Cécile-Marie Dupin

Mélanie Pinon

Karine Jaggi

Celina Teixera

Aurèle Sagne

Noelia Delicado

Public health nursing education viewed through the lens of superdiversity: a resource for global health

Keywords: Bologna process, Competencies, Diversity, Global Health, Nursing curricula

Background: Nurses are increasingly confronted with the challenge of globalization and the acceleration of migratory flows. This reality affects the notion of culture and its influence on health-related behaviors. The state of health of the population in the Canton of Geneva, where there is a wide diversity of origins, is characterized by significant differences. The term "superdiversity" is used to describe the increasing complexity in ethnic diversity due to migration and social stratification. Nursing education in Geneva, influenced by the Bologna Process, appears appropriate for superdiverse contexts of care, with the development of dedicated competencies. Aim: This discussion paper aims to examine the academic curricula implemented in Geneva in the light of the concept of superdiversity. Main text: In Geneva, nursing education and curricula in public health are based on a competence framework for nursing care divided into 7 roles and educational tracks. Bachelor's-level nurses know how to assess a care problem quickly and solve it effectively by setting relevant priorities, and do so based on evidence. The curricula aim to teach nurses to design population and individual interventions in their superdiverse context.

Discussion: Education should enable students to develop their role as health promoters for the well-being of patients and communities, taking into account cultural complexity. Conclusions: Superdiverse contexts highlight the role of nurse educators in preparing future generations of public health nurses.

Background

From vocational to academic nursing programs

The nursing profession has experienced fundamental transitions and transformations over the past 50 years. Faced with the health care needs of the twenty-first century [START_REF] Wood | Foundation Initiative on the Future of Nursing[END_REF], it is difficult to see how nurses could develop essential skills (providing patient-centered care, working in interdisciplinary teams, improving the quality of continuous care, using information systems, and evidencebased practice) without the benefit of university education [START_REF] Norman | Nursing must be a graduate profession (well, he would say that, wouldn't he!)[END_REF]. Amid the academic evolution of nursing in Europe, the Bologna Process aims to harmonize higher education by converging towards a common European system, in which different national systems share Bachelor's, Master's, and Doctorate degrees [START_REF] Spitzer | Reforms in nursing education across Western Europe: from agenda to practice[END_REF][START_REF] Spitzer | Reforms in nursing education across Western Europe: implementation processes and current status[END_REF][START_REF] Zabalegui | Changes in nursing education in the European Union[END_REF]. Historically, European higher education was reserved for the upper classes and had no place for schools of nursing. Previously, nurses were typically trained at the vocational level and obtained their education at institutions other than higher education entities [START_REF] Collins | The impact of the Bologna process on nursing higher education in Europe: a review[END_REF]. Switzerland is one such European country, where nursing education has only recently begun to evolve from vocational education into undergraduate and graduate education, aided by the Bologna Process. Such transitions aim to facilitate the integration of scientific knowledge into clinical practice, an approach known as Evidence-Based Practice (EBP). The premise of EBP is that rather than focusing their practice solely on traditions and knowledge, professionals should seek information rooted in scientific development [START_REF] Melnyk | The establishment of evidence-based practice competencies for practicing registered nurses and advanced practice nurses in real-world clinical settings: proficiencies to improve healthcare quality, reliability, patient outcomes, and costs: EBP competencies for practice[END_REF][START_REF] Newhouse | Creating infrastructure supportive of evidence-based nursing practice: leadership strategies[END_REF]. Similarly, Evidence-Based Nursing (EBN) is a concept that embraces not only research results, but also all other sources of clinical knowledge (expertise, intuition, clinical insight, and perspicacity), as well as patient preferences, in order to make informed decisions [START_REF] Dicenso | Evidence-based nursing: A guide to clinical practice[END_REF].

The public health perspective in nursing education

Public and community health share a common objective: improving the health status of individuals, collectively rather than individually [START_REF]A Conceptual Framework for Action on the Social Determinants of Health. & Commission on the Social Determinants of Health[END_REF]. Today, the increase in social and territorial health inequalities and lifestyle changes, and their consequences on the health status of populations, call for actions on environments, living environments, and the social determinants of health (SDH), achieved through intersectoral and participatory programs [START_REF]A Conceptual Framework for Action on the Social Determinants of Health. & Commission on the Social Determinants of Health[END_REF]. Action and research for population intervention planning must take into account SDH, which offers a wealth of factors to inform decision-making in health promotion. Research conducted in the field of nursing must contribute to the production of useful and usable knowledge [START_REF] Hallberg | Moving nursing research forward towards a stronger impact on health care practice?[END_REF][START_REF] Hallberg | Challenges for the future nursing research: Providing evidence for health-care practice[END_REF], particularly through intervention research, in order to evaluate existing strategies and contribute to improving the health of populations [START_REF] Richards | The state of European nursing research: dead, alive, or chronically diseased? A systematic literature review: reviewing the state of European nursing research[END_REF][START_REF] Richards | The second triennial systematic literature review of European nursing research: impact on patient outcomes and implications for evidence-based practice[END_REF]. In addition, empowerment strategies for communities targeted by health promotion actions must influence the conditions in which people are born, grow, live, work, and age [START_REF]A conceptual framework for action on the social determinants of health: Debates, policy & practice, case studies[END_REF].

Nursing education's transition to higher education has made nurses better-prepared for their future roles, enabling them having a positive impact on the health of individuals and populations in terms of health promotion.

Main text

Globalization in public health: diversity and disparity Global health Study, research, and practice into global health places a priority on improving health and achieving equity in health for all people worldwide [START_REF] Koplan | Towards a common definition of global health[END_REF]. Global health emphasizes transnational health issues, determinants, and solutions; it involves many disciplines within and beyond the health sciences; it promotes interdisciplinary collaboration; and is a synthesis of population-based prevention with individual-level clinical care [START_REF] Koplan | Towards a common definition of global health[END_REF]. Diversity stemming from migration is one of Switzerland's key characteristics, notably in Geneva Canton. In 2017, this urban canton was home to almost 500,000 people, making it the sixthlargest canton in Switzerland in terms of populationone that grew by 6.9% between 2012 and 2017), in no small part due to migration. In 2017, 62.5% of the population consisted of migrants, compared to 37.2% for Switzerland as a whole [START_REF]Health in Geneva Canton[END_REF]. This diversity stemming from migratory movement is a source of enrichment, but also contributes to the existence of health, social, and economic disparities in Geneva Canton (see Table 1).

The concept of superdiversity

The scientific literature explores the cultural problems encountered by these populations, their state of health, and their means of access to care [START_REF] Ruiz-Casares | Access to health care for undocumented migrant children and pregnant women: the paradox between values and attitudes of health care professionals[END_REF]. The concept of "superdiversity" relates to the differential convergence of factors surrounding patterns of immigration arising from the complex interplays between newcomers' experiences, opportunities, constraints, and trajectories, and the wider set of social and economic relations within the places where they reside. Such factors include: country of origin (comprising a variety of possible subset traits such as ethnicity, language[s], religious tradition, regional and local identities, cultural values and practices), migration channel (often related to highly gendered flows and specific social networks), legal status (determining entitlement to rights), migrants' human capital (particularly educational background), access to employment (which may or may not be available to immigrants), locality (related especially to material conditions, but also the nature and extent of other immigrant and ethnic minority presence), transnationalism (emphasizing how migrants' lives are lived with significant reference to places and peoples elsewhere) and the frequently uneven responses by local authorities, service providers, and local residents (which often tend to function by way of assumptions based on previous experiences with migrants and ethnic minorities) [START_REF] Vertovec | Super-diversity and its implications[END_REF][START_REF] Zeeb | Superdiversitya new concept for migrant health?[END_REF]. Superdiversity offers a fresh and innovative way of understanding local levels of disparity nested in the challenges of contemporary global health, and appears to be a promising lens through which to analyze public health nursing education.

The need for a fresh perspective on disparity and diversity in 2020 While diversity is not a new concept in nursing, further integration of cultural diversity in educational systems and curriculum design for nursing education can positively influence how future nurses integrate the characteristics of superdiverse contexts in their practices.

The new Swiss community health education system

Since the promulgation of the Bologna Process, a number of different strategies have been adopted by individual countries, the European Union, governments, and professions in order to achieve the outcomes established by the Bologna Declaration. At country level, new policies to change the educational framework, or create the conditions for a new one, have been determined by individual governments responsible for higher education systems, individual universities, and professional associations and networks [START_REF] Palese | Bologna process, more or less: nursing education in the European economic area: a discussion paper[END_REF]. In Switzerland, the HES-SO (Hautes Ecoles de Santé Romande, western Switzerland's applied science university network) provides an education that prepares students for professional activities requiring the application of scientific knowledge and methods, for the first cycle of studies: the Bachelor's degree corresponds to 180 credits in the European Credits Transfer System (ECTS). With nine different courses and 3814 students, the HES-SO's Health Department is the largest health university in Switzerland and the only one to offer the entire University of Applied Sciences (UAS) syllabus for health. For Geneva, the Best Practice KFH [START_REF]Project for the Final Competencies for Health Professions in the Universities of Applied Sciences[END_REF] provides a systematic list of competences targeted by the Bachelor's degree in nursing. The competences covered by the Nursing Framework Curriculum express the knowledge and know-how that a specialist must possess to accomplish his or her main tasks. This definition of "competence" uses the terminology of the Copenhagen process (an EU project for the creation of a European vocational training area), which provides a framework for competence models. In this terminology, a "competence" refers to the ability to apply knowledge, know-how and interpersonal skills in a regular or new job. This ability is defined in terms of purpose, autonomy, sense of initiative, responsibilities, relational context, resource use, and profile requirements for a person with a Bachelor's degree in nursing. Each competence has four elements: (1) Cognitive competence, which involves the use of theories/concepts and tacit knowledge gained through experience; (2) Functional competence, which implies a mastery of the skills and know-how necessary to perform a practical function; (3) Personal competence, which implies the ability to know how to behave in a given situation or in a specific professional situation; (4) Ethical competence, which implies reference to certain personal and social values.

Professionals from a UAS background are called upon to deal with problematic, complex, and hard-to-predict situations. Their professional interventions call simultaneously on specialized knowledge and varied methods of action for interventions that are inherently singular, since they are intended for human beings [START_REF]Framework for Bachelor education in Nursing[END_REF]. Bachelor's nurses mobilize their skills, knowledge and professional attitude to provide supportive, preventive, therapeutic, palliative, and educational care oriented towards the person, family, or community. Bachelor's-level nurses know how to quickly grasp a care problem and solve it effectively by setting relevant priorities, and do so based on evidence, whilst observing professional ethics [START_REF]Republic and canton of Geneva[END_REF].

The Swiss community nursing education aims to educate nurses in critical thinking as well as enabling them to act with the highest degree of professionalism.

Future challenges for public health nursing education

Information and Communications Technology (ICT) plays a role in nursing student education, improving practices and adjusting them more appropriately to the challenges faced by professionals. However, for nursing, rather than investing in more technology and education, institutions and departments should aim to give more recognition, and respond better, to academics' specific discipline-related needs, so as to reflect the practical realities of nursing education. This constitutes a challenge to traditional teaching models [START_REF] Petit Dit Dariel | Developing the serious games potential in nursing education[END_REF].

The Geneva context, characterized in particular by growing health inequalities and diversity, requires dedicated education about how to act on the environment and SDH, intersectoral (transversal) actions, and design participatory programs [START_REF] Hawe | What is population health intervention research?[END_REF]. This relates to the advancement of knowledge about promising modes of action, SDH, and the development of strategies for their evaluation [START_REF] Dupin | Pistes de réflexion pour l'évaluation et le financement des interventions complexes en santé publique[END_REF]. Health literacy refers to the individual's ability to obtain, understand, and use the information required to take the appropriate decisions to remain in good health [START_REF] Kickbusch | Health Literacy. The Solid Facts[END_REF]. The concept was originally confined to individuals' ability to read and understand written information, but has now been extended to many other factors affecting an individual's ability to have access to, understand, and use information about health and health services [START_REF] Batterham | Health literacy: applying current concepts to improve health services and reduce health inequalities[END_REF]. In Geneva, amid high levels of migration, health literacy levels may reflect the diverse makeup of the Canton's population [START_REF] Balcou-Debussche | Promoting health education in a context of strong social and cultural heterogeneity: the case of Reunion Island[END_REF]. Public health interventions may even increase social health inequities, in line with the "inverse prevention law", which states that those in most need of preventive interventions are the least likely to receive them, whereas interventions should be of greater benefit to disadvantaged groups [START_REF] Lorenc | What types of interventions generate inequalities? Evidence from systematic reviews[END_REF].

Public health nursing education faces a twofold challenge: educating nurses using appropriate teaching strategies in view of their professional specifics, and designing population and individual interventions for superdiverse contexts.

Superdiversity and health-promoting nursing

The curricula provided by the HES-SO Health courses is relevant to society because it addresses the present and future health needs of the population and is adapted to the Swiss health system [START_REF]Republic and canton of Geneva[END_REF] [START_REF] Jackson | A review of nurse educator career pathways; a European perspective[END_REF]. In Geneva, nursing education is based on a competence framework for nursing care, divided into 7 roles and tracks: content derived from scientific knowledge (disciplinary and contributory): nursing science, health sciences, human sciences, research (processes and methods); professional content: methods, approaches and tools of the profession, clinical skills; practical clinical periods: 6 periods of practical education; and a Bachelor's dissertation that contributes to the integration of research results into professional practice. Community health education should enable students to become health promotersand ensure that as health promoters, nurses use their expertise and influence to promote the health and well-being of patients and communities. The dimensions of the role of health promoter (or at least its significant aspects) include: health promotion, health education, prevention, and quality of life (individual-group-community). Today, the holistic nature of community practice and the diversity of practice learning environments provide students with opportunities to develop a range of skills for contemporary community nursing [START_REF] Cable | Inspiring undergraduates towards a career in community nursing: Clare Cable and colleagues look at what must be done to create evidence-based models for placements that go beyond traditional clinical areas[END_REF].

Academic curricula must enable nurses to meet these challenges and play this role to the full, as is already acknowledged in various countries, developing 1) public health/community health competences, 2) research competences, and 3) clinical nursing competences [START_REF] Clark | Global and public health core competencies for nursing education: a systematic review of essential competencies[END_REF].

Conclusions

Superdiversity demonstrates that cultural change does not occur overnight: it occurs over years and generations.

Cross-cultural values are needed in a cross-cultural world, and nurse educators will need to lead the way in preparing future generations of international nurses [START_REF] Collins | The impact of the Bologna process on nursing higher education in Europe: a review[END_REF]. Crosscultural research among nurse educators is limited [START_REF] Jackson | A review of nurse educator career pathways; a European perspective[END_REF], but important: nurse educators are on the front line when it comes to educating the next generation of nurses [START_REF] Råholm | Nursing education in Denmark, Finland, Norway and Sweden -from Bachelor's degree to PhD: nursing education in Scandinavian countries[END_REF].

Table 1

 1 Geneva Canton health data (Excerpt adapted from[START_REF]Health in Geneva Canton[END_REF])

	Health indicators	Migratory	Geneva	Switzerland
		status	%	%
	Proportion of individuals	Non-immigrant	84.7	86.7
	with a (very) good self-assessed state of health	Immigrants 1st & 2nd gen.	82.7	83.1
	Proportion of individuals	Non-immigrant	5.3	4.1
	with serious limitations in activities usual for others	Immigrants 1st & 2nd gen.	5.6	4.3
	Proportion of individuals	Non-immigrant	12.2	6.7
	with symptoms of depression	Immigrants 1st & 2nd gen.	13.5	11.8
	Proportion of individuals	Non-immigrant	9.7	7.9
	with poor social support	1st & 2nd gen.	14.7	13.7
		Immigrants
	Individuals affected by	Non-immigrant	42.5	47
	pollution at work	1st & 2nd gen.	54.2	50.5
		Immigrants
	Proportion of individuals	Non-immigrant	12.2	13.3
	suffering from physical tiring postures, lifting or stress at work (painful or	Immigrants 1st & 2nd gen.	19.5	22.1
	moving heavy loads,
	lifting or moving persons)
	Proportion of individuals	Non-immigrant	20.6	17.6
	suffering from emotional fatigue at work (burnout)	Immigrants 1st & 2nd gen.	24.3	21.9

Acknowledgements

We would like to thank David and Naomi Buick for support with language revision.

Funding

The University of Applied Sciences and Arts Western Switzerland supported CMD and ND for this study.

Availability of data and materials

Data sharing is not applicable to this article as no datasets were generated or analyzed during the current study.

Ethics approval and consent to participate Not applicable.

Consent for publication

Not applicable.

Competing interests

The authors declare that they have no competing interests.

Publisher's Note

Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.


Ronan Thibault
email: ronan.thibault@chu-rennes.fr

Stephan C Bischoff

Prof Ronan Thibault

Zhang et al entitled 'ESPEN guideline on hospital diet nutrition'

Keywords: food intake, diets, malnutrition

The objective of our guideline was actually to give for the first time at an international level and from an academic society, clear recommendations about how to manage and prescribe diets in hospital. Indeed, our guideline is only about oral nutrition, not about medical nutrition such as oral nutritional supplements, enteral or parenteral nutrition. To these aims we invite the authors to refer to the numerous disease-related ESPEN guidelines. Despite food is considered as a care since the greek Antiquity (Hippocratus, 5 th century BC), recommendations about this topic were deeply lacking.

In English language, the term 'hospital nutrition' is used quite synonymous to 'hospital food', or even 'hospital diet', whereas the term 'hospital diet nutrition' is not really established. We have intentionally chosen the wording 'hospital nutrition' to emphasize the fact that a major aim of food supply at hospital is to act as a part of therapy and thus to help patients improving their health and getting better. In particular, our goal is that hospital nutrition, put into practice through the newly proposed 'hospital diet', would help preventing malnutrition or avoid its worsening. Of course, hospital nutrition will never substitute to enteral and parenteral nutrition whenever it is needed. In our guideline, the authors will find any information they need for prescribing diets, and choosing the right ones indicated for particular diseases.

Nutritional status is indeed an important factor that needs to be assessed and considered for the selection of the diet. Symptoms and wills of patient are also of importance in this context and need to be considered; however it addresses something else. Symptoms cover more than nutritional status and will of patients is even in some extent independent of nutritional status.

For example, we recommend in malnourished patients or those at risk for malnutrition to use a protein-and energy-enriched diet named 'hospital diet' to prevent malnutrition or avoid its Accepted manuscript / Final version

Acknowledgement

None.

We thank very much Dr. Zhige Zhang and colleagues for their interest in our recently published 'ESPEN guideline on hospital nutrition' and for their lauding words [1]. We also noticed theirs words of criticism to which we would like to reply briefly. worsening. Therefore, screening and assessment for malnutrition according to the "GLIM criteria" is a need that exists independently from symptoms and will of the patients [2]. In conclusion, we hope that you and many others will profit from this guideline and thank again for the comments.

Funding statement

This ESPEN hospital nutrition guideline was solely financed by ESPEN, the European Society for Clinical Nutrition and Metabolism.

Author contributions

RT & SCB wrote the letter; both authors approved the final submitted version of the manuscript.

Conflict of interest

The authors declare no conflicts of interest with regard to this letter.


Laurent Barbiéro
email: barbiero@lmtg.obs-mip.fr

José P De Queiroz Neto

Gilles Ciornei

Arnaldo Y Sakamoto

Benjamin Capellari

Erminio Fernandes

Vincent Valles

GEOCHEMISTRY OF WATER AND GROUND WATER IN THE PANTANAL GEOCHEMISTRY OF WATER AND GROUND WATER IN THE NHECOLÂNDIA, PANTANAL OF MATO GROSSO, BRAZIL: VARIABILITY AND ASSOCIATED PROCESSES

Keywords: concentration, alkalinity, calcite, saline lakes, Nhecolândia, Pantanal, Brazil

A distinctive feature of the Nhecolândia, a sub-region of the Pantanal wetland in Brazil, is the presence of both saline and freshwater lakes. Saline lakes used to be attributed to a past arid phase during the Pleistocene. However, recent studies have shown that saline and fresh water lakes are linked by a continuous water table, indicating that saline water could come from a contemporary concentration process. This concentration process could also be responsible for the large chemical variability of the waters observed in the area. A regional water sampling has been conducted in surface and sub-surface water and the water table, and the results of the geochemical and statistical analysis are presented. Based on sodium contents, the concentration shows a 1: 4443 ratio. All the samples belong to the same chemical family and evolve in a sodic alkaline manner. Calcite or magnesian calcite precipitates very early in the process of concentration, probably followed by the precipitation of magnesian silicates. The most concentrated solutions remain under-saturated with respect to the sodium carbonate salt, even if this equilibrium is likely reached around the saline lakes. Apparently, significant amounts of sulfate and chloride are lost simultaneously from the solutions, and this cannot be explained solely by evaporative concentration. This could be attributed to the sorption on reduced minerals in a green sub-surface horizon in the "cordilhieira" areas. In the saline lakes, low potassium, phosphate, magnesium, and sulfate are attributed to algal blooms. Under the influence of evaporation, the concentration of solutions and associated chemical precipitations are identified as the main factors responsible for the geochemical variability in this environment (about 92 % of the variance). Therefore, the saline lakes of Nhecolândia have to be managed as landscape units in equilibrium with the present water flows and not inherited from a past arid phase. In order to elaborate hydrochemical tracers for a quantitative estimation of water flows, three points have to be investigated more precisely: (1) the quantification of magnesium involved in the Mg-calcite precipitation; (2) the identification of the precise stoichiometry of the Mg-silicate; and (3) the verification of the loss of chloride and sulfate by sorption onto labile iron minerals.

INTRODUCTION

The presence of salt is frequently used for reconstructing paleoenvironments. The reconstruction is based on various features, extending from the morphology of saline areas to the chemical profile of salinity. Due to their high solubility, salts generally indicate an arid phase in a present or past climate but are quickly eliminated when the climate turns wet again. In the Nhecolândia, a sub-region of the Bazilian Pantanal wetland (Figure 1) located between the Taquari and the Negro rivers, there are many saline round lakes ("Salinas"), which are considered as characteristic of the area [START_REF] Cunha | Análise química das águas. Cobre do Jauru : lagoas alcalinas do Pantanal[END_REF][START_REF] Brum | Níveis de nutrientes minerais para gado, em lagoas no Pantanal Sul Mato-Grossense[END_REF][START_REF] Mourão | Alguns factores limnológicos relacionados com a íchtiofauna de baías e salinas do pantanal da Nhecolândia, Mato Grosso do sul, Brasil[END_REF]). Different hypotheses have been formulated to explain the origin of these salinas and their associated sandy banks (called "Cordilheiras"), and their genesis is still under debate. One hypothesis, which does not consider the presence of salts, involves the shifting of river courses. The regularly shaped lakes would then result from depressions surrounded by cut-off meander banks. Similarly, banks with short-cut meanders would turn into cordilheiras, as suggested by Wilhelmy (1958) and later corroborated by [START_REF] Ab'saber | O Pantanal Mato Grossense e a teoria dos refugios[END_REF]. Another hypothesis involves wind deflation in combination with high salinity of soils [START_REF] Almeida | Excursion Guidebook 1. 18th International Geography Congress[END_REF]) and/or accumulation of sand-size particles as in the "Sebkha" dune type [START_REF] Tricart | El Pantanal : Un ejemplo del impacto de la Geomorphologia sobre el medio ambiente[END_REF]. [START_REF] Klammer | Die Palaeowuste des Pantanal von Mato Grosso und die pleistozane Klimageschichte des brasilianischen Randtropen[END_REF] conceded that it is only a partial explanation, since some areas have such paleodunes without the accompanying lakes. Moreover, no deposit features of these paleodunes have ever been identified in the soils [START_REF] Colinvaux | Amazonian and neotropical plant communities on glacial time-scales. The failure of the aridity and refuge hypotheses[END_REF]. [START_REF] Eiten | Classificação da vegetação do Brasil[END_REF] attributed the lakes to a karstic or pseudo-karstic system. In all these studies, the presence of salts is attributed to an old phenomenon and, in particular, to the alternations of wet and arid phases during Pleistocene (Ab'Saber 1988), which have been questioned today [START_REF] Colinvaux | Amazonian and neotropical plant communities on glacial time-scales. The failure of the aridity and refuge hypotheses[END_REF]. [START_REF] Klammer | Die Palaeowuste des Pantanal von Mato Grosso und die pleistozane Klimageschichte des brasilianischen Randtropen[END_REF] even proposed the term "paleodesert" to explain the presence of salty terminal lakes.

In recent studies, [START_REF] Fernandes | Le « Pantanal da Nhecolândia » Mato Grosso. Cadre physique et dynamique hydrologique[END_REF], [START_REF] Neto | Dinâmica hídrica de uma lagoa salina e seu entorno na área do Leque, Nhecolândia, Pantanal -MS. II Simpósio sobre Recursos Naturais e Sócio-econômicos do Pantanal[END_REF][START_REF] Sakamoto | Topografia de lagoas salinas e seus entornos no Pantanal de Nhecolândia. II Simpósio sobre Recursos Naturais e Sócio-econômicos do Pantanal[END_REF] have shown the presence of a continuous water table between the saline and the nonsaline lakes, which are supplied yearly by fresh water during floods of the river Taquari. The non-saline lakes and rivers contain sodic/calcic/(sometimes potassic) and carbonate/chloride waters, whereas the saline lakes contain sodic-carbonate water. The salty lakes are always 0.5 to 3 m lower than the surrounding fresh water lakes and should be continually supplied through the saturation zone by diffusing sub-surface flow. This would imply, contrary to the previous hypotheses, that the salty lakes do not result from a past arid phase but from present day processes.

The objectives of this paper are to verify whether the geochemical features of the salty lakes could result from the present-day concentration of the poorly mineralized waters and whether this concentration process could explain the large chemical variability observed in this region.

MATERIALS AND METHODS

Site

The Pantanal of Mato Grosso, near the geographic center of South America in Brazil, is known as the world's largest wetland [START_REF] Alho | Environmental degradation in the Pantanal ecosysthem[END_REF]). However, it is perhaps one of the most unknown regions of the globe, as scientific information is surprisingly scarce (cf. [START_REF] Por | The Pantanal of Mato Grosso (Brazil). World's Largest Wetlands[END_REF]. Its landscape comprises a variety of ecological sub-regions (Da Silva and Abdon 1998), including river corridors, gallery forests, perennial wetlands and lakes, seasonally flooded grasslands, and terrestrial forests. Put together, these natural features form a large and biologically diverse ecosystem [START_REF] Gottgens | The case of the Paraguay-Paraná waterway ("Hidrovia") and its impact on the Pantanal of Brazil: a summary report to the Society of Wetlands Scientists[END_REF].

Situated between 16 ° and 20 ° S and 58 ° and 50 ° W, the total extent of the Pantanal is about 200,000 km² [START_REF] Por | The Pantanal of Mato Grosso (Brazil). World's Largest Wetlands[END_REF] (Figure 1). The north, east, and south borders are clearly marked by the Brazilian highlands at an altitude of about 400 m (Chapada dos Parecis, Serra São Jeronimo, Chapada dos Guimarães, Serra do Maracajú, Serra do Bodoquena). There is an opening in the North, through which the Paraguay River flows southward. In the South, the Paraguay River crosses the narrows between the mountains in an area called "Fecho dos Morros," considered to be the limit of the upper Paraguay basin. The surrounding mountains are all Precambrian or Paleozoic. They are locally iron-and manganese-rich and also contain large areas of calcareous rocks. Quaternary sediments, alluvial products of the Paraguay River effluents [START_REF] Klammer | Die Palaeowuste des Pantanal von Mato Grosso und die pleistozane Klimageschichte des brasilianischen Randtropen[END_REF] and tributaries, cover the plain. The elevation of the alluvial plain ranges from 100 to 200 m above sea level, with a slight North-South and East-West gradient. This vast plain provides a gigantic natural flood control device for the storm waters resulting from torrential rainfall during the wet period. Each year, the heavy tropical rains cause the main tributaries supplying the Pantanal waters to overflow. With the flood, the depressions are inundated and form extensive lakes, which coalesce into larger waterbodies. During the dry season, the floodwaters recede, resulting in a complex mosaic of grasslands and forests dotted with countless lakes and marshes.

Nhecolândia is a sub-region of the Pantanal wetland directly influenced by the Taquari River in the West and the Negro River in the South (Figure 2); the system of round lakes (saline or non-saline) is particularly well-developed here. During the dry season, these lakes cover about 30 % of the area. Among all the lakes of Nhecolândia, [START_REF] Morrison | Identificação das lagoas salinas da região da Nhecolândia -Pantanal, através de técnicas de sensoriamento remoto -III Simpósio sobre Recursos Naturais e Sócio-econômicos do Pantanal[END_REF] identified 499 salty lakes, which make up about 1 % of the total surface area. The soil cover consists of sandy soils with small patches of clay and lime soils. High sodium contents are observed locally, particularly in the Southern Nhecolândia. The most frequent soil ("Plintossolos" according to the Brazilian classification) is characterized by a low organic matter content and the presence of a deep green horizon, hardening irreversibly after air drying [START_REF] Sakamoto | Dinâmica hídrica em uma lagoa salina e seu entorno no Pantanal da Nhecolândia: contribuição ao estudo das relações entre o meio físico e a ocupação, Fazenda São Miguel do Firme[END_REF]. The seasonal floods of Nhecolândia floodplain occur in three ways: (1) the overbank flow of the Taquari river across its natural levees, (2) a backwater effect caused by the flooding of the Paraguay and Negro rivers and (3) local rainfall on lands with gentle slopes where drainage to river courses is delayed [START_REF] Hamilton | Potential effects of a major navigation project (Paraguay-Parana hidrovia) on inundation in the Pantanal floodplains[END_REF]. The backwater effect caused by the Paraguay and Negro rivers can locally and temporarily reverse the flow of some tributaries [START_REF] Hamilton | Dynamic of floodplain inondation in the alluvial fan of the Taquari River (Pantanal, Brazil)[END_REF]. The local hydrologic regime is much more complex, and the ground-water flows connecting the many lakes of the Nhecolândia are not yet understood. The Pantanal has a tropical semi-humid climate, classified as "Aw" type in the Köppens classification. The average air temperature is about 32 °C in summer. The winter season is dry and cold, and frost can form during the occasional influx of polar air masses from the south (IBGE 1989). The mean annual temperature is 25 °C. The mean annual precipitation is 1000 mm, and most rainfall occur between October and April [START_REF] Alho | Environmental degradation in the Pantanal ecosysthem[END_REF]. The annual evapotranspiration is about 1400 mm, giving a hydrologic deficit of about 400 mm.

The landscape is constituted by special features with typical regional denominations, which will be used throughout the article (Figure 3): -The "lagoas" are temporary or permanent lakes of the most variable forms and dimensions. They can reach approximately two meter depths.

-The "salinas" are permanent salty lakes. There are generally 500 to 1000 m in diameter, 2 to 3 m deep (during the dry season), and most commonly, are well delimited and/or isolated by a stripe of dryland or "cordilheiras." -The "cordilheiras" are narrow (200-300 m wide) and elongated sand hills (2 to 5 m high) covered by savanna vegetation (Cerrado).

-The "vazantes" are natural drainage channels flowing periodically from lagoas during the flooding periods. They can be several kilometers long and are generally 10 to 30 m wide.

-The "corixos" are small periodic watercourses with their own riverbeds that link adjacent lagoas during flood periods. Their dimensions are similar to those of the vazantes.

Sampling

Water samples were collected during the period 1994 to 1999 in lagoas and salinas (41 samples), rivers (5 samples), vazantes and corixos (7 samples), and piezometers located in cordilheiras (12 samples). Samples were taken in the Negro River, the Abobral River, and three sites of Nhecolândia : Fazenda São Miguel do Firme, Fazenda Nhumirim and Fazenda Berenice (Figure 2). All the waters from lagoas, salinas, and watercourses were collected at about 1 m from the shoreline and at about 0.2 m in depth. Around the piezometers that were sampled, the depths of the water ranged between 1 to 2 m near the salinas or lagoas and between 4 and 6 m in the middle of the cordilheiras. About two or three liters of solution were taken from the piezometers with a manual vacuum pump before sampling. Water was collected only once from each sampling site and preserved at a temperature of 4 °C until analysis. All samples were stored in acid rinsed opaque polyethylene containers.

Chemical Analyses

All the analyses were performed in the laboratory at the Sao Paulo University, Brazil, as well as in IRD Dakar, Senegal. The pH, electrical conductivity, and temperature were measured on non-filtered samples. The samples were then filtered with 0.45-µm cellulose acetate filters, and the total alkalinity was determined by acid titration with HCl [START_REF] Gran | Determination of the equivalence point in potentiometric titrations[END_REF]. Silica content was measured by colorimetry (ammonium molybdate method, [START_REF] Charlot | Dosage Colorimétrique des Eléments Minéraux[END_REF]. Total magnesium, sodium, calcium, and potassium concentrations were measured by atomic absorption spectrometry (PERKIN ELMER 2000[START_REF] Fassel | Quantitative elemental analysis by plasma emission spectroscopy[END_REF]). Chloride, sulfate, nitrate, and phosphate concentrations were analyzed by capillary electrophoresis (WATERS, Capillary Ion Analyzer).

Data Analyses and Activity Coefficient Calculations

The considerations on solution/mineral equilibria are based on the activity coefficients of the dissolved ions, which have not been measured but estimated from the analyses. The ion pair model "AQUA" (Valles and De Cockborne 1992) derived from "GYPSOL" (Valles and Bourgeat 1988) was used for these calculations. This model is not based on the Scatchard's extension of the Debye-Hückel's law [START_REF] Scatchard | Concentrated solutions of strong electrolytes[END_REF]) but on a specific extension that takes into account the solvent/solute interactions under strong ionic strengths (Valles, pers. Comm.)

Statistical Approach An analysis of the variance and standard deviation was performed using the "AQUA" model on the following bulk parameters: Carbonate Alkalinity, K + , Na + , Ca 2+ , Mg 2+ , Cl -, and SO4 2-. A principal component analysis (PCA) was performed, based on the correlation matrix, in order to sort the data and chemical parameters according to the factors that might explain the variability in the chemical characteristics of the sampling.

Concentration Diagrams

Data from all the samples were treated together and are presented in the concentration diagrams, regardless of whether they represent surface waters or ground waters. The concentration diagrams were built using Na + as a conservative tracer to estimate the concentration factor. As a result, the concentration factor is underestimated if a Na-salt precipitates (for example halite: NaCl; natron: Na2CO3.10H2O; trona: Na2CO3.NaHCO3.2H2O). In the case of very mineralized waters, this hypothesis needs to be verified.

Residual Alkalinity, Definition, and Property

Alkalinity is the sum of the weak base concentrations multiplied by the number of protons each base can neutralize, minus the number of protons in the solution [START_REF] Stumm | Aquatic Chemistry. An Introduction Emphasing Chemical Equilibria in Natural Waters[END_REF]. In most soils and natural waters, the alkalinity is generally due to carbonate species (i.e., carbonate alkalinity), neglecting H + and OH -concentrations, organic anions, complex ions of phosphorus, silica, aluminum, and boron [START_REF] Vorob'yeva | The nature of soil alkalinity and methods of it[END_REF]Zamana 1984, Keller et al. 1987):

Carbonate alkalinity = [HCO3 - ] + [CO3 2-
] where square brackets [ ] denote total concentration expressed in equivalent per liter (eq L -1 ). The concept of residual carbonates derived originally from [START_REF] Eaton | Signifiance of carbonates in irrigation waters[END_REF] was later redefined in terms of "residual alkalinity" as the difference between carbonate alkalinity and calcium amounts in the solution [START_REF] Hardie | The evolution of close basin brines[END_REF][START_REF] Van Beek | The alkalinity of alkali soils[END_REF][START_REF] Droubi | Generalized residual alkalinity concept; Application to prediction of the chemical evolution of natural waters by evaporation[END_REF]. When evaporation concentrates a solution up to calcite precipitation, two cases may arise. 1) Calcium equivalent is greater than the carbonate alkalinity, in which case, calcium molality increases and alkalinity decreases. The solution then evolves in a saline manner. 2) Calcium equivalent is less than the carbonate alkalinity, causing the molalities to change in the opposite direction and the solution to evolve in an alkaline manner by concentration. After each mineral precipitation, changes are observed in the rate of concentration of the elements. When saturation with respect to a new mineral is reached, the concentration of certain elements can decrease, increase again, or simply fluctuate along the evaporation processes. This concept is used here in order to interpret the changes in the evolution of each element as waters become more saline.

Simulation

The evolution of major ions along the concentration gradient was simulated using the "AQUA" model. The simulation starts from a poorly mineralized solution to a 4000 times more concentrated one. In this calculation, the CO2 partial pressure was kept constant and equal to 10 -3,5 atm, which is not PCO2 in the field but the average value of PCO2 when the pH was measured in the laboratory. The possible precipitation of calcite, magnesite, magnesian silicate (sepiolite), and amorphous silica were activated during the simulation. The results of the simulation are compared to the distribution of the observed data in the concentration diagrams.

RESULTS

The ionic strength of the solutions varied from 0.159 10 -3 to 0.376 (i.e., in a 1/2365 ratio). The most diluted solution was sampled in a corixo, whereas the most concentrated one came from the piezometer S13 near the "Sao Miguel do Firme" salina. The descriptive statistics for each element are given in Table 1. Sodium and carbonate alkalinity showed the largest standard deviation in the data set. According to the sodium content, the most mineralized solution is 4443 times more concentrated than the least mineralized one. The changes in ionic strength came together with changes in the chemical profile of the solutions as presented on the Piper and Schöeller diagrams (Figures 4 and5). The fresh waters had a carbonate/chloride and sodic/potassic chemical profile, whereas the most mineralized waters had a carbonate and sodic type. The pH values ranged from 7.05 to 9.91. Silica contents were particularly high in this alkaline environment, ranging from 0.18 to 4.35 mmol L -1 , although some samples had a relatively low SiO2 content compared to the rest of the sampling. The correlation matrix (Table 2) showed a close relationship between Na + and carbonate alkalinity. A moderately close relationship was observed between these variables (Na + , carbonate alkalinity) and Cl -, SO4

, and K + . The examination of the singular values (Table 3) revealed that the axis of the first factorial plan accounted for 58.12 % and 20.5 % of the variance of the data set. The first axis opposed concentrated waters of the salinas and associated piezometers to the fresh waters of the rivers, corixos and vazantes (Figures 6 a andc). The second axis opposed samples with high Ca 2+ and Mg 2+ contents to the rest of the sampling. The third axis opposed samples with relatively high Ca 2+ and low Mg 2+ to samples with low Ca 2+ and high Mg 2+ (Figure 6 b andd). Equilibrium diagrams indicate that the less mineralized solutions are under-saturated with respect to calcite, whereas most of the solutions are at equilibrium or slightly over-saturated with respect to that mineral (Figure 7a). The ten most concentrated solutions reached the equilibrium with respect to magnesite (Figure 7b). All the samples are under-saturated with respect to neutral salts like gypsum (CaSO4,2H2O; Figure 7c) or halite (NaCl; Figure 7d). The most concentrated solution remains under-saturated with respect to the sodium carbonates (Na2CO3.10H2O; Figure 7e; Na2CO3.NaHCO3.2H2O; Figure 7f), although this salt was identified in the field around some salinas, for example "Salina das Pedras" in the Berenice farm. This confirms that the sodium molality is adequate to estimate a concentration factor. Even for the most dilute lagoas, solutions are well above the quartz solubility, and most samples are near the equilibrium with respect to amorphous silica. The equilibrium with respect to Mg-silicate (stevensite, sepiolite...) is reached (Figure 7g). On the concentration diagrams (Figure 8), the solid lines are unit slope lines, (i.e., a hypothetical evolution proportional to the sodium contents). The pH values and alkalinity increase with the mineralization of the solutions. In Figures 8a and8b, the plots show a similar distribution, (i.e., pH and alkalinity increasing proportionally to the sodium molalities from (Na + ) = 0.07 to 1.5 meq L -1 and less steadily for higher sodium molalities). The chloride molalities also increase along the concentration gradient (Figure 8c). However, the plot shows a decrease for sodium molalities close to 5.2 meq L -1 . After this value, the chloride contents increase again and more steadily than the sodium molalities, but the 1:1 line, drawn from the most diluted solutions, is not reached, even for the most concentrated solutions. The sulfate plot (Figure 8d) is more scattered but shows a similar behavior to that of chloride. The calcium and magnesium contents increase until sodium molalities are close to 1.5 meq L -1 (Figures 8e and8f), and they then level off, while the scatter of the data increases. Potassium and phosphate concentrations increase as waters become more saline (Figures 8g and8h), with a slope close to 1:1 (i.e., proportionally to the sodium molalities). However, some points clearly depart from the rest of the sampling, having lower values. For these samples, similar behavior is noted on the scatter plots of potassium and phosphate, but also magnesium and possibly sulfate. Total silica contents are close to 1 meq L -1 for sodium molalities, ranging from 0.07 to 7.5 meq L -1 , and they then increase in the most mineralized samples (Figure 8i). The simulation of evaporation of dilute water (dotted lines on Figure 8) agrees well with the evolution highlighted from the concentration diagrams of the observed data. With respect to the elements that are little or not controlled, a good agreement with the evolution of alkalinity, pH, potassium, and silica is noted. In spite of a more scattered plot, the simulation agrees with the significant control of Ca and Mg. However, the simulation is not in agreement with the evolution of the chloride and sulfate ions.

DISCUSSION

The first axis of the Principal Component Analysis indicates the global concentration of the solutions. Therefore, concentration of dissolved elements, mainly due to evaporation, seems to be the principal process responsible for the chemical variability in the Nhecolândia. All the samples seem to belong to the same geochemical family. The close relationship between carbonate alkalinity and the elements that are generally used as concentration tracer (Na + , Cl -) indicates that the carbonate alkalinity is not strongly affected by control processes when the waters concentrate, evolving in an alkaline manner. The second variability factor in the chemical data set is the control of Ca 2+ and Mg 2+ , which are not correlated with the solutes not or weakly controlled, like Na + and carbonate alkalinity.

Ca

2+ is most likely controlled by calcite precipitation along the concentration gradient. In the fresher waters, carbonate alkalinity is higher than the amount of calcium, as illustrated by the Schoeller diagram (Figure 5). Calcite residual alkalinity is positive. Thus, when the solutions concentrate and calcite precipitates, calcium concentration decreases and the carbonate alkalinity increases, although less rapidly than sodium molalities, because a part of the alkalinity is taken up from solution by calcite formation. This evolution is consistent with the law of calcite residual alkalinity. The third axis of the PCA is more difficult to interpret because 78.6% of the variance is already explained with the first factorial plan (Table 3). The difference observed for Mg between the data and the simulation could be explained if calcite was a magnesian variety, thus simultaneously controlling Ca 2+ and Mg 2+ molalities. However, the concomitant uptake of Ca 2+ and Mg 2+ and the precipitation of Mg-calcite cannot be the sole geochemical process responsible for the control of Mg 2+ molalities. The third axis of the PCA, opposing Ca 2+ and Mg 2+ , suggests another mechanism independent of the control of Ca 2+ . The saturation with respect to magnesite is reached only by some solutions. Therefore, the contribution of this mineral to Mg 2+ control is unlikely. Rather, magnesium molalities could be controlled by formation of a magnesian silicate (e.g., stevensite, sepiolite, Mg-montmorillonite, or amorphous Mg-silicates), which is frequent in alkaline environments [START_REF] Garrels | Origin of the chemical composition of some springs and lakes[END_REF], Gac et al. 1977[START_REF] Jones | Hydrochemistry of the lake Magadi basin, Kenya[END_REF], Jones and Galand 1988, Valles et al. 1989). The equilibrium diagram (Figure 7g) indicates that formation of magnesian silicates is indeed possible. Mg initially could be buffered by formation of Mg-calcite and subsequently by precipitation of a Mg-Silicate. The high silica contents observed in the most concentrated waters (pH > 9) can be attributed to the dissociation of orthosilicic acid (Si(OH)4) into SiO(OH)3 -as indicated by the simulation. In short, the evaporative concentration and the associated geochemical processes (calcite or Mg-calcite precipitation, Mg-silicate formation) may well be responsible for about 92 % of the variance in the sampling (PC axis 1, 2, and 3).

The evolution of the potassium contents along the concentration gradient suggests that exchange processes in the soil are insignificant, which was expected because of the sandy soil texture. High-Na solutions that are low in potassium, phosphates, magnesium, and sulfate contents were sampled in various salinas distant from each other. It is therefore likely that a regional-scale process controls these elements. It affects the free water of the salina without affecting the solution in the neighboring water table. It is probably related to the algal bloom frequently observed in the salinas of the Nhecolândia. The geochemical processes previously described cannot explain the decrease in sulfate and chloride amounts in waters with intermediate ionic strengths. Clearly, processes involving large sulfate and chloride losses are at work here. Similar sulfate variations have been observed in the alkaline Magadi basin in Africa [START_REF] Jones | Hydrochemistry of the lake Magadi basin, Kenya[END_REF]. The two processes evoked are reduction and sorption. Although we found no evidence for sulfate reduction during prospecting in the field, it is a likely process in this environment. A comparison of the chloride and sulfate versus sodium plots (Figures 8 c andd) suggests that Cl -and SO4 2-have been involved in a same process. It is becoming increasingly accepted that Fe solutionmineral equilibrium is often controlled by a labile "ferroso-ferric hydroxide" [START_REF] Ponnamperuma | The chemistry of submerged soils[END_REF][START_REF] Ponnamperuma | Redox equilibria in flooded soils I. The iron hydroxyde systems[END_REF] or green rusts [START_REF] Trolard | Identification of a Green Rust mineral in a reductomorphic soil by Mössbauer and Raman spectroscopies[END_REF]). Among the compensating interlayer anions, OH -can be partially substituted for Cl -, SO4

, or CO3

2- [START_REF] Bourrié | Iron control by equilibria between hydroxy-Green Rusts and solutions in Hydromorphic soils[END_REF]. The low Cl -and SO4 2-concentration in waters of intermediate ionic strength could also be attributed to substitutions in such reduced minerals, particularly in the green horizons frequently observed at about 1 to 4 m depth in the mountain range areas [START_REF] Fernandes | Le « Pantanal da Nhecolândia » Mato Grosso. Cadre physique et dynamique hydrologique[END_REF]. The reversibility of the precipitation/dissolution reaction of green rusts, in agreement with their well-known lability, could explain that a proportion of lost SO4

2-and Cl -are released near the temporary oxidized salinas. Specific studies based on the sampling of free soil solution and its conservation in anoxic conditions are currently in progress to verify this hypothesis. The chemical evolution of the waters in this part of the Pantanal wetland is in its broad outline, similar to that observed in some areas of continental Africa, North America, or Europe, although the climatic conditions and the sedimentary framework are clearly different. For example, the Tisza valley in Hungary, the lower Danube plain in Romania, the Nebraska Sand Hills in North America, and the Chad Lake or salty lakes along the oriental rift in Ethiopia or Kenya show similar chemical composition and processes as water becomes concentrated due to evaporation (Gac et al. 1977[START_REF] Jones | Hydrochemistry of the lake Magadi basin, Kenya[END_REF][START_REF] Droubi | Generalized residual alkalinity concept; Application to prediction of the chemical evolution of natural waters by evaporation[END_REF]. Waters originating from old cratons generally have a carbonate-dominating chemical composition and evolve in a sodic alkaline manner under the influence of evaporation. Therefore, this similarity with the African craton is probably due to the geological characteristics of the high Paraguay basin, whereby the Nhecolândia is supplied by waters from the old Brazilian craton.

CONCLUSIONS AND PERSPECTIVES

The presence of saline lakes (Salinas) is a peculiarity of the Nhecolândia, a subregion of the Pantanal wetland. Until now, the salt has always been attributed to alternating humid and arid phases during Pleistocene (i.e., inherited from the past). The geochemical analyses presented in this paper indicates a unique geochemical family of waters evolving currently in an alkaline manner under the influence of evaporation. The geochemical composition changes gradually from weakly mineralized waters that flood the region during the rain season to the strongly mineralized ones in the salinas. The processes responsible for most of the changes in the chemical characteristics of the water are the precipitation of calcite or Mg-calcite and probably the formation of Mg-silicates as waters become more saline.

Although evaporation can account for most of the chemical variability in the region, the geographical distribution of a number of landscape distinctive features seems to interfere with this scenario. In particular, sulfate and chloride values show the most significant deviation from an evaporation-controlled concentration pattern. This may be due to the fact that labile iron minerals cause extensive substitution in the green horizons in the cordilheira areas. However, this hypothesis needs to be verified by specific sampling of soil and soil solution preserved from contact with the atmosphere. The next research efforts should focus on the water and solute flows in the landscape to explain how wetlands subjected to the same amount of evaporation can have such different chemical characteristics. Our study has indeed shown that the range of water mineralization detected in this regional sampling from fresh to saline water (approximately 4500 times) cannot result from a yearly accumulation but must arise from several decades of functioning of this ecosystem. It follows that any modification of the environment that could lead to the possible desalinization of a salina would cause an irreversible damage. The salinas are an essential component of the principal economical activity of this region (i.e., cattle breeding). Being located in the extreme lowlands, these salinas provide water even during the driest periods, as well as valuable mineral complements for cattle, which feed primarily on poorquality local grass [START_REF] Comastri | Forage species introduction and evaluation on semicleared ancient levees in the Nhecolandia subregion of the Brazilian Pantanal[END_REF]. The salinas must, therefore, be regarded as a fragile resource requiring sustainable management. : Corixo; 2 : Negro River; 3 : Lagoa; 4 and 5 : Water table in cordilheira; 6 : Salina.

  Wilhelmy, M. 1958. Das Grosse Pantanal. Die Weltumschau 18:555-559.

Figure 1 .

 1 Figure 1. Location of the Pantanal wetland.

Figure 2 .

 2 Figure 2. Location of the study site in the Nhecolândia, Mato Grosso do Sul state, Brazil.

Figure 3 :

 3 Figure 3: Schematic distribution of the Nhecolândia landscape features.

Figure 4 .

 4 Figure 4. Piper diagram showing dissolved species distribution.

Figure 5 .

 5 Figure 5. Schoeller diagram of three representative fresh (a) and concentrated (b) waters.

Figure 6 .

 6 Figure 6. Results of the Principal Component Analysis (PCA) calculations (a and b :

Figure 7 .

 7 Figure 7. Diagrams showing equilibrium conditions in solution for a) calcite, b) magnesite, c)

Figure 8 .

 8 Figure 8. Concentration diagrams (solid line = unit slope line; dotted line = simulation,

ACKNOWLEDGMENTS

This work has been financed by the FAPESP 97/11799-5 (Fundação de Amparo a Pesquisa do Estado de São Paulo). The authors are very grateful for the field assistance provided by EMBRAPA-Pantanal.


domain: chim phys

text:
Robert F Tournier
email: robert.tournier@lncmi.cnrs.fr

Liquid-liquid transitions due to melting temperatures of residual glassy phases expected in Pt57Cu23P20

Bulk glasses are obtained by quenching melts of various compositions. The initial temperature before quenching is chosen above the liquidus temperature (Tl) of materials assuming that the melt is homogenous. Glassy items are formatted above the glass transition temperature Tg below a crystallization temperature called Tx. First-order transitions at Tx transform melts into composites containing crystals and new glassy phases, melting at temperatures (Tn+) much higher than (Tl). The first-order transitions at Tx were studied at Caltech Pasadena by cooling and heating a melt of Pt57Cu23P20. A recent model predicting the formation enthalpies of these new composites at Tx and the melting temperatures (Tn+) of glassy fractions is applied to this alloy.

1-Introduction

.

.

.

Phase 3 obtained by heating the melt from the glassy state, has been attributed to the presence, above Tg, of residual bonds in all glasses, melted at temperatures Tn+ higher than Tm

 [START_REF] Tournier | Undercooled Phase Behind the Glass Phase with Superheated Medium-Range Order above Glass Transition Temperature[END_REF]. The non-classical model of homogeneous nucleation was recently completed, leading to the prediction of Phase 3 transformations in glassy phases at new temperatures Tx which are driven by enthalpy [START_REF] Tournier | Multiple melting temperatures in glass-forming melts[END_REF]. The melt above Tg is viewed as containing residual bonds (after configurons formation [START_REF] Ojovan | Thermodynamic parameters of bonds in in glassy materials from viscosity temperature relationships[END_REF][START_REF] Ojovan | Connectivity and glass transition in disordered oxide systems[END_REF][START_REF] Ojovan | Ordering and structural changes at the glass-liquid transition[END_REF][START_REF] Ojovan | Revealing Structural Changes at Glass Transition via Radial Distribution Functions[END_REF]) at a critical threshold up to a first-order transition at T = Tx [START_REF] Tournier | Undercooled Phase Behind the Glass Phase with Superheated Medium-Range Order above Glass Transition Temperature[END_REF]. Above Tx, new glassy Phases 3 of lower enthalpy, could be formed with a glass transition temperature Tg' equal to (2Tm-Tg) = 1142.6 K which remains virtual because (Tg') is higher than their melting temperatures (Tn+) [START_REF] Tournier | Multiple melting temperatures in glass-forming melts[END_REF].

First-order transitions occurring near Tg = 505 K in Pt57Cu23P20 were varying between Tx = 535.6 K and 548.8 K during heating . These transition temperatures slightly increased because the liquid enthalpy, relaxed at low heating rates, induced entropy and enthalpy variations due to the long annealing (15 hours) initially applied at Tg and to very low heating rates (0.2-10 K/mn) up to Tm [START_REF] Na | Observation of an apparent firstorder glass transition in ultrafragile Pt-Cu-P bulk metallic glasses[END_REF]Figure 1E. All latent heats of transitions at Tx, even those observed by undercooling, were attributed to the melt crystallization which increased from 20 J/g near Tg to 68.5 J/g at Tm [START_REF] Na | Observation of an apparent firstorder glass transition in ultrafragile Pt-Cu-P bulk metallic glasses[END_REF] in contradiction with our description of a new phase formation which is entropically driven.

The second objective is to show when these findings are compatible with a glass formation, following an increase of residual bond fraction at the transition at Tx, driven by the configuron entropy toward a new Phase 3 of lower enthalpy. These bonds may disappear at temperatures Tn+ higher than Tm as already observed in many glasses and predicted by non-classical nucleation equation [START_REF] Tournier | Undercooled Phase Behind the Glass Phase with Superheated Medium-Range Order above Glass Transition Temperature[END_REF][START_REF] Tournier | Dewetting Temperatures of Prefrozen and Grafted Layers in Ultrathin Films Viewed as Melt-Memory Effects[END_REF][START_REF] Tournier | Building and breaking bonds by homogenous nucleation in glass-forming melts leading to three liquid states[END_REF]. They give rise to a glass phase fraction in the melt above Tx. The maximum fraction of atoms involved into the glass phase is defined by the latent heat inducing transition at Tx.

The third objective is to predict the multiple melting temperatures (Tn+), higher than Tm, of these new glassy fractions and the total melting heat of Pt57Cu23P20, including the additional latent heat recovered at Tn+.

2-Practical Equations Applied to Liquid Pt57Cu23P20 Enthalpies

There are 3 fragile liquid states having enthalpies equal to lsHm, gsHm and lgHm where Hm is the melting enthalpy [START_REF] Tournier | Fragile-to-fragile liquid transition at Tg and stable-glass phase nucleation rate maximum at the Kauzmann temperature[END_REF]:

 ls (θ = 0) = ε ls0 = θ g + 2, ε gs (θ = 0) = ε gs0 = 1.5θ g + 2, θ 0m 2 = 8 9 ε ls0 - 4 9 ε ls0 2 , θ 0g 2 = 8 9 ε gs0 - 4 9 ε gs0 2 , ∆ε lg (θ) = [ε ls -ε gs ] = [ε ls0 -ε gs0 -θ 2 ( ε ls0 θ 0m 2 ⁄ - ε gs0 θ 0g 2 ⁄ )],
where (0m) and (0g) are the reduced and calculated Vogel-Fulcher-Tammann (VFT) temperatures higher than (-2/3) for fragile liquids. The enthalpy coefficients devoted to Pt57Cu23P20 are: Liquid 1

ε ls = 1.61301 (1 -θ 2 0.27743 ⁄ ) (1)
Liquid 2 ; (3).

ε gs = 1.41952(1 -θ 2 0.36622 ⁄ ), (2)

3-First-order Transitions Driven by the Entropy of Phase 3 during the First Heating

The singular enthalpy coefficients lg of Phase 3 are: 0, lg0/2 = -0.096745, ±0.14993*, lg0 = ±0.19349, lg (0m) = -0.34418, and (-0.33342 = -0.14933 -0.19349) and expected to correspond to various percolation thresholds [START_REF] Tournier | Multiple melting temperatures in glass-forming melts[END_REF][START_REF] Tournier | Undercooled Phase Behind the Glass Phase with Superheated Medium-Range Order above Glass Transition Temperature[END_REF][START_REF] Hasmy | Percolation transitions in compressed SiO2 Glasses[END_REF]. The entropy variation of Phase 3 from the solidus melting temperature (Ts = Tm = 823.8 K) down to the Kauzmann temperature TK = 364.43 K is equal to (-1/Tm) assuming that Hm = 1 J/g. The entropy variation of Phase 3 in Eq. ( 4), up to a temperature T, starts from the temperature TK:

𝑆(𝑇) = 2(1.93805)∆𝑆 𝑚 (𝑇-𝑇 𝐾 ) 𝑇 𝑚 -2∆𝑆 𝑚 𝐿𝑛( 𝑇 𝑇 𝐾 )(1.93905). (4)
For T = Tx S(Tx) is equal to the entropy change produced by the first-order transition which is equal to [lg(Tx)+ 0.34418]/Tx = 0.47928/Tx = 0.0008719 J/K/g at Tx = 548.8 K with Hm = 1 J/g, lg (Tx) = 0.13342 and TK = 364.63 K. The enthalpy coefficient inducing the first-order transition is equal to (-0.34418) deduced from  2 =  2 0m in Eq. ( 1) and lg ( 2 0m) = -0.34418 in Eq. ( 3). The measured latent heat at Tx is (49 J/g = 0.71533×Hm = 0.71533×68.5 J/g) [START_REF] Na | Observation of an apparent firstorder glass transition in ultrafragile Pt-Cu-P bulk metallic glasses[END_REF] and the latent heat coefficient, being higher than (0.47928), is enhanced by adding the singular enthalpy coefficients (0.096745+0.14993), leading to the theoretical value (0.72596×68.5 = 49.7 J/g). This glassy phase, having a very low enthalpy, cannot exist above Tm with a melting temperature Tn+ = 1.72596 Tm, which would be higher than Tg' = 1.38699 Tm = 1142.3 K. This glassy phase is melted at Tm = 823.8 K. First-order transitions temperatures lower than Tx = 548.8 K are calculated with Eq. ( 4) and temperature (TK) equal to 364.4 K in agreement with experimental latent heats. For Tx = 535.6 K, the measured latent heat (38.7 J/g) corresponds to a fraction (38.7/68.5 = 0.56496) of Hm and to an entropy of transition (0.0008327 J/K/g = (0.34418+lg)/Tx= 0.44598/535.6) with TK = 364.63 K and lg = 0.1018. The singular latent heat coefficient (0.096745) is added to (0.44598) to attain the theoretical value (0.54273) during the transition and a latent heat of 37.2 J/g. For Tx = Tg = 505 K, the highest relaxed entropy after isothermal annealing could be (0.0007306 = (0.34418+lg)/Tg) for lg = 0.02482 and TK = 364.63 K and the relaxed enthalpy (0.369×68.5 = 25.3 J/g) [START_REF] Na | Observation of an apparent firstorder glass transition in ultrafragile Pt-Cu-P bulk metallic glasses[END_REF]. The various values of lg depend on the enthalpy fraction which is relaxed during annealing at Tg and slow heating up to Tx. All these enthalpy changes are driven by the entropy of Phase 3 without any crystallization.

4-First-Order Transitions Driven by the Enthalpy of Phase 3 during Supercooling

The first-order transition temperatures obtained by supercooling are predicted using the non-classical nucleation model leading to nucleation temperatures (n-) in Liquid 2 defined in Eq. [START_REF] Ha | D. Supercooled liquids and polyamorphism[END_REF] [26]:

ε g0 θ n- 2 θ 0g 2 ⁄ + 3θ n-+ 2 -ε gs0 -∆ε = 0, or ε gs (θ = 0) = (3θ n-+ 2 -∆ε)/(1 - θ n- 2 θ 0g 2 ) ( 5
)
where  is equal to the singular values of the enthalpy coefficient of Phase 3. The initial enthalpy coefficient lg at the supercooling temperature would be much higher than (-0.34418) after 15 differential scanning calorimetry (DSC) cycles at 0.17 K/s from 1173 K to 373 K [START_REF] Na | Observation of an apparent firstorder glass transition in ultrafragile Pt-Cu-P bulk metallic glasses[END_REF] and equal to the enthalpy coefficient (lg = 0) of homogeneous liquid. The transitions during undercooling occur between 635 K and 689 K starting from the cooling enthalpy (lg = 0) as shown in Figure 2, using Eq. ( 5),  = 0.096745, 0.19349, 0.246675, and 0.34418 respectively and gs0 and  2 0g given by Eq. ( 2). These new transitions lead to new glassy Phases 3 which are accompanied by crystallization of the other liquid fraction. There is an experimental jump of undercooling rate between 689 K and 713 K corresponding to that of singular values from (-0.19349) to (-0.246675) in rough agreement with a group of 25 undercooling rates between 140 and 189 K following 15 previous thermal cycles [START_REF] Na | Observation of an apparent firstorder glass transition in ultrafragile Pt-Cu-P bulk metallic glasses[END_REF]Figure S4c. The residual glassy phases, in these conditions, are formed at temperatures Tx = 635, 689, 713 K and 750 K through first-order transitions inducing crystallization and melted after reheating at Tn+ = 903.5 K, 983.2 K, 1027 K and 1107 K respectively. The lowest enthalpy of Phase 3 is found again for  = 0.34418 without being accompanied by complementary enthalpy coefficients at Tx = 750 K leading to Tn+ = 1107 K. The nucleation of crystallization, at weak undercooling rate, starts in Figure 3 from lg = -0.34418 instead of zero in Figure 2. A first-order transition is expected at Tn+ = 1107 K in spite of an overheating at 1173 K. Eq. ( 5) is applied for (gs0 = 1.41952 -0.34418 = 1.07534), ( 2 og = 0.36622) as in Eq. ( 2), ( = 1-0.34418 = 0.65582) and leads to a nucleation temperature (742.1 K) near the experimental value (737.4 K). All measured latent heats [START_REF] Na | Observation of an apparent firstorder glass transition in ultrafragile Pt-Cu-P bulk metallic glasses[END_REF] were viewed as 'crystallization' enthalpies including those of glassy fractions from Tg to Tm and were represented by Eq. ( 6) including the latent heats of Phases 3 for Tx ≤ 548.8 K:

h cr (T) = 70.2[1 -484 T ⁄ ] 8.04 , (6)
The 'crystallization' heat hcr at Tm = 823.8 K was 69.2 J/g, applying Eq. ( 6). The highest crystallization temperature occurred at 737.4 K instead of 742.1 K with a 'crystallization' heat (hcr = 67.82 J/g). This homogeneous nucleation temperature is obtained with Eq. ( 5) for gs0 = 1.06795 instead of 1.07534, and  = 0.64883. The initial enthalpy (lg) before supercooling is (1.06795-1.41952 = -0.35157) instead of (-0.34418) corresponding to a 'crystallization' heat (67.82 J/g) deduced from Eq. ( 6). The 'crystallization' at 737.4 K starts from an undercooling rate (86 K) during the first thermal cycle and at 720.9 K from an undercooling rate (103 K) for the 15 th thermal cycle and a 'crystallization' heat (67.35 J/g), weakly reduced (67.82-67.35 = 0.47 J/g) associated with a weak increase of  up to 0.3585. This result confirms the existence of a second group of undercooling rates between 86 and 103 K inducing crystallization during the first DSC cycles [START_REF] Na | Observation of an apparent firstorder glass transition in ultrafragile Pt-Cu-P bulk metallic glasses[END_REF]. The glassy Phase 3 would be formed and melted through a first-order transition at 1107.3 K during the first thermal cycles as shown in Figure 3 and as already observed in Cu46Zr46Al8 [3;27]. The 'crystallization' heat hcr during supercooling, including the latent heat of glassy Phase 3, depends on singular value (). For  = 0.096745 and Tx = 635 K, the latent heat hcr is equal to -62.9 J/mole in Eq. [START_REF] Miltenburg | Calorimetric of a new solid phase in Triphenylphosphite[END_REF]. For  = 0.19349, Tx = 689 K, hcr = -66.1 J/mole in Eq. [START_REF] Miltenburg | Calorimetric of a new solid phase in Triphenylphosphite[END_REF]. For  = 0.246675, Tx = 713 K, hcr = -67.1 J/mole as shown in Figure 2. The missing melting heats (0.096745 Hm), (0.19349 Hm), (0.246675 Hm) and (0.34418 Hm) of Phases 3 are recovered at Tn+ = 1.096745 Tm, 1.19349 Tm, 1.246675 Tm and 1.34418 Tm respectively. The enthalpy of the crystallized fraction included in the 'crystallization' heat hcr is weakly reduced from Hm = 68.5 to 62.9 J/g when the elapsed time in the undercooling rate T increases. This phenomenon were already observed after annealing a glass-forming melt at temperatures lower than Tx [START_REF] Tournier | Multiple melting temperatures in glass-forming melts[END_REF][START_REF] Jiang | Crystallization in Pd40Ni40P20 glass[END_REF].

A measurement of melting heat Hm must eliminate the glassy fraction of configurons. The melt must be overheated above Tg' if possible, annealed above Tm to induce new growth nuclei able to crystallize the melt at Tm without undercooling. Eq. ( 5) predicts here a nucleation temperature of complete crystallization at 844 K with  = 1. The glassy fractions have been melted in Pt57Cu23P20 leading to Hm = 68.5 J/g [START_REF] Na | Observation of an apparent firstorder glass transition in ultrafragile Pt-Cu-P bulk metallic glasses[END_REF].

Conclusions:

The first-order transitions observed near Tg = 505 K in Pt57Cu23P20 at various temperatures varying from 535.6 to 548.8 K, are entropically driven during heating and lead to the formation of glassy Phases 3 with lower enthalpies at Tx without crystallization at these temperatures.

The first-order transitions observed by supercooling at the homogeneous nucleation temperatures Tn-= Tx between 635 and 750 K are driven by an increase of singular values of configuron enthalpies and lead to the formation of various Phases 3, being glassy from Tx to their melting temperature (Tn+). All these first-order transitions are accompanied by crystallization.

The measured crystallization enthalpy hcr, equal to 68.5 J/g, observed at the solidus temperature Ts, is complete. The total melting heat, including the latent heat expected at Tn+ above Tm resulting from the melting of glassy Phase 3, which are formed at Tx by undercooling, is equal to hcr ≤ 68.5 J/g. The crystallization heat slightly decreases with the elapsed time in the undercooled state and the annealing time between Tg and Tx.

This work shows that glass-forming melts are composed of crystallized fractions or liquid fractions and glassy fractions, melting at temperatures Tn+ much higher than the crystal melting temperature.

T The presence of glassy phases above the crystal melting temperature, after a first-order transition at Tx, obtained by undercooling below Tg and reheating, has for consequence that the crystallization heat must be measured by cooling the melt, if possible, from the second glass transition temperature (Tg'), and in all cases, by annealing it above Tm to grow new nuclei and crystallizing it without undercooling. *A latent heat is expected at Tn+ = 1.14766×Tm in the absence of long annealing at Tg [START_REF] Tournier | Undercooled Phase Behind the Glass Phase with Superheated Medium-Range Order above Glass Transition Temperature[END_REF][START_REF] Tournier | Building and breaking bonds by homogenous nucleation in glass-forming melts leading to three liquid states[END_REF].

Phase 3

 3 ∆ε lg (θ) = [ε ls -ε gs ] = [0.19349 -1.93805 × θ 2 ]

Figure 1 :

 1 Figure 1: First-order transition at Tx = 548.8 K during heating. Observed in [1]Figure 1E. T0m = 389.9 K. Increase of the enthalpy after 15 hours of annealing at Tg = 505 K. Melting temperature Ts = 823.8 K. Enthalpy coefficient (-0.34418) resulting from the transition driven by the entropy at Tx. Transformation of Phase 3 in a new glass at Tx = 548.8 K with an enthalpy coefficient ( = -0.72596) during the first heating and melting at Tm = 823.8 K.

Figure 2 :

 2 Figure 2: First-order transitions starting from the homogeneous liquid state (lg = 0). Nucleation of Phase 3 leading to crystallization for various undercooling rates (from 74 to 189 K). The enthalpy change starts from 0 toward four singular values of  in Eq. (5) equal to -0.096745, -0.19349, -0.246675 at 635, 689 K, 713 K and 750 K leading to the formation of glassy phases 3 and to spontaneous crystallization. Melting temperatures Tn+ = 903.5 K, 983.2 K, 1027 K and 1107.3 K. Transitions at Tx described in [1]Figure S4c. The 'crystallization' heat is equal to hcr for lg = -1.

Figure 3 :

 3 Figure 3: Nucleation of crystallization at weak undercooling rate (82 K) from lg = -0.34418. The enthalpy coefficient change starting from -0.34418 toward -1, the crystal enthalpy coefficient with  = 0.65582 in Eq.(5). Transitions at Tx described in[START_REF] Na | Observation of an apparent firstorder glass transition in ultrafragile Pt-Cu-P bulk metallic glasses[END_REF]FigureS4c. The 'crystallization' heat is equal to hcr for lg = -1.

Acknowledgments:

The author is grateful to M.I. Ojovan whose information's about percolation of configurons helped to improve the paper.