Bulk Organic Matter Techniques

The abundance and ratios of important elements in biological cycles (e.g., C, H, N, O, S, and P) provide the basic foundation of information on organic matter cycling. For example, concentrations of total organic carbon (TOC) provide the most important indicator of organic matter since approximately 50% of most organic matter consists of C. As discussed in chapter 8, TOC in estuaries is derived from a broad spectrum of sources with very different structural properties and decay rates. Consequently, while TOC provides essential information on spatial and temporal dynamics of organic matter it lacks any specificity to source or age of the material. 

In the case of nutrients,source components have been modeled as conservative mixtures (Cmix) of riverine and marine end-members using the following equation  

Terrigenous soils (surface)/forest litter Freshwater phytoplankton 

Marine/estuarine phytoplankton C—4 salt marsh plants Benthic microalgae C-3 Freshwater/brackish marsh plants 

Emergent macrophytes -26.0 8.0 +90 Caraco et al. (1998) Raymond and Bauer, (2001b) 

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There are two main aims in applications of PTLC in organic geochemistry (1) assessment of the bulk group composition of soluble organic matter by its fractionation and (2) separation of a particular selected group of compounds with geochemical meaning. The important factor in technique selection should be the repeatability of... 

Due to the complexity of organic matter sources in estuaries and the aforementioned problems associated with making only bulk measurements to constrain them, the application of chemical biomarkers has become widespread in estuarine research (see review, Bianchi and Canuel, 2001). The term biomarker molecule has recently been defined by Meyers (2003, p. 262) as compounds that characterize certain biotic sources and that retain their source information after burial in sediments, even after some alteration. This molecular information is more specific and sensitive than bulk elemental and isotopic techniques in characterizing sources of organic matter, and further allows for identification of multiple sources (Meyers, 1997, 2003). 

Pathways of carbon flow in natural environments have also been reconstracted using bulk stable carbon and nitrogen isotopes as well as compound-specific isotopic analysis of individual biomarker lipid component (Hayes et al, 1990) based on the fractionations involved during primary (photosynthetic) and secondary (heterotrophic) processes. Recently, compound-specific radiocarbon analysis of individual biomarker hpid has been shown to be a valuable technique to determine the source of marine organic matter (Eglinton et al., 1997). 

In this technique, bulk dried samples are heated in an inert helium atmosphere, where upon thermo-vaporization and pyrolysis, hydrocarbons are quantified by flame-ionisation detection. Compounds occurring as free gases and liquids in sediments are separated from those that occur in bound form, or as particulate organic matter by temperature control. The S [-detector signal records free hydrocarbons, which are thermo-vaporizable at 300°C, and the S2-detector signal measures those compounds liberated during programmed pyrolysis from 300 to 550°C. 

Aging and fossilization of wood are the exceptions in nature since the bulk of the organic matter is destroyed by microbial decomposition in the course of time. The biochemical subunits of plants are "recycled" and incorporated into new life in an eternal succession. Sometimes wood contains some antimicrobial compounds which prevent the usual destruction. The oldest samples of air-kept wood are dated to 290000 years while water-logged specimens from ship wrecks, bulwarks and posts are supposed to be as old as 8500 years [98]. Different physical and chemical techniques were applied to the analysis of "archaeological" wood and to the estimation of appropriate conservation means for the future [99], but TA is rare. 

Both XRF and PIXE techniques are extensively used in biological and medical sciences for elemental analysis because of their ability in ultratrace analysis of K, Ca, Mn, Fe, Cu, Zn, Se, etc. in organic material. The bulk of living matter consists of the 11 major elements H, C, N, O, Na, Mg, P, S, Cl, K, and Ca. 

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