A first quantitative estimate of trace metal fluxes from Amazon river and its main tributaries

Abstract

The trace metal (V, Cr, Mn, Co, ell, Zn, As, Rb, Sr, Mo, Cd, Sb, Cs, Ba, U) concentrations and temporal variabilities of the Amazon river and its main tributaries are studied on time series basis in the major tributaries of Amazon river (Negro, Madeira and Solimbes Rivers) and at Obidos station on the Amazon mainsteem which represents 90% of the total discharge of Amazon river to the Ocean. Variations of river chemistry may reflectvariations of the sources. The "Shield" rivers(as the Rio Negro) have typically depleted concentrations in As, Sr, Ba, Cu, and V as compared with Andean rivers. Elements such Mn and As are mainly transported by the flood flows. These elements are known to be concentrated in lateric (ferricrete) soils which represent 80% in the Amazon basin, suggesting that these elements are washed away in solution during the high discharge. Moreover, these elements can be stored in the surrounding floodplain areas (varzea) where deposition/resuspension cycles as well as the exchange rate between floodplain and mainstream channel may control at least partially the temporal variation of redox element concentrations such Mn and As. Implication on these results on the trace element flux from Amazon River to the Atlantic Ocean is discussed.

Continental bedrock and riverine fluxes of strontium and neodymium isotopes to the oceans

“…How the isotope composition changes with water discharge is not known. The total annual Sr flux calculated here (0.171 Mt yr −1 ) is slightly higher than that calculated by Vance et al [2009] for the combined Amazon, Tapajos and Xingu (0.159 Mt yr −1 ), but both are lower than the flux calculated using the monthly time series data of Sr and runoff (0.205 Mt yr −1 [ Seyler et al , 2003]), indicating that Sr fluxes based on few data are uncertain by at least 20%, even for a hydrologically less dynamic river such as the Amazon. Reducing uncertainties in river fluxes and isotope composition require long‐term time series data of Sr concentration and isotope composition.…”

“…We take these values as representative of the total water discharge of the Amazon River system (6300 km 3 yr −1 ), a value that is uncertain by at least 10%. We also note that dissolved Sr concentrations of the Amazon decrease slightly with increasing water discharge [ Seyler et al , 2003]. Palmer and Edmond [1992] sampled the Amazon at Obidos in June 1976 and 1977 under high‐flow conditions.…”

Assessment of Arsenic Contamination in the Red River: High Resolution Monitoring Coupled With Spatial Analysis by Gis

“…After complete cooling, the digested solution was evaporation to dryness. Each sample was brought to 10 ml using 150µl HNO 3 (14M super pure and double deionized (milli-Q®) water [18,20].…”

“…Homogenized sample aliquots were filtered on site using 0.2µm Sartorius® cellulose acetate filters. Filtrates were collected in 14cc polypropylene tube, previously decontaminated and thoroughly rinsed with the filtrate, acidified (HNO 3 super pure grade; 1 : 1000) and stored at 4 °C until analysis [18].…”

“…The average dissolved As concentrations were 2.86 µg/l and 3.45 µg/l in high water and low water levels, respectively, showing the slight diminution of dissolved As concentrations in high water condition due to the dilution effect. This dilution phenomenon of dissolved metal concentrations by water discharge was observed in many rivers in the world such the Mekong [16], the Yellow [21], the Garonne [4], the Amazone [18] or the Mississippi [19].…”