Christian and Lomholt, Steen: Recent depositional
conditions in Egens Vig, Denmark. Geografisk
Tidsskrift 85: 20-26,
Sediment distribution in a
low energy embayment, Egens Vig, depends both on
topography and hydrography. There is a clear distinction
between sediments in the shallow inshore water and that
in the central basin. The distinction is shown both in a
cluster analysis and in a Qda-Mj diagram. The transport
direction at the sediment surface differs from that 10
cm below. This difference, as well as lithological
shifts at the depths of 7cm and 17 cm, are correlated
with diebacks in eel-grass.
Christian Christiansen, and
Steen Lomholt Geological Institute, University of
Aarhus, Langelandsgade, Bygn. 521, 8000 Aarhus C,
Denmark*), present adress: Danish Energy Agency,
Landemærket 11, 1119 København K, Denmark.
Hydrography, sediment distribution, grain size measures,
eel-grass, Egens Vig.
During the last two decades
there has been great interest in the study of
depositional conditions of marine sediments. However,
the very varied conditions which have been found on
shelves and in inland waters, make it desirable to
collect information from a wide variety of environments.
The present study deals with a
semi-enclosed, microtidal embayment on the Kattegat
coast of Denmark. Most of the existing papers on marine
sediments in Danish waters have dealt with the Wadden
Sea on the exposed tidal North Sea coast (Gry, 1942;
Hansen, 1951; Hansen, 1956; Olsen, 1958; Jacobsen, 1962;
Bartholdy, 1980; Pejrup, 1980 and Pejrup, 1981). Work in
the northeastern part of the North Sea has mainly been
done by Dutch authors (Van Weering, 1915, 1981, 1982;
Van Weering et al. 1973 and Wan Weering and Qvale,
1983). Only a few authors have dealt with conditions in
inner Danish waters (e.g. Jørgensen, \911; Christiansen
and Lomholt, 1980; Christiansen et al., 1981 a and
Chrstiansen et al. 1981 b).
The physical setting
Egens Vig is a small,
semi-enclosed embayment on the north coast of Kalø Vig,
Denmark. There are two inlets to the embayment with
depths of 11 m and 6 m. (Fig. 1). They are separated by
a moraine ridge. The area of the bay is about 4.0
km2, the volume \5.1 x 106
m3, with a mean depth of 3.9 m. On the basis
of bottom topography, Egens Vig can be divided into two
parts: 1) A basin area with depths exceeding 4 m, and 2)
a shallow area (<2 m) near the coast. The slope
between 2 and 4 metres depth occupies only a small area.
Fig. 1. Locational map showing sampling
stations and mean grain size of surface sediments. 72-3
ø '/3-4 ø <>> 4 ø Fig. 1. Oversigtskort visende
prøvetagningsstationer samt bundsedimentets
Egens Vig is a micro-tidal
environment with a tidal range of 0.40 m. The
meteorological sea level fluctuations are much larger.
Winds from the W and N give positive (up to + 1.5 m)
deviations from DNN (Danish Ordnance Datum). Winds from
the S and E give negative deviations (down to - 1.2 m).
There is also a significant seasonal variation in mean
sea level: it is lowest (- 0.18 m) in April and highest
(+ 0.20 m) in November. The freshwater discharge to the
bay is estimated to be only 250 1/s and is therefore not
significant. Periodically the surface salinity in Egens
Vig is inversed. This inversion is caused by a
threelayer circulation (Christiansen et al., 1981 b).
seasonal fluctuations of redox potential (Eh)
sediment in the basin. The O mV isoline is located
deeper than 10 cm in spring, but is found near the
Fig. 2. Eh and organic
content of the sediment. A) In the spring (790531). B)
In the late summer (790831). From: Christiansen and
Lomholt (1980). Fig. 2. Redoxpotentiale og organisk
indhold i sedimentet A) Om foråret (790531) B) I
Eh depends on grain size and organic content
in the sediment, as well as the oxygen saturation and
stratification of the water. Eh is therefore
high in the spring when there is plenty of oxygen in the
water. In the autumn Eh is low in the central
basin because of low oxygen content in the water. This
in turn is due to a persistent pycnocline 2 m over the
bottom so that the bottom water is stagnant (Fig. 2)
(Christiansen and Lomholt,1980).
Bottom sediments were
collected from 11 stations in Egens Vig (Fig. 1) using a
gravity corer with an inner diameter of 7.8 cm. Two
samples at each station were taken at depths of 0-1.5 cm
and 10-11.5 cm. The position of the vessel during
sediment sampling and hydrographic measurements were
plotted by means of Decca. The accuracy of the plots can
be estimated to be within ± 10m. Information on current
velocitites and directions was collected by the direct
reading current meter Braystroke MK 11. Salinity and
temperature were determined by the use of EIL MC-5
salinometers. Water density was calculated according to
We used standard sieving (ASTM
certificate sieves at 4\/2 scale) and pipette analyses
on samples from each of the stations. The sediments were
classified according to Folk and Ward (1957) and Buller
and McManus (1975). The QDa-Md system is usually based
on graphical reading on the log-frequency curve (in mm).
We have used readings from 0 probability curves,
transformed back into mm. Our Q-type cluster analyses
are in accordance with Parks (1966). We have used 1)
mean grain size, 2) sorting, 3) skewness, 4) kurtosis,
5) % <37yu, 6) Eh and 7) organic content
as components in the cluster analyses. (Table 1).
Fig. 3. Seasonal variation in A)
Salinity in the surface and at the depth of 2 m. B)
Temperature at the depth of 2 m. Fig. 3. Scesonmæssige
variationer i A) Saltholdigheden i overfladen og i 2 m 5
dybde. B) Temperaturen i 2 m's dybde.
Salinity and temperature
Salinity in Egens Vig
depends strongly on the water exchangebetween the Balitc
and the North Sea. Surface salinityis lowest in the
spring due to freshwater runoff from the Baltic (Fig.
3). Normally, there is only a small differencein
salinity between the surface and a depth of 2 m. An
exception was the period from January to April 1978,
when the embayment was covered with ice. During this
Table 1. Data used in the cluster
analysis. Sample 2-0 = surface sample frorr, station 2.
Sar.ple 2-10 = sarr.pie fror. 10 er,' s depth at station
Fig. 4. A) Grain size distribution of
surface sediments. B) Grain size distribution of
sediments from the depth of 10 cm. Fig. 4. A)
Overfladesedimentets kornstørrelsesfordeling B)
Kornstørrelsesfordelingen i W em's dybde.
period the salinity was
measured through holes in the ice. Most probably,
therefore, the very low surface salinities in the period
were due to meltwater in the holes. Our measurements of
salinity in the central parts of the embaymentwere more
sporadic. But, a persistent halocline existed in the
central basin from 1.4. to 20.6.1978 and in June, August
and October, 1979.
In order to eliminate diurnal
fluctuations temperature was measured at the depth of 2
m. Seasonal variations were about 20°C. Greater
variations can normally be expected as both the summers
of 1978 and 1979 were windy and cold. We will not go
into further details on the temperature, as the
stratification of the water mass is more depended on the
salinity. Within our range of salinity a change of l°/oo
has the same effect on density as a change in
temperature of 6°C.
Current velocities are highest
in the two inlets to the embayment. In calm weather when
currents are generated by the tide, the current
velocities are 12-14 cm/s near the surface and 6-8 cm/s
near the bottom. With winds from the W (10-12 m/s)
current velocities can rise to respectively 40 cm/s and
In the central
basin current velocities and directions
measured by following drift-buoys released at station
2 at depths of 2 and 4 m. In all cases the buoys
near station 8. Current velocities were
always low (<5
The surface sediment
distribution (Fig. 4) reflects the bottom topography. On
the basis of grain size Egens Vig can be divided into
two sedimentary provinces. According to the Shepard
(1954) classification, sediments in the cental part
(stations 2, 3, 5 and 11) can be grouped as silt-sandy
silt, whereas sediments in the shallow parts near the
coast (stations 7, 8, 9 and 10) are sand. Sediments in
the two inlets (station 1 and 4) with relatively high
current velocities resemble the shallow water sediments
in spite of the greater depths.
Our data show that grain size
at the sediment surface is almost everywhere very
similar to that 10 cm below. The exceptions are stations
2 and 6. At station 6 the sand content rises from 63% at
10 em's depth to 85% at the surface. This could be the
result of the recent construction of a pleasure boat
marina near this station. At station 2 the sand content
changes from 86% at 10 em's depth to 43% at the surface.
The general similarity conceals intervening
irregularities. In a description of the cores, Lomholt
(1979) observed either a lithological shift or a layer
of organic matter at the depth of 7 cm at stations 2, 6,
8 and 9. At station 1 and 4 coring depths were only a
Fig. 5. R-type cluster analysis of
sediment parameters (see table 1). Fig. 5.
Klynge-analyse af R-typen.
cluster analysis (Fig. 5) shows that Md, O(,
Kg can be grouped with a high (r = 0.987) correlation
coefficient. The fraction <37yu and the organic
show poor correlations. Eh is negatively
with the other parameters (r = -0.821)
and is an important
environmental indicator in Egens
Vig (Christiansen and
Lomholt, 1980). The R-type
cluster analysis shows that
the elements in the
analysis have their own characteristica.
none of them have been eliminated in the
cluster analysis as proposed by Parks (1966).
Q-type cluster analysis (Fig. 6) shows two distinct
groups. Group A consists of samples from the
high energy areas near the shore and in
the inlets. Group
B represents samples from the low
energy central basin.
Fig. 5 also shows that group A
can be divided into four
subdivisions and group B
into two subdivisions at the r =
Fig. 6. Q-type cluster analysis of
sediment parameters (see table 1). Fig. 6.
Klynge-analyse af Q-typen.
0.7 level. The
QDa-Md distribution both in the surface
(Fig. 7) and the -10 cm sediment also clearly
divides Egens Vig into two regions.
Following Buller and McManus
(1975) the surface sediments in the central area at
stations 2, 3, 5, and 11 are »fine quiet-water sediments
(IF)«. In the Tay Estuary such sediments are deposited
from suspension under conditions of very low current
velocities and only slight surface wave activity (Table
2). The sediments at station 6 are »coarse quiet-water
sediments (1C)«, i. e. lag sediment. This interpretation
is not reasonable. The aberration is probably a result
of recent engineering activity near station 6.
Table 2. Relationships between QDa-Md
environmental and process analogues.
Sediments on the intertidal
flats at stations 7, 8, and 10, as well as those at
stations 1 and 4 in the inlets, are characterized as
»fine fluviatile sediments (3F)«. These sediments are
deposited from suspension and graded suspension under
conditions of low current velocities and only slight
wave action. Sediments at station 9 are »fine beach
sediments (SF)« deposited from both suspension and bed
A comparison of-10 cm and
surface samples (Fig. 7) shows that sediments at station
2 and 8 change »key« from IF to 3F. Sediments at station
10 change from 3F to IF while at station 6 they change
from 1C to IF.
Trends in grain size
In a theoretical
investigation McLaren (1981) provides a
Fig. 7. Egens Vig sedimenterne
indplaceret i QDa-Md diagram Fig. 7. QDa-Md diagram
of the sediments.
method for a rapid
determination of probable relationships between
depositional environments and sediment transport
directions. The theoretical background have been
questioned by Bartholdy (in press).
(op. cit.) a sediment trend matrix
was set up for
Egens Vig (Fig. 8).
The grain size characteristics
used to identify sediment trends are mean grain size,
sorting and skewness. Kurtosis is not considered a
measure that can provide further information, a view
shared by several authors (e.g., Blatt et al., 1972;
McLaren, 1981 and Christiansen and Miller, 1982).
Depending on the trend, the
sediments at one station can be sources for the
sediments at another, or they can not. The trends in the
matrix (Fig. 8) suggest the following:
i) station 1 can
be the source for stations 2, 3, 4, 5, 8
ii) station 2 can
be the source for stations 3, 5, 8 and 11.
station 3 can not be a source.
iv) station 4 can
be the source for stations 3, 5 and 11.
v) station 5
can be the source for station 3.
Fig. 8. Matrix over udgangssediment
- aflejringssediment relationer. Fig. 8. Sediment
Fig. 9. Mulige
sedimenttransportretninger A) For stationerne på lavt
vand. B) For stationer på dybere vand. Fig. 9.
Possible sediment transport directions. A) From shallow
water stations. B) From deep water stations.
vi) station 7 can
be the source for stations 2, 3, 4, 5, 8
vii) station 8 can be the source for stations 3, 5
viii) station 9 can be the source for
stations 2, 3, 4, 5, 8
ix) station 10
can be the source for stations 1, 2, 3, 4, 5,
x) station 11 can not be a source.
Because of engineering
activity near station 6, this section has been omitted
in the above relationships. From the above we can
conclude that the two stations in the inlets, as well as
the stations in shallow water, can be sources for
stations in the central basin (Fig. 9). Shallow water
stations as possible sources for central basin stations
are also observed in Knebel Vig a few kilometers to the
South (Christiansen et al., 1981 c).
Fig. 10. Ændringer i mulige
transport retninger fra 10 cm's dybde til overfladen.
Fig. 10. Changes in sediment transport directions
between the surface and 10 em's depth.
The sediments from 10 cm below
the surface show very similar trends. The differences in
trends are shown in Fig. 10. The most pronounced
difference is that at the depth of 10 cm station 8 could
not be a deposit from the sources 2, 7, 9 and 10.
Within this low-energy
embayment there is a clear difference in depositional
conditions between the shallow nearshore water and the
central basin (see Fig. 6 and Fig. 7). The difference is
reflected in grain size parameters as well as in organic
content and redox potential. In the QDa-Md diagram the
two stations in the inlets to the embayment (stations 1
and 4) are classified with the shallow water stations.
It is therefore tempting to ascribe the above
differences in depositional conditions by hydrodynamics:
The relatively high current velocities in the inlets
produce the same depositional conditions as wave
activity does in shallow water. In these relatively
high-energy areas the sediments are coarser, better
sorted, more negatively skewed, with a high redox
potential and a low organic content. In the low-energy
areas in the central basin the sediments are finer,
poorly sorted, more positively skewed, with a low redox
potential and a high organic content.
hydrodynamics is not the only governing factorfor
deposition, for example, the content of material
<37ju at stations 4 and 8
is comparable with a ratio of 0.85 (Table 1). Yet the
organic content at station 4 is more than 5 times that
at station 8, and redox potential at 4 is negative as
against the positive redox potential at station 8. This
suggests that the position of stations either above
(station 4) or below (station 8) a pycnocline (Fig. 3)
is also a governing factor.
Both the difference in
possible source-deposit relationships between surface
sediments and sediments from the depth of 10 cm, and the
lithological shift or layer of organic matter at the
depth of both 7cm and 17 cm, could have the same cause.
Using the highest rates of sedimentation (4 mm/year)
from the more protected Knebel Vig nearby (Christiansen
et al., 1981 c) the -7 cm level corresponds to 1961 and
the -17 cm level corresponds to 1934. This is in good
agreement with data from the more exposed parts of Kalø
Vig where the -20 cm level corresponds to 1934
(Vandkvalitetsinstituttet, 1980). Both in the sixties
and in the thirties die-backs in eel-grass produced
similar near-shore changes at Kyholm (Christiansen et
al. 1981 a). The observed differences in source-deposit
relationships in Egens Vig could therefore also be a
result of the disappearance of eel-grass. This
hypothesis is corobborated by the presence of
high-organic horizons in most of the cores, and in the
majority of these there are eelgrass fragments. The
eelgrass hypothesis could also explain an anomaly in the
Pb-210 activity profile at depths of 20 to 25 cm in Kalø
Vig (Vandkvalitetsinstituttet, 1980). This anomaly, with
signs of sediments-mixing, could be the result of the
disappearance of eel-grass which acts as sediment
To-day there is no vegetation
below the depth of 5 m in Egens Vig and alomst none in
other parts of Kalø Vig (Mathiesen and Mathiesen, 1977).
We therefore conclude that vegetation can be a major
sedimentational parameter even in areas where no
vegetation is found to-day.
J., 1980: Sediments and dynamics in the Varde Å
estuary. Geografisk Tidsskrift 80, 64-71.
(in press): Recent sedimentologi i Ho Dyb's
Midddleton, G., and Mur ray, R., 1972: Origin of
rocks. Englewood Cliffs, J. J., Prentice
Hall, 634 pp.
Buller, A. T.
and Mc M anus, J., 1975: Sediments of the Tay Estuary
l. Bottom sediments of the upper and upper middle
Proc. Roy. Soc. Edinburgh 75, 41-63.
Christoffersen, H., Dalsgaard, J. and Nørnberg, P., 1981
a: Coastal and near-shore changes correlated with
dieback in Eel-grass (Zostera marina, L.). Sediment.
Geol. 28, 163-173.
Christoffersen, H. and Lomholt, S., 1981 b:
Characteristics of three-layer circulation and inverse
surface salinity gradients in two small semi-enclosed
embayments. Nordic Hydrology 12, 119-128.
Christoffersen, H. and Schuhz, K. E., 1981 c:
Hydrography, sediments and sedimentation in a low energy
embayment, Knebel Vig, Denmark. Geogr. Ann. 63 (A),
C. and Lomholt, S., 1980: On non-biological changes
in Eh in a marine sediment. Vatten 36, 295-300.
C. and Miller, P., 1983: Spartina in Mariager Fjord,
Denmark. The effect on sediment parameters. Earth
Processes and Landforms. 8, 55-62.
Folk, R. L.
and Ward, W. C., 1957: Brazos River bar, a study in
the significance of grain-size parameters. J.
1942: Das Wattenmeer bei Skallingen. Folia Geographica
Danica 11, l.
1951: Preliminary report on the sediments of the
Danish Wadden Sea. Medd. fra Geol. Foren. 12, 1.
1956: The sedimentation along the Rømø-dam.
fra Geol. Foren. 13, 2.
1962: Morfologiske og hydrografiske undersøgelser
flod- og ebbeskår i tidevandsrender. Geografisk
8., 1977: The sulfur cycle of a coastal marine sediment.
Limnol. Oceangr. 22, 814-832.
1979: Undersøgelser i Egens Vig. Unpublished. M.
report. Geol. Inst. Aarhus Universitet.
1981: An interpretation of trends in grain size
measures. J. Sediment. Petrol. 51, 611-624.
Olsen, H. A.,
1958: The influence of the Rømø Dam on the sedimentation
in the adjacent part of the Danish Wadden Sea.
Geografisk Tidsskrift 58, 119-140.
Parks, J. M.,
1966: Cluster analysis applied to multivariate geologic
problems. J. Geol. 74, 703-715.
1980: The turbidity maximum in the northern part of
Ho Bugt. Geografisk Tidsskrift 80, 72-77.
1981: Bottom sediments in Ho Bugt - a wadden sea
environment. Geografisk Tidsskrift 81, 11-16.
1983: Et metodestudium af den suspenderede
i et vadehavsmiljø. Meddelelser
Laboratoriet. Bd. XXIX.
P., 1954: Nomenclature based on sand-silty-clay ratios.
J. Sediment. Petrol. 24, 151-158.
1980: Aarhus Bugt-Kaløvig 1978-1979,
Report Nr. 10.
T. C. E., 1975. Late quarternary history of the
Skagerak; an interpretation of acoustical profiles.
Van Weering, T. C. E.,
1981: Recent sediments and sediment transport in the
North Sea; surface sediments of the Skagerak. In: Nio,
S. D., Schütterhelm, R. T. E. and Van Weering, T. C. E.
(eds.), Holocene marine sedimentation in the North Sea
basin. Spec. Publ. Int. Assoc. Sedimentol. 5, 335-359.
T. C. E., 1982: Recent sediments and sediment
transport in the northeastern North Sea; pistoncores
Skagerak. Proc. KNAW, Ser. B, 85, 155-201.
T. C. E. and Qvale, G., 1983: Recent sediments
foraminiferal distribution in the Skagerak, Northeastern
North Sea. Mar. Geol., 52, 75-99.
1976: A nummerical model of the effect of reactor
cooling on fjord circulation. SMHI. Nr. RHO 6.