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Isotope Content (isotope + content)
Selected AbstractsCarbon and nitrogen isotope composition of bulk soils, particle-size fractions and organic material after treatment with hydrofluoric acidEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 3 2005M. W. I. Schmidt Summary Soils and sediments contain only small amounts of organic matter, and large concentrations of paramagnetic metals can give poor solid-state nuclear magnetic resonance (NMR) spectra of organic matter. Pretreatment of samples with hydrofluoric acid (HF) dissolves significant proportions of the mineral matrix and extracts paramagnetic elements. We investigated the effects of 10% HF treatment on the stable isotope content of carbon (C) and nitrogen (N) of organic matter from soils, composts and shales. Additionally we inferred molecular and isotopic characteristics of lost materials from calculations of isotope mass balances. Treatment with HF enriched C and N in mineral samples substantially (factors 2.5,42.4), except for Podzol B horizons (1.1,1.7) and organic material (1.0,1.3). After treatment most of the C (59.7,91.7%) and N (53.7,86.6%) was recovered, although changing C/N ratios often indicated a preferential loss of N-rich material. Isotope ratios of C and N in the remaining material became more negative when net alterations exceeded 0.3,. The isotope ratios of the lost material contained more 13C (1,2,) and 15N (1,4,) than the initial organic matter. Acid hydrolysis typically removes proteins, amino acids and polysaccharides, all of which are enriched in 13C, and in the case of proteins and amino acids, enriched in 15N as well. We conclude that HF treatment released fresh, soluble, probably microbial, biomass in addition to carbohydrates. Net changes of the bulk chemical composition of organic matter were small for most soils, size fractions and plant material, but not for samples containing little organic matter, or those rich in easily soluble organic matter associated with iron oxides, such as Podzol B horizons. [source] Organic carbon and carbon isotopes in modern and 100-year-old-soil archives of the Russian steppeGLOBAL CHANGE BIOLOGY, Issue 10 2002Margaret S. Torn Abstract Archived soils can provide valuable information about changes in the carbon and carbon isotope content of soils during the past century. We characterized soil carbon dynamics in a Russian steppe preserve using a 100-year-old-soil archive and modern samples collected from the same site. The site has been protected since 1885 to the present, during which time the region has experienced widespread conversion to cultivation, a decrease in fire frequency, and a trend of increasing precipitation. In the preserve, the amount of organic carbon did not change appreciably between the 1900 and 1997 sampling dates, with 32 kg C/m2 in the top meter and a third of that in the top 20 cm. Carbon and nitrogen stocks varied by less than 6% between two replicate modern soil pits or between the modern sites and the archive. Radiocarbon content decreased with depth in all sites and the modern SOM had positive , values near the surface due to nuclear weapons testing in the early 1960s. In the upper 10 cm, most of the SOM had a turnover time of 6,10 years, according to a model fit to the radiocarbon content. Below about 10 cm, the organic matter was almost all passive material with long (millennial) turnover times. Soil respiration ,14CO2 on a summer day was 106,109,, an isotopic disequilibrium of about 9, relative to atmospheric 14CO2. In both the modern and archive soil, the relative abundance of 13C in organic matter increased with depth by 2, in the upper meter from ,13C = --26, at 5 cm to --24, below a meter. In addition, the slope of ,13C vs. depth below 5 cm was the same for both soils. Given the age of the soil archive, these results give clear evidence that the depth gradients are not due to depletion of atmospheric 13CO2 by fossil fuel emissions but must instead be caused by isotopic fractionation between plant litter inputs and preservation of SOM. Overall, the data show that these soils have a large reservoir of recalcitrant C and stocks had not changed between sampling dates 100 years apart. [source] Transit time distributions of a conceptual model: their characteristics and sensitivitiesHYDROLOGICAL PROCESSES, Issue 12 2010S. M. Dunn Abstract The internal behaviour of a conceptual hydrological and tracer transport model, STREAM, has been examined through generation of transit time distributions for the model. The model has been applied to a small sub-catchment of the Lunan Water in the east of Scotland where daily precipitation and stream water samples have been analysed for isotope content. Transit time distributions are generated by numerically tracking pulse inputs of tracer to the model and evaluating the simulated stream outputs. A set of baseline simulations was first established through calibration to time series of stream flow. A series of model experiments was then undertaken to assess the sensitivity of the simulated transit time distributions to different model parameterizations, flow paths and mixing assumptions. The results of the analysis show that the model transit time distributions do not conform to any simple statistical function and that their characteristics can be significantly altered depending on how the model is set up. The analysis provided valuable insight into the functioning of the model and could be usefully applied to other model codes. Comparison of the transit time distributions generated by conceptual models with data-based empirical evidence of distributions gives the potential to close the gap in understanding the physical explanation for why catchment systems behave as they do. Copyright © 2010 John Wiley & Sons, Ltd. [source] Seven-Year Results of Thinning and Burning Restoration Treatments on Old Ponderosa Pines at the Gus Pearson Natural AreaRESTORATION ECOLOGY, Issue 2 2004Kimberly F. Wallin AbstractWe examined the 7-year effects of three restoration treatments on leaf physiology and insect-resistance characteristics of pre-settlement age ponderosa pines (Pinus ponderosa Dougl. ex Laws.) at the Gus Pearson Natural Area (GPNA) in northern Arizona. Restoration treatments were: (1) thinned in 1993 to approximate pre-Euro-American settlement stand structure, (2) thinned plus prescribed burned in 1994 and 1998, and (3) untreated control. Tree physiological and insect-resistance characteristics were measured in year 2000, 7 years after thinning, using the same procedures as an earlier study performed in 1996. Consistent with the 1996 results, pre-dawn water potential in 2000 was consistently lower in the control than both thinned treatments. Both thinned treatments continued to have increased foliar nitrogen concentration in leaves 7 years after treatment. However lower leaf nitrogen concentration in the thinned and burned compared with the thinned treatment suggests lower nitrogen availability to trees in repeatedly burned plots. Analysis of leaf gas exchange characteristics and carbon isotope content (,13C) suggests continued stimulation of photosynthesis by both thinning treatments. Differences among treatments in resin volume, a measure of bark beetle resistance, depended on season of measurement. Trees in both thinning treatments continued to have increased leaf toughness, a measure of resistance to insect folivores. Our results show that many beneficial effects of restoration treatments on carbon, water, and nitrogen relations and insect-resistance characteristics of pre-settlement ponderosa pines continue to be expressed 7 years after treatment at the GPNA. [source] Detection of royal jelly adulteration using carbon and nitrogen stable isotope ratio analysisRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 2 2006A. Stocker Stable isotope ratios (13C/12C and 15N/14N) were measured in royal jelly (RJ) samples by isotope ratio mass spectrometry (IRMS) to evaluate authenticity and adulteration. Carbon and nitrogen isotope contents (given as delta values relative to a standard, ,13C, ,15N) of RJ samples from various European origins and samples from commercial sources were analyzed. Uniform ,13C values from ,26.7 to ,24.9, were observed for authentic RJ from European origins. Values of ,15N ranged from ,1.1 to 5.8, depending on the plant sources of nectars and pollen. High ,13C values of several commercial RJ samples from ,20.8 to ,13.3, indicated adulteration with high fructose corn syrup (HFCS) as a sugar source. Use of biotechnologically produced yeast powder as protein source for the adulterated samples was assumed as ,15N values were lower, as described for C4 or CAM plant sources. RJ samples from authentic and from adulterated production were distinguished. The rapid and reliable method is suitable for urgent actual requirements in food monitoring. Copyright © 2005 John Wiley & Sons, Ltd. [source] | ||||||||||