Geoscience Reference
In-Depth Information
2
.
C)
Organic content of lake sediments (LOI, % dw; LOI
−
50
Polyhumic
dystrophic
lakes
40
Humic
materials:
C/N: 10 -20
30
20
Minerogenic
matter
(sand-silt):
C/N: 15-25
10
Plankton:
C/N: 5.6
Oligohumic
lakes
0
Fig. 4.3
Lake classification from the
relationship between the C/N ratio and
the loss on ignition (LOI) of surficial
sediments. (Modified from Håkanson
1995.)
0 5 10 15 20 25
C/N ratio of
lake sediments
Eutrophic
lakes
Oligotrophic
lakes
Autotrophy
used, is based on the relationship between the
organic content (estimated by determining loss on
ignition) and the ratio between the carbon con-
tent and the nitrogen content of lake sediments
(Fig. 4.3). This sedimentological classification
system has much in common with the informa-
tion given in Fig. 4.1 for lake classifications.
Three main types of matter in lake sediments can
be recognized and each has different chemical
characteristics (see Hansen 1961; Håkanson &
Jansson 1983).
1
The average composition of planktonic mater-
ials (autochthonous organic matter) is C
106
N
16
P,
which gives a C/N ratio of about 5.6, and the loss
on ignition (LOI) is usually less than 20% dry
weight (dw). This group also includes hydro-
genous materials precipitated out of solution and
biogenous materials (from organisms).
2
Allochthonous organic matter (e.g. humus)
generally (see Gjessing 1976; Thurman 1985) has
a C/N ratio of 10 -20 and a LOI of
as shore sediments, glacial deposits, turbidites
from turbidity currents, delta sediments, mixed
bioturbated sediments or annually layered,
laminated sediments; see e.g. Sly 1978), (iii) sys-
tems based on sediment colour and/or specific
characteristics (such as black sediments as a
reflection of anoxic conditions, brown sediments
reflecting oxic conditions, light grey calcareous
deposits, greenish grey siliceous deposits, grey
sediments rich in fibre, very soft brownish sedi-
ments, such as gyttja (sedimentary peat consisting
mainly of plant and animal residues precipitated
from standing water) and dy (finely divided,
partly decomposed organic material), and black
manganese nodules; see e.g. Håkanson & Jansson
1983), (iv) systems based on chemical properties
(see Table 4.4), or (v) systems that focus on the
geological rather than the geographical origin
of the sediments and distinguish between, for
example, glacial, fluvial, post-glacial or aeolian
deposits.
20% dw.
3
Minerogenic (inorganic) matter (such as sand
and silt) generally has a C/N ratio of 15-25 and
a LOI of
>
4.2.1.1 Suspended particulate matter (SPM) in lakes
20% dw.
Further classification schemes related to lake
sediments include those based on (i) grain size
(gravel, sand, silt or clay; see e.g. Friedman &
Sanders 1978), (ii) form-creating processes (such
<
The total amount of any substance
X
in the water
is often separated into a particulate phase, the
only phase subject to gravitational sedimenta-
tion, and a dissolved phase, generally the most
