Composition of Dissolved Organic Matter

The concentrations of DOC in major rivers typically range from 250 to 750 pM, and concentrations in the surface ocean range from 60 to 90 J.M (Table I). Most of the river data compiled in Table I are from the Amazon River system (Hedges et al., 1994, 2000), the Parana River system (Depetris and Kempe, 1993), and the Mississippi River (Benner and Opsahl, 2001). The seawater data are from surface water samples collected in the Pacific and Atlantic Oceans (see Table I for references). Total hydrolyzable neutral sugars (glucose, galactose, mannose, xylose, fucose, rhamnose, and arabinose) account for about 1-2% of river DOC and 2-6% of ocean DOC, indicating 

TABLE I Typical Chemical Characteristics of DOM from Major Rivers (Amazon, Parana, and Mississippi) and Surface Waters of the Open Ocean (Pacific and Atlantic) 

Chemical characteristics Major carbon functional groups Major rivers Surface ocean Reference 

Note Humic substances (HS) are operationally defined as DOC that is retained on XAD-2 or XAD-8 resins. UDOM is operationally defined as DOC that is retained by a membrane with a 1 nm pore size and 1000 Da molecular weight cutoff. 13C-NMR spectroscopy was used for analysis of carbon functional groups, which are presented as a percentage of the total organic carbon in the sample. THNS, total hydrolyzable neutral sugars THAA, total hydrolyzable amino acids. 

It is somewhat surprising that these two major classes of biochemicals account for such a small percentage of the DOC in these environments. Neutral sugars and amino acids typically account for 30-60% of the carbon in herbaceous vascular plant tissues and phytoplankton biomass, whereas 

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McCarthy, M. D., J. I. Hedges, and R. Benner. 1993. The chemical composition of dissolved organic matter in seawater. Chemical Geology 107 503-507. 

As discussed in Section V, the spectrum of substrates and substrate proxies currently used to measure enzyme activities in marine systems is limited and most likely does not adequately represent the macromolecules actually available to aquatic microbial communities. Despite progress in recent years, our knowledge of the molecular structure and composition of dissolved organic matter is still only rudimentary. Although carbohydrates constitute an estimated 25-50% of DOC in seawater (Benner et al., 1992),... 

Fischer, H., Meyer, A., Fischer, K., and Kuzyakov, Y. (2007). Carbohydrate and amino acid composition of dissolved organic matter leached from soil. Soil Biol. Biochem. 39, 2926-2935. 

Starikova, N.D., Yablokova, O.G. and Korzhikova, L.I., 1976. Determining the molecular composition of dissolved organic matter by gel filtration. Oceanology, 16 571 -575. 

Gigliotti, G., Kaiser, K., Guggenberger, G. and Flau-maier, L. (2002) Differences in the chemical composition of dissolved organic matter from waste material of different sources. Biology and Fertility of Soils 36, 321-329. 

Spark KM, Swift RS (2002) Effect of soil composition and dissolved organic matter on pesticide sorption. Sci Total Environ 298(1-3) 147-161... 

Munster, U., and R. J. Chrost. 1990. Origin, composition, and microbial utilization of dissolved organic matter. In Aquatic Microbial Ecology (J. Overbeck and R. J. Chrost, Eds.), pp. 8-46. Springer-Verlag, Berlin. 

Sun, L., E. M. Perdue, J. L. Meyer, and J. Weis. 1997. Use of elemental composition to predict bioavailability of dissolved organic matter in a Georgia river. Limnology and Oceanography 42 714—721. 

IV. RELATIONSHIPS BETWEEN THE CHEMICAL COMPOSITION AND BIOREACTIVITY OF DISSOLVED ORGANIC MATTER... 

IV. THE EFFECT OF DISSOLVED ORGANIC MATTER COMPOSITION ON HYDROPHOBIC ORGANIC CONTAMINANT SPECIATION... 

Coagulation processes in estuaries are affected by other factors such as clay composition, particle size, and concentration of dissolved organic matter, to mention a few. For example, early work has shown that metal hydroxides can flocculate from dis-solved/colloidal organic matter during the mixing of river-derived iron and seawater in the mixing zone of estuaries (Sholkovitz, 1976, 1978 Boyle et al, 1977 Mayer, 1982) (more details are provided on metal colloidal interactions in chapter 14). Surface sediments in... 

Foreman, C.M., and Covert, J.S. (2003) Linkages between dissolved organic matter composition and bacterial community. In Aquatic Ecosystems Interactivity of Dissolved Organic Matter (Findlay, S.E.G., and Sinsabaugh, R.L., eds.), pp. 343-359, Academic Press, New York. 

Aluwihare, L. I., Repeta, D. J., and Chen, R. F. (2002). Chemical composition and cycling of dissolved organic matter in the Mid-Atlantic Bight. Deep-Sea Research II49, 4421—4443. 

Inside a landfill leachate plume the environment is characterized by the presence of reduced species and high concentrations of dissolved organic matter. This environment is partly due to the composition of the leachate from the landfill and partly due to microbial processes in the plume. Since this environment is very different from that of uncontaminated, oligotrophic, often aerobic aquifers surrounding the plume, the composition of the microbial population of the plume is dramatically different from the indigenous microbial population of the uncontaminated aquifer. 

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