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Table 1. State variables modeled in MOSES. State variable Units Estuaries are characterized by a strong diversity in car­ bon sources. This is because of the existence of an 3 Fast-decay detritus g- intertidal habitat, the supply of nutrients and organic 3 Slow-decay detritus g- material from the river and from the sea and the input of 3 gCm- Freshwater diatoms matter from human origin. If turbidity remains limited, 3 Freshwater flagellates g- estuaries can also support a high primary production 3 Brackish and marine diatoms g- as nutrients are abundant. Nevertheless, estuaries are 3 Cm- Brackish and marine flagellates usually heterotrophic ecosystems (Billen et aI. , 1991; 3 gCm- Micro-zooplankton Smith & Hollibaugh, 1993) where respiratory process­ 3 Brackish meso-zooplankton gCm- 3 es exceed in situ production. Marine meso-zooplankton gCm- 2 3 gCm- The Westerschelde estuary (260 km in SAWES, Hyperbenthos 3 gSim- Detrital silicate 1991) drains about 21580 square kilometres ofland in 3 gSim- Dissolved silicate one of the most densely populated and highly industri­ 3 gNm- Nitrate and nitrite alised regions of Europe (Wollast, 1988). This estuary 3 gNm- Ammonia is unusual due to the high degree of eutrophication 3 gOm- Oxygen which results from the discharge of untreated wastes 3 gCl m- Chlorides (Heip, 1988) and due to the high residence time of the 3 gm- Suspended matter water masses (Soetaert & Herman, 1995a).

This volume of the Highlights of Astronomy contains the Invited Discourses and the proceedings or summaries of Joint Discussions, Special Sessions, and Working Group Meetings held at the XIInd IAU General Assembly in August 1994 in The Hague. While the three Invited Discourses are reproduced in the order of their appearance in the meeting programme, the Joint Discussions have been reordered according to their topics. Not included in this volume are the proceedings of the GA Symposia which will be published individually in the IAU Symposia series. I am most grateful to the authors of the invited discourses for preparing manuscripts in spite of heavy other commitments. It is a pleasure to express my appreciation of the work by Dr. Jacqueline Bergeron in organizing the XXIInd General Assembly, and I wish to thank all authors and meeting chairpersons for their cooperation and for providing their contributions in time to meet the customary publication schedule of this series. Special thanks are due to Ms. Monique Leger-Orine from the IAU office for considerable and patient assistance in the final editing, and to Dr. Tom Herbst from the Max­ Planck-Institute for Astronomy for permission to reproduce on the cover of this volume one of his IR images of Jupiter obtained just after the Comet Shoemaker-Levy 9 impact, one of the definite Highlights of Astronomy in 1994.

More than twenty years ago, as a fledgling graduate some peculiar aspects of the genetics of these student who was just starting to learn about these organisms but to pay respects to the two volumes of organisms that would become my primary research Carr of Whitton that played important roles in my focus, the publication of Noel Carr and Brian own thinking about cyanobacteria (and no doubt in Whitton's The Biology of the Blue-Green Algae in the development of many others as well). Contri­ 1973 was an event of great significance. Until the buting authors were asked to describe not only what appearance of this treatise, there was no single volume we know at present, but also to point out things we available that presented a broad overview of the don't know yet. I have attempted to assemble a book biology and biochemistry ofthese organisms. Nearly that would stimulate graduate students and other ten years later, I was privileged to be a contributing researchers in the same way that I wasaffected by the author to Carr and Whitton's sequel volume The books mentioned above. Biology of the Cyanobacteria. Although the It appears that cyanobacterial molecular biologists intervening period had been marked by heated debates have indeed paid attention to the admonition of their over the taxonomy and taxonomic position of the erstwhile colleague, W Ford Doolittle, to 'study organisms, it was also a time when the comparative those things that cyanobacteria do well.

For centuries the Roman Catholic Church has been concerned with the moral implications of medical practice. Indeed, until two decades ago, Catholic moral theologians were the major source of moral guidance, scholarly reflection and teaching on a variety of medical-moral topics, particularly those bearing on human life. Many, not only those within the Catholic communion, turned to the Church for guidance as each new possibility for altering the conditions of human life posed new challenges to long held moral values. Two decades ago, the center of gravity of ethical reflection shifted sharply from theologians and Christian philosophers to more secular thinkers. A confluence of forces was responsible for this metamorphosi- an exponential rate of increase in medical technologies, expanded education of the public, the growth of participatory democracy, the entry of courts and legislation into what had previously been private matters, the trend of morality towards pluralism and individual freedom and the depreciation of church and religious doctrines generally. Most significant was the entry of professional philosophers into the debate, for the first time. It is a curious paradox that, until the mid-sixties, professional philosophers largely ignored medical ethics. Today they are the most influential shapers of public and professional opinion.

From mulching to greenhouses, the air space between the cover and the soil surface is the key to the classification of climates under cover. The same mechanism governs environments produced by the various covers. This book describes and analyses all the different environments from mulching to greenhouses. The relationship between plants and environment is another important topic in the book. Stress is placed on the link between quantitative phenomena and qualitative analyses. Most phenomena involved are nonlinear and non-steady-state. An approach called System Dynamics is used, and simulation models developed in the simulation language CSMP are fully used. The subjects covered are of relevance to graduate students, to scientists and researchers in agriculture and biological sciences and, of course, to agricultural organizations in both the developing and developed countries.

G. MICHAUD Dipartement de Physique Universiti de Montrial c. P. 6128, succursale A Montrial, Que. , H3C 317 Canada The aim of IAU Symposium 145 was to use the photospheric abundances of the chemical elements to give us some hint of the past evolution and of the current structure of stars. At the invitation on the Bulgarian Academy o/Sciences, it brought together one hundred and fifty one scientists from 21 countries to 71atni Pjasaci (Golden Sands), Bulgaria, for a five day meeting. The processes discussed included accretion, mass loss, mass exchange, convection, turbulence, meridional circulation, and diffusion in addition to nuclear reactions. Observationally, spectroscopy was involved. New telescopes and instruments have considerably extended the scope of spectroscopy over the last few years. Space telescopes, such as IUE, have allowed the development of far UV spectroscopy. The access to the infrared has proven critical for probing cool stars. Large ground based telescopes have allowed fainter objects to be observed especially when they are equipped with more efficient detectors such as CCDs and Reticons. The co-adding of digitalized photographic plates has extended their usefulness. It has become possible to make high resolution, high signal to noise observations of objects that could only be observed at low resolution in former days. Weak lines can now be measured with accuracy, allowing the precise determination of the abundances of elements as rare as lithium and the determination of precise limits to isotopic ratios.

Much of the excitement in modern Solar Physics has come from the realisation that the Sun is a plasma and that this plasma is interacting with the magnetic field in a wide variety of subtle ways. As well as being of great interest in their own right the observed plasma phenomena on the Sun are of much wider importance, since they reveal to us details of basic phenomena that are expected to be occurring throughout the universe. It was with this in mind that 173 solar physicists from 17 countries gathered together in Bangalore with an air of anticipation. We were not disappointed as we received the warmest of welcomes from our graceful and charming host,Vinod Krishan. She and her colleagues worked tirelessly to make our stay a most memorable one and to ensure that the meeting ran with calm and efficiency. In addition to being stimulated by an excellent series of talks on the up-to-the­ minute advances in our subject, it was a pleasure to make new friendships from so many countries and to learn, in particular, of the Solar Physics being done in India which has a great tradition and is of a high standard. Furthermore, we enjoyed hearing about Indian culture and appreciating its beauty, especially on our day's tour into the countryside to visit some Hindu and Jain temples.

There has been a great advance in the understanding of processes of meta- morphism and of metamorphic rocks since the last edition of this book appeared. Methods for determining temperatures and pressures have become almost routine, and there is a wide appreciation that there is not a single temperature and pressure of metamorphism, but that rocks may preserve, in their minerals, chemistry and textures, traces of their history of burial, heating, deformation and permeation by fluids. However, this excit- ing new knowledge is still often difficult for non-specialists to understand, and this book, like the first edition, aims at enlightenment. I have concen- trated on the interpretation of the plate tectonic settings of metamorphism, rather than following a geochemical approach. Although there is an impress- ive degree of agreement between the two, I believe that attempting to discover the tectonic conditions accompanying rock recrystallization will more readily arouse the interest of the beginner. I have used a series of case histories, as in the first edition, drawing on my own direct experience as far as possible. This m