The Pulse of the Amazon: Fluxes of Dissolved Organic Carbon, Nutrients, and Ions From the World's Largest River

The Amazon River drains a diverse tropical landscape greater than 6 million km(2), culminating in the world's largest export of freshwater and dissolved constituents to the ocean. Here, we present dissolved organic carbon (DOC), organic and inorganic nitrogen (DON, DIN), orthophosphate (PO43-), and major and trace ion concentrations and fluxes from the Amazon River using 26 samples collected over three annual hydrographs. Concentrations and fluxes were predominantly controlled by the annual wet season flood pulse. Average DOC, DON, DIN, and PO43- fluxes (+/- 1 s.d.) were 25.5 (+/- 1.0), 1.14 (+/- 0.05), 0.82 (+/- 0.03), and 0.063 (+/- 0.003) Tg yr(-1), respectively. Chromophoric dissolved organic matter absorption (at 350 nm) was strongly correlated with DOC concentrations, resulting in a flux of 74.8 x 10(6) m(-2) yr(-1). DOC and DON concentrations positively correlated with discharge while nitrate + nitrite concentrations negatively correlated, suggesting mobilization and dilution responses, respectively. Ammonium, PO43-, and silica concentrations displayed chemostatic responses to discharge. Major and trace ion concentrations displayed clockwise hysteresis (except for chloride, sodium, and rubidium) and exhibited either dilution or chemostatic responses. The sources of weathered cations also displayed seasonality, with the highest proportion of carbonate- and silicate-derived cations occurring during peak and baseflow, respectively. Finally, our seasonally resolved weathering model resulted in an average CO2 consumption yield of (3.55 +/- 0.11) x 10(5) mol CO2 km(-2) yr(-1). These results represent an updated and temporally refined quantification of dissolved fluxes that highlight the strong seasonality of export from the world's largest river and set a robust baseline against which to gauge future change.

Automated summary

The study reveals that the fluxes of dissolved organic carbon and nitrogen in the Amazon River are primarily controlled by the seasonal flood pulse, and various ion concentrations and fluxes exhibit distinct response patterns, reflecting the seasonal characteristics of the river.