From the Andes to the Atlantic: the Evolution of Organic Matter in the Amazon River System
Abstract
We compare the compositions of dissolved, fine and coarse particulate organic matter fractions (DOM, FPOM and CPOM respectively) from 31 river sites in Bolivia and Peru with 18 sites along the Amazon mainstem. The diversity of sites - ranging from wet and dry Andean headwater environments, to depositional foreland reaches, to major lowland rivers - allows us to assess the compositional evolution of organic matter along a 5000 km transect draining Peru and a 3000 km transect draining Bolivia. Organic matter size fractions were assessed by concentration, elemental (%OC, %N, C/N), isotopic (13C, 14C, 15N), lignin phenol, hydrolysable amino acid, and mineral surface area analyses. Similar to previous results from the lower Amazon and from Bolivian tributaries, the degree of mineral association was the most important factor in determining the composition of riverine organic matter. However, organic matter within a size class evolves considerably from the Andes to the lowlands. The Bolivian transect showed OM fractions becoming more diagenetically altered downstream, but the Peruvian transect showed a more complicated picture. Together, data suggest that underlying changes to sediment surface area and mineralogy may be the primary control of organic matter composition with fractions, as well as between fractions. These findings highlight the importance of organo-mineral associations and the need to describe mineral phases associated with riverine organic matter.
- Publication:
-
AGU Spring Meeting Abstracts
- Pub Date:
- May 2005
- Bibcode:
- 2005AGUSM.H23C..03A
- Keywords:
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- 0400 Biogeosciences;
- 1040 Isotopic composition/chemistry;
- 1055 Organic geochemistry;
- 1615 Biogeochemical processes (4805);
- 1806 Chemistry of fresh water