bakker and Schelling, 1989).
For sand
For clay/loam
M50 between (µ
µm)
50-105
Extremely fine
Extremely fine sandy
105-150
Very fine
Very fine sandy
150-210
Moderately fine
Moderately fine sandy
210-420
420-2000
Moderately coarse
Very coarse
Moderately coarse sandy
Very coarse sandy
Organic matter content
The organic matter content is expressed on the fraction < 2 mm and based on 105 °C dry
weight of the total soil. With respect to the organic matter content, two basic groups can
be discerned (fig. I.5): Mineral soil/sediments having less than 15-30 wt% organic matter
and organic soil/sediment with more than 15-30 wt.% organic matter. The latter group is
in Dutch referred to as “moerig”, which is here consequently translated as “peaty”.
Soil/sediments having more than 35-70 wt% rganic matter (peat) are not further
differentiated into texture, whereas the remaining organic rich soil/sediment is further
divided into sand or clay (fig. I.5). For the mineral soil/sediment, the normal textural
classification applies (fig. I.1 and I.2).
The classification of organic rich soils and sediments is empirical and based on the
experience that sandy samples are more easily classified as organic matter rich than
clayey samples that have the same amount of organic matter. In other words, the finer the
texture, the higher the organic matter content should be to fall within the same class. As
mentioned by De Bakker and Schelling (1989), this effect is not fully understood, but it is
assumed that samples that fall onto the lines in figure I.5 have more or less a constant
volume fraction of mineral and organic matter.
Notice at last that in contrast to the textural classifications, the classification of
organic matter content uses the weight percentages based on the total soil, so including
the organic matter and carbonate content. When present in significant amounts, the
carbonate content should be added to the sand+silt fraction in order to derive the
appropriate organic matter class in figure I.5.
Carbonate content
Another important property of the soil/sediment is the carbonate content, expressed as the
weight percentage CaCO3 (105 °C dry weight). Often, the amount of inorganic CO2 is
estimated and allocated to calcium, i.e. assuming pure calcite. The following empirical
classification is used for the Dutch soils (De Bakker and Schelling, 1989):
• Less than 0.5 wt% = non-calcareous (no reaction with 10% HCl)
• Between 0.5 wt% and 1 wt% = carbonate-poor (audible reaction with 10 % HCl)
• More than 1 wt% = calcareous, (visible reaction with 10% HCl).
Carbonate content is mainly used in the further classification of fluviatile and marine
soils, as the Pleistocene soils (sand and loess) are generally non-calcareous.
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Figure I.5 Classification of organic matter content according to Stiboka (e.g. De Bakker and Schelling,
1989). If present in significant amounts, the amount of carbonate material should be added to the sand and
silt fraction. Peat, clayey (sandy) peat and peaty (sandy) clay are considered as organic rich or peaty
material, whereas the remaining groups are regarded as mineral material. Grey lines in the field of humic
clay (sand) separate the humic poor, moderately humic and humic clay (or sand). NEN-classification is
comparable and only uses a slightly different terminology (NEN, 1989). The grey line on the right side of
the triangle indicates the upper textural limit found in the Netherlands (80 wt. % clay fraction).
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