Delta 15N Research Articles

Status and diet in precontact highland Ecuador.

Excavation at the Ecuadorian highland site of La Florida in suburban Quito revealed six deep shaft tombs yielding high-status individuals (n = 9) as well as apparent sacrifices and other low-status individuals (n = 23). Determination of sex and age at death of the recovered skeletal remains resulted in a sample of 32 individuals aged from approximately 7 to 50 years of age. The sample of 18 individuals over the age of 18 years included 14 females and 4 males. Temporally, the remains are assigned to the Chaupicruz Phase (circa 100 to 450 AD) of the Regional Developmental Period. In this study, we analyze stable isotopes of carbon and nitrogen from human bone in order to compare the diets of the high- and low-status individuals. Stable carbon isotope analyses were carried out on preserved protein and biological apatite (bioapatite), and stable nitrogen isotope analyses were carried out on preserved protein. There is a statistically significant difference in delta 13C between the two groups for both protein and mineral sources of carbon with evidence for the greater consumption of maize in the high-status group. There is no significant difference in delta 15N between the two groups, nor is there a significant difference in the spacing between protein and mineral delta 13C values between the two groups. Ethnohistorical evidence for the 16th century AD provides the expectation that the only dietary difference was the higher consumption of animal protein by the elite. There is no evidence for this based on the bone chemistry data from La Florida.(ABSTRACT TRUNCATED AT 250 WORDS)

Fractionation of nitrogen isotopes by mixed ruminal bacteria.

Mixed ruminal bacteria were cultured with glucose, cellulose or no carbohydrate, and ammonium bicarbonate or casein hydrolysate. Changes in amounts of bacterial ammonia and non-ammonia N were measured. Ratios of N isotopes expressed as delta 15N (delta 15N) were measured by isotope ratio mass spectrometry. When bacteria were cultured with glucose and ammonium bicarbonate, bacterial delta 15N decreased from .9 to -5.8/1000 and residual ammonia delta 15N increased from -1.4 to 12.7/1000. Fractionation of N isotope occurred during ammonia incorporation because the difference between delta 15N of ammonia and delta 15N of bacteria (delta 15N) was 18.8/1000 (P < .01). However, when casein hydrolysate was the N source, delta 15N between non-ammonia and bacteria averaged only 1.3/1000 (P > .1), indicating no fractionation of N isotopes occurred during utilization of amino acids. The amount of bacterial N was highest at 24 h of incubation when cellulose was the carbohydrate source. At that time, delta 15N between ammonia and bacteria was 8.9/1000 when ammonia was the N source, but delta 15N between non-ammonia and bacteria was 1.7/1000 when casein hydrolysate was the N source. Bacterial N decreased after 24 h when cellulose was the source of carbohydrate. Results indicate that fractionation of N isotopes occurred during ammonia incorporation, but not during incorporation of N from amino acids, deamination, and release of ammonia. Fractionation of N isotopes during incorporation of ammonia N may be used as a marker to study N metabolism by ruminal bacteria.

Indigeneity of organic matter in fossils: a test using stable isotope analysis of amino acid enantiomers in Quaternary mollusk shells.

Comparison of the delta 13C values of D and L enantiomers of individual amino acids was used to evaluate the presence of amino acid contaminants in Quaternary land snails. Measurements of delta 13C values of amino acid D and L enantiomers determined by combined gas chromatography, combustion, isotope-ratio mass spectrometry are reported. Conventional combustion techniques, following separation of aspartic acid and glutamic acid enantiomers by liquid chromatography, were also used to determine delta 13C as well as delta 15N values. Thoroughly cleaned samples ranging in age from 7000 to > 100,000 yr B.P. are shown to have analytically identical delta 13C values for the D and L enantiomers of each amino acid, thus confirming that the amino acids are indigenous to the shells, even in Pleistocene samples. On the other hand, partially cleaned material shows divergence of isotopic values, thus indicating the presence of amino acid contaminants and emphasizing the importance of proper cleaning procedures. This approach provides a powerful method for assessing the indigeneity of amino acids in fossils.

Temporal trends in stable isotopes for Nubian mummy tissues.

From Meroitic to Christian times (350 B.C.-A.D. 1400), Sudanese Nubia experienced political, economic, cultural, and environmental upheaval. Change in any one of these aspects of ancient lifeways can affect subsistence. Dietary patterns from this period are reconstructed by measuring stable carbon and nitrogen isotope ratios in tissue samples from 146 mummies excavated from five sites in the Wadi Halfa area. On average, delta 13C values of bone collagen, muscle, and skin indicate high consumption levels of C3 plants (presumably wheat or barley staples, mixed vegetables, and fruits) throughout the sequence. However, during the X-Group period (A.D. 350-550), there is a statistically significant increase in consumption of C4 plants (millet or sorghum), which are predominant in both the archeological record and in modern crop production for most of the Northern Sudan. The X-Group period was also associated with a low Nile and political and economic restructuring. Increased use of C4 plants on a seasonal basis is also indicated by shifting delta 13C values along hair shafts for both X-Group and Christian periods. delta 15N values suggest that the major source of protein for all time periods came from herbivorous animals. A small, but significant increase in 15N over the 1,000-year sequence could be the result of fertilization.

The effects of feeding regimen and dietary sucrose supplementation on natural abundance of 15N in some components of ruminal fluid and plasma of sheep.

An experiment was conducted to investigate the effects of changes in ruminal conditions arising from feeding and sucrose supplementation to the diet on the natural abundance of 15N (delta 15N value) of some biological components and of feces and urine in sheep. Four wethers fitted with ruminal fistulas were fed on alfalfa hay cubes with or without sucrose either 2 or 12 times daily. With twice-daily feeding, the delta 15N values of ruminal ammonia and plasma urea decreased after feeding, whereas only small changes were observed throughout the sampling period with 12 times daily feeding. With 12 times daily feeding with and without sucrose, the delta 15N values of ruminal ammonia were higher (P < .05) than those of the diet and plasma urea. The delta 15N values of ruminal bacteria were lower (P < .05) than those of ruminal ammonia but higher (P < .05) than those of the diet. The delta 15N values for feces were higher (P < .05) than those of the diet, and no differences (P > .25) were observed between the delta 15N values of urine and those of the diet. Dietary sucrose supplementation lowered (P < .05) the delta 15N values of ruminal ammonia but had no effect (P > .10) on values for ruminal bacteria and plasma urea. Nitrogen excretion in urine was decreased (P < .05) by sucrose supplementation to the diet, but the delta 15N value of urine showed no effect (P > .25) of sucrose addition.(ABSTRACT TRUNCATED AT 250 WORDS)

Carbon and nitrogen stable isotopic signatures of human dietary change in the Georgia Bight

Measurement of carbon and nitrogen stable isotope ratios (delta 13C and delta 15N) in samples of human bone collagen (n = 93) from a temporal series of four prehistoric (early preagricultural, late preagricultural, early agricultural, late agricultural) and two historic (early contact, late contact) periods from the Georgia Bight, a continental embayment on the southeastern U.S. Atlantic coast, reveals a general temporal trend for less negative delta 13C values and less positive delta 15N values. This trend reflects a concomitant decrease in emphasis on marine resources and increased reliance on C4-based resources, especially maize. This dietary reorientation is most apparent for the early agricultural sample (AD 1150-1300), coinciding with the Mississippian fluorescence in the eastern United States. There is, however, a shift toward the use of C3 (non-maize) foods during the last prehistoric period (AD 1300-1450), which is likely related to environmental stress and social disruption. A heavier use of maize and terrestrial resources in general after the establishment of mission centers on barrier islands is indicated. A reduced dietary breadth during the mission period may have contributed to the extinction of these populations in the eighteenth century.

The use of stable isotopes for food web analysis

General aspects in isotope biogeochemistry was summarized with emphasis on delta 15N and delta 13C contents in plants and animals in natural ecosystems. In the estuary, the variation of isotope ratios were principally governed by the mixing of land-derived organic matter, marine phytoplankton, and seagrasses. A clear cut linear relationship between animal delta 15N and its trophic level was obtained in the Antarctic food chain system. Several current efforts to use the stable isotopes for food web analysis were demonstrated for some terrestrial and marine systems as well as human food web.

Determination of the abundance and isotope composition of nitrogen within organic compounds: a sealed tube technique for use with static vacuum mass spectrometers

A technique for the determination of the abundance and isotopic composition of nitrogen within organic compounds is described. It is intended for use with high-sensitivity static vacuum mass spectrometers. The accuracy of the abundance determination is +or-5% by weight and replicate delta 15N determinations of nitrogen for five organic compounds were all within +or-8%. The compounds selected contained nitrogen within a variety of organic structures and with different types of nitrogen bonding including -NO2, -NH2, C identical to N, C=N, and C-N. In no case were detectable amounts of nitrogen oxides formed during oxidation. Blank analyses suggest that meaningful N abundance and delta 15N determinations can be performed on materials containing greater than 20 ppm nitrogen by weight.

THE FATE OF APPLIED NITROGEN IN A FRASER VALLEY SOIL USING 15N IN FIELD MICROPLOTS

A tracer (15N) study using fallowed field microplots was conducted at Agassiz Research Station to examine the fate of applied N over an entire year. The tracer confirmed nontracer (difference between fertilized and control treatments) observations that applied N does not leach beyond the rooting zone (45 cm) during the growing season, despite the considerably more than average precipitation that occurred in July, but that all residual [Formula: see text] is leached over the winter. The tracer did, however, show that net immobilization of applied N occurred late in the fall resulting in 17% of the N recovered in the 75-cm profile 1 yr after application even though the nontracer method showed that none of the applied N remained. There was significant net mineralization of soil N over the summer (100 kg N ha−1 from early May to late August) and nitrification of the applied [Formula: see text] (120 kg ha−1) was essentially complete within 14 d of application. Tracer analyses suggested that 36% of the applied [Formula: see text] was immediately fixed by the clays but after 14 d in the field it decreased to less than 1%. The fixed [Formula: see text] remained at this level throughout the rest of the year. The apparent large decrease in fixed [Formula: see text] within the first 14 d may have been an analytical artifact which resulted when the initial soil was air dried. Negligible denitrification was observed during the growing season despite the soil remaining quite moist throughout most of the year. Delta 15N measurements of total N, fixed [Formula: see text] and extractable inorganic N fractions showed only enrichment of total N. The delta 15N results support the observation that denitrification tends to be low under Agassiz soil and weather conditions. Comparisons and contrasts to previously reported similar tracer studies in Ottawa were made. Key words: Leaching, clay fixation, N mineralization, N immobilization, nitrification, denitrification, delta 15N

High-precision determination of nitrogen stable isotope ratios at the sub-nanomole level

Describes a mass spectrometer, gas inlet and operating protocol which have been developed for the purpose of making stable isotope measurements of subnanomole quantities of nitrogen gas. The mass spectrometer achieves high levels of sensitivity by operating in the static vacuum mode; the levels of precision attainable have been assessed in a number of ways. The instrument is capable of obtaining comparative nitrogen isotopic compositions ( delta 15N values) to a precision of +or-0.240/00 from samples of 0.4 nmol, as determined from a zero-enrichment test performed throughout a single day on 40 consecutive samples. The absolute accuracy of the method, as derived from measurements on samples of known isotopic compositions, is about +or-0.50/00. The instrument was designed to work routinely with samples of between 0.07 and 0.4 nmol of nitrogen but is demonstrated that the equipment can handle 20 pmol quantities of gas. The performance is difficult to quantify at these low levels since the inlet system does not have the facility to reproducibly introduce such small gas samples.

Unusual stable isotope ratios in amino acid and carboxylic acid extracts from the Murchison meteorite.

Much effort has been directed to analyses of organic compounds in carbonaceous chondrites because of their implications for organic chemical evolution and the origin of life. We have determined the isotopic composition of hydrogen, nitrogen and carbon in amino acid and monocarboxylic acid extracts from the Murchison meteorite. The unusually high D/H and 15N/14N ratios in the amino acid fraction (delta D = 1,370% after correction for isotope exchange; delta 15N = 90) are uniquely characteristic of known interstellar organic materials. The delta D value of the monocarboxylic acid fraction is lower (377%), but still consistent with an interstellar origin. These results confirm the extraterrestrial origin of both classes of compound, and provide the first evidence suggesting a direct relationship between the massive organo-synthesis occurring in interstellar clouds and the presence of pre-biotic compounds in primitive planetary bodies. The isotope data also bear on the historical problem of distinguishing indigenous material from terrestrial contaminants.

Stable nitrogen isotope ratios of bone collagen reflect marine and terrestrial components of prehistoric human diet.

The delta 15N values of bone collagen from Eskimos and from Northwest Coast Indians dependent on salmon fishing are about 10 per mil more positive than those from agriculturalists in historic times. Among prehistoric humans, two groups dependent on marine food sources show bone collagen delta 15N values that are 4 to 6 per mil more positive than those from two agricultural groups. The nitrogen isotope ratios of bone collagen from prehistoric inhabitants of the Bahamas are anomalously low for reasons that relate to the biogeochemical cycle of nitrogen in coral reefs.