Nitrogen isotopic studies

Nadelhoffer, K.J. and Fry, B. 1994 Nitrogen isotope studies in forest ecosystems. In Lajtha, K. and Michener, R.H., eds.. Stable Isotopes in Ecology and Environmental Science. Blackwell Scientific Publications 22 4. 

Kreitler, C.W. 1975 Determining the Source of Nitrate in Ground Water by Nitrogen Isotope Studies. 

The generally low d N of terrestrial systems is typically retained in sludge and particulate matter produced by sewage plants. Nitrogen isotopic studies in a number of coastal systems have demonstrated that this low d N propagates into the benthic food web and can be used to quantify the impact ofsoHd materials in sewage on the nearshore biota (Rau et al., 1981 Spies et al., 1989 Tucker et al., 1999 Van Dover et al., 1992). 

Russell S. S., Arden 1. W., and Pillinger C. T. (1996) A carbon and nitrogen isotope study of diamond from primitive chondrites. Meteorit Planet. Sci. 31, 343-355. 

Kreitler C. W. (1975) Determining the source of nitrate in groundwater by nitrogen isotope studies Austin, Texas, University of Texas, Austin, Bureau Econ. Geol. Rep. Inv. 83. 

These large differences in N content emphasize just one of the several contrasts between carbon and nitrogen isotopic studies of sedimentary OM. While in the former, it can normally be assumed that each component makes a proportional contribution to the bulk C-isotopic composition, this may not be the case with N isotopes. The N-rich fraction can determine the isotopic character of the sediment, even if it does not volumetrically dominate the OM assemblage. Conversely, the degraded, N-poor woody and grass cuticle fragments that occur in many lake sediments will not seriously distort the N-isotopic signature of the waterbody preserved in the autochthonous om (see, for example, Yoshioka, et al, 1989 Talbot Johannessen, 1992). 

Nitrogen isotopic studies of organic matter production and sedimentation in modern lakes are few in number, but those that exist do provide us with some insights into the range of composition among modern phytoplankton assemblages, and in some cases they also allow us to compare the OM composition with that of ambient DIN and some of the major DIN sources. 

Nitrogen isotope studies in palaeolimnology sampling and measurement... 

One way to determine just where a given reaction stands on the El-E2-ElcB spectrum is to study isotope effects, which ought to tell something about the behavior of bonds in the transition state. For example, CH3CH2NMe3 showed a nitrogen isotope effect of 1.017, while PhCH2CH2NMe3" gave a corres-... 

Keegan, W.F. and DeNiro, M.J. 1988 Stable carbon- and nitrogen- isotope ratios of bone collagen used to study coral-reef and terrestrial components of prehistoric Bahamian diet. American Antiquity 53 320-336. 

Nitrogen isotope ratios ( N/ " N) inerease from plants to herbivores to eami-vores and ean be used to estimate the degree of camivory in human diets. Some field studies observe a greater differenee in 5 N between trophie levels in dry, hot habitats than in wet, cool ones. Two hypotheses have been proposed to explain this variation in difference in 8 N between trophic levels. (1) Elevated excretion of -depleted urea in heat/water-stressed animals (2) recycling of nitrogen on protein-deficient diets. Both predict increased diet-tissue 8 N difference under stress. 

Our results do not support the protein stress model. However, this model may apply in cases where stress is intermittent and results in tissue loss, as observed in the study of crows (Hobson and Clark 1992). Low protein levels throughout life after weaning may have produced overall slow and reduced rate of growth rather than tissue loss. Adult rats fed protein-deficient diets after maturation show systematic losses of nitrogen from most tissues that are in proportion to their turnover rates and masses (Uezu et al. 1983). Perhaps tissue nitrogen isotope enrichment may occur under these conditions. New experiments are needed to evaluate this hypothesis. 

The mean difference between collagen and flesh (A Nco.f) values for the first sacrificed pairs (91 days after birth) is 0.3 1.09%o while that for third pairs (171 days after birth) is 1.4 0.45%o. This result was unanticipated but seems robust. This indicates the relationship between diet and tissue 8 N and age is complex and varies between tissues. Future studies of diet-tissue nitrogen isotope spacing will have to consider age effects. This contrasts with carbon isotopes (Ambrose and Norr 1993), where we have observed little increase in 8 C with age in the same individuals. 

Steele, K.W. and Daniel, R.M.J 1978 Fractionation of nitrogen isotopes by animals a further complication to the use of variations in the natural abundance of for tracer studies. Journal of Agricultural Science, Cambridge 90 7-9. 

Heaton, T.H.E. (1987). Isotopic studies of nitrogen in the hydrosphere and atmosphere a review. Chemical Geology 0sotope Geoscience), Vol. 59, pp. 87-102. 

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