Document Type

Poster

Publication Date

9-2011

Journal / Book Title

25th International Meeting on Organic Geochemistry (IMOG), Interlaken, Switzerland, Sept. 18-23, 2011

Abstract

In studies of the organic matter (OM) fraction of marine, estuarine, fluvial, or lacustrine sediments, one of the most fundamental distinctions to be made is that between terrestrial and aquatic OM. To supplement the parameters commonly used for this purpose (e.g., C/N and stable isotope ratios), we proposed the Vinylguaiacol/Indole or VGI ("Veggie") ratio, defined as [vinylguaiacol / (indole + vinylguaiacol)] using data produced by analytical pyrolysis-gas chromatography/mass spectrometry of dried, homogenized sediment samples [1]. The ratio employs the peak areas of these two compounds on the mass chromatograms of their molecular ions (m/z 150 and 117, respectively). Major pyrolysis products of terrestrial plant lignin include a variety of methoxyphenols, notably 4-vinylguaiacol. In contrast, aquatic algae and bacteria characteristically produce distinctive organonitrogen compounds upon pyrolysis, particularly indole, derived from the amino acid tryptophan. The end member VGI ratio value of 1.00 is nearly obtained for reference land plant matter, such as maple wood (Fig. 1d). The end member value of 0.00 is obtained for cultured microbes, including Escherichia coli (Fig. 1a). Vinylguaiacol and indole are commonly detected in Recent sediment pyrolysates. We hypothesized that their relative quantities therein should be proportional to the contributions of land plant and aquatic OM, respectively [1]. While soil microbes in terrestrial OM would lead to a diminution of VGI values, stable isotope and C/N ratios would likely be similarly perturbed.

Systematic variations in VGI ratio values are observed among estuarine sediments from southern New York and New England (USA). Samples taken from Spartina peat marshes at the mouths of major rivers entering Long Island Sound have high (> 0.8) VGI ratio values. Jamaica Bay (New York), behind an Atlantic barrier island and with marsh islands and multiple urbanized tidal creeks, displays a very wide VGI range (Fig. 1b,c), affected by proximity to stands of marsh vegetation, bathymetry, and sediment grain size. Sediments from New Haven (Connecticut) harbour show a diminution in VGI values from 0.66 at the mouth of a river in the innermost harbour to 0.08 at the harbour entrance over a distance of only 4 km, as terrestrial influences wane moving towards open water. In Long Island Sound, deep water sediments show a strong predominance of aquatic OM (VGI about 0.05), while nearshore sediments collected close to the mouths of rivers have a greater terrestrial OM component (VGI of 0.15 to 0.23). The results demonstrate a precipitous decrease in the relative amounts of unaltered land plant OM in the offshore direction, but also that a minor fraction persists in deeper water environments.

[1] Micic et al., 2010, Org. Geochem. 41:971-974.

Comments

Note: The parameter has been renamed. It is now called the Vinylguaiacol/Indole Index (VGII) or simply the "Veggie Index". (Ref: Kruge M.A. (2015) Analytical pyrolysis principles and applications to environmental science. In, M. Barbooti, ed., Environmental Applications of Instrumental Chemical Analysis. CRC Press, Boca Raton (FL), p. 533-569.)

Published Citation

Kruge, M.A., Kevin Olsen, K.K., Slusarczyk, J.W., Gomez, E., 2011, The Vinylguaiacol/Indole or VGI ("Veggie") Ratio: Assessing relative contributions of terrestrial and aquatic organic matter to sediments. 25th International Meeting on Organic Geochemistry, Interlaken, Switzerland, Sept. 18-23, 2011.

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