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Migration processes of _1hn1_1hn3_1hn7Cs in the drinking water reservoir Lago Maggiore [Elektronische Ressource] : measurements and modeling / von Viktoryia Putyrskaya

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229 pages
137Migration processes of Cs in the drinking water reservoir Lago Maggiore: Measurements and Modeling DISSERTATION Zur Erlangung des akademischen Grades Doctor rerum naturalium (Dr. rer. nat.) vorgelegt: der Fakultät Mathematik und Naturwissenschaften der Technischen Universität Dresden von Viktoryia Putyrskaya geboren am 05.06.1980 in Vileika, Belarus Gutachter: Prof. Dr. habil. Gert Bernhard Prof. Dr. Eckehard Klemt Eingereicht am: 19.05.2010 Tag der Verteidigung: 22.10.2010 ABSTRACT 137Artificial Cs has been introduced into the environment for more than half a century. Its first appearance in central European lake sediments corresponds to the nuclear weapons testing in the 1960s. The largest contamination of European lakes and rivers occurred as a consequence of the fallout after the Chernobyl accident in spring 1986. In this work the 137migration behaviour of artificial Cs in Lago Maggiore and other pre-alpine lakes as a consequence of these fallouts was studied. Lago Maggiore is one of the largest drinking water reservoirs in the south of the Alps. -2 137After the Chernobyl accident roughly 20 kBq·m of Cs were deposited onto the lake surface. From 2003 to 2005 bottom sediment cores and water samples were collected at 7 137different locations of Lago Maggiore.
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137
Migration processes of Cs in the drinking water reservoir
Lago Maggiore: Measurements and Modeling



DISSERTATION

Zur Erlangung des akademischen Grades

Doctor rerum naturalium
(Dr. rer. nat.)

vorgelegt:
der Fakultät Mathematik und Naturwissenschaften
der Technischen Universität Dresden

von
Viktoryia Putyrskaya

geboren am 05.06.1980 in Vileika, Belarus



Gutachter: Prof. Dr. habil. Gert Bernhard
Prof. Dr. Eckehard Klemt


Eingereicht am: 19.05.2010
Tag der Verteidigung: 22.10.2010


ABSTRACT
137Artificial Cs has been introduced into the environment for more than half a century. Its
first appearance in central European lake sediments corresponds to the nuclear weapons
testing in the 1960s. The largest contamination of European lakes and rivers occurred as a
consequence of the fallout after the Chernobyl accident in spring 1986. In this work the
137migration behaviour of artificial Cs in Lago Maggiore and other pre-alpine lakes as a
consequence of these fallouts was studied.
Lago Maggiore is one of the largest drinking water reservoirs in the south of the Alps.
-2 137After the Chernobyl accident roughly 20 kBq·m of Cs were deposited onto the lake
surface. From 2003 to 2005 bottom sediment cores and water samples were collected at 7
137
different locations of Lago Maggiore. Data on the Cs distribution in tributaries, lake
137
water, suspended matter, bottom sediments, and the Cs association to different
geochemical fractions are presented in this work.
137
To model the run-off of Cs from the watershed into the lake a compartment model was
137used. For modeling the input of Cs into and the vertical distribution within the
sediment a diffusion–convection type model was developed. This model takes into
account the uptake of activity by sedimentation, fixation and redissolution, retarded
diffusion, the influence of competing ions on the retarded diffusion within the sediments,
and compaction of sediments. The results of the parameter optimization – mainly the
137
sedimentation rate and the Cs distribution coefficient K , which determines the uptake d
of activity into the sediment – are discussed and compared with those of other European
137lakes characterized by similar Cs deposition levels but different limnological
properties.
137To estimate the bioavailability of Cs, its activity concentrations in fish samples from
Lago Maggiore were measured. Combining the existing data with our measurements,
137Cs fish–water concentration ratios were calculated and compared with those for other
137lakes which were affected by similar Cs contamination.


iii ZUSAMMENFASSUNG
137Das künstliche Radionuklid Cs wurde seit über einem halben Jahrhundert in die Natur
eingebracht. Sein erstes Erscheinen in Sedimenten der zentraleuropäischen Seen
korrespondiert mit den Nuklearwaffentests in den 60er-Jahren des 20. Jahrhunderts. Die
stärkste Kontaminierung der europäischen Seen und Flüsse entstand als Folge des
radioaktiven Niederschlags nach dem Unfall in Tschernobyl im Frühjahr 1986. In dieser
137Arbeit wurde das Migrationsverhalten des künstlichen Cs im Lago Maggiore und
anderen Seen im Alpenvorland als Folge dieses Niederschlags untersucht.
Der Lago Maggiore zählt zu den größten Trinkwasserreservoiren südlich der Alpen. Nach
-2 137dem Unfall in Tschernobyl gingen ungefähr 20 kBq·m des Cs auf die Oberfläche des
Sees nieder. Im Zeitraum von 2003 bis 2005 wurden Sedimentkerne und Wasserproben
an sieben unterschiedlichen Stellen des Lago Maggiore entnommen. Diese Arbeit
137beschäftigt sich mit Daten über die Verteilung des Cs in den Zuflüssen, dem Wasser
137des Sees, in Schwebstoffen und Bodensedimenten und mit der Assoziierung von Cs
mit verschiedenen geochemischen Fraktionen.
137Um den Abfluss des Cs aus dem Wassereinzugsgebiet in den Fluss zu modellieren,
wurde ein Compartmentmodell verwendet. Zur Modellierung der Aufnahmemenge von
137
Cs im Sediment und der vertikalen Verteilung innerhalb dessen wurde ein Diffusions-
Konvektions-Modell entwickelt. Dieses Modell berücksichtigt die Aufnahme von
Aktivität durch Sedimentation, Fixierung und Rücklösung, retardierte Diffusion, die
Verdichtung des Sediments sowie den Einfluss konkurrierender Ionen auf die retardierte
Diffusion innerhalb des Sediments. Die Ergebnisse der Parameteroptimierung – im
137Wesentlichen die Sedimentationsrate und der Cs-Verteilungskoeffizient K , welcher d
die Aufnahme der Aktivität in das Sediment determiniert – werden erörtert und mit denen
137
anderer europäischer Seen, die eine ähnliche Cs-Deposition, aber unterschiedliche
limnologische Eigenschaften aufweisen, verglichen.
137 137Zur Beurteilung der Bioverfügbarkeit von Cs wurde die Cs-
Aktivitätskonzentrationen von Fischproben aus dem Lago Maggiore gemessen. Aus
137bereits existierenden Daten und unseren Messergebnissen wurden Cs Fisch-Wasser
Konzentrations-Verhältnisse errechnet und mit denen für andere Seen, die von ähnlichen
137
Cs-Kontaminationen betroffen sind, verglichen.
v
TABLE OF CONTENT

LIST OF SYMBOLS ................................................................................ xi
GLOSSARY ............................................................................................. xv
INTRODUCTION ..................................................................................... 1
1. RADIOCAESIUM IN THE ENVIRONMENT.................................... 5
1.1 Sources of radiocaesium in the environment ............................................................ 5
1.2 Chemical properties of radiocaesium........................................................................ 7
1.2.1 Binding of radiocaesium on clay minerals ........................................................ 7
1.2.2 Binding of radiocaesium on humic substances................................................ 10
2. CHARACTERISTICS OF LAGO MAGGIORE............................... 13
2.1 Origin and morphology........................................................................................... 13
2.2 Hydrological and geological features of the drainage basin................................... 15
2.3 Climatic and meteorological characteristics ........................................................... 18
2.4 Knowledge on the present radioecological situation .............................................. 20
3. MATERIALS AND METHODS......................................................... 21
3.1 Description of sampling positions .......................................................................... 21
3.2 Lake water sampling............................................................................................... 23
3.2.1 Sampling of water and suspended matter with the “Midiya” system.............. 23
3.2.2 Pore water sampling........................................................................................ 26
3.2.3 Temperature, pH, oxygen concentration measurements.................................. 26
3.2.4 Distribution coefficient and competing ions.................................................... 27
3.3 Sediment sampling.................................................................................................. 29
3.3.1 Sampling of sediments with a gravity corer..................................................... 29
3.3.2 Sediment samples preparation for gamma-spectrometry ................................ 30
3.4 Gamma-spectrometric analyses with BEGe detectors and LabSOCS.................... 34
1373.5 Particle-size analysis and sequential extraction of Cs ........................................ 36
vii Table of content

3.5.1 Grain-size distribution analysis....................................................................... 36
3.5.2 Sequential extraction of caesium ..................................................................... 37
2103.6 Determining the age of sediments using Pb method........................................... 40
3.6.1 CRS and CIC approaches ................................................................................ 42
137 241
3.6.2 Cs and Am method ................................................................................... 43
4. MONITORING OF WATER AND SEDIMENTS IN LAGO
MAGGIORE ............................................................................................ 45
4.1 Water measurements............................................................................................... 45
137
4.1.1 Concentration of dissolved and particulate Cs in Lago Maggiore and its
tributaries.................................................................................................................. 46
4.1.2 Temperature, pH and dissolved oxygen concentration.................................... 48
4.1.3 Competing ions ................................................................................................ 48
4.1.4 Measured distribution coefficient K ............................................................... 51 d
1374.1.5 Other measurements of Cs in water of Lago Maggiore and its tributaries. 52
137 2104.2 Vertical Cs and Pb distributions in the sediments .......................................... 56
4.2.1 Measured vertical distributions of activity concentration and bulk density of
sediment cores from different positions .................................................................... 56
4.2.2 Introduction of turbidites................................................................................. 65
4.2.3 Discussion on the vertical distributions........................................................... 67
4.3 Association of radiocaesium to different geo-chemical fractions........................... 71
4.3.1 Grain-size distribution of sediments and organic matter content ................... 71
137
4.3.2 Sequential extraction of Cs in the sediment................................................. 73
4.3.3 Classification of positions................................................................................ 76
210
4.4 Dating of sediment with Pb................................................................................. 79
210
4.4.1 Results and discussion on Pb dating............................................................ 79
4.4.2 General conclusions on dating the sediments.................................................. 89
5. MODELING OF RADIOCAESIUM IN WATER AND SEDIMENTS
OF LAGO MAGGIORE ......................................................................... 91
5.1 Main processes in the “diffusion-convection” type model..................................... 92
viii Table of content
5.1.1 Sorption............................................................................................................ 92
5.1.2 Sedimentation and compaction........................................................................ 95
5.1.3 Diffusion and turbation.................................................................................... 97
5.1.4 Radioactive decay .......................................................................................... 102
5.1.5 Complete system of coupled differential equations ....................................... 103
5.2 Initial and boundary conditions ............................................................................ 104
5.2.1 Initial conditions ............................................................................................ 104
5.2.2 Boundary conditions ...................................................................................... 104
5.4 Introduction of turbidites ...................................................................................... 111
5.5 Finite-element method for modeling the radionuclides in the sediment............... 112
5.6 Results of modeling radiocaesium in the sediments of Lago Maggiore from
different positions ....................................................................................................... 113
5.7 Discussion on modeling: Free and dependent fit parameters ............................... 126
137
5.8 Comparison of Cs behaviour in Lago Maggiore and other European lakes..... 131
1375.8.1 Cs in lake water ......................................................................................... 132
1375.8.3 Cs in sediments .......................................................................................... 134
5.9 General conclusions on modeling......................................................................... 136
6. RADIOCAESIUM ACTIVITY CONCENTRATION IN FISH.......139
137
6.1 Dynamic model for Cs uptake by fish and the concentration ratio................... 139
137
6.2 Cs in fish from different lakes .......................................................................... 141
137
6.3 Cs in fish in Lago Maggiore ............................................................................. 143
CONCLUSIONS .....................................................................................149
ACKNOWLEDGEMENTS....................................................................153
REFERENCES .......................................................................................155
LIST OF PUBLICATIONS RELEVANT TO THE THESIS ..............167
APPENDIX A: Activity concentration of radionuclides in the sediments of Lago
Maggiore.....................................................................................................171
APPENDIX B: Bulk density of the sediments of Lago Maggiore.......................200
ix Table of content

APPENDIX C: Results of grain-size distribution analyses................................203
APPENDIX D: Results of 5-step sequential extraction procedure ......................204
APPENDIX E: Constant rate of supply model for sediment dating.....................205
APPENDIX F: Example of modeling: Mathematical code for Matlab.................208
x

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