Sources of Dissolved Organic Carbon

Excellent overviews of the sources and composition of DOC in aquatic ecosystems are provided in Chapters 1, 2, and 4. In this chapter, I focus on sources of DOC at large spatial scales. 

For lakes, relationships between DOC concentration and some measure of the relative size of the drainage area (e.g., drainage area/lake area ratio) and between DOC concentration and water residence time can be used to estimate the importance of autochthonous DOC by extrapolation. In the study of Experimental Lakes Area lakes by Curtis and Schindler (1997), the y intercept of the DOC concentration versus catchment/lake area ratio (the DOC value at minimal catchment area) is approximately l-2mgL 1. In the same study, the asymptote of the DOC concentration versus water residence time relationship at infinitely long residence times is roughly 2-3 mg L-1. This would suggest that for lakes in this region, autochthonous sources account for perhaps as much as 3 mg L 1 of the DOC present. 

Stable carbon isotope ratios have also been used to determine the sources of lake DOC. Baron et al. (1991) used 13C analysis to show that autochthonous sources dominated the DOC of an alpine lake during most periods while allochthonous sources dominated the DOC in a subalpine lake. The high DOC concentrations observed during spring snowmelt and early summer in both lakes, however, were mostly derived from allochthonous sources. As with streams and rivers, synoptic regional studies of 13C and 14C would provide important new information on broad spatial patterns and controls on the sources of DOC in lakes. 

In contrast to rivers and lakes, autochthonous processes appear to be the overwhelmingly dominant source of DOC in the oceans. In a survey of shallow and deep waters of the Atlantic and Pacific Oceans, Opsahl and Benner (1997) used concentrations of lignin in DOM to determine that terrigenous matter accounted for only 0.7-2.4% of the DOC present. Terrigenous DOC concentrations were about 2.6 times higher in the Atlantic than in the Pacific Ocean, presumably because of the 3.6 times greater riverine water discharge to the Atlantic. 

A recent study of rainwater DOC suggested that rain also may be a significant source of DOC to the open ocean. The DOC concentration of marine rain was reported to be 0.3 mg L 1 and the global rainwater DOC flux to the oceans was estimated to be 0.43 x 1012 gC yr 1, about the same magnitude as the river flux of DOC (Willey et al., 2000). 

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Figure 1. Allochthonous and autochthonous sources of dissolved organic carbon in natural waters. (Reproduced with permission from reference 1. Copyright 1985 Kluwer Academic Publishers.)...

Schindler, J. E., and D. P. Krabbenhoft. 1998. The hyporheic zone as a source of dissolved organic carbon and carbon gases to a temperate forested stream. Biogeochemistry 43 157-174. 

Findlay, S., R. L. Sinsabaugh, D. T. Fischer, and P. Franchini. 1998. Sources of dissolved organic carbon supporting planktonic bacterial production in the tidal freshwater Hudson River. 

Hemond, H. F. 1990. Wetlands as the source of dissolved organic carbon to surface waters. In Organic Acids in Aquatic Ecosystems (E. M. Perdue and E. T. Gjessing, Eds.), pp. 301-313. Wiley, New York, NY. 

Meyer, J.L., J. Bruce Wallace, and S.L. Eggert. 2000. Leaf fitter as a source of dissolved organic carbon in streams. Ecosystems 1 240-249. 

Bianchi, T.S., Filley, T., Dria, K., and Hatcher, P.G. (2004) Temporal variability in sources of dissolved organic carbon in the lower Mississippi River. Geochim. Cosmochim. Acta 68, 959-967. 

Wheeler, P.A., Watkins, J.M., and Hansing, R.L. (1997) Nutrients, organic carbon, and organic nitrogen in the upper water column of the Arctic Ocean implications for the sources of dissolved organic carbon. Deep Sea Res. 44, 1571-1592. 

Porubsky, W. P., Velasquez, L., andjoye, S. B. (2008b). Nutrient replete benthic microalgae as a source of dissolved organic carbon to coastal waters. Estuaries and Coasts. 

FIGURE I Molecular weight distribution (thousands of daltons) of dissolved organic carbon in wet precipitation, throughfall, A and B horizon soil solution, and stream water at Hubbard Brook, New Hampshire. Source Adapted from McDowell (1982) and Cole et al. (1984). 

FIGURE 7 Flux of dissolved organic carbon in precipitation, throughfall, organic soil horizons, and mineral soil horizons in a cool temperate and wet tropical forest (kg ha). Source of data McDowell and Likens (1988) and McDowell (1998). Illustration by L. Isaacson, University of New Hampshire. 

Aitkenhead-Peterson, J. A. 2000. Source, production and export of dissolved organic carbon and nitrogen. Ph.D. Dissertation, University of New Hampshire. 

Cole, J. J., W. H. McDowell, and G. E. Likens. 1984. Sources and molecular weight of dissolved organic carbon in an oligotrophic lake. Oikos 42 1-9. 

Dalva, M., and T. R. Moore. 1991. Sources and sinks of dissolved organic carbon in a forested swamp catchment. Biogeochemistry 15 1-19. 

Moore, T. R., and L. Matos. 1999. The influence of source on the sorption of dissolved organic carbon by soils. Canadian Journal of Soil Science 79 321-324. 

Hinton, M. J., S. L. Schiff, and M. C. English. 1998. Sources and flowpaths of dissolved organic carbon during storms in two forested watersheds of the Precambrian Shield. Biogeochemistry 41 175—197. 

Schiff, S., R. Aravena, E. Mewhinney, R. Elgood, B. Warner, P. Dillon, and S. Trumbore. 1998. Precambrian Shield wetlands Hydrologic control of the sources and export of dissolved organic carbon. Climatic Change 40 167—188. 

Manganese, because of its relative stability in seawater (Ehrlich, 1990), is a potentially important energy source associated with hydrothermal vents. The high flux of reduced Mn2+ to neutral to slightly alkaline oxygenated waters and the relatively low amount of dissolved organic carbon, make hydrothermal... 

In combination with the flux of dissolved organic carbon (DOC), which may add another 20 10 " mol yr (Otto 1996 Table 9.7), a total carbon release from deep-sea sediments of about 120 10 mol yr seems to be the best recent approximation regarding all sources of uncertainty. 

Source, Nature, and Distribution of Dissolved Organic Carbon in SoUs... 

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