Geoscience Reference
In-Depth Information
100
90
Schierstein
Kostheim
Koln
Dusseldorf
80
70
60
50
40
30
20
10
0
Fig. 4.7 Grain-size dependencies of cadmium concentrations in sediment samples from German rivers. (Modified from Förstner &
Salomons 1981.)
surface water from the colder, heavier deep
water). Some lakes are constantly mixed and do
not develop a thermocline, but most lakes, and
certainly those in northern and boreal landscapes,
develop a thermocline in the summer. The sur-
face water (the epilimnion) is fundamental for the
primary production of matter. Many important
sedimentological processes take place in the
deep-water zone (
action, sedimentation rates generally increase
from the wave base to the deepest parts of the
lakes. The coarsest materials (sand, gravel) are
often found in shallow waters.
3 Current action can dominate in certain areas,
such as in narrow straits and along the shoreline.
Then the 'Hjulström-curve' (see Fig. 1.5) gives
the relationship between critical erosion and
critical deposition of materials.
4 Slope-induced (gravity) turbidity currents
appear on bottoms inclined more than about
4 -5% (Håkanson 1977), and bioturbation gen-
erally prevails in oxic sediments (see Table 4.4),
where the macro- and meiofauna cause a mixing
of the sediments.
hypolimnion).
There are some basic rules regulating sedi-
mentation in lakes (e.g. Thomas et al. 1976;
Golterman et al. 1983; Håkanson & Jansson
1983; Colman et al. 2000; and Fig. 4.8).
1 River action dominates the sedimentological
properties in river-mouth areas, where deltas
may be formed if the amount of sandy materials
carried by the tributaries is large enough. Within
these areas, sedimentation rates generally decrease
with distance from the mouth, and so does the
grain size of the settling particles.
2 In open-water areas, dominated by wind/wave
=
4.2.2.2 Determination of bottom dynamic conditions
in lakes
The following processes influence internal load-
ing and bottom dynamic (E, T and A) conditions
Search WWH ::




Custom Search