Inorganic Carbon in Sediments

The purpose of this section was to study the biogeochemical characteristics of IC in the Changjiang River Estuary sediments and its contribution to the 

1 Spatial Distribution of Carbonate in the East China Sea Sediment 

In the ECS continental shelf surface sediments, carbonate is the most abim-dant in the outer continental shelf sediments (Lin et al., 2002b). The highest content, up to 90%, was found in the area where the Kuroshio Current intruded on the ECS continental shelf. Common carbonate content on the shelf is in the range of 10% to 30%. Values greater than 25% were observed mostly in areas directly under the path of the Kuroshio Current. Most sediments are biogenic carbonate along the southeastern part of the outer shelf (Gao et al., 2006). This resulted in that the carbonate is rich in coarse sediment and poor in fine sediment (Fig. 4.11, Yang et al., 2002). 

In the northern ECS mud area and its surrounding area, carbonate content in the surface sediments is less than 5%, much lower than that in other areas of the ECS. Evidence indicated that the sediments in this area are a mixture of the Yellow River, the Changjiang River, and resuspended matter adjacent to the mud area (Yang et al., 2002). Distribution of carbonate in the surface sediments of these areas can be divided into four zones (Fig. 4.12) a relatively high carbonate content zone ( 1.2%) in the coastal area, a low carbonate content zone in the middle continental shelf sand area ( 1.2% in most of this area, 1.0%), a high carbonate content zone in the middle continental 

2 Inorganic Carbon Forms in the Changjiang River Estuary Sediments 

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With the exception of instrumental dry combustion methods [32], the techniques referred to above for the analysis of organic (and total) carbon in sediments are time consuming (e.g. 2-3h). An instrumental technique described by Van Hall and Stenger [33] makes use of a non-dispersive infrared detector and measures the carbon dioxide resulting from the combustion of the carbonaceous compounds. Total and inorganic carbon can be differentiated by the use of different combustion columns and temperatures. 

From Figure 9.1, it can be seen that the major form of carbon in the atmosphere is C02(g), constituting over 99% of atmospheric carbon. Carbon dioxide makes up 0.035% by volume of atmospheric gases, or 350 ixatm = 350 ppmv. The atmosphere has a mass of CO2 that is only 2% of the mass of total inorganic carbon in the ocean, and both of these carbon masses are small compared to the mass of carbon tied up in sediments and sedimentary rocks. Therefore, small changes in carbon masses in the ocean and sediment reservoirs can substantially alter the CO2 concentration of the atmosphere. Furthermore, there is presently 3 to 4 times more carbon stored on land in living plants and humus than resides in the atmosphere. A decrease in the size of the terrestrial organic carbon reservoir of only 0.1% y-1 would be equivalent to an increase in the annual respiration and decay carbon flux to the atmosphere of nearly 4%. If this carbon were stored in the atmosphere, atmospheric CO2 would increase by 0.4%, or about 1 ppmv y-l. The... 

Carbonate is an important composition of inorganic carbon in marine sediments. Up to now, the research into inorganic carbon concentrates mostly on the source, distribution, dissolution, and precipitation of carbonate in sediments. For example, in the western South China Sea, the contents of carbonate in the north and mid-southern areas are high, but low in the middle and southeast areas. The distribution characteristics are controlled by terrigenous material supply and are in close relationship with the extent of the shelf and the gradient of the slope. The contents of carbonate are highest in the area... 

Li XG, Li N, Song JM (2004a) Determination for the different combined-form inorganic carbon in marine sediments. Chin J Anal Chem 32(4) 425-429 (in Chinese with English abstract)... 

The concentration of inorganic carbon in marine sediments is mainly controlled by the following factors (1) The supply speed of autogenetic CaCOs by... 

Li XG, Song JM, Yuan HM (2005) Inorganic carbon of sediments in the Yangtze River Estuary and Jiaozhou Bay. Biogeochemisty 77(2) 177-197... 

Niu LF, Li XG, Song JM, Yuan HM, Li N, Dai JC (2006) Iron and inorganic carbon in Liaodong Bay sediments of Bohai Sea, China. Acta Oceanol Sin 25(4) 53-64 Nixon SW (1993) Nutrients and coastal waters Too much of a good thing Oceanus 36(22) 38-47... 

Total carbon The sum of inorganic and organic carbon in sediment that can be measured by combustion at 800-1000 °C with an elemental analyzer. 

Lead is widely distributed in the earth s crust. The principal lead ores are galena, cerrusite, and anglesite containing lead sulfide, lead carbonate, and lead sulfate, respectively. Alkyllead compounds exist as byproducts from abiotic and biotic methylation of inorganic lead in sediments [2]. 

In experiments where Mono Lake water was acidified to remove carbonate and bicarbonate ions and again adjusted to pH 10, more than 90 percent of the soluble plutonium moved to the sediment phase. When carbonate ion concentration was restored, the plutonium returned to solution—strong evidence of the importance of inorganic carbon to solubility in that system(13). Early studies with Lake Michigan water, which has low DOC, had also implicated bicarbonate and carbonate as stabilizing ligands for plutonium at pH 8(14). This latter research characterized the soluble species as mainly anionic in character. 

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