Geological Survey of Denmark and Greenland Bulletin
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Nr. 4, Review of Survey activities 2003, pp. 37-40 |
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37
The Danish Nationwide Aquatic Monitoring Programme
(Kristensen et al. 1991; Kronvang et al. 1996) is one of the
most comprehensive in Europe and, compared with other
national programmes, was put in place at an early date: the
systematic monitoring of freshwater lakes began in 1989. As
with all such programmes of long-term environmental mon-
itoring, its value multiplies with time as an increasing num-
ber of scientific hypotheses can be tested and management
questions addressed using the growing body of data.
However, the aquatic monitoring data, as for many natural
systems, are limited to the scale of decades and so may not
identify important longer-term trends or be useful in the
determination of `baseline' (pre-industrial or pre-agricultural
impact) conditions.
(Kristensen et al. 1991; Kronvang et al. 1996) is one of the
most comprehensive in Europe and, compared with other
national programmes, was put in place at an early date: the
systematic monitoring of freshwater lakes began in 1989. As
with all such programmes of long-term environmental mon-
itoring, its value multiplies with time as an increasing num-
ber of scientific hypotheses can be tested and management
questions addressed using the growing body of data.
However, the aquatic monitoring data, as for many natural
systems, are limited to the scale of decades and so may not
identify important longer-term trends or be useful in the
determination of `baseline' (pre-industrial or pre-agricultural
impact) conditions.
The study of lake sediments, palaeolimnology, offers a
means of extending the monitoring of lake status back in
time and can be used to determine baseline conditions (e.g.
for water chemistry variables), to define trends and rates of
change, and to identify the causes of change (Battarbee
1999). The data obtained from palaeolimnological studies
can provide a yardstick against which current and future
changes may be assessed. Furthermore, restoration targets for
lakes impacted by for example enhanced nutrient loading,
will be aided by a knowledge of the environmental conditions
of a pre-disturbance state, defining both potential targets for
restoration and the limits to what a restoration project might
achieve (Battarbee 1999).
time and can be used to determine baseline conditions (e.g.
for water chemistry variables), to define trends and rates of
change, and to identify the causes of change (Battarbee
1999). The data obtained from palaeolimnological studies
can provide a yardstick against which current and future
changes may be assessed. Furthermore, restoration targets for
lakes impacted by for example enhanced nutrient loading,
will be aided by a knowledge of the environmental conditions
of a pre-disturbance state, defining both potential targets for
restoration and the limits to what a restoration project might
achieve (Battarbee 1999).
Application of palaeolimnology to the EU's
Water Framework Directive
Water Framework Directive
Palaeoecology has been a core area of research at the
Geological Survey of Denmark and Greenland (GEUS),
going back to the earliest days of the Geological Survey of
Denmark (Rasmussen 1988). This long tradition has been
followed and developed by successive research teams with
new skills and techniques being taken on board. For example,
advances in numerical techniques in the 1980s led to the
development of transfer function methods for estimating
past water chemistry variables from the microfossil record
(Birks et al. 1990). Over the last 13 years, a transfer function
to estimate past in-lake nutrient (Total Phosphorus, TP) con-
centrations for Danish lakes from sedimentary diatom assem-
Geological Survey of Denmark and Greenland (GEUS),
going back to the earliest days of the Geological Survey of
Denmark (Rasmussen 1988). This long tradition has been
followed and developed by successive research teams with
new skills and techniques being taken on board. For example,
advances in numerical techniques in the 1980s led to the
development of transfer function methods for estimating
past water chemistry variables from the microfossil record
(Birks et al. 1990). Over the last 13 years, a transfer function
to estimate past in-lake nutrient (Total Phosphorus, TP) con-
centrations for Danish lakes from sedimentary diatom assem-
blages has been created, developed and applied in many stud-
ies (e.g. Anderson & Odgaard 1994; Bennion et al. 1996;
Bradshaw 2001; Bradshaw et al. 2002).
ies (e.g. Anderson & Odgaard 1994; Bennion et al. 1996;
Bradshaw 2001; Bradshaw et al. 2002).
The wealth of palaeolimnological data on numerous fresh-
water and brackish lakes in Denmark, accumulated over
many years, provides a crucial resource relevant to the imple-
mentation of the European Union's Water Framework
Directive. This Directive, from 2000, aims to achieve a `good'
ecological status for all EU water bodies by the year 2015.
One of the key considerations of the Water Framework
Directive is the determination of baseline conditions, or `ref-
erence status', the yardstick against which contemporary
water quality status can be assessed and future targets can be
realistically defined. The reference status need not, of course,
be a stable condition, nor will the unimpacted status be the
same for different lakes in different landscapes (Søndergaard
et al. 2003).
many years, provides a crucial resource relevant to the imple-
mentation of the European Union's Water Framework
Directive. This Directive, from 2000, aims to achieve a `good'
ecological status for all EU water bodies by the year 2015.
One of the key considerations of the Water Framework
Directive is the determination of baseline conditions, or `ref-
erence status', the yardstick against which contemporary
water quality status can be assessed and future targets can be
realistically defined. The reference status need not, of course,
be a stable condition, nor will the unimpacted status be the
same for different lakes in different landscapes (Søndergaard
et al. 2003).
Using the geological record to assess the changing status
of Danish lakes
of Danish lakes
Emily G. Bradshaw and Peter Rasmussen
Fig. 1. Map of Denmark with the 21 lakes (blue dots) included in addi-
tional palaeolimnological analyses made for the European Union's Water
Framework Directive report (Amsinck et al. 2003) and other lakes (red
dots) mentioned in the text.
Geological Survey of Denmark and Greenland Bulletin 4, 3740 (2004) © GEUS, 2004
Two recent reports (Amsinck et al. 2003; Søndergaard et
al. 2003) that are the result of collaboration between the
National Environmental Research Institute (NERI), the
Danish Forest and Nature Agency, the Danish counties and
the Survey, set the foundations for implementation of the
EU's Water Framework Directive for Danish lakes. The
archive of palaeolimnological data collated by the Survey over
many years, and complemented by parallel studies at NERI,
proved an invaluable basis for the consideration of reference
status for Danish lakes. In addition, new analyses (diatoms,
GEUS; cladocerans, NERI) were made for 21 lakes (Fig. 1)
for four time-slices: 1850, 1900, 1950 and 2000. This study
was made possible, on a very limited budget, due to the well-
kept archive of lake sediments held by GEUS: lake sediment
cores that had been sampled and dated for a previous pollen-
based study (Nielsen 2003) were made available for addi-
tional analyses.
National Environmental Research Institute (NERI), the
Danish Forest and Nature Agency, the Danish counties and
the Survey, set the foundations for implementation of the
EU's Water Framework Directive for Danish lakes. The
archive of palaeolimnological data collated by the Survey over
many years, and complemented by parallel studies at NERI,
proved an invaluable basis for the consideration of reference
status for Danish lakes. In addition, new analyses (diatoms,
GEUS; cladocerans, NERI) were made for 21 lakes (Fig. 1)
for four time-slices: 1850, 1900, 1950 and 2000. This study
was made possible, on a very limited budget, due to the well-
kept archive of lake sediments held by GEUS: lake sediment
cores that had been sampled and dated for a previous pollen-
based study (Nielsen 2003) were made available for addi-
tional analyses.
Lake eutrophication a long-term view
In addition to the Survey's long tradition of pollen analysis,
many lake sediment-based studies have utilised the tech-
many lake sediment-based studies have utilised the tech-
niques of diatom and plant macrofossil analyses. The exam-
ple given here (Fig. 2) shows data from Søgård Sø. On the
basis of the macrofossil data for aquatic plants, the record has
been divided into three stages. The lower section of the sedi-
ment core (c. 200 to 147 cm) records sparse remains of sub-
merged macrophytes, but a relatively well-developed com-
munity of floating-leaved plants (e.g. Nymphaea: waterlily).
In this earlier part of the record, the diatom assemblage
reflects high total phosphorus concentrations in the lake. The
second stage (c. 147 to 78 cm) shows a much expanded veg-
etation of submerged aquatic macrophytes (e.g. Stratiotes
aloides: water-soldier; Nitella and Chara: stoneworts; Pota-
mogeton: pondweed). Egg-cocoons of the leech Piscicola geome-
tra also indicate the presence of submerged macrophytes at
this time (Odgaard & Rasmussen 2001). The third stage
(c. 78 to 0 cm) sees a greatly reduced number of plant macro-
fossil remains and P. geometra cocoons in the sediment, coin-
ciding with a major increase in the diatom-inferred TP
concentration.
ple given here (Fig. 2) shows data from Søgård Sø. On the
basis of the macrofossil data for aquatic plants, the record has
been divided into three stages. The lower section of the sedi-
ment core (c. 200 to 147 cm) records sparse remains of sub-
merged macrophytes, but a relatively well-developed com-
munity of floating-leaved plants (e.g. Nymphaea: waterlily).
In this earlier part of the record, the diatom assemblage
reflects high total phosphorus concentrations in the lake. The
second stage (c. 147 to 78 cm) shows a much expanded veg-
etation of submerged aquatic macrophytes (e.g. Stratiotes
aloides: water-soldier; Nitella and Chara: stoneworts; Pota-
mogeton: pondweed). Egg-cocoons of the leech Piscicola geome-
tra also indicate the presence of submerged macrophytes at
this time (Odgaard & Rasmussen 2001). The third stage
(c. 78 to 0 cm) sees a greatly reduced number of plant macro-
fossil remains and P. geometra cocoons in the sediment, coin-
ciding with a major increase in the diatom-inferred TP
concentration.
The record from Søgård Sø demonstrates the pattern of
eutrophication seen in many Danish lakes during the last
century. Before 1940 the lake had a rich aquatic macrophyte
century. Before 1940 the lake had a rich aquatic macrophyte
vegetation, but with increased nutrient
concentrations in the 1940s and later,
this macrophyte cover disappeared. This
example is from just one of many Dan-
ish lakes that have been the subject of
palaeolimnological studies.
concentrations in the 1940s and later,
this macrophyte cover disappeared. This
example is from just one of many Dan-
ish lakes that have been the subject of
palaeolimnological studies.
Figure 3 summarises some of the
results from the study of 21 Danish
lakes carried out in connection with the
Water Framework Directive report
(Amsinck et al. 2003). The results of the
analysis of sedimentary diatom remains
suggest that many of the lakes under-
went eutrophication during the past
150 years, but that in-lake nutrient
concentrations were already surpris-
ingly high for many sites in 1850. This
conclusion is supported by the few
studies of longer lake sediment se-
quences for Danish lakes, e.g. Langesø
(Anderson & Odgaard 1994), Dallund
Sø (Bradshaw 2001), Gudme Sø and
Sarup Sø (unpublished data, P. Ras-
mussen and E.G. Bradshaw) that de-
monstrate that some lakes have been im-
pacted by human activities over the
scale of centuries and millennia. Thus,
lakes carried out in connection with the
Water Framework Directive report
(Amsinck et al. 2003). The results of the
analysis of sedimentary diatom remains
suggest that many of the lakes under-
went eutrophication during the past
150 years, but that in-lake nutrient
concentrations were already surpris-
ingly high for many sites in 1850. This
conclusion is supported by the few
studies of longer lake sediment se-
quences for Danish lakes, e.g. Langesø
(Anderson & Odgaard 1994), Dallund
Sø (Bradshaw 2001), Gudme Sø and
Sarup Sø (unpublished data, P. Ras-
mussen and E.G. Bradshaw) that de-
monstrate that some lakes have been im-
pacted by human activities over the
scale of centuries and millennia. Thus,
defining a true baseline condition for many lakes
38
Fig. 2. Summary stratigraphic data for Søgaard Sø (unpublished data, P. Rasmussen and
N.J. Anderson).
requires the consideration of long time periods, only obtain-
able by use of the geological record.
able by use of the geological record.
Environmental management requires both
foresight and geological perspectives
foresight and geological perspectives
The study of palaeolimnological records has much to con-
tribute to lake management questions and problems. As well
as determining when and to what extent Danish lakes were
influenced by human activities, sites may be identified that
have experienced relatively little impact over time and thus
may be of greater conservation value (again, providing the
yardstick against which to judge contemporary systems).
Also, rates of change can be informative with respect to the
resistance of ecosystems to forcing events and the likelihood
of future stability.
tribute to lake management questions and problems. As well
as determining when and to what extent Danish lakes were
influenced by human activities, sites may be identified that
have experienced relatively little impact over time and thus
may be of greater conservation value (again, providing the
yardstick against which to judge contemporary systems).
Also, rates of change can be informative with respect to the
resistance of ecosystems to forcing events and the likelihood
of future stability.
Pressing environmental problems and management ques-
tions, for example those posed by the EU Water Framework
Directive, must draw on knowledge and experience gained
over many years. The Danish Nationwide Aquatic
Monitoring Programme has provided a rich resource to draw
on when addressing the requirements of this Directive,
putting Denmark in a stronger position than many other
European countries. The long tradition of environmental his-
tory research in Denmark, at the Survey in particular, has
likewise provided a strong base of knowledge, the fruits of
which continue to be harvested, as illustrated by the response
to the demands of the Water Framework Directive.
Directive, must draw on knowledge and experience gained
over many years. The Danish Nationwide Aquatic
Monitoring Programme has provided a rich resource to draw
on when addressing the requirements of this Directive,
putting Denmark in a stronger position than many other
European countries. The long tradition of environmental his-
tory research in Denmark, at the Survey in particular, has
likewise provided a strong base of knowledge, the fruits of
which continue to be harvested, as illustrated by the response
to the demands of the Water Framework Directive.
The management questions and the demands of the
Danish society in the future may not be predictable today
(e.g. problems relating to climate change). Therefore, the
importance of maintaining relevant and well-established
monitoring programmes for natural systems cannot be over-
stated (see also Sand-Jensen 1997; Wolf 2003). Their contin-
uation, however, requires foresight and a belief in investment
for the future. Another illustration of this comes from the
area of forest history research. Since 1948, Survey scientists
have monitored natural forest development in Denmark, one
of the longest surveys of its kind in Europe. The experience
and knowledge gained has been of vital importance for the
understanding of natural forest processes and for nature con-
servation in Danish forests.
(e.g. problems relating to climate change). Therefore, the
importance of maintaining relevant and well-established
monitoring programmes for natural systems cannot be over-
stated (see also Sand-Jensen 1997; Wolf 2003). Their contin-
uation, however, requires foresight and a belief in investment
for the future. Another illustration of this comes from the
area of forest history research. Since 1948, Survey scientists
have monitored natural forest development in Denmark, one
of the longest surveys of its kind in Europe. The experience
and knowledge gained has been of vital importance for the
understanding of natural forest processes and for nature con-
servation in Danish forests.
Once interrupted or discontinued, the value of a moni-
toring programme diminishes greatly. In the same way,
research expertise developed over many years is a valuable
resource that grows over time to become more than the sum
of a research group's parts. Without the foresight to support
and continue relevant and successful programmes, the
knowledge-base that has been built up can rapidly disinte-
grate, but the effects of this may only be fully appreciated in
subsequent decades (see e.g. Sand-Jensen 1995).
research expertise developed over many years is a valuable
resource that grows over time to become more than the sum
of a research group's parts. Without the foresight to support
and continue relevant and successful programmes, the
knowledge-base that has been built up can rapidly disinte-
grate, but the effects of this may only be fully appreciated in
subsequent decades (see e.g. Sand-Jensen 1995).
Of human history, Anne Knudsen, chief editor of the
national Danish newspaper Weekendavisen, has incisively
stated that: "Lacking knowledge of history leaves us vulnera-
ble and wide open to cock-and-bull stories and demagogy".
The same can also certainly be said for environmental history.
For example, based on limited information, it is a commonly
held belief that the pollution of Danish lakes is a relatively
modern phenomenon, associated with post-industrial popu-
lation growth and agricultural development. The study of
environmental history shows us that this is a misconception.
stated that: "Lacking knowledge of history leaves us vulnera-
ble and wide open to cock-and-bull stories and demagogy".
The same can also certainly be said for environmental history.
For example, based on limited information, it is a commonly
held belief that the pollution of Danish lakes is a relatively
modern phenomenon, associated with post-industrial popu-
lation growth and agricultural development. The study of
environmental history shows us that this is a misconception.
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Fig. 3. Mean diatom-inferred total phosphorus values (DI-TP) for the
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Authors' address
Geological Survey of Denmark and Greenland, Øster Voldgade 10, DK-1350 Copenhagen K, Denmark. E-mail: egb@geus.dk
Geological Survey of Denmark and Greenland, Øster Voldgade 10, DK-1350 Copenhagen K, Denmark. E-mail: egb@geus.dk
