On 14 October 2004 Prof. Dr. Harald Sioli passed away in Plön. His professional life was strongly focussed on the Amazon region. In 1934, before the beginning of the Second World War, he went to Brazil to initiate and conduct ecophysiological studies on toads in the dry northeastern part of the country. His studies were interrupted by the war. In 1945, after the release from war-related internment, he started the first limnological investigations in Amazonia. But he looked at the Amazon region not as a limnologist but in the sense of Bluntschli as a unit of land, water, and forest, as a landscape-ecologist, a term first used by Troll.
Based on the local terminology of white-water, black-water, and clear-water used by the local population and first mentioned by Wallace in scientific literature in the middle of the last century, Sioli applied hydrochemical and physical parameters to elaborate a scientific classification system of Amazonian rivers. He studied the relationship between water quality and soil conditions and was a pioneer in describing the large scale hydrogeochemical structure of the Amazon basin.
He explained the existence of the large fringing floodplains of the Amazon River and its major tributaries with sea level oscillations during glacial and interglacial periods. He related the various types of floodplains and their specific structures to differences in the sediment load of the rivers, which he explained by geological and geomorphological differences in the respective catchment areas and variations of vegetation cover. Some decades later his considerations were confirmed by his collaborator, the mineralogist, Georg Irion.
The extreme nutrient poverty of many Amazonian streams and rivers led to Sioli’s statements about the poverty of soils in the catchment areas. He contradicted public opinion about the high fertility of Amazonian soils and pointed to the low agricultural potential of Central Amazonia during a period when the Brazilian government began to initiate plans for large scale agro-industrial development of the region. Therefore, in the middle of the 1970s, he was often heavily criticized by Brazilian development planners. Today we know that these critics were wrong.
The strong recognition of Sioli’s work resulted in his appointment in 1957 by the Max-Planck-Society as Director of the Plöner Hydrobiologische Anstalt, known as Max-Planck-Institute for Limnology (MPIL). From Plön he continued his work in the Amazon region in collaboration with Djalma Batista, at that time Director of the National Institute for Amazonian Research (INPA) at Manaus. In 1965, they co-founded the international scientific journal AMAZONIANA that publishes limnological and landscape-ecological articles about the Neotropis. In 1966, the Max-Planck-Institute for Limnology was divided into two departments. Sioli became Director of the Department for Tropical Ecology and focussed his activities on studies of the Amazon. In 1969 a contract for scientific collaboration was signed between the Brazilian Research Council (CNPq) and the Max- Planck-Society (MPG). The contract was renewed and amplified in 1984.
After his retirement in 1978, the collaboration between INPA and MPIL Plön continued as did Sioli’s engagement with tropical ecology. His landscape-ecological research approach, that he presented at many international congresses, was of interest to many ecologists, not only those in the tropics. With more than 150 publications in scientific journals and his book which was edited in 1984 and entitled, “The Amazon: Limnology and Landscape Ecology of a Mighty Tropical River and its Basin” he has made a fundamental and everlasting contribution to tropical ecology.
The impact of Sioli’s activities reached far beyond the impact of his scientific publications. His very early warnings about the destruction of the Amazon rain forest and his appeals to protect the area for the benefit of nature and the local population including the Amerindian tribes, were heavily criticized by some politicians and development planners, but received endorsement from Brazilian scientists and were enthusiastically accepted by Brazilian students. This development fortified the ideas for the need of environmental protection in Brazil. Some of the students, influenced by his ideas during the sixties and seventies, are today leading scientists and administrators in Brazilian state and governmental organizations and have introduced ecological aspects into politics, planning and administration.
He dedicated the last years of his life to writing his memoirs. This impressive document shows the transition of science from pre-war travel documents of natural historians to modern natural sciences accompanied by profound changes in the political and socio-economic conditions of the Brazilian society.
Harald Sioli held many positions in international associations and working groups such as: membership in the Sectional Committee for Productivity of Freshwater (International Biological Project 1962-1969), membership in the Commission on Ecology (International Union for Conservation of Nature and Natural Resources 1963-1974) and was President of the Association of Tropical Biology (1971-1973). He was also a corresponding member of the Brazilian Academy of Sciences and a honorary member of the Society for Tropical Ecology. He received many awards such as: the Brazilian Order of the Southern Cross Officers Rank (1967), the Science for Amazonia medal from the Brazilian National Institute for Amazon Research (1977), a Medal from the Foundation La Salle of Natural Sciences First Class (1990) and Gran Cruz, the highest Brazilian award for scientific work (2000). In 1990, the first International Symposium on the Great Rivers of Latin America was dedicated to Harold Sioli as the “Father of South American River-Limnology.”
With Harald Sioli we have lost a great tropical ecologist.
Sioli, H. (ed.) 1984. The Amazon: Limnology and landscape ecology of a mighty tropical river and its basin.- Dr. W. Junk Publishers, Kluwer Academic Publishers Group, Dordrecht, Boston, Lancaster. 763 pp.