ENVIRONMENTAL ISOTOPES HYDROLOGICAL CYCLE

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1 ENVIRONMENTAL ISOTOPES in the HYDROLOGICAL CYCLE Principles and Applications W. G. Mook editor VOLUME I INTRODUCTION THEORY METHODS REVIEW by Willem G Mook Centre for Isotope Research Groningen

2 The designations employed and the presentation of material throughout the publication do not imply the expression of any opinion whatsoever on the part of UNESCO and/or IAEA concerning the legal status of any country, territory, city, or its authorities, or concerning the delimitation of its frontiers or boundaries. SC-2000/WS/58

3 UNESCO/IAEA Series on Environmental Isotopes in the Hydrological Cycle Principles and Applications Volume I Volume II Volume III Volume IV Volume V Volume VI Introduction: Theory, Methods, Review Atmospheric Water Surface Water Groundwater: Saturated and Unsaturated Zone Man's Impact on Groundwater Systems Modelling Ar H He C Kr C ENVIRONMENTAL ISOTOPES in the HYDROLOGICAL CYCLE H O C N S He Ar Contributing Author J.J.de Vries, Free University, Amsterdam

4 PREFACE The availability of freshwater is one of the great issues facing mankind today - in some ways the greatest, because problems associated with it affect the lives of many millions of people. It has consequently attracted a wide scale international attention of UN Agencies and related international/regional governmental and non-governmental organisations. The rapid growth of population coupled to steady increase in water requirements for agricultural and industrial development have imposed severe stress on the available freshwater resources in terms of both the quantity and quality, requiring consistent and careful assessment and management of water resources for their sustainable development. More and better water can not be acquired without the continuation and extension of hydrological research. In this respect has the development and practical implementation of isotope methodologies in water resources assessment and management been part of the IAEA s programme in nuclear applications over the last four decades. Isotope studies applied to a wide spectrum of hydrological problems related to both surface and groundwater resources as well as environmental studies in hydro-ecological systems are presently an established scientific discipline, often referred to as Isotope Hydrology. The IAEA contributed to this development through direct support to research and training, and to the verification of isotope methodologies through field projects implemented in Member States. The world-wide programme of the International Hydrological Decade ( ) and the subsequent long-term International Hydrological Programme (IHP) of UNESCO have been an essential part of the well recognised international frameworks for scientific research, education and training in the field of hydrology. The International Atomic Energy Agency (IAEA) and UNESCO have established a close co-operation within the framework of both the earlier IHD and the ongoing IHP in the specific aspects of scientific and methodological developments related to water resources that are of mutual interest to the programmes of both organisations. The first benchmark publication on isotope hydrology entitled Guidebook on Nuclear Techniques in Hydrology was realised in 1983 through the activity of the joint IAEA/UNESCO Working Group on Nuclear Techniques established within the framework of IHP, and it has been widely used as practical guidance material in this specific field. In view of the fact that the IHP s objectives include also a multi-disciplinary approach to the assessment and rational management of water resources and taking note of the advances made in isotope hydrology, the IAEA and UNESCO have initiated a joint activity in

5 preparation of a series of six up-to-date textbooks, covering the entire field of hydrological applications of natural isotopes (environmental isotopes) to the overall domain of water resources and related environmental studies. The main aim of this series is to provide a comprehensive review of basic theoretical concepts and principles of isotope hydrology methodologies and their practical applications with some illustrative examples. The volumes are designed to be self-sufficient reference material for scientists and engineers involved in research and/or practical applications of isotope hydrology as an integral part of the investigations related to water resources assessment, development and management. Furthermore, they are also expected to serve as Teaching Material or text books to be used in universities and teaching institutions for incorporating the study of "isotopes in water" in general into the curriculum of the earth sciences. Additionally the contents can fulfil the need for basic knowledge in other disciplines of the Earth Sciences dealing with water in general. These six volumes have been prepared through efforts and contributions of a number of scientists involved in this specific field as cited in each volume, under the guidance and coordination of the main author/co-ordinating editor designated for each volume. W.G.Mook (Netherlands), J.Gat (Israel), K.Rozanski (Poland), W.Stichler (Germany), M.Geyh (Germany), K.P.Seiler (Germany) and Y.Yurtsever (IAEA, Vienna) were involved as the main author/co-ordinating editors in preparation of these six volumes, respectively. Final editorial work on all volumes aiming to achieve consistency in the contents and layout throughout the whole series was undertaken by W.G.Mook (Netherlands). Mr.Y. Yurtsever, Staff Member of the Isotope Hydrology Section of the IAEA; and Ms. A. Aureli, Programme Specialist, Division of Water Sciences of UNESCO, were the Scientific Officers in charge of co-ordination and providing scientific secretariat to the various meetings and activities that were undertaken throughout the preparation of these publications. The IAEA and UNESCO thank all those who have contributed to the preparation of these volumes and fully acknowledge the efforts and achievements of the main authors and coordinating editors. It is hoped that these six volumes will contribute to wider scale applications of isotope methodologies for improved assessment and management of water resources, facilitate incorporation of isotope hydrology into the curricula of teaching and education in water sciences and also foster further developments in this specific field. Paris / Vienna, March 2000

6 PREFACE TO VOLUME I The first volume in the series of textbooks on the environmental isotopes in the hydrological cycle is the result of a re-orientation and in part extension of the lecture notes I used during the years I was teaching the hydrology students of the Free University of Amsterdam an annual course in Isotope Hydrology. During these years my colleague and friend, Joe Pearson, and I set ourselves to publish the lecture notes, but did not find the time for the accomplishment of this task. Now I have come to realise how much he taught me and I gratefully acknowledge those days. The need for international agreement on definitions and the use of symbols can not be sufficiently emphasised. In this introductory volume I have aimed at consistency as well as mathematical and physical correctness. However, it is unavoidable that, for historical reasons, the same consistency could not be continued in all subsequent volumes. The second important aim of this volume has been to present no equations dealing with isotopes without the proper and understandable mathematical derivation. After an introductory chapter on the hydrological cycle, this volume contains the principles of radioactivity and of the isotope effects for stable isotopes. The elements of hydrogen, carbon and oxygen are being treated in detail, as they form the "heart" of isotopic applications in the water cycle. The contribution of the other isotopes is discussed less extensively in this volume. Concrete isotopic applications in hydrology, here only touched at in an illustrative manner, have become greatly expanded by my colleagues in the next volumes. We felt that it is preferable that subjects of more general interest to the other volumes, such as the aqueous chemistry of inorganic carbon, the treatment of water samples in the field and in the laboratory, the techniques of isotopic analyses, the statistical treatment of data, should be treated in the first volume. This series of 6 volumes are meant to be textbooks. This leads to certain requirements different from the existing handbooks. Especially in this introductory volume I have kept the number of references to literature minimal, in favour of the readability of the text.

7 I owe much gratitude to the "former" co-workers of "my lab" for their assistance in reading the manuscript, making many corrections, pointing out subjects that were failing and explanations that could not well be understood, in short for their continuing hospitality. To my colleagues co-authors of this series I want to express my appreciation for our highly stimulating and pleasant co-operation. Groningen, 29 February 2000 Willem G Mook

8 CONTENTS 1 THE GLOBAL CYCLE OF WATER Introduction The hydrosphere Origin of water on earth The hydro-tectonic cycle Distribution of water over the various reservoirs The global water budget Components of the hydrological cycle Evaporation Precipitation and atmospheric circulation Discharge from the continents Groundwater Continental water surplus and water use The hydrosphere and global change Climatic change The human factor Irrigation Wetland drainage Ground cover damage Deforestation Interbasin diversion Streamflow management Land use changes Isotopes in the hydrological cycle ATOMIC SYSTEMATICS AND NUCLEAR STRUCTURE Atomic structure and periodic table of the elements Structure of the atomic nucleus Stable and radioactive isotopes Mass and energy ABUNDANCE AND FRACTIONATION OF STABLE ISOTOPES Isotope ratios and concentrations Isotope fractionation Kinetic and equilibrium isotope fractionation Theoretical background of equilibrium fractionation... 39

9 3.5 Fractionation by diffusion Relation between atomic and molecular isotope ratios Relation between fractionations for three isotopic molecules ABUNDANCE VARIATIONS BY NATURAL PROCESSES Use of δ values and isotope references Tracer concentration, amount of tracer Mixing of reservoirs with different isotopic composition Mixing of reservoirs of the same compound Isotopic dilution analysis Mixing of reservoirs of different compounds Isotopic changes in Rayleigh processes Reservoir with one sink Reservoir with two sinks Reservoir with one source and one sink, as a function of time Reservoir with one source and one sink, as a function of mass Reservoir with two sources and sinks, with and without fractionation 64 5 RADIONUCLIDE DECAY AND PRODUCTION Nuclear instability Nuclear decay and radiation Negatron decay Positron decay Electron capture Alpha decay Spontaneous and induced fission, neutron emission Recoil by radioactive decay Nuclear reactions Natural production Anthropogenic releases of radionuclides EQUATIONS OF RADIOACTIVE DECAY AND GROWTH Law of radioactive decay Half-life and mean life Activity, specific activity and radionuclide concentration Mixture of independent radioactivities Branching decay Radioactive decay series Secular equilibrium Transient equilibrium No-equilibrium Accumulation of stable daughter product... 85

10 6.8 Radioactive growth NATURAL ABUNDANCE OF THE STABLE ISOTOPES OF C, O AND H Stable carbon isotopes The natural abundance Carbon isotope fractionations Reporting 13 C variations and the 13 C standard Survey of natural 13 C variations Atmospheric CO Seawater and marine carbonate Vegetation and soil CO Fossil fuel Global carbon cycle Groundwater and riverwater Stable oxygen isotopes The natural abundance Oxygen isotope fractionations Reporting 18 O variations and the 18 O standards Survey of natural 18 O variations Seawater Precipitation Surface water Climatic variations Relation between 13 C and 18 O variations in H 2 O, HCO 3, and CO Stable hydrogen isotopes The natural abundance Hydrogen isotope fractionations Reporting 2 H variations and the 2 H standard Survey of natural 2 H variations Relation between 2 H and 18 O variations in water NATURAL ABUNDANCE OF RADIOACTIVE ISOTOPES The radioactive carbon isotope Origin of 14 C, decay and half-life Reporting 14 C variations and the 14 C standard Survey of natural 14 C variations Atmospheric CO Vegetation and soils Seawater and marine carbonate Groundwater C age determination Dating groundwater Dating groundwater with DIC

11 The origin of 14 C in DIC The chemical/isotopic mass balance Isotopic exchange in an open system Dating groundwater with DOC Relation between 13 C and 14 C variations The radioactive hydrogen isotope Origin of 3 H, decay and half-life Reporting 3 H activities and the 3 H standard Survey of natural 3 H variations Comparison of 3 H and 14 C variations Relation between 3 H and 14 C in the atmosphere Relation between 3 H and 14 C in groundwater CHEMISTRY OF CARBONIC ACID IN WATER Introduction Carbonic acid equilibria The equilibrium constants Ideal solutions Seawater Brackish water Carbonic acid concentrations Examples for closed and open systems Comparison of freshwater and seawater exposed to the atmosphere For freshwater For seawater System open for CO 2 escape and CaCO 3 formation Starting conditions Escape of CO Precipitation of CaCO System exposed to CO 2 in the presence of CaCO Closed system, mixing of freshwater and seawater WATER SAMPLING AND LABORATORY TREATMENT Water sampling and storage Sampling bottles General field practice Precipitation Surface water Unsaturated zone water Groundwater Geothermal water Laboratory treatment of water samples The 18 O/ 16 O analysis of water

12 Equilibration with CO 2 for mass spectrometric analysis Other methods The 2 H/ 1 H analysis of water Reduction of H 2 O to H 2 for mass spectrometric analysis Other methods The 3 H analysis of water Water purification H enrichment Preparation of gas for PGC of 3 H The 14 C analysis of dissolved inorganic carbon In the field In the laboratory The 13 C/ 12 C analysis of dissolved inorganic carbon MEASURING TECHNIQUES Mass spectrometry for stable isotopes Physical principle Reporting stable isotope abundance ratios Measurement of 2 H/ 1 H in H Measurement of 15 N/ 14 N in N Measurement of 13 C/ 12 C and 18 O/ 16 O in CO Comparison with machine reference Calibration Isotopic corrections O correction for water CO 2 equilibration Normalisation Measurement of 18 O/ 16 O and 17 O/ 16 O in O Radiometry for radioactive isotopes Gas counters Ionisation chamber Proportional counter Geiger Müller counter Counter operation Liquid scintillation spectrometer Physical principle Counter operation Mass spectrometry for low-abundance isotopes Principle and application of AMS Reporting 14 C activities and concentrations The choice of variables The standardisation The question of isotope fractionation The question of radioactive decay

13 Definition of the 14 C standard activity Final definitions Special cases Hydrology Oceanography and atmospheric research Geochemistry Enhanced 14 C radioactivity C ages Summary NATURAL ISOTOPES OF ELEMENTS OTHER THAN H, C, O Helium Origin and characteristics Experimental and technical aspects Sources of 3 He Natural abundance Applications Principle of 3 H/ 3 He dating Mass spectrometric measurement of 3 H through 3 He Lithium Natural abundance Experimental and technical aspects Applications Beryllium Origin and characteristics Experimental and technical aspects Natural abundance Applications Boron Natural abundance Experimental and technical aspects Applications Nitrogen Experimental and technical aspects Natural abundance and isotope fractionation Applications O/ 16 O in nitrate Aluminium Origin and characteristics Experimental and technical aspects Natural abundance Applications Silicon Origin and characteristics

14 Natural abundance Experimental and technical aspects Applications Sulphur Experimental and technical aspects Natural abundance Applications Chlorine Radioactive 36 Cl Origin and characteristics Experimental and technical aspects Abundance in nature Applications Dating old water Infiltration of young water Stable 35 Cl and 37 Cl Natural abundance and applications Experimental and technical aspects Argon Origin and characteristics Experimental and technical aspects Natural abundance Applications Krypton Origin and characteristics Experimental and technical aspects Natural abundance Applications Iodine Origin and characteristics Experimental and technical aspects Natural abundance Applications Decay series The uranium series U/ 234 U Th 234 U dating Ra and 222 Rn Pb Experimental and technical aspects The actinium series The thorium series

15 13 ERRORS, MEANS AND FITS Errors Precision and accuracy Definitions Significant figures and digits Uncertainties Instrumental uncertainties Mean values Distribution of data Standard deviation Precision of data Precision of the mean Statistical uncertainties Error propagation Standard deviation Weighted mean Least-squares fit Fit to a straight line Fit to non-linear curves Chi-square test REFERENCES 257 LITERATURE 263 IAEA PUBLICATIONS 265 CONSTANTS 268 SYMBOLS AND UNITS 269 SUBJECT INDEX 271

UNIT 10 RADIOACTIVITY AND NUCLEAR CHEMISTRY

UNIT 10 RADIOACTIVITY AND NUCLEAR CHEMISTRY student version www.toppr.com Contents (a) Types of Radiation (b) Properties of Radiation (c) Dangers of Radiation (d) Rates of radioactive decay (e) Nuclear