Study Area
The Caquetá River basin is a western Amazonian affluent of Andean origin, formed at 3,850 m above sea level (a.s.l.) by the confluence of three different minor tributaries in the Peñas Blancas Páramo, located in the East Mountain Chain in the Southeast Region in Colombia (IGAC, 1996). It runs over 1,200 km in a southeast direction before it merges to the main channel of the Amazon River, crossing the Caquetá, Putumayo, and Amazonas departments in Colombia, until it’s named the Rio Japurá at the Colombian-Brazilian border (IGAC, 1996, 1999).
The upper section of the Caquetá River drains most of the western uplift of the Guyana Shield, a formation from the Miocene characterized by a crystalline basement. Shields are very evolved soils with low nutrient and organic contents. Above 500 m a.s.l. (Figure 2a), the aquatic systems of the Caquetá́ basin are typically Andean ecosystems with dominant rocky substrates, abrupt slopes, and high flow (Figure 2b). Below the 500 m a.s.l., denoted as Amazonian Piedmont, aquatic ecosystems are characterized by basement alluvial fans (Figure 2b) of volcanic origin with elements from the Andes Mountain chain (Hoorn, 1994; Galvis et al. , 2007).