Professor Dr. Harald Sioli, founder of Amazonian Limnology and a major influential campaigner for the conservation of the region, died on Thursday, 14 October 2004, aged 94. He was the former Director of the Department of Tropical Ecology of the Max-Planck-Institute for Limnology, Plön. Most of his career was dedicated to research — medical, physiological, and, primarily, limnological — in Brazil. In 1954 he became head of the Department of Limnology of what was then the newly founded Instituto Nacional de Pesquisas da Amazônia (INPA) in Manaus. He returned to Germany in 1956 as Head of the Department and Director of the Hydrobiological Institute in Plön, later the Max-Planck Institute for Limnology (MPIL), which resulted in the long-term collaboration with INPA that continues today.

We owe to Harald Sioli the classification of the Amazonian rivers (black-, white-, and clearwater) and their inundation systems (igapó and várzea), and the entire basis of our understanding of much of Amazonian ecology and limnology. With his explanations (his warnings) that the deforestation of the Amazon would lead to a major increase in atmospheric carbon, it was Harald Sioli who, unwittingly, gave rise to the widely cited myth of the Amazon as “the lungs of the planet.”

Two issues of Amazoniana were dedicated to Prof. Sioli on the occasion of his 90^th birthday — Volume 16(3/4) and Volume 17(1/2). In the first of these, Dr Wolfgang Junk (2001) wrote an appraisal of Sioli's scientific work and published his curriculum vitae, including a full listing of his scientific publications. Pages 169–172 of Volume 18(1/2) of Amazoniana provided a series of short memoirs and comments from numerous world-renowned scientists, friends, and colleagues, including such as Sir Ghillean Prance, Dr Jürgen Haffer, Dr Eneas Salati, Dr Herbert Schubart, Prof. Ernesto Medina, Prof. Nigel Smith, Prof. Loki Schmidt, Dr William Rodrigues, and Dr Jorge Arias. Wolfgang Junk, Director of the Working Group for Tropical Ecology of the MPIL, wrote “During his active working period and also thereafter, Professor Sioli exerted a strong influence on the development of tropical ecology at an international level and created an everlasting monument — his pioneering scientific work about Amazonia” (in litt., 18 October 2004).