Sediment budget of the Napo River, Amazon basin, Ecuador and Peru

Abstract

International audienceThe Upstream-downstream sediment budget along the Napo River (100520 kill 2, 6300 m(3) s(-1)) was studied in the Andean foothills of Ecuador, at the west of the Amazon basin. A comparative study was made during four hydrological cycles (2001-2005) for three hydrological stations located upstream, and during one hydrological cycle (2004-2005) for the Fourth one located near the mouth of the Napo River (region of Iquitos in Peru). This analysis showed an unusual increase in the concentration of suspended sediment recorded for the western part of the Amazon plain. Like the runoff (81 l s(-1) km(2)), which is a world's maximum, the erosion rate (1160 t km(-2) year(-1), i.e. 47% of total suspended solid (TSS) export at the exit of Ecuador), one of the highest for a floodplain basin is the result of a stepper slope than in the rest of the Andean foothills, where typically sedimentation phenomena are predominant, and can be explained in part by a greater tectonic activity. Similar phenomenes were evidenced in small mountainous rivers in New Guinea (Milliman and Syvitski, 1992; Milliman, 1995). On the headwaters of the Napo River drainage basin, the tectonic uplift causes the Pastaza Megafan's existence. This progressively diverts the Course of Napo River towards north and also provokes the remobilization of fine fluvial deposits. Moreover, this geodynamic trend is completed by the impact of volcanic eruption, earthquakes and landslides. The combination of these phenomena, so common in the region, has provided a large sediment transfer, not only at present but also in the past, as can be confirmed by the presence of incised terraces, mainly formed by volcanic materials. Then, these results were compared with a similar Study carried out further south in the Madeira basin at the Bolivian foothills. These studies show the spatio-temporal variability of the relation between sediment transfer and geodynamic processes at the Andean Piedmont

Reproduction, feeding and migration patterns of Prochilodus nigricans (Characiformes: Prochilodontidae) in northeastern Ecuador

“…During the dry season, many of those habitats revert again to black water conditions. The northeastern Ecuadorian Amazon receives high precipitation (2.9 m yr -1 ) and has a runoff regime characterized by extreme sensitivity to rain events with flash floods (Laraque et al, 2009). A major increase in rainfall occurs between April and July.…”

“…During 1999, monthly observations of black prochilodus were made at six stations along the Aguarico River, covering an elevation gradient of 205-465 m, along with various environmental features (Fig. 1a, Laraque et al (2009), but in 1999, waters rose relatively higher and then declined to lower levels in the dry season. The annual hydrological cycle was divided into four seasons: I -Rising water (1 February to 30 April), IIFlood (1 May to 31 July), III -Falling water (1 August to 31 October); and IV -Low water (1 November to 31 January).…”

How important is it to integrate riverine suspended sediment chemical composition with depth? Clues from Amazon River depth-profiles

“…This vertical sorting leads to an increase in suspended particulate matter (SPM) concentration with depth, which has to be taken into account when estimating sediment fluxes of large rivers flowing in deep channels (e.g. Filizola, 2003;Laraque et al, 2009;Bouchez et al, 2010a;Lupker et al, 2011). In addition, vertical sorting leads to a coarsening of suspended sediments with depth.…”

Weathering Intensity in Lowland River Basins: From the Andes to the Amazon Mouth

“…This was done for the Amazon Basin only in a handful of studies 12,18,20 . Values for E were taken from multi-annual time series of sediment gauging performed within the framework of the HyBAm (Hydrology of the Amazon Basin, http://www.ore-hybam.org) program [21][22][23][24] . Similar rates were obtained when using denudation rates derived from cosmogenic, in situ-produced 10 Be [ref.…”