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Three symposia on environmental geochemistry in tropical countries, held in Niter6i, Brazil (1993), in Cartagena, Colombia (1996) and in Nova Friburgo, Brazil (1999), made it very clear that tropical geochemistry is of world standard and fast increasing in multi disciplinarily and impact on important geochemical paradigms. It has additionally strong links with the economy of tropical countries, such as mining and industrialisa tion and is in full development for treating environmental problems caused by human activities of urban or industrial origin. We must compliment Prof. Jorge Abriio and his colleagues in Brazil and Dr. Gloria Prieto and her colleagues in Colombia for these ini tiatives. The participation of respectively 180 and 150 scientists, coming from 15 different countries for the first and second symposia, has shown that a large interest exists for tropical environmental geochemistry. It also demonstrates the necessity to understand tropical environmental problems. The organisation of a large international symposium is not possible without the assistance of state and federal authorities, for which those of Brazil and Colombia have to be complimented. The 3rd Symposium on Environmental Geochemistry in Tropical Countries was the last of the series and was attended by 22 countries and 170 participants and treated a number of related environmental and economic problems.
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Environmental Science Series editors: R. Allan . U. Forstner . W. Salomons Springer-Verlag Berlin Heidelberg GmbH Luiz Drude Lacerda . Ricardo Erthal Santelli Egbert Duursma . Jorge Joao Abrao (Eds.) Environmental Geochemistry in Tropical and Subtropical Environments With 128 Figures and 80 Tables , Springer Editors Prof. Luiz Drude de Lacerda Instituto de Ciencias do Mar, Universidade Federal do Ceara, Av. Aboli- 6 8 10 12 17080 ±890 - . 20420 ±1600- 20 22 24 "U Fig. 2.6. Core BM6 (Lake Barombi, Cameroon). Simplified lithological log compared with profiles of TOC, C, arboreal pollen contents and C/N ratios. The wavy lines on the lithological log indicate slump intervals (after Giresse et aI. 1994) The geochemical parameters indicate the existence of two main units. The lower unit (from the base up to 11 m) is characterised by TOC, C/N and £513 C values that show large amplitudes of variation around 8%, 18 and in the range -24 to -30%0, respectively. In the upper unit, by contrast, these parameters show little variation, with average values around 5%, 15 and -32%0, for TOC, C/N and £513 C, respectively. 14 A. Sifeddine . D. Wirrmann 2.4 Interpretation and Discussion For the different studied sites, organic matter with 613C values between -8 and -36%0 is broadly characteristic not only of aquatic plants and/or phytoplankton but also land plants from forest or savanna environments. Thus, the 613C value alone cannot be used to interpret the results in terms of changing environmental conditions. On the other hand, the C/N ratios for all sites lie in the range 5-40, which enables discrimination between lacustrine and terrestrial environments. However, in the latter case, the C/N ratio does not allow a distinction to be made between forest and savanna environments. In order to discriminate a dominant lacustrine component with respect to terrestrial inputs, and also to differentiate forest from savanna environments, it is proposed here to cross correlate the C/N and 6 13 C values (Fig.2.7a). The interpretations are then confronted with palynological results expressed as percentage abundance of arboreal pollen (%AP). For Lake Ossa, the combination of C/N and 6 13 C data on a cross-plot diagram (Fig.2.7b) shows a general distribution of points lying close to