Phosphorus transport by the largest Amazon tributary (Madeira River, Brazil) and its sensitivity to precipitation and damming

Abstract

Phosphorus transport by the largest Amazon tributary (Madeira River, Brazil) and its sensitivity to precipitation and damming. AbstractOriginating in the Bolivian and Peruvian Andes, the Madeira River is the largest tributary of the Amazon River in terms of discharge. Andean rivers transport large quantities of nutrient-rich suspended sediments and are the main source of phosphorus (P) to the Amazon basin. Here, we show the seasonal variability in concentrations and loads of different P forms (total, particulate, dissolved and soluble reactive P) in the Madeira River through eight field campaigns between 2009-2011. At our sampling reach (Porto Velho, Brazil), the Madeira River transports about 177-247 Gg P yr -1 , mostly linked to particles (~85%). Concentrations and loads of all P have a maximum at rising waters and a minimum at low waters. Total P concentrations were substantially lower at a given discharge at falling water than at a similar discharge at rising water, indicating a clockwise hysteresis. The peak of P concentrations matched the peak of rainfall in the upper basin, suggesting an influence of precipitation-driven erosion.Projected precipitation increase in the eastern slopes of the Andes could enhance sediment yield and hence the P transport in the Madeira River. However, as most of the P is particulate, we hypothesize that the planned proliferation of hydropower dams in the Madeira basin has the potential to reduce P loads substantially, possibly counteracting precipitation-related increases. In the long term, this could be detrimental to highly productive downstream floodplain forests that are seasonally fertilized with Prich deposits.

Turbidity and dissolved organic matter as significant predictors of spatio‐temporal dynamics of phosphorus in a large river‐floodplain system

“…P occurs as dissolved and particulate inorganic and organic forms. In the present study, P was mainly in particulate form, similarly to other turbid rivers (Almeida et al, 2015;Pedrozo & Bonetto, 1987). A substantial part of the PP carried by the Middle Paraná River is deposited in floodplain lakes during high waters (Maine et al, 2004).…”

“…of P by acting as storage sites for particles (González-Sanchis, Murillo, Cabezas, Vermaat, & Comín, 2015;Kiedrzyńska et al, 2008;Maine, Suñe, & Bonetto, 2004). In contrast, other authors have shown that floodplains are P sources due to the exportation of the dissolved fraction (Almeida et al, 2015;Fisher & Acreman, 2004;Reavis & Haggard, 2016). The spatial dynamics of P also shows variable trends; while some studies have shown an increasing concentration from the main channel (MC) to the floodplain (Roberto, Santana, & Thomaz, 2009;Villar, de Cabo, Vaithiyanathan, & Bonetto, 1999); other studies have shown the opposite (González-Sanchis et al, 2015;Maine et al, 2004).…”

Extreme floods increase CO2 outgassing from a large Amazonian river

“…), and the climate is humid tropical, with mean annual precipitation of about 2000 mm (Moreira‐Turcq et al ). This high annual precipitation is unevenly distributed across the year (Villar et al ), so that discharges in the Madeira River can vary by one order of magnitude between low and high waters, averaging 19,000 m 3 s −1 at Porto Velho (Almeida et al ) and 31,000 m 3 s −1 at the mouth (Moreira‐Turcq et al ). The Bolivian plain, after the headwater tributaries exit the Andes, is characterized by the occurrence of large wetlands.…”

Hydropeaking Operations of Two Run-of-River Mega-Dams Alter Downstream Hydrology of the Largest Amazon Tributary

“…River, the largest source of water, sediments, and nutrients to the Amazon River mainstem (McClain and Naiman, 2008;Almeida et al, 2015).…”