1、第三章第三章 同位素示蹤技術(shù)同位素示蹤技術(shù) (Isotope Tracer Method and Technology )1. 基本原理基本原理Table 1. Estimates of quasi-natural sources of lead, cadmium and mercury in the EMEP domain樣品被高溫燃燒，成為CO2, N2, SO2，然后進(jìn)入質(zhì)譜儀。采取重輕同位素比。一般誤差在：0.1 to 0.2, or 0.5 (S).4基本公式：2. 實(shí)證實(shí)證Case Study 2.1 碳同位素示蹤及其應(yīng)用碳同位素示蹤及其應(yīng)用The distribution of

2、13C values for water, sediments and biota from Redfish Bay, Texas. This is one of the early illustrations ofthe potential usefulness of 13C values in marine food web studiesFigure 2. The distribution of sediment 13C values in the Eastern Gulf of Mexico nearshore zone showing a distinct gradient from

3、riverine sediment at about 27 inshoreup to marine values of 21 offshore 2.2 硫同位素示蹤及其應(yīng)用硫同位素示蹤及其應(yīng)用 2.3 氮同位素示蹤及其應(yīng)用氮同位素示蹤及其應(yīng)用13 2.4 多同位素示蹤技術(shù)及其應(yīng)用多同位素示蹤技術(shù)及其應(yīng)用 3 同位素示蹤技術(shù)及其應(yīng)用同位素示蹤技術(shù)及其應(yīng)用(Casciotti et al., 2002) displays a pictogram tracing the sample gas flowing initially from the sample vial to the mass spe

4、ctrometer (MS).Seawater and freshwater samples are prepared using denitrifying bacteria that reduce nitrate (NO3-) to nitrous oxide (N2O) using the following pathway (Sigman et al., 2001): NO3- = NO2- = NO = N2O = N2 Sealed vials containing the N2O sample gas are then transferred to the mass spectro

5、meter laboratory for stable isotope analysis of d15N and d18O. there is an increase in the carbon-13 content (13C/12C ratio) and nitrogen-15 content (15N/14N ratio) of the organism due to selective metabolic loss of carbon-12 (12C) and nitrogen-14 (14N) during food assimilation and growth (Figure 1)

6、. How can isotopes be used to determine who is eating who?Mapping Spatial Variability in Marsh Redox Conditions Using Biomass Stable Isotopic CompositionsCarol Kendall, Steven Silva, Daniel Steinitz, Erika Wise, Cecily Chang (USGS, Menlo Park CA); Jerry Stober, Phyllis Meyer (USEPA, Athens GA)Photos

7、ynthesis and carbon cycling: Terrestrial plants fix atmospheric CO2 by two main photosynthetic reaction pathways: the Calvin-Benson, or C3, and the Hatch-Slack, or C4. C3 plants convert atmospheric CO2 to a phosphoglycerate compound with three C atoms while C4 plants convert CO2 to dicarboxylic acid

8、, a four-C compound. Carbon isotopes are strongly fractionated by photosynthesis and the C3 and C4 processes involve different isotopic fractionation, with the result that C4 plants have higher delta13C values ranging from -17o/oo to -9o/oo with a mean of -13o/oo relative to PDB, while C3 plants sho

9、w delta values ranging from -32o/oo to -20o/oo with an average value of -27o/oo. Most terrestrial plants are C3, all forest communities and most temperate zone plant communities of all kinds being dominated by C3 plants. The native plant populations of North America and Europe are almost exclusively

10、 C3. Over 80% of crop plants are C3. C4 plants are characteristically found in hot, arid environments: a selective advantage of C4 photosynthesis is more efficient use of water. Some crops of immense importance are C4 plants: maize, sorghum, millet, and sugar cane. The 13C value is a standard method for distinguishing the C3 and C4 plant groups