C/N ratios in a sediment core from Nakaumi Lagoon, southwest Japan. Usefulness as an organic source indicator.

Abstract

The weight ratio of total organic carbon to total nitrogen (C/N ratio) in 20 meters of sediment core from Nakaumi Lagoon (coastal brackish lake), Japan is examined for its suitability as an organic source indicator. The C/N ratio depth profile is compared to the depth profiles of other proxies, i.e., weight ratio of total organic carbon to total organic nitrogen (C/N org. ratio), stanol compositions, n-alkane compositions and the hydrogen-index by Rock-Eval pyrolysis.The C/N ratios of the lagoonal sediments, which have been deposited over the last ca. 8,000 years, have a different profile from that of the C/N org. ratio and other proxies due to the effects of a constant level of inorganic nitrogen (N inorg. : ca. 0.04%) in the sediments. When C org. content is less than 1 wt%, the presence of N inorg. lowers the C/N ratio considerably, giving an inaccurate indication of organic source. C-N and C/N ratio-C org. plots are useful for evaluating the effect of N inorg. ; if the depth profiles of the C/N ratio and C org. content exhibit similar trends, this is taken as a warning that the apparent variation in the C/N ratio should be carefully examined in conjunction with the other plots and proxies. It is also found that the C/N org. ratio itself also tends to increase due to the preferential decomposition of nitrogen compounds, and that in sediments containing high proportions of planktonic organic matter (OM), the sensitivity of the C/N ratio to changes in the proportions of planktonic-terrestrial OM is relatively low. lignin phenols, are not easily analyzed due to chemical complexity. Hence, the C/N ratio, having recently become easier to obtain through the popularization of rapid elemental analysis techniques, appears to be an effective and simple indicator of organic source, particularly in lacustrine depositional environments, including estuaries.The C/N ratio in aquatic systems is governed by the mixing of terrestrial and autochthonous OM

Hydrogen sulfide and organic carbon at the sediment–water interface in coastal brackish Lake Nakaumi, SW Japan

“…The C/N ratios of the surface sediment organics in Lake Nakaumi analyzed in this study are 7-9 at most sampling stations in the lake. Figure 4 shows that TOC has a good correlation with TN with positive slope of about 8.7, which indicates that this organic matter is derived mainly from planktic organisms (Bordowskiy 1965;Sampei and Matsumoto 2001). Lake Nakaumi is likely to be rich in planktic organics: the water depth is shallow; the lake is easily stratified and bottom water is seasonally anoxic; and both primary productivity and sedimentation rates are high (1-2 mm year -1 ; Nakano-umi and Shinji-ko Research Group et al 1987;Shinji-ko Research Group et al 1986;Sampei et al 1997a).…”

Changes in C<sub>3</sub>/C<sub>4</sub> vegetation in the continental interior of the Central Himalayas associated with monsoonal paleoclimatic changes during the last 600 kyr

“…The low C/N values indicated that autochthonous organic matter most likely contributed to the sediments. It is pointed out that conventional C/N ratio (TOC/TN ratio) sometimes leads to an incorrect interpretation due to abundant inorganic nitrogen (IN) input (Sampei et al, 1997;Sampei and Matsumoto, 2001;Meyers, 2003). Plot of the TOC versus TN concentration of the RB core indicated that contribution of IN is significant in the sediments (Fig.…”

Organic matter in coal seam-VI of the Barapukuria coal field in Bangladesh

“…C/N ratio of planktonic organic matter in sedimentary environments increases with decomposition rate of the organic matter (Tissot and Welte, 1984). High cellulose and lignin composition of vascular terrestrial plants, along with low protein content, result in C/N ratio valueslarger than 15 (Meyers, 1994(Meyers, , 1997Sampei and Matsumoto, 2001). The C/N ratios in the studied coal samples are 20 (BCMCL1), 21 (BCMCL2), 19 (BCMCL3), 21 (BCMCL4), 20 (BCMCL5), 14 (BCMCL6), 19 (BCMCL7), and 16 (BCMCL8), respectively, with mean C/N ratio of 19 (Table II).…”

“…Terrestrial vascular plants and their derivatives in sediments have C/N ratios of greater than 15 (Ertel and Hedges, 1984;Sampei and Matsumoto, 2001) and those of wood, leaf and macrophytee specially high at 209, 28 and 39, respectively (Hedge et al, 1986). Generally, planktonic organic matters deposited in deep-sea sediments contain C/N values higher than 10 to 15 (Müller, 1977) owing to the preferential loss of nitrogen relative to carbon (Müller, 1977).…”

“…The C/N ratiois widely used to the indicative of sedimentary organic matter, as it is distinguish between algal and terrestrial plant origins of organic matter (Meyers, 1994;Sampei and Matsumoto, 2001;Perdue and Koprivnjak, 2007;Hossain et al, 2009). Terrestrial vascular plants and their derivatives in sediments have C/N ratios of greater than 15 (Ertel and Hedges, 1984;Sampei and Matsumoto, 2001) and those of wood, leaf and macrophytee specially high at 209, 28 and 39, respectively (Hedge et al, 1986).…”