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This chapter discusses fatty acids, the building blocks of lipids, which represent a significant fraction of the total lipid pool in aquatic organisms. It explores how chain length and levels of unsaturation (number of double bonds) have been shown to be correlated to decomposition, indicating a pre- and postdepositional selective loss of short-chain and polyunsaturated fatty acids. In contrast, saturated fatty acids are more stable and typically increase in relative proportion to total fatty acids with increasing sediment depth. Polyunsaturated fatty acids (PUFAs) are predominantly used as proxies for the presence of “fresh” algal sources, although some PUFAs also occur in vascular plants and deep-sea bacteria. Thus, these biomarkers represent a very diverse group of compounds present in aquatic systems. The numerous applications of fatty acid biomarkers to identifying the sources of organic matter in lakes, rivers, estuaries, and marine ecosystems are discussed.

The slow dynamics of polymer chains involves extended spatial scales, exceeding many repeat units and making the behavior largely independent of chemical structure. This universality allows modeling of structural and dynamic properties without detailed consideration of the chemical structure. The Rouse and reptation models, for unentangled and entangled chains respectively, are reviewed with an emphasis on their ability to quantitatively describe experimental data. The chapter also discusses the coupling model, which makes various predictions based on general properties of relaxation in complex, correlated systems. Applications of polymers in which chain diffusion is the central mechanism are described.

Kinetics considers the rates of different processes. Chemical kinetics refers to the rates and mechanisms of chemical reactions and mass transfer (diffusion). Recall that since thermodynamic equilibrium implies that the rates of all processes are zero, time is not a thermodynamic variable. Rather, time is the new parameter introduced by the consideration of kinetic processes. The rate of a kinetic process and how it depends on time is determined, in part, by the degree of the deviation from equilibrium. If the deviation from equilibrium is small, the rate decreases (without changing sign) as the system approaches equilibrium. If the deviation from equilibrium is large, the situation is more complicated. For example, non-monotonic (including oscillatory) processes are possible. The sign of the rate can change during such processes; that is, the reaction can proceed in one direction and then the other. Additionally, if the deviation from equilibrium is large, small changes to the system can produce very large changes in the rate of the kinetic process (i.e. chaos). Non-equilibrium, yet nearly stationary states of the system can arise (i.e. states that exist for a very long time). Finally, if the deviation from equilibrium is very large, the system can explode (i.e. the process continues to accelerate with time). In this chapter, we develop a formal description of the kinetics of rather simple chemical reactions. Consecutive and parallel reactions will also be considered here. A more general approach (irreversible thermodynamics) will be considered in Chapter 9. In Chapter 10, we examine diffusive processes. Then, in Chapter 11, we consider the kinetics of heterogeneous processes. In order to start the study of chemical reaction kinetics, we must first define what we mean by the rate of reaction. Consider the following homogeneous reaction: . . . Cl2 + 2NO → 2NOCl. (8.1) . . .

Everyone who knows Lois Weisberg has a story about meeting Lois Weisberg, and although she has done thousands of things in her life and met thousands of people, all the stories are pretty much the same. Lois (everyone calls her Lois) is invariably smoking a cigarette and drinking one of her dozen or so daily cups of coffee. She will have been up until two or three the previous morning, and up again at seven or seven-thirty, because she hardly seems to sleep. In some accounts—particularly if the meeting took place in the winter—she’ll be wearing her white, fur-topped Dr. Zhivago boots with gold tights; but she may have on her platform tennis shoes, or the leather jacket with the little studs on it, or maybe an outrageous piece of costume jewelry, and, always, those huge, rhinestonestudded glasses that make her big eyes look positively enormous. “I have no idea why I asked you to come here, I have no job for you,” Lois told Wendy Willrich when Willrich went to Lois’s office in downtown Chicago a few years ago for an interview. But by the end of the interview Lois did have a job for her, because for Lois meeting someone is never just about meeting someone. If she likes you, she wants to recruit you into one of her grand schemes—to sweep you up into her world. A while back, Lois called up Helen Doria, who was then working for someone on Chicago’s city council, and said, “I don’t have a job for you. Well, I might have a little job. I need someone to come over and help me clean up my office.” By this, she meant that she had a big job for Helen but just didn’t know what it was yet. Helen came, and, sure enough, Lois got her a big job. Cindy Mitchell first met Lois twenty-three years ago, when she bundled up her baby and ran outside into one of those frigid Chicago winter mornings because some people from the Chicago Park District were about to cart away a beautiful sculpture of Carl von Linne´ from the park across the street.