Stable Isotopes

position within the food web and to trace the origin of trophic resources exploited by the species, respectively. Stable isotope analysis is especially advantageous when investigating the feeding ecology and habitat use of marine mammals, where it is often impossible to directly observe feeding or migratory behaviour (Alves-Stanley and Worthy, 2009; Newsome et al., 2010a), and provides information on assimilated foods (not just ingested foods) as well as time-integrated information (Dalerum and Angerbjörn, 2005). Moreover, the complex spatial, temporal and behavioural variation in trophic systems makes linking foraging behaviour to prey populations difficult (Kelly, 1996). Augmenting traditional dietary information with stable isotope data can improve our understanding of the trophic ecology of marine mammals in many instances. Over the last 10years, the number of ecological studies using stable isotopes to investigate the diet of marine mammals has grown (reviewed in Newsome et al., 2010a). The methodology has been used to address a broad range of topics, including the foraging ecology and migration patterns of wild populations [e.g. killer whales (Herman et al., 2005; Newsome et al., 2009); dolphins (Knoff et al., 2008; Barros et al., 2010)], exposure to organochlorides and heavy metals [e.g. killer whales (Krahn et al., 2008); dolphins (Borrell et al., 2006)], and historic

Direct measurement of de novo lipogenesis has not previously been possible in humans. We measured de novo hepatic lipogenesis in normal men by means of stable isotopes and by combining the acetylated-xenobiotic probe technique with mass isotopomer analysis of secreted very low density lipoprotein-fatty acids (VLDL-FA). Sulfamethoxazole (SMX) was administered with [13C]acetate during an overnight fast followed by refeeding with

Generally, however, the variation in the isotope data described here illustrates the potential of stable isotopes to clarify hydrological dynamics within a headwater lowland wetland. The combination of a seasonal trend in rain water isotope composition and a temporally consistent groundwater signature demonstrates the relative importance of precipitation and groundwater contributions to different parts of the wetland. Discrimination of wetland water sources is dependent upon whether discrete compositions occur and it is important to acquire a temporally specific end-member data set (i.e. atmospheric, ground- and surface- water). However, the paper shows the extent to which wetland water sources may vary seasonally over comparatively short distances and demonstrates the importance of determining the stratigraphy of the site.

Reference [4] observed that the δ 18 O and δ 2 H values of precipitation that have not been evaporated are linear- ly related by the equation δ 2 H = 8 δ 18 O + 10. This equation, known as the Global Meteoric Water Line (GMWL), is based on precipitation data from locations around the globe, and has an r 2 > 0.95. This high correlation coeffi- cient reflects the fact that the oxygen and hydrogen stable isotopes in water molecules are intimately associated. The slope and intercept of any Local Meteoric Water Line (LMWL), which is the line derived from precipitation collected from a single site or set of “local” sites, can be significantly different from the GMWL.

The magnitude of response of the upper trophic level consumers to altered flow in the Caloosa- hatchee estuary based on stable isotopes was less relative to the lower trophic level consumers. One explanation is that these upper trophic level con- sumers, which are generally more mobile, migrated out of the Caloosahatchee estuary during high flow and continued to feed on resources with similar iso- tope values. However, this seems unlikely given the species considered were sampled within the estuary during both collection periods and a number of stud- ies have demonstrated that estuarine consumer spe- cies exhibit site fidelity and their tissues reflect the organic matter close to the areas they inhabit (Dee- gan & Garritt 1997, Guest & Connolly 2004). Rather, the absence of significant changes in the isotopic val- ues in the upper trophic levels of the Caloosahatchee estuary may indicate that the duration of high fresh- water flow was too short to elicit a shift in the isotope values of these larger bodied species. This delay could result from (1) slower muscle tissue turnover rates in higher trophic level and larger species (Logan & Lutcavage 2010) and/or (2) a lag associated with movement of different isotopic values through the food web (e.g. Guelinckx et al. 2007, Jennings et al. 2008). This has consequences for using stable iso- topes to assess trophic ecology of species that have

Point measurements of stable isotopes are one tool that can be utilized to highlight these patterns of ecohydrological movement. In isotope hydrology, the isotopic signa- ture of surface, soil and groundwater can be used to interpret water movement in the environment (Gazis and Feng, 2004). Isotopes are atoms of the same element with a differing number of neutrons. Stable isotopes area not radioactive and therefore do not decay, making them useful in environmental study (Kendall and Caldwell, 1999). The use of the ratio of heavy to light isotopes, rather than a simple measurement of heavy or light, highlights the mixing and division of isotopic pools during natural processes (Fry, 2006). Table 3.1 shows the relative abundance of the light and heavy forms of O, H and N. Chemical, physical, and biological processes preferentially utilize lighter isotopes of a given element due to differences in the energy needed for breaking the stronger bonds of heavier elements (Clark and Fritz, 1997; Coplen et al., 1999). Hydrological dynamics are revealed by inter and intra-pool variation of stable isotope ratios across the landscape, which can be used to understand the mixing, residence times and flux pathways of surface and subsurface water pools (Barnes and Turner, 1999; Gazis and Feng, 2004).

Recent studies on coral reef fishes have successfully employed chemical tagging techniques to quantify local patterns of larval retention and dispersal. Experiments in which larvae were marked via tetracycline immersion of embryos have shown larval dispersal to be more limited than previously thought. However, this technique is limited to fishes that lay eggs on artificial substrata. More recently, a new chemical marking technique has been developed which can be applied to all reef fishes. Females are injected with enriched stable isotopes, such as 137 Ba, and the chemical signature is maternally transmitted to embryos and is deposited at the core of the otoliths of larvae. While this technique has been validated for a few species and applied in the field to estimate local dispersal patterns, further laboratory experiments are necessary to determine appropriate injection concentrations and assess any negative effects on larval and adult condition.

can be captured alive and injected with trace amounts of rare, stable isotopes. Laboratory experiments have shown that soluble forms of 137 Ba, when injected into gravid females, are subsequently transmitted through the egg and incorporated into the core of the otoliths of offspring larvae. These marks can be detected (using Inductively Coupled Plasma Mass Spectrometry ICP-MS) as a low ratio of 138 Ba/ 137 Ba that is unique to the otoliths of juveniles derived from injected females. Field trials for the clownfish, Amphiprion percula and the butterflyfish Chaetodon vagabundus show that large numbers of barium tagged juveniles can be recaptured at natal locations (Almany et al. 2007). Thorrold et al. (2006) presented some qualitative observations that there were no negative effects on the adult survival or reproduction, nor were there any effects on the larval growth and survival. However, further laboratory studies are required to confirm that barium unequivocally marks larvae of a range of species and that barium toxicity does not affect adult reproduction or larval growth or survival.

Abstract. Stable isotope signatures provide an integral fin- gerprint of origin, flow paths, transport processes, and res- idence times of water in the environment. However, the full potential of stable isotopes to quantitatively characterize sub- surface water dynamics is yet unfolded due to the difficulty in obtaining extensive, detailed, and repeated measurements of pore water in the unsaturated and saturated zone. This pa- per presents a functional and cost-efficient system for non- destructive continual in situ monitoring of pore water stable isotope signatures with high resolution. Automatic control- lable valve arrays are used to continuously extract diluted water vapor in soil air via a branching network of small mi- croporous probes into a commercial laser-based isotope an- alyzer. Normalized liquid-phase isotope signatures are then obtained based on a specific on-site calibration approach along with basic corrections for instrument bias and temper- ature dependent isotopic fractionation. The system was ap- plied to sample depth profiles on three experimental plots with varied vegetation cover in southwest Germany. Two methods (i.e., based on advective versus diffusive vapor ex- traction) and two modes of sampling (i.e., using multiple per- manently installed probes versus a single repeatedly inserted probe) were tested and compared. The results show that the isotope distribution along natural profiles could be resolved with sufficiently high accuracy and precision at sampling in- tervals of less than four minutes. The presented in situ ap- proaches may thereby be used interchangeably with each other and with concurrent laboratory-based direct equilibra- tion measurements of destructively collected samples. It is thus found that the introduced sampling techniques provide powerful tools towards a detailed quantitative understand- ing of dynamic and heterogeneous shallow subsurface and vadose zone processes.

The current references of body composition are based on body mass index assessed in healthy children, but their individual interpretation should be made with cau- tion. The use of stable isotopes, such as deuterium oxide, may constitute a useful tool, safe and more reliable for the determination of body composition. Thus, it would be extremely important to become familiar with this method, which can identify more reliably the overweight and obesity.

The structure of the nucleus of radioactive isotopes is unstable, and a disintegration occurs with emis- sion of an ionizing radiation. The radioactive iso- topes can be identified by the detection of this radi- ation. On the contrary, the structure of the nucleus of stable isotopes is stable and no disintegration occurs. Stable isotopes contain one or more additional neu- trons and therefore are heavier than the normally abundant isotope of the considered atom. Because of this difference in atomic weight, the stable isotopes can be identified and differentiated by mass spec- trometry. Some isotopes are naturally occurring, oth- ers are manmade. The natural occurrence varies very much from one isotope to another.

Bosten Lake Basin are sensitive to the climate change of the local region. This finding is consistent with the re- sults from analyzing the relationship of historic trends between climate variables and runoff [16]. Studies have indicated that the main factor causing Bosten Lake to gradually become a mild salt lake from a fresh lake was the irrigation and industrial wastewater drainage [24]-[26]. Our results provide further evidence using stable isotopes, proving that wastewater has significantly affected the TDS of Bosten Lake.

composition of the diet (DeNiro and Epstein 1978; 1981). There have been major advances in understanding the relationship between diet and consumer isotope ratios (e.g. trophic level effects; Hedges and Reynard 2007; O’Connell et al. 2012), but some bodily processes and conditions of production, such as manuring cereal crops, may complicate these models further (Fraser et al. 2011). For the most part, stable isotopes represent dietary protein consumption, but in low-protein diets, stable carbon isotopes may also represent contributions from lipids and carbohydrates (Schulting 2018). Stable isotopes represent an average isotope ratio of the dietary protein over the duration of bone turn-over, often estimated to be between 10 and 20 years. The period of bone turn-over can vary between skeletal element and over age, as well as responding to factors which effect physiological processes, such as pregnancy and starvation (Hamilton et al. 2013, 31). For this reason, the preference in archaeology is to compare averages between populations or groups, rather than between individuals.

Cernusak, Lucas A., Barbour, Margaret M., Arndt, Stefan K., Cheesman, Alexander W., English, Nathan B., Feild, Taylor S., Helliker, Brent R., Holloway-Phillips, Meisha M., Holtum, Joseph A.M., Kahmen, Ansgar, McInerney, Francesca A., Munksgaard, Niels C., Simonin, Kevin A., Song, Xin, Stuart-Williams, Hilary, West, Jason B., and Farquhar, Graham D. (2016) Stable isotopes in leaf water of terrestrial plants. Plant, Cell & Environment, 39 (5).

when compared to other marine species found in New Zealand (Table 5); it is likely that the 3 hagfish species from this study generally feed 1 to 3 trophic levels above primary consumers (i.e. TL3 to TL5). N. binipli- cata had the lowest δ 15 N values. This species is rela- tively small with a slender body (Richardson & Jowett 1951) and is very active when observed using baited underwater video (Zintzen et al. 2012). Stable isotopes suggest that this species employs an active feeding strategy, consuming small carrion and also actively preying on inver tebrates from soft sediments. A closely associated species, Neo myxine sp. 1, was also observed actively hunting live Cepola haastii, a ben- thic fish species (Zintzen et al. 2011).

Overall, the parasite’s taxonomy in combination with its way of nutrient uptake determines its trophic position with respect to the host. Although there are no data available regarding stable isotope composition of acan- thocephalans, the results of the present study were in line with some other groups of parasites, which share a similar absorptive feeding strategy. For example, ces- todes were reported to be depleted in δ 15 N and δ 13 C [14, 17, 20]. These findings were also opposed to a predator–prey relationship, that defines parasites as con- sumers, which feed on their hosts [29]. Cestodes as well as acanthocephalans take up nutrients through the body surface (tegument) and assimilate compounds, which were previously processed by the host. These metabolites (pep- tides, amino acids, carbohydrates mono-oligosaccharides) are depleted in heavier stable isotopes, as due to the kinetic isotope effect, lighter isotopes are favored in biochemical reactions [30]. Parasites, in general, face limitations in metabolism and energy utilization under anaerobic conditions and various macromolecules have to be assimilated via the tegument [31]. It is also known that endoparasites are not able to synthetize several complex molecules such as purine nucleotides, fatty acids, sterols, and some amino acids de novo. The only source for these molecules remains the host’s me- tabolism [31, 32]. Ammonia to be excreted by the host, Table 2 Mean values ± CI with t (95%; f = n-1) × s/ √ n of δ 13 C and δ 15 N in per mil calculated for host tissues and parasites

isotopic evidence for evaporation does not in itself provide a warning signal of water resource sensitivity, data collected over time and analyzed in combination with information on regional climate and hydrology could be used to characterize and monitor surface water resource susceptibility to climate change [1]. The comparison of the isotopic signature of precipitation to potable water can also provide important information regarding the resi- dence time of water in human-dominated hydrologic systems. At a regional level, the difference in isotopic ra- tios between precipitation and tap water can be attributed to hydrological factors such as water transit times from the source to the consumer. Management of water resources requires that the human interactions, known pertur- bations, and natural processes in the hydrologic cycle be fully understood. This information will enhance know- ledge about site-specific hydrology, water management, water supply infrastructures, and regional hydroclima- tological impacts [1]. This work utilizes stable isotopes δ 18 O and δD to delineate the residence time of water in a

I also thank everyone at the Earth System Science department at UCI for making me feel welcome in Croul Hall. I am deeply grateful to Sue Trumbore and Xiaomei Xu for allowing me to use their lab facilities and automated isotope ratio mass spectrometer which made this thesis possible. Coincidentally, it was also Xiaomei who got me started in the lab when I first arrived at Caltech. I am indebted to everyone who worked in the N. Mudd basement stable isotope lab and who were always willing to answer questions, including Xiaomei, Julianna Fessenden, Sally Newman, Nami Kitchen, Zhengrong Wang, Julie O’leary, Thom Rahn and Hagit Afek. They also made it a very pleasant working

breeding population with good probability when combin- ing morphometric measurements and stable isotope signa- tures of their feathers [56, 57]. Therefore, we predicted that if migratory connectivity is high, birds captured at different sites in the wintering range would differ from each other. We took samples from birds captured at several sites in sub-Saharan Africa that we divided in three main regions: the westernmost area located in southern Mauritania/ northwest Mali (hereafter Mauritania/Mali), the western- central area in Niger, and the eastern area in Kenya. We ex- pected to find differences in morphometric measurements and stable isotope compositions of feathers among birds from these three main areas. Given the lack of reference material from the breeding grounds, our project focused on the differentiation of distinct wintering populations.

Previous work can be summarized in the following state- ments which guided the design of our study: (i) a combi- nation of hydrometric and hydrochemical data decreases ill- posedness of an inverse problem, (ii) parameter optimiza- tion/estimation should be conducted on the scale of the ap- plication, (iii) determination of pore water stable isotope con- centrations allow tracking water particles under variable nat- ural boundary conditions over months to years. As mentioned above, pore water stable isotope profiles have so far neither been rigorously tested for their applicability to calibrate soil hydraulic properties in the vadose zone in a humid climate, nor which is the most efficient way to do so. This study will fill this research gap by focusing on three different ap- proaches to include pore water isotope concentrations in an inverse modelling framework and thus answering the follow- ing research questions: do stable water isotope profiles as a solitary optimization target provide enough information to derive soil hydraulic properties and solute transport parame- ters? Does a combination of pore water isotope profiles and soil moisture time series as parallel optimization targets re- sult in a realistic “well-calibrated” (Gupta et al., 2005) pa- rameter representation? Is the sequential use of soil mois- ture data to determine first the soil hydraulic properties and using the pore water isotope information to estimate the so- lute transport parameters afterwards the best way to derive a “well-calibrated” soil physical model? The objective of this paper is to investigate these questions in a comparative study applying all optimization approaches to three different sites and thus a range of soil types. The different inverse model approaches that include either pore water stable isotope con- centrations alone or in combination with soil moisture data in a parallel or subsequent manner are compared with regard to the model performances and their parameter identifiabil- ity. In addition, the model realism concerning water balance and transit time estimations are compared to see how much