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sediment record (Sturm 1975; Sturm & Matter
1978; Ludlam 1981; Eden & Page 1998; Ambers
2001). These 'turbidites' can be deposited at any
season of the year and may often be separated
from 'ordinary' lamina by a greater thickness
and often by a different colour or grain size
distribution. It should be noted that turbidity
currents triggered by subaquatic landslides can
travel very fast and influence large parts of lakes
(Inouchi et al. 1996; Evans & Slaymaker 2004).
They generally appear more frequently in large
and deep lakes; large and shallow lakes are
dominated by wind-induced resuspension.
30
60
C
15
30
Sed
0
0
0 0.50 1.00
100%
dissolved
phase
100%
particulate
phase
4.3.2 Lake-level fluctuations
Particulate fraction ( PF )
Water-level fluctuations are common in many
reservoirs, but also in natural lakes depending
on changes in, for example, land-use practices
or precipitation (Thompson & Baedke 1995;
Kato et al. 2003). The situation in Lake Aral is
a famous example of this, but there are many
less well-known situations, for example Lake
Kinneret, Israel (Håkanson et al. 2000). Evid-
ently, there are close links between changes in
water level and lake morphometry. If the water
level goes down, the lake area will be smaller,
the wave base lower and the sediments and
substances continuously accumulated below
the previous wave base will be exposed and
influenced by wind-induced wave activities. So,
resuspension is likely to increase for some time
after the lowering of the wave base. Connected
to this, the concentration of suspended parti-
culate matter (SPM) is also likely to increase.
This means that the water clarity will also be
reduced, and this will influence the primary pro-
duction of phytoplankton and benthic algae. If
there are changes in primary production there
are also probable alterations in secondary pro-
duction of zooplankton and fish.
Fig. 4.14 Calculations illustrating the important role of
the particulate fraction in mass-balance calculations
(annual simulations for a lake with an area = 1km 2 ; mean depth
= 10 m; catchment area = 10 km 2 ; mean annual precipitation =
650 mm yr 1 ; mean tributary concentration = 26 μ gL 1 of total
phosphorus; and a settling velocity of 5 m yr 1 for the particulate
fraction).
sedimentation rate (dimension 1/time) by division
with the mean depth of the lake. The sedimenta-
tion rate regulates sedimentation, and hence also
internal loading in lakes. Figure 4.14 illustrates
the very important role that the PF value plays
for the concentration of phosphorus in water and
for sedimentation of phosphorus. It is evident
that the PF value influences the concentration in
lake water: the higher the particulate fraction
and the less in dissolved form, the higher the
sedimentation and the lower the concentration in
water, and vice versa. This is a general principle
valid for all substances.
4.3 PROCESSES AND IMPACTS OF NATURAL AND
ANTHROPOGENIC DISTURBANCE EVENTS
4.3.1 Storms and mass movements and
earthquake records in lake sediments
4.3.3 Lake sediment pollution
This section addresses the transport of pollu-
tants to, within and from lakes. In soils, water is
the main transport medium for pollutants and
the migration of chemical pollutants is therefore
Many studies have reported how storms, turbid-
ity currents, earthquakes, landslides, etc. influence
lakes and cause clearly distinguishable layers in the
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