Data from: Chemodiversity of dissolved organic matter in the Amazon Basin

Regions in the Amazon Basin have been associated with specific
biogeochemical processes, but a detailed chemical classification of the
abundant and ubiquitous dissolved organic matter (DOM), beyond specific
indicator compounds and bulk measurements, has not yet been established.
We sampled water from different locations in the Negro, Madeira/Jamari and
Tapajós River areas to characterize the molecular DOM composition and
distribution. Ultrahigh-resolution Fourier transform ion cyclotron
resonance mass spectrometry (FT-ICR-MS) combined with excitation emission
matrix (EEM) fluorescence spectroscopy and parallel factor analysis
(PARAFAC) revealed a large proportion of ubiquitous DOM but also unique
area-specific molecular signatures. Unique to the DOM of the Rio Negro
area was the large abundance of high molecular weight, diverse
hydrogen-deficient and highly oxidized molecular ions deviating from known
lignin or tannin compositions, indicating substantial oxidative processing
of these ultimately plant-derived polyphenols indicative of these black
waters. In contrast, unique signatures in the Madeira/Jamari area were
defined by presumably labile sulfur- and nitrogen-containing molecules in
this white water river system. Waters from the Tapajós main stem did not
show any substantial unique molecular signatures relative to those present
in the Rio Madeira and Rio Negro, which implied a lower organic molecular
complexity in this clear water tributary, even after mixing with the main
stem of the Amazon River. Beside ubiquitous DOM at average H ∕ C and O ∕ C
elemental ratios, a distinct and significant unique DOM pool prevailed in
the black, white and clear water areas that were also highly correlated
with EEM-PARAFAC components and define the frameworks for primary
production and other aspects of aquatic life.