Investigation of the delta^13 C and delta^15 N of individual compounds, commonly referred to as compound specific isotope analysis (CSIA), along with traditional techniques such as stomach content, dietary tracers, and bulk stable isotopic analysis (BSIA), provide a detailed description of trophic dynamics of organisms. CSIA analysis of amino acids (CSIA-AA) in particular, has been used successfully in marine, estuarine, and more recently, terrestrial systems to estimate trophic position (TP) among organisms. Despite the analytical potential of this technique, its application in freshwater systems has remained limited. The goal of this dissertation is to bridge this knowledge gap by assessing the validity and efficacy of the CSIA-AA technique, through studies ranging from laboratory microcosm experiments, to natural freshwater ecosystems in Alabama. In Chapter 2, patterns of trophic enrichment were investigated in a freshwater phytoplankton-grazer model through a controlled feeding experiment in microcosms. Trophic fractionation among amino acids was consistent with previously published results from marine studies. TP determined by CSIA-AA provided a better estimate of trophic status than BSIA, extending the potential of this technique in freshwater systems. Chapter 3 examined the isotopic underpinnings of the phenotypic plasticity in bluegills from the Sipsey River main channel and its backwater habitats, thereby extending CSIA-AA to fluvial and lacustrine environments. BSIA of delta^13 C indicated that the main channel bluegills were subsidized by allochthonous detrital carbon, compared to bluegills from the two floodplain lakes that relied on submerged macrophytic vegetation. Estimates of trophic length using CSIA placed bluegills from all three sites at comparable TP, between trophic levels 3 and 4, suggesting some degree of omnivory. In Chapter 4, the biotic factors affecting the significant difference in mercury concentrations between the largemouth bass from the Sipsey and Black Warrior Rivers were identified, using dual CSIA of triglyceride fatty acids (TGFA; delta^13 C) and amino acids (delta^15 N). Results indicate that increased presence of sulfate-reducing bacteria, coupled with detritus based food web, was the primary driver of the elevated mercury levels in the Sipsey bass. Data presented in this dissertation clearly demonstrate the potential of CSIA-AA and CSIA-TGFA to provide high-resolution insights into complex food web interactions.

The use of Compound-specific Stable Isotope Analysis (CSIA) is increasing in many areas of science and technology for source allocation, authentication, and characterization of transformation reactions. Until now, there have been no textbooks available for students with an analytical chemical background or basic introductory books emphasising the instrumentation and theory. This book is the first to focus solely on stable isotope analysis of individual compounds in sometimes complex mixtures. It acts as both a lecture companion for students and a consultant for advanced scientists in fields including forensic and environmental science. The book starts with a brief history of the field before going on to explain stable isotopes from scratch. The different ways to express isotope abundances are introduced together with isotope effects and isotopic fractionation. A detailed account of the required technical equipment and general procedures for CSIA is provided. This includes sections on derivatization and the use of microextraction techniques in GC-IRMS. The very important topic of referencing and calibration in CSIA is clearly described. This differs from approaches used in quantitative analysis and is often difficult for the newcomer to comprehend. Examples of successful applications of CSIA in food authenticity, forensics, archaeology, doping control, environmental science, and extraterrestrial materials are included. Applications in isotope data treatment and presentation are also discussed and emphasis is placed on the general conclusions that can be drawn from the uses of CSIA. Further instrumental developments in the field are highlighted and selected experiments are introduced that may act as a basis for a short practical course at graduate level.

The 20th century has experienced environmental changes that appear to be unprecedented in their rate and magnitude during the Earth’s history. For the first time, Stable Isotopes as Indicators of Ecological Change brings together a wide range of perspectives and data that speak directly to the issues of ecological change using stable isotope tracers. The information presented originates from a range of biological and geochemical sources and from research fields within biological, climatological and physical disciplines covering time-scales from days to centuries. Unlike any other reference, editors discuss where isotope data can detect, record, trace and help to interpret environmental change. Provides researchers with groundbreaking data on how to predict the terrestrial ecosystems response to the ongoing rapid alterations Reveals how ecosystems have responded to environmental and biotic fluctuations in the past Includes examples from research by a wide range of biological and physical scientists who are using isotopic records to both detect and interpret environmental change

Compound specific isotope analysis of individual amino acids (CSI-AA) is a powerful tool for tracing nitrogen (N) source and transformation in biogeochemical cycles. Specifically, the delta15N value of phenylalanine (delta15N Phe) represents an increasingly used proxy for baseline delta15N values, with particular promise for paleoceanographic applications. Further, multiple studies have shown that delta15N values of Phe and glutamic acid (Glu) can be coupled to provide precise estimates of trophic position (TP), while simultaneously decoupling baseline delta15N values from the effects of trophic transfer. However, current derivatization/gas chromatography (GC) methods require expensive and relatively uncommon instrumentation, and have relatively low precision, posing significant issues for many potential applications. Here we present a new approach to CSI-AA based on a high-pressure liquid chromatography (HPLC) purification of underivatized amino acids, followed by offline elemental analysis-isotope ratio mass spectrometry (EA-IRMS). The utility of this approach is demonstrated in two different applications using natural materials: 1) the construction of a high precision paleoceanographic record from the delta15NPhe in proteinaceous coral tissue and 2) the TP estimation of five marine organisms using the coupled delta15N values of Glu and Phe. Both demonstrations were compared to values measured by an established GC based method. In all cases both methods produced equivalent values, however, values generated by the new HPLC/EA-IRMS approach had higher average precision in all cases. These results demonstrate that this approach represents a viable alternative to traditional GC based methods for delta15NAA measurement and may therefore allow significant expansion of CSI-AA applications, requiring only commonly available instrumentation to produce high precision delta15N AA values.