Metals, Metalloids and Radionuclides in the Baltic Sea Ecosystem docx

Trace Metals in the Environment 5
Metals, Metalloids
and Radionuclides in
the Baltic Sea Ecosystem
Trace Metals in the Environment 5
Series Editor."
Jerome O. Nriagu
Department of Environmental and Industrial Health
School of Public Health
University of Michigan
Ann Arbor, Michigan 48109-2029
USA
Other volumes in this series."
Volume 1"
Volume 2:
Volume 3"
Volume 4:
Heavy Metals in the Environment, edited by J P. Vemet
(Out of Print)
Impact of Heavy Metals on the Environment, edited by
J P. Vernet (Out of Print)
Photocatalytic Purification and Treatment of Water and
Air, edited by D.F. Ollis and H. A1-Ekabi (Out of Print)
Trace Elements- Their Distribution and Effects in the
Environment, edited by B. Markert and K. Friese
Trace Metals in the Environment 5
Metals,
Metalloids
and Radionuclides in
the Baltic Sea Ecosystem

Piotr Szefer
Department of Food Sciences
Medical University of Gdahsk
80-416 Gdahsk, Poland
2002
ELSEVIER
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To memory of my Parents
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vii
Acknowledgements
I particularly wish to express my special appreciation to Professor Jerome
Nriagu, the Editor of
the Science of the Total Environment, for encouraging me to
write this book. I would like to thank Mrs. Mary Malin and Mr. Peter Henn, the
Senior Publishing Editors, Mrs. Conny Kreinz, the Production Editor, as well as
Mr. Simon Richert from Elsevier, for their co-operation, understanding and great
patience. I particularly wish to thank Elsevier for their willingness to add extra
material, even at a late date, to ensure that the book is up to date. I am also very
grateful to Dr. Eric I. Hamilton, the Editor-in-Chief of

the Science of the Total
Environment,
for his critical and constructive remarks concerning all my
manuscripts published in the journal; scientific content of these papers constitutes
important part of the book.
My most sincere thanks are extended to Dr. Geoffrey E Glasby, Marine and
Environmental Consultant from Sheffield, for many stimulating discussions during
his visits to my laboratory. I am also especially indebted to Professor Philip
S. Rainbow from the Natural History Museum in London for much helpful dis-
cussion which undoubtedly contributed to improvement of the book quality. My
wife Krystyna and daughter Magdalena are heartily thanked for their patience
and support. I would like to thank Dr. A. Lataia and Dr. J. Warzocha for their
help in the collection of literature data concerning geographical distribution of
phyto- and zoobenthos in the marine environments.
I am grateful to various publishers and authors for permission to use figures,
tables and photographs from previously published papers which are their copyright.
Many thanks to Urszula Wawrzyfiska and Maksymilian Biniakiewicz from Prin-
ting-house of the Foundation for the Development of Gdafisk University who
have contributed to the text typesetting of the manuscript.
Gdatisk
Spring 2001
Piotr Szefer
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Preface
"The external world has proved
to be surprisingly obedient to logic".
Bertrand Russel
The Baltic Sea is a unique basin, being productive with intensive fishing po-
tential and has therefore been the object of many studies. It is a brackish, non-
tidal, relatively shallow and semi-enclosed sea. The Baltic is located at a high lati-

tude, hence one of its characteristic features is ice. Another unique geographical
pattern are the archipelagos located off the coast of Stockholm which consist of
more than 25 000 islands. The relative ionic concentration of toxic substances e.g.
chemical elements is generally higher in the low-saline Baltic Sea than compared
to the North Sea. The drainage area is densely populated, heavily industrialised
and is characterized by intensive agriculture. Therefore this sea is thought to be
extremely polluted and, with a wide range of contributing factors to its level of
pollution, there are obvious implications for the people, flora and fauna in the
surrounding Baltic states.
Although the Baltic Sea is divided into natural basins by bottom topography
and into economic sectors by man it represents an integrated system, highly sensi-
tive to what happens in its contact zones with the adjacent North Sea, the land
and the atmosphere. Areas suffering from pollution are unevenly distributed
within the sea. Among the key factors influencing this distribution are: distance
from the transition zone between the North Sea and the Baltic Sea; local hydro-
logic and hydrographic conditions; the catchment area of the adjacent rivers and
the extent of conservation measures in the adjacent areas. At the end of the
1960s great attention was paid to the marked deterioration of water and biota in
the Baltic Sea, resulting in the preparation and signing of the Convention on the
Protection of the Marine Environment of the Baltic Sea Area (i.e. the Helsinki
x PREFACE
Convention) by all riparian countries. Considering the geopolitical situation in
this region, the Helsinki Convention of 1974 should be regarded as a unique in-
ternational agreement, covering all sources of pollution of the open sea areas of
the Baltic. However, until 1992 the coastal zones were not included in the Hel-
sinki Convention.
Since the beginning of the 1980's, a series of assessments covering the wide
range of ecological problems has been published by the Helsinki Commission
(HELCOM). These assessments, prepared by numerous expert groups, summarise
scientific results from the beginning of the century and reflect the present status

of knowledge resulting from the research and monitoring programmes. The
achievements of these collective studies are utilised in this book as valuable back-
ground information and are cited under the name HELCOM. Also since the
1980's, our knowledge of the biogeochemistry of the Baltic Sea has improved re-
markably with results being published at first mostly in national journals and later
also in international journals with a biogeochemical and environmental pollution
orientation. This book has partly synthesised the wide-ranging research done, and
it is envisaged that it will prove to be a valuable addition to the literature.
The book discusses the distribution and cycling of metals, metalloids and
radionuclides in the Baltic Sea and, where needed, in adjacent northern or other
seas. The main aim of the book is to acquaint the reader with the distribution,
bioavailability, fate and sources of chemical pollutants in the Baltic environment
(seawater, suspended matter, bottom sediments, ferromanganese concretions, sea-
weed, plankton, molluscs, crustaceans, nereids, fish, waterfowls, marine mam-
mals). The distribution of pollutants in the atmosphere (aerosol, wet and dry
fall-out) as well as in the rivers of the Baltic catchment have also been consid-
ered. Justification for such an approach is that the atmosphere and most seas do
not have borders, even in the case of such a basin as the semi-enclosed Baltic Sea
which is connected with the North Sea via the Danish Straits. Therefore chemical
elements and radionuclides are often transported long distances from their emis-
sion sources via atmospheric circulation, sea currents and rivers. Since the marine
cycle of bioelements such as C, N, P and Si is often strictly related to the fate of
metals and metalloids, some aspects concerning these nutrients have also been in-
cluded in the book.
Because some organisms e.g. marine mammals, waterfowls and fish can be ef-
fective carriers of pollutants from even remote areas, concentration data for Bal-
tic migrants were compared together (where needed) with those corresponding to
non temperate zones e.g. sub-Arctic waters of the Northern Hemisphere. In the
case of sedentary organisms, such as phyto- and zoobenthos, worldwide data were
cited in the book because of the universal biomonitoring significance and utilisa-

tion of the sedentary bottom animals (e.g. Mytilidae) having a similar affinity to
most trace elements irrespective of their geographical habitation. Knowledge of
the chemical composition of Baltic benthal organisms and those from other geo-
graphical areas allows us to estimate the pollution status of compared marine en-
PREFACE xi
vironments, although it should be borne in mind that some environmental pa-
rameters e.g. salinity can influence bioaccumulation of several trace elements in
biota.
In order to set the data in context, characteristics of the main features of both
the abiotic (general characteristics, distribution, hydrological and geochemical
features), and biotic (taxonomy- classification to particular categories, habitat,
food habits) compartments of the Baltic Sea are presented. Particular compo-
nents of the Baltic ecosystem are considered as potential monitors of pollutants.
Budgets of chemical elements and the ecological status of the Baltic Sea in the
past, present and future are presented. Estimates of health risks to man in re-
spect to some toxic metals and radionuclides in fish and seafood are briefly dis-
cussed. The book is mainly directed to marine chemists, geochemists, environ-
mentalists, biologists, ecologists, ecotoxicologists, educators in marine sciences as
well as to students of oceanography. Although the Baltic Sea has been widely
studied it is hoped that the book makes possible the identification of gaps in our
environmental knowledge with certain sections establishing possible priorities, key
areas or strategies for future research.
Piotr Szefer
Gdafisk, Poland
Spring 2001
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xiii
Contents
Acknowledgements vii
Preface ix

Chapter 1 Introduction 1
Chapter 2 Air and Water as a Medium for Chemical Elements 43
Chapter 3 Biota as a Medium for Chemical Elements 181
Chapter 4 Deposits as a Medium for Chemical Elements 467
Chapter 5 Bioavailability and Biomagnification
of Chemical Elements and Radionuclides
565
Chapter 6 Sources of Chemical Elements 603
Chapter 7 Monitors of Baltic Sea Pollution 649
Chapter 8 Estimate of Health Risk 687
Chapter 9
Global Input of Chemical Elements
and Pollution Status of the Baltic Sea 697
Author Index 711
Species Index 735
Subject Index 739
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Chapter 1
Introduction
A. CHARACTERISTICS OF THE BALTIC SEA BASIN
Regional setting
The general characteristics (meteorology and chemical oceanography; fishes
and fisheries, pollution, geology, international management and co-operation) of
the Baltic Sea including environmental state of its particular subareas have been
well and detailed described in a number of major text books, monographs, re-
ports and articles (see for example: Manheim, 1961; Hartmann, 1964; Fonselius,
1969; Magaard and Rheinheimer, 1974; Lomniewski et al., 1975; Gudelis and
Emelyanov, 1976; Millero, 1978; Dybern and Fonselius, 1981; Ehlin, 1981;
Blazhchishin and Lukashev, 1981; Grasshoff and Voipio, 1981; H~illfors et al.,
1981; Kullenberg, 1981; Lisitzyn and Emelyanov, 1981; Ojaveer et al., 1981; Sj6-

blom and Voipio, 1981; Winterhalter et al., 1981; Blazhchishin, 1982a, 1982b,
1982c; Emelyanov and Pustelnikov, 1982; Elmgren, 1984; Fonselius et al., 1984;
Falkenmark, 1986; HELCOM, 1986, 1998a; Augustowski, 1987; Franck et al.,
1987; Ambio, 1990a, 1990b; Anon, 1990; Gran61i et al., 1990; Mikulski, 1991;
Emeis et al., 1992; Matthfius, 1992, 1993a, 1993b; Matth~ius and Francke, 1992;
Winterhalter, 1992; Bergstr6m and Carlson, 1993; H~gerhfill, 1994; Majewski and
Lauer, 1994; Emelyanov, 1995; Harff et al., 1995; HELCOM, 1996; Huckriede et
al., 1996; Trzosifiska and Lysiak-Pastuszak, 1996; Gingele and Leipe, 1997; Jensen
et al., 1997, 1999; Lemke et al., 1997, 1998; Rheinheimer, 1998; Jansson and
Dahlberg, 1999; Lysiak-Pastuszak, 1999; Sokolov and Wulff, 1999; Falandysz et al.,
2000; Kautsky and Kautsky, 2000; Blomqvist and Heiskanen, 2001; Lemke et al.,
2001) and therefore it is not the intention to repeat this published information.
2 INTRODUCTION
Rather attention will be directed forward the presentation of these basic environ-
mental problems shortly which are linked with the fate of selected chemical ele-
ments in the Baltic Sea.
The Baltic Sea is a young postglacial inland sea, with its drainage basin over
four times its sea area (Fig. 1.1). The drainage basin- densely inhabited and ur-
banised is used mainly for agricultural and industrial purposes (Falandysz et al.,
2000). The Baltic Sea is connected to the North Sea (Atlantic Ocean) via the
0 200 400
kilometres
- Watershed
m"
Norway
Finland
Sweden
Russia
Denr
/50 +

Germany
Fig. 1.1. Map of the Baltic Sea showing its large drainage basin. After Bergstr6m and Carlsson (1993);
modified.
A. CHARACTERISTICS OF THE BALTIC SEA BASIN
Kattegat and narrow inlets of the Belt Sea and Sound - the transition zone. The
Baltic Proper is the largest subdivision of the Baltic Sea. It has a surface area of
211 069 km 2 (51% of the whole sea) and the volume of 13 045 km 3 (60 % of the to-
tal) (Melvasalo et al., 1981; HELCOM, 1990, 1996). It covers the area between the
Darss Sill (18 m depth) in the transition zone and the Gulfs of Bothnia, Finland
and Riga. Several regions are distinguished based on the bottom topography: the
Arkona Basin, the Bornholm Basin and the Gotland Basin (Fig. 1.2). The Gotland
Basin in subdivided into its eastern and western parts. The Gdafisk Basin is
a southward extension of the Eastern Gotland Basin; it is frequently treated as
a separate natural region because the Gdafisk Deep (max. depth 118 m) acts as
a sink for the suspended matter carried by the Vistula River, which is the largest
river draining the Baltic Proper (Falandysz et al., 2000).
Continuous inflow of more saline water from the North Sea into the Baltic
Sea is hampered by shallow sills. Only major inflows, approximately 100 km 3 in
volume, reach the Bornholm Basin. To renew the deep or intermediate water lay-
q ,
w r o, I
,_ F E" Gotlan.~ '~ ~k~Rigal
.~_ -"-'~"~ornholm'
' ~1
Fig. 1.2. Map of the Baltic Sea showing its subareas. After Danielsson (1998).
4 INTRODUCTION
ers in the Gotland and Gdafisk Basins, even greater volumes of dense oceanic
water of high salinity, low temperature and high oxygen concentration are re-
quired. These proceed in cascades eastward and northward through the Sfupsk
Furrow which has a sill depth of approximately 60 m. Major inflows occur at ir-

regular intervals, mostly in winter. Their impact depends not only on the volume
but also on its salinity and the duration of the event. The causes of these inflow-
ing water are not well understood but meteorological and hydrological conditions
play a great role (Falandysz et al., 2000).
Due to an extensive river run-off, there are pronounced horizontal salinity
gradients in the surface layers of the Baltic Sea (Fig. 1.3). Moreover, rivers flow-
ing into the Baltic Sea carry various types of pollutants that could negatively af-
fect the ecological balance of the sea (Falkenmark, 1986). The salinity of surface
water is highly variable within each region. In the Baltic Proper, it ranges from
about 1 psu in estuarine areas up to 9 psu in the western region (HELCOM,
1986).
Cyberski (1995) reported statistically significant long-term trends in the sea-
sonal outflows of the rivers draining into the Baltic whereas the mean annual
flow rates of most rivers displayed only some fluctuations with time. These sea-
sonal changes began in the 1920s and have accelerated since the 1970s. They co-
incide with the energy crisis and the resulting attempts to improve water storage
facilities for electricity generating stations. Seasonal variations in the river outflow
to the Baltic Sea as well as recent climatic changes may also affect different ele-
~~B ~ Bay 9J~'~km3
.e/
@5.0 km 3
psu /f
P" /" ,~
458
k~/Gulf of
/ 3
~Finland~ m
Baltic Proper / ~_ 5.45 psu/
2'
3psu ,J~~/, Riga~

,'
/_5.,3psu!
34 km 3
Fig. 1.3. Annual water exchange between the Baltic regions (km3), mean long-term salinity of surface water
(psu) and regional riverine inflow (km 3, thick arrows). After Falandysz et al. (2000); modified.
A. CHARACFERISTICS OF THE BALTIC SEA BASIN
ments in the water balance. As an example, they may influence the salinity, one
of the fundamental factors controlling environmental conditions and the distribu-
tion of biological species within the Baltic Sea (Falandysz et al., 2000).
A horizontal salinity gradient also exists in the deep waters of the Baltic
Proper. Fonselius et al. (1984) studied 100-year series of salinity data. They found
that salinity varied from over 14 psu to about 21 psu in the near-bottom layer of
the Bornholm Deep, whereas in the southern and northern basins these variations
were less, e.g. from over 11 to 14 psu in the Gotland Deep.
Changes in the surface water temperature in the Baltic Sea are governed by
the increased continental influence in the east and the considerable north-south
extent of the Baltic Sea (Melvasalo et al., 1981). In the Baltic Proper, the average
winter sea surface temperatures are around 2~ The extent of ice cover is very
variable, depending on the severity of winter and the region (Majewski and
Lauer, 1994). The mean sea surface temperature is 16-18~ in the southern part,
about 16~ in the central part and 15-16~ in the northern part of the Baltic
Proper during August. During 1989-1993, the mild winters caused positive water
temperature anomalies (HELCOM, 1996). The deep waters have more or less
stable temperatures (5-8~ which are influenced by the frequency and season of
the major inflows.
The relationships between separate elements of water budget and seasonal
variations in water temperature result in marked vertical gradients in water den-
sity of the Baltic Sea. In summer, warm surface water is separated from the cold
winter water by the thermocline at a water depth of approximately 20 m. The
main barrier between the low salinity upper (isohaline) layers and higher salinity

(heterohaline) deep layers occurs at 40-70 m, on the average, depending on the
region and the period under consideration. Major inflows of water from the
North Sea significantly change the location of the permanent halocline within the
water column and the relative volumes of the isohaline and heterohaline layers
(Falandysz et al., 2000).
The residence time of Baltic Sea water, estimated from the salinity distribu-
tion, to be in the range of 20-35 years, varies spatially. Those elements which
take part in the biogeochemical processes spend much shorter time in the Baltic.
Wulff et al. (1990) calculated that the average residence times for silicate, phos-
phorus and nitrogen compounds are 13, 11 and 5 years, respectively.
Flora and fauna in the Baltic Sea
The main natural factor determining the occurrence of species in the Baltic is
low salinity, which limits the occurrence of many marine species as well as fresh
water species resulting in a relatively low biodiversity (Falandysz et al., 2000).
Most of the typically marine species (e.g. Echinodermata, Porifera, Anthozoa) do
not occur in this region or occur on the edge of their distribution range, therefore
even small changes in environmental conditions may influence their spatial distri-
bution. A decreasing number of marine species along with diminishing salinity
6 INTRODUCTION
(due to increasing distance from the Danish Straits) is a characteristic feature of
the Baltic Sea. The least number of species occur in waters with salinity ranging
from 5 to 8 psu, that is, salinity of the northern part of the Baltic. Baltic Proper is
thus a region intermediary between Kattegat and transition zone, reach in marine
species, and Bothnian Sea, where only a few marine species occur. The low tem-
perature is also important factor limiting immigration of marine organisms into
the Baltic (Dahl, 1956; Segerstr~le, 1957, 1972; Remane, 1958). In addition, the
relatively young age of the Baltic having been a brackish sea for only 6000 years,
should be taken into account. There are therefore not many species which can
be regarded as typical Baltic, brackish-water species. Most species have immi-
grated to the Baltic Sea from near-by seas and freshwater bodies during different

periods up its evolution, beginning with the last glacial period (about 12,000 years
ago). There are four groups of natural immigrants in the Baltic flora and fauna.
The first group consists of Northwest European euryhaline marine and brackish-
water species, e.g.
Macoma balthica -
Bivalvia and
Clupea harengus-
Pisces, and
the second are freshwater species, e.g.
Theodoxus fluviatilis -
Gastropoda and
Perca fluviatilis -
Pisces (Falandysz et al., 2000). The third and fourth groups in-
clude glacial relikts which reached the Baltic either through ice-dammed lakes
from the Syberia, e.g.
Saduria entomon -
Isopoda,
Mysis relicta -
Mysidaecea, or
by a westerly route through the sea, e.g.
Astarte borealis -
Bivalvia,
Pontoporeia
femorata -
Amphipoda. This migration process still continues (Dahl 1956; Seger-
str~ile 1957; Jansson, 1972; Magaard and Rheinheimer, 1974; Elmgren, 1984; Lo-
zan et al., 1996).
The main coastal and marine biotopes
Sandy coasts (moraine landscape formed by glacial and postglacial processes)
dominate the shores of Germany, Poland, Lithuania, Russia, Latvia as well as

southern Sweden. Sandy coasts often have an accumulative-abrasive character;
sandy beaches and dunes in various stages of succession (from white, green, grey
dunes to brown dunes covered by forests - e.g. Leba in Poland) are typical ele-
ments of such coasts. High active cliffs, so-called moraine cliffs built of clays and
sands are also present. In the western part (e.g. Rtigen Island) cliff and rocky
coasts (bedrock on Bornholm) are found (Falandysz et al., 2000).
In the southern part of the Baltic Proper the characteristic elements are la-
goons: Szczecin Lagoon (Oder Haft), Vistula Lagoon and Curonian Lagoon. The
coastal lakes are also typical elements of the southern coasts.
They are a few types of coastal salty meadows as well as coastal bogs which
are a typical element of the coastal marshes. These are pit bogs of two types -
"high" fed by rain waters and "low"- fed by ground and surface waters. Large pit
bog complexes are located along the southern coasts (e.g. along Lebsko Lake in
Poland). "Low" pit bogs do not form large complexes, but are dispersed as small
patches along the entire coast in meadow and pasture complexes.
The pelagic coastal biotopes are found within depths down to 15-25 rn where
interactions between waves and the see floor usually occur. Pelagic offshore bio-
A. CHARACTERISTICS OF THE BALTIC SEA BASIN
topes are the water body of the open Baltic Sea area deeper than 15-25 m usu-
ally without interaction between wave orbits and the sea floor. The offshore bio-
topes can be divided into water body above and below the halocline (Falandysz et
al., 2000).
The sea floor of the coastal zone is dominated by sandy sediments mixed with
gravel deposits. In the deep water zone, silty sediments prevail (Loz~n et al.,
1996; HELCOM, 1998a).
Eutrophication
Seasonal and annual variations in the concentrations of nutrients in the Baltic
Sea have been widely studied and extensively described in the scientific literature.
Because of the differences in climate and bathymetry within the Baltic Sea, they
are usually referred to particular regions and/or water bodies (Melvasalo et al.,

1981; HELCOM, 1987, 1990, 1993, 1996).
Seasonal fluctuations in the nutrient concentrations in surface waters of the
Bornholm and Gdafisk Deeps and the southern part of the Gotland Basin, aver-
aged over 20 years, show distinct temporal and spatial differences in the accumu-
lation pattern during the winter as well as the uptake by autotrophic organisms
during spring. There is a time-lag of about 2-4 weeks in the accumulation and as-
similation peaks, when moving from the Arkona Basin toward the northern Bal-
tic. Another time-lag, of about 1-2 weeks, occurs between the coastal zone and
the off-shore areas (Falandysz et al., 2000).
In the 1990s, the winter nutrient concentrations in the photic layer become
much more equal throughout the off-shore area of the Baltic Proper. However,
exceptions were found in the northern Baltic (the Landsort Deep with much ele-
vated phosphate and nitrate content), as well as in the southern Baltic (the
Gdafisk Deep with much elevated nitrate content). Comparing with the 1960s, an
overall concentration increase took place: 1.5-5 times for nitrate and 2-3.5 times
for phosphate, depending on the region. During the vernal phytoplankton blooms
the pool of assimilable nitrogen and phosphorus compounds was already con-
sumed by June-July in all areas except the estuaries. Nitrate depletion in warm
water creates conditions promoting the growth of blue-green algae, which are
able to make use of N 2 and add several hundred thousand tons of nitrogen to the
waters of the Baltic Proper. From summer until December nitrogen is a limiting
nutrient in the Baltic ecosystem, and the nitrogen content appears to be almost
balanced in most regions, with respect to input versus uptake. However, some ex-
ceptions were recognised,
viz.
the Pomeranian Bay and the most inner part of the
Gulf of Gdafisk, where phosphorus has becomes a temporary limiting nutrient
at the beginning of summer since the 1980s (Trzosifiska, 1992; Falandysz et
al., 2000).
In contrast to nitrate and phosphate, silicate has never been the limiting factor

for productivity of the Baltic Proper. However, since the 1980s, almost complete
silicate consumption has occasionally occurred following vast phytoplankton
8 INTRODUCTION
blooms. In spite of some decline found in the 1990s in the silicate uptake, ampli-
tudes in silicate concentrations were high, 5-7 mmol
m -3
annually. Seasonal fluctua-
tions of silicate display evident changes as a consequence of the autumnal species
development. Such fluctuations were previously observed for the phosphate and
nitrate, as well. Recently they flattened in the southern Baltic, where extremely
low concentrations of nitrate and phosphate and the supersaturation of surface
water with oxygen cover the whole summer and autumn, until December. This
situation can be partly attributed to mild winters and variations in the riverine
run-off. The accumulation of nutrients starts in January-February. At the peak of
nutrient concentration during winter, the mean molar ratio of nitrate to phos-
phate is approximately 7 in the Bornholm Deep and the Gotland Basin, but as
high as 10 in the Gdafisk Deep. When compared with the 1960s, this means an
increase in the N/P ratio by few percent for the off-shore regions, and by 50 %
for the Gdafisk Basin (Falandysz et al., 2000).
Before the eutrophication accelerated in the 1970s, the N/P ratios in the tro-
phic zone of the Baltic Proper were significantly lower than the Redfield ratio
(16:1), which reflected the steady state relations between the environment and
the biota in the ocean. Even so, nitrate and phosphate have been taken up in
proportions approximating the Redfield ratio. HELCOM (1987) investigated the
uptake of nitrogen and phosphorus during the vernal phytoplankton bloom in the
Bornholm Basin and found the relation to be about 15:1. A somewhat lower
mean value (14:1) was found for the spring/summer species in the southern Bal-
tic, including the off-shore and coastal areas (HELCOM 1996). Interregional def-
ferences were, however, considerable. The mean uptake ratio of silicate versus
phosphate was close to the Redfield ratio; it ranged from 13:1 in the Gotland Ba-

sin to 18:1 in the Bornholm Deep.
Variations observed in saturation with oxygen in the near-bottom water layer
reflect a seasonality in the oxygen utilized in respiration and remineralisation pro-
cesses, though they are to a certain extend overwhelmed by the hydrographic oc-
currences, such as occasional oceanic inflows, relatively slow water advection, ver-
tical density gradient weakening northwards and the long stagnation period. Sub-
stantial fluctuations in the phosphate concentrations are connected with their re-
suspention or remobilization from the bottom sediments in accordance with alter-
nating oxygen conditions. Silicate also accumulates in the deep waters whenever
dissolved oxygen concentrations decline. On the other hand, decreasing redox po-
tential promotes the denitrification activity. It has been calculated that denitrifica-
tion is responsible for the overall nitrogen loss of 470000 tons annually
(HELCOM, 1990).
A variety of the input and sink mechanisms, as well as temporal and spatial
differences in their efficiency, do not permit any realistic mass balance calcula-
tions. Nevertheless, nutrient budgets calculated by Wulff and Stigebrandt (Ambio,
1990) for phosphorus, nitrogen and silicate in particular parts of the Baltic Sea in
1971-1981 are very impressive and contain some management implications re-
garding the desired reduction in the pollution loads.
A. CHARACTERISTICS OF THE BALTIC SEA BASIN
The first signs of the increasing fertility were reported in the mid-1970s (Mel-
vasalo et al., 1981, HELCOM, 1987). The long-term trends, calculated by means
of approximately 20 year data series, were in most cases highly significant and
positive from the statistical point of view. In surface water of the Baltic Proper,
the mean annual accumulation rates of phosphate during the winter seasons
ranged from 0.015 to 0.26 mmol
m -3
and of nitrate from 0.17 do 0.34 mmol m -3,
depending on the region. Even a higher rate, exceeding 2-4 times that of the sur-
face water, was found for phosphate in the deep water layers. In spite of anoxic

conditions, nitrate accumulated in some water layers of the Baltic deep basins
(Nehring, 1989).
In the 1980s, when loads from external sources were still high, the rate of
eutrophication slowed down. The most characteristic feature of that period was
the long-lasting stagnation in the Baltic deep waters, the longest ever been ob-
served during the Twentieth century. As a result of the diminishing salinity and
increasing temperature of the deep waters, the weakening vertical density gradi-
ent supported downward transport of oxygen and upward transport of nutrients
over a vast area of bottom at the intermediate water depths (HELCOM, 1990).
The long-term increase in the phosphate and nitrate concentrations continued,
but was, interrupted by periods with decreasing concentrations. It has been found
almost cyclic behaviour in the phosphate and nitrate accumulation in the Gdafisk
Deep of 3 and 6-7 years (HELCOM, 1990). This was probably caused by varia-
tions in the atmospheric circulation affecting both the riverine run-off and the
oceanic inflows.
At present, the concentrations of assimilable compounds of phosphorus, nitro-
gen and silicates in the photic zone of the Baltic Proper are at a stable level,
though sufficiently high to support intensive primary production. During the last
few decades the phytoplankton primary production has almost doubled in some
areas, with a resultant doubling of phytoplankton biomass and its subsequent
sedimentation (Ambio, 1990).
Biological effects of eutrophication
Eutrophication is considered to be the main anthropogenic factor influencing
life in the Baltic. The most important effects of eutrophication are such as in-
creasing primary production, decrease in water transparency and increased or-
ganic matter sedimentation resulting in oxygen depletion occurrence. There is not
much evidence of primary production increase, mainly due to large natural an-
nual phytoplankton variability, relatively infrequent sampling, influence of local
factors and, finally, changes in measurement techniques. However, intensity of
phytoplankton blooms may be a general indicator of primary production increase.

More frequent blooms of toxic algae may also be related to eutrophication. In the
Baltic Proper, no major negative effects related to harmful algae have been ob-
served during phytoplankton blooms, although blue green algae, toxic to mam-
mals, have been found, e.g.
Nodularia spumigena, Anabaena lemmermanii, Micro-
10 INTRODUCTION
cystis aeruginosa, Aphanizomenon flos-aquae,
and also
Dinophysis acuminata,
D. norvegica
and
Prorocentrum minimum.
It has proved difficult to establish
trends in the abundance and biomass of zooplankton, mainly due to lack of long-
term measurements and to changes in sampling methodology. Distinctive, often
drastic, changes, which might be an indirect indication of the influence of euthro-
phication on Baltic marine life, were observed in benthic macroalgae and vascular
plant composition and distribution, during the 1970s. A decrease in water trans-
parency may explain the decrease in depth range of bottom plants. Such changes
were observed along the coasts of Latvia, Lithuania, Russia, Poland, Germany
and the southern coast of Sweden.
Fucus vesiculosus
communities underwent the
most drastic changes, and the community has vanished in some regions. In the
shallow littoral zone, many species of red and brown algae have become extinct,
e.g.
Fucus vesiculosus, Furcellaria lumbricalis.
Others, e.g. vascular plants such as
sea grass -
Zostera marina

occur within more limited areas. In their place, oppor-
tunistic green algae
(Enteromorpha intestinalis, Cladophora
sp.) and filamentous
red algae from the Ectocarpaceae genus
(Ectocarpus
and
PilayeUa)
have become
dominant (Falandysz et al., 2000).
Long-living bottom fauna also reflect the adverse effects of excessive nutrient
discharges to the marine environment. Bottom organisms depend on food of pe-
lagic origin. Increased sedimentation results in both positive and negative changes
in benthos. Positive effects include an increase in biomass and abundance of mac-
rozoobenthos observed in some regions above the halocline. Negative effects in-
clude a decrease in species diversity through elimination of species less resistant
to environmental changes and a concomitant increase in opportunistic species.
The most drastic, adverse changes are noted below the halocline. Long-term oxy-
gen deficits, resulting from increased sedimentation, caused changes in species
composition, domination structure, including, in some cases, even the total disap-
pearance of the macroscopic life on the bottom. In the first half of the twentieth
century, Bornholm, Gdansk and Gotland Basins were inhabited by numerous bot-
tom fauna species. The total extinction of macrozoobenthos on the Bornholm Ba-
sin bottom was observed for the first time in the early 1950. Presently, the bottom
of deeps below 70-80 rn depth, shows no signs of macroscopic life, and sediments
are covered by anaerobic bacteria. There is a lot to suggest that oxygen deficiency
in the deep water has contributed to low effectiveness of cod spawning. Cod may
hatch only in waters of 10-11 psu minimum salinity, which allows spawn to float
in pelagic zone. In less saline waters the cod eggs fall down to the bottom and
die. In the Bornholm Basin, where waters are sufficiently saline for effective

spawning, oxygen deficits occurring lately as a result of lack of inflows and
eutrophication, became a limiting factor in deep water zone (< 70 m). Also, ob-
served recently, decrease in salinity causing halocline uplift, which in turn, widens
the water layer not influenced by convection mixing, diminishes effectiveness of
cod spawning. In the shallow littoral zone, increasing sedimentation of organic
matter together with a lack of water mixing contribute to summer oxygen deft-