Geoscience Reference
In-Depth Information
Effective fetch (km)
1 2 4 8 16 32 64 128 256
0
5
10
Erosion (E)
15
D
ET
= (30.4
.
EF)/(EF + 34.2)
Fig. 4.6
The erosion, transport and
accumulation (ETA) diagram showing the
relationship between the effective fetch
(EF, i.e. the free water surface over which
winds influence waves), the water depth
and the potential bottom dynamic
conditions for individual sites in lakes.
D
TA
is the wave base (WB), i.e. the
water depth separating T and A areas.
D
TA
can be predicted from the given
equation. The mean EF value for an entire
lake can be approximated by
√
Area.
(Modified from Håkanson 1999.)
20
25
30
Transportation (T)
35
Accumulation (A)
D
TA
= (45.7
.
EF)/(EF + 21.4)
40
45
50
Table 4.5
The relationship between bottom dynamic conditions (erosion, transportation and accumulation) and the physical,
chemical and biological character of the surficial sediments of Lake Lilla Ullevi Bay (in Lake Mälaren), Sweden. Mean values and
coefficients of variation (CV) in parentheses:
n
=
number of analyses. (Raw data from Ryding & Borg 1973.)
Category
Characteristic
Erosion
(
n
=
15)
Transportation
(
n
=
10)
Accumulation
(
n
=
14)
Physical parameters
Water depth (m)
Water content (% ww)
Bulk density (g cm
−3
)
Organic content
(loss on ignition, % dw)
Nitrogen
Phosphorus
Carbon
13.0 (0.41)
32.6 (0.28)
1.71 (0.087)
4.6 (0.48)
17.5 (0.31)
67.4 (0.14)
1.26 (0.079)
10.7 (0.43)
31.6 (0.25)
94.1 (0.024)
1.03 (0.019)
24.3 (0.10)
Nutrients (mg g
−1
dw)
0.6 (0.67)
0.8 (0.50)
0.5 (1.0)
1000-2000
24.6 (0.42)
0.8 (1.0)
41 (0.46)
18 (0.50)
23 (0.35)
3.4 (0.35)
2.8 (0.75)
22.7 (0.74)
3000-4000
53.5 (0.27)
3.5 (0.74)
111 (0.24)
31 (0.42)
40 (0.20)
10.7 (0.14)
1.6 (0.31)
10.4 (0.16)
6000-7000
41.3 (0.077)
2.5 (0.60)
189 (0.090)
59 (0.10)
57 (0.18)
Benthic biomass (mg ww m
−2
)
Chemically mobile elements
(see also P) (mg g
−1
dw)
Metals (
Iron
Manganese
Zinc
Copper
Nickel
μ
gg
−1
dw)
resuspension is a natural phenomenon on T
areas. It should be stressed that fine materials
are rarely deposited as a result of simple vertical
settling in natural aquatic environments. The
horizontal velocity component in lake water is
generally at least ten times larger, sometimes up
to 10,000 times larger, than the vertical com-
ponent for fine materials or flocs which settle
according to Stokes' law (see Bloesch & Burns
1980; Bloesch & Uehlinger 1986).
Resuspension is the physical (advective) trans-
port of matter from sediments back to water and
mixing is the upward and downward transport
of dissolved and suspended particulate matter
across the thermocline (the thermocline is the zone
in the water that separates the warmer, lighter
