Besides being the largest evaporative basin in the planet, Amazônia also holds one of the largest diversity in plants, animals, and aquatic environments. The latter is largely composed of fresh waters, although saline environments may be found in the eastern part of the basin, where it meets the Atlantic Ocean. The largest volume of fresh water are associated with the rivers, followed by the floodplain lakes, which are of crucial importance for fisheries. The rivers may vary from the mighty Amazon to tiny streams (“igarapés”). Depending o its geographical position and the type of soil they are draining, rivers in Amazônia may have different colors ad chemical composition. The white water rivers, with headwaters in the Andes or sub-andean regions, are rich in suspended solids, with a “milk and coffee” colour, and pH close to neutrality. The black-water rivers generally drain podzolic soils from the cristaline shield; they are poor in suspended solids, rich in humic and fulvic acids, with an acid pH. The clear water rivers originates in the cristaline shield or the sedimentary highland terrain; they generally have a variable chemical composition, ranging from rich to very poor, depending on the terrain they are draining; they carry virtually no suspended solids.
For millions of years, the Amazonian rivers remained untouched by humans. However, over the last decades, human activities have started to affect the structure and functioning of the Amazonian rivers, especially the small streams and rivers. It is widely known the problem of mercury contamination of waters and biota resulting from gold mining. Another emerging problem is the effect of land use changes in the biogeochemistry of rivers. The population in the region has increased manifolds, and are specially concentrated in relatively large urban centers. As a consequence, untreated domestic sewage are being directly dumped to rivers, drastically altering the structure and functioning of some of them. The objective of this talk is, therefore, to show how the several water focused LBA projects are studying the relationship between anthropogenic actions and the structure and functioning of Amazonian rivers, at different scales.