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).