Multiple-tracer based characterisation of a river catch- ment in the Pamir Mountains Dissertation zur Erlangung des Doktorgrades der Naturwissenschaften (Dr. rer. nat.) der Naturwissenschaftlichen Fakultät III Agrar- und Ernährungswissenschaften, Geowissenschaften und Informatik der Martin-Luther-Universität Halle-Wittenberg vorgelegt von Frau Christiane Meier geb. am 25.12.1983 in Rodewisch 1. Gutachter: Prof. Dr. Ralf Merz 2. Gutachter: Prof. Dr. Michael Zech Tag der Verteidigung: 05.05.2020 Für meine Familie Acknowledgements i Acknowledgements Without the support of numerous persons and institutions this dissertation would not have been possible to realize it in this form. I would like to take this opportunity to express my sincere thanks for the many and varied experiences I have made. I would like to thank my PhD supervisor and first reviewer Prof. Dr. Ralf Merz, who has al- ways supported my work with patience and perseverance. Further, I would like to thank my second reviewer Prof. Dr. Michael Zech, for the intensive discussions in connection with my work, which helped me to answer questions from an- other point of view. My special thanks go to Dr. Stephan M. Weise - for the research project, the theme, the joint fieldwork, the professional talks, the patience and encouraging support. Without Dr. Karsten Osenbrück (WESS - University of Tübingen) and Dr. Michael Seitz (Goe- the-University Frankfurt) and their passion for transit times and lithium isotopes, respec- tively, I would not have been able to enter this exciting field of lithium isotopes and would not have been able to carry out the isotope measurements - thank you very much! I would also like to thank: Dr. Kay Knöller, Petra Blümel, Silke Köhler, Daniela Reichert, Gabriele Stams, Wolfgang Städter from the Department of Catchment Hydrology in Halle and Dr. Sybille Mothes, Dr. Hans-Joachim Stärk, Jürgen Steffen from the Department of Analytics in Leipzig for extensive measurements of water isotopes, major ions and trace elements and technical support in la- boratory work. Prof. Dr. Lothar Ratschbacher and Nicole Malz from the University of Ressources (TUBA) Freiberg for the bedrock samples and for the rock analyses. The group of Isotopegeochemistry at the Eberhard Karls University Tübingen, and the labor- atory of Isotopegeochemistry and Geochronology at the University of Freiberg for the possi- bility of strontium isotope measurements. The Institute of Environmental Physics at the Ruprecht-Karls-University of Heidelberg for Noble Gas Analysis. The Helmholtz Centre for Environmental Research - UFZ for the provision of all workplace resources including the particularly important and very good IT support by Detlef Russ, Bernd Herrmann and Kai Morlock. The Federal Ministry of Education and Research (BMBF) and the Helmholtz Interdiscipli- nary GRADuate School for Environmental Research (HIGRADE) for financial support. The PAMIR-water team, in particular Malte Knoche, Wolfgang Busch, Dr. Stefan Geyer and Dr. Eric Pohl for field work and fruitful discussions. Acknowledgements ii I would also like to thank: My „coffee team“ Dr. Karin Bräuer, Dr. Stephan Weise and Daniela Reichert for their persis- tent support - with coffee, cake, discussions, motivation. Dr. Cornelia Wilske, for all-embracing support, technical and personal discussions, labora- tory work, proofreading - partly from the other side of the world. My PhD comrades and friends Dr. Christin Müller, Dr. Christina Jeschke, Dr. Jana Schmidt, Dr. Ulf Mallast - it was fun to do a doctorate with you, to discuss, to laugh, to go to conferences. My student colleagues Maria Brehme, Tobias Hartmann and Julianna Regenauer for their very good cooperation - especially as substitutes during my parental leave. All my friends and my colleagues at the German Environment Agency for their encouraging words and support during my PhD sabbatical. My special thanks go to my parents, brother with family, parents-in-law and grandparents, who always supported my work with great interest. The greatest thanks go to my husband and my children, without their motivation, tireless support this study would not have been possible. This study is dedicated to A.M., L.A.M., F.J.M.. Abstract iii Abstract The Pamir Mountains in Tajikistan are part of a semi- to cold-arid mountain region in Cen- tral Asia. Its snow and glacier deposits are the source of one of the largest Central Asian riv- ers - the Amu Darya. The development of the further availability of these important fresh water resources depending on high impact from factors such as climate change is in the cen- tral focus of this study. For this, the actual hydrological condition of the high-alpine catch- ment of the Gunt river is supposed exemplary for the Pamir. By application of hydrochemical tracers (major ions and physico-chemical parameters) and isotope hydrological methods ( 2H, 3H, 18O, 7Li, 87Sr/86Sr, noble gases) basic hydrological processes are identified and described. This multi-tracer approach allows to get a detailed picture on the flow regime and δ δ δ chemical evolution of the river water of two to three circles of season and gives the fact that the catchment area of the Gunt is a geomorphologically young catchment area, which reacts fast on hydrological changes due to its climatically, geological and geomorphological condi- tions. There are clear regional and seasonal variations in all investigated parameters. The catchment area can be subdivided into northern catchment areas, southern catchment areas, the eastern plateau, which is mainly characterized by the lake Yashilkul and the main river Gunt collecting all hydrogeochemical signals. In data of the 18O and 2H values and the ma- jor anions and cations, a clear annual cycle is recognizable. This has shown that snow melt- δ δ ing and glacier melting are the dominant processes for runoff formation and that runoff is less strongly fed by large groundwater deposits. By determining the transit time with 3H/3He, it became clear that at exemplary cold springs the transit time is less than two years, and in wells in the steep northern subcatchments and in the southern subbasins and the Gunt river itself the transit time is less than ten years. Only the hot springs show transit times of at least twenty years and more. Therefore, it can be assumed that the meltwater is not strongly retained in deeper aquifers. The glaciers in the catchment area of the Gunt are also affected by strong melting processes. This in turn would mean that the investigated catchment is very sensitive to any changes of water input from the available current glacier decreases and the current meteorological circulations containing poor precipitation from the Atlantic, the Mediterranean, the Caspian Sea and the Persian Gulf and it also would be affected by increasing water scarcity in the next decades. Zusammenfassung iv Zusammenfassung Das Pamirgebirge in Tadschikistan ist Teil einer semi- bis kaltariden Bergregion in Zentrala- sien. Seine Schnee- und Gletscherablagerungen sind die Quelle eines der größten zentralasi- atischen Flüsse - des Amu Darya. Die Entwicklung der weiteren Verfügbarkeit dieser wichti- gen Süßwasserressourcen in Hinblick auf bevorstehende Veränderungen durch den Klima- wandel steht im Mittelpunkt dieser Studie. Dazu wird der tatsächliche hydrologische Zu- stand des hochalpinen Einzugsgebietes des Gunt Flusses exemplarisch für den Pamir be- schrieben. Durch den Einsatz von hydrochemischen Tracern (Hauptionen und physikalisch- 18 2 7Li, 87Sr/86Sr, 3H/3He) werden grundlegende hydrologische Prozesse identifiziert und beschrieben. Dieser chemische Parameter) und isotopenhydrologischen Methoden (δ O, δ H, δ Multi-Tracer-Ansatz ermöglicht es, ein detailliertes Bild über das Abflussregime und die che- mische Entwicklung des Flusswassers über zwei bis drei hydrologische Jahre zu erhalten und zeigt, dass das Einzugsgebiet des Gunt ein geomorphologisch junges Einzugsgebiet ist, das aufgrund seiner klimatischen, geologischen und geomorphologischen Bedingungen schnell reagiert. Bei allen untersuchten Parametern gibt es deutliche regionale und saisonale Schwankungen. Das Einzugsgebiet lässt sich klar unterteilen in nördliche Einzugsgebiete, südliche Einzugsgebiete, das östliche Plateau, welches hauptsächlich durch den See Yashil- kul geprägt ist, und den Hauptfluss Gunt, der alle Si 18O 2H Werten sowie in den Hauptan- und kationen ist ein klarer Jahreszyklus erkennbar. gnale in sich vereint. Sowohl in den δ Dies zeigt, dass Schnee- und Gletscherschmelze die dominierenden Prozesse für die Abfluss- und δ bildung sind und dass der Abfluss weniger stark von großen Grundwasservorkommen ge- speist wird. Durch die Bestimmung der Verweilzeit mit 3H/3He wird deutlich, dass die mitt- lere Verweilzeit an ausgewählten kalten Quellen und Brunnen der steilen nördlichen Tei- leinzugsgebiete weniger als zwei Jahre beträgt sowie in den südlichen Einzugsgebieten und dem Fluss Gunt selbst die mittlere Verweilzeit weniger als zehn Jahre beträgt. Nur die hei- ßen Quellen weisen durchschnittliche Verweilzeiten von mindestens zwanzig Jahren und mehr auf. Daher ist davon auszugehen, dass das Schmelzwasser nicht in tieferen Grundwas- serleitern stark zurückgehalten wird. Auch die Gletscher im Einzugsgebiet des Gunt sind von starken Schmelzprozessen betroffen. Dies wiederum bedeutet, dass das untersuchte Ein- zugsgebiet sehr empfindlich auf Veränderungen der hydrologischen Rahmenbedingungen, wie zum Beispiel das Abschmelzen der Gletscher und die aktuellen meteorologischen