Repeta, D. J. Woods Hole Oceanographic Institution,
Quan, T. J. University of California, San Diego,
Accardi, A. Woods Hole Oceanographic Institution,
Aluwihare, L. I. Woods Hole Oceanographic Institution,

Dissolved organic matter (DOM) in rivers and lakes has previously been shown to have a higher C/N ratio, a more aromatic character, and absorb light more strongly than DOM in marine waters. These compositional differences have led to the inference that marine and freshwater DOM are chemically distinct, reflecting differences in the major biochemical constituents of their presumed sources (terrestrial plants and marine algae). However, most previous studies were made on DOM collected by adsorption onto hydrophobic resins, which retain only a small fraction of the total DOM. Using ultrafiltration, we have collected the > 1 kD size fraction of DOM from geographically diverse rivers and lakes in the US and compared its spectrometric and molecular properties with DOM collected from surface sea water and porewaters recovered from marine sediments. We find that acyl polysaccharide previously identified in sea water is a major constituent of fresh water DOM as well. Like sea water, the NMR spectra of fresh water DOM have major resonances from carbohydrate (5-5.5 ppm, 3.5-4.5 ppm, 1.3 ppm) acetate (2.0 ppm), and lipids (1.3 ppm, 0.9 ppm). Molecular level analyses of monosaccharides released by acid hydrolyses show the same major neutral sugars (galactose, glucose, mannose, fucose, xylose, rhamnose, and arabinose) in a similar ratio to sea water. Our results suggest microalgae are a major source of persistent DOM in freshwater environments, and that a significant fraction of DOM supplied to the ocean by rivers is not of terrestrial origin.
Day: Monday, Feb. 1
Time: 02:00 - 02:30pm
Location: Eldorado Hotel
Code: SS34MO0200E