Identification and apportionment of nitrate sources in the phreatic aquifers in Northern Jordan using a dual isotope method (δ15N and δ18O of NO3-)

Nitrate contamination in stream water and groundwater is a serious environmental problem that arises in areas of high agricultural activities or high population density. It is therefore important to identify the source and flowpath of nitrate in water bodies. In recent decades, the dual isotope analysis (δ15N and δ18O) of nitrate has been widely applied to track contamination sources by taking advantage of the difference in nitrogen and oxygen isotope ratios for different sources. However, transformation processes of nitrogen compounds can change the isotopic composition of nitrate due to the various redox processes in the environment, which often makes it difficult to identify contaminant sources. To compensate for this, the stable water isotope of the H2O itself can be used to interpret the complex hydrological and hydrochemical processes for the movement of nitrate contaminants. Therefore, the present study aims at understanding the fundamental background of stable water and nitrate isotope analysis, including isotope fractionation, analytical methods such as nitrate concentration from samples, instrumentation, and the typical ranges of δ15N and δ18O from various nitrate sources. In addition, we discuss hydrograph separation using the oxygen and hydrogen isotopes of water in combination with the nitrogen and oxygen isotopes of nitrate to understand the relative contributions of precipitation and groundwater to stream water. This study will assist in understanding the groundwater flowpaths as well as tracking the sources of nitrate contamination using the stable isotope analysis in combination with nitrate and water.

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Challenging in Rats the Use of 13C Spirulina as Reference Protein for the Dual Isotope Method to Determine Amino Acid Bioavailability (P08-061-19)

Current Developments in Nutrition ◽

10.1093/cdn/nzz044.p08-061-19 ◽

2019 ◽

Vol 3 (Supplement_1) ◽

Author(s):

Romain Tessier ◽

Nadezda Khodorova ◽

Juliane Calvez ◽

Daniel Tomé ◽

Claire Gaudichon

Keyword(s):

Amino Acid ◽

Goat Milk ◽

Protein Digestibility ◽

Male Rats ◽

National Agency ◽

Dual Isotope ◽

Isotope Method ◽

Reference Protein ◽

Bonferroni Test

Abstract Objectives In order to establish DIAAS in humans, the FAO recommended to develop a new method to measure indispensable amino acid (IAA) digestibility. This method uses two isotopic labeling, one for the protein to test and one for a reference protein. Spirulina was chosen as the 13C reference protein due to its commercial availability and affordability. However, the real digestibility of spirulina protein has not been measured in vivo. This work aims to assess the digestibility of spirulina and its repeatability in different meal tests in rats. Methods 23 Wistar male rats were fed a test meal containing 0.5 g of 15 N protein from either spirulina (n = 7), sunflower n = 8) or goat milk isolate (n = 8) and 10 mg of 13C labeled spirulina. Rats were euthanized 6 h after the meal and their digestive luminal contents (stomach, small intestine, ileum, caecum, colon) were collected. Protein digestibility was determined for the test and the reference proteins by measuring 15 N and 13C enrichments in the digesta by EA-IRMS. Caecal IAA digestibility of 13C spirulina was determined by measuring the quantity of AA in the caecum by UPLC and the 13C enrichment in AA by GC-C-IRMS. Group effects were tested using one way ANOVA and differences between groups using Bonferroni test. Results Six hours after ingestion, most of the dietary 15 N and 13C were found in the caecum and colon. But there at least twice more 15 N nitrogen in the caecum and colon in the spirulina group than in the two other groups. Therefore, spirulina protein digestibility (86.0 ± 0.7%) was lower (P < 0.001) than sunflower (95.1 ± 0.5%) and goat milk digestibility (97.2 ± 0.2%). 13C spirulina digestibility tended to be different (P = 0.06) when mixed to spirulina (90.6 ± 0.6%), sunflower (88.8 ± 0.5%) or goat milk (89.0 ± 0.5%) isolates. The caecal IAA digestibility of 13C spirulina was lower in the spirulina group than in sunflower and goat milk groups for every IAA tested, and the mean was 91.6 ± 0.2% for sunflower, 91.4 ± 0.4% for goat milk and 85.4 ± 0.6% for spirulina. Conclusions Spirulina protein is of lower digestibility than other animal or plant proteins. Protein and amino digestibility of a tracer dose of 13C spirulina appears to vary depending on the protein component of the meal. These results question the use of spirulina as a reference protein for the dual isotope method. Funding Sources French Research National Agency (ANR), SOFIPROTEOL. Supporting Tables, Images and/or Graphs

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Dual-Isotope Method for Determination of Human Zinc Absorption: The Use of a Test Meal of Turkey Meat

Journal of Nutrition ◽

10.1093/jn/115.1.111 ◽

1985 ◽

Vol 115 (1) ◽

pp. 111-122 ◽

Cited By ~ 37

Author(s):

Peter R. Flanagan ◽

James Cluett ◽

Michael J. Chamberlain ◽

Leslie S. Valberg

Keyword(s):

Test Meal ◽

Zinc Absorption ◽

Dual Isotope ◽

Turkey Meat ◽

Isotope Method

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Nitrogen Cycle Dynamics Revealed Through δ18O-NO3− Analysis in California Groundwater

Geosciences ◽

10.3390/geosciences9020095 ◽

2019 ◽

Vol 9 (2) ◽

pp. 95

Author(s):

Nate Veale ◽

Ate Visser ◽

Bradley Esser ◽

Michael Singleton ◽

Jean Moran

Keyword(s):

United States ◽

Land Use ◽

Oxygen Isotope ◽

Nitrogen Cycle ◽

The United States ◽

Nitrate Contamination ◽

Nitrate Sources ◽

Oxygen Isotope Fractionation ◽

Dual Isotope ◽

Quality Issue

Nitrate is a significant water-quality issue in California, the United States as a whole, and the world. Critical to addressing nitrate contamination is understanding the presence and extent of denitrification, and further refining the techniques used to identify nitrate sources. The use and understanding of nitrate isotopic signatures to identify nitrate sources have advanced tremendously; however, knowledge gaps remain concerning specific fractionation pathways and the role of denitrification in altering source values. Using a large unique database of California groundwater nitrate isotopic compositions, we explored the utility of nitrate–oxygen isotope ratios in determining specific nitrate origins. Lawrence Livermore National Lab (LLNL) samples were supplemented by United States Geological Society (USGS) data to create a dataset of over 1200 dual-isotope results. Methods used at LLNL allowed for the determination of δ15N-NO3−, δ18O-NO3−, δ18O-H2O, δ2H-H2O, excess air, major dissolved gases, and excess N2. Results were examined for the degree to which δ18O-NO3− conforms to the model of nitrification in which two atoms of oxygen are sourced from ambient water and one from the atmosphere. Almost 80% of the results fall within one standard deviation of predicted values. However, 19% of samples had significantly higher values, suggesting the preservation of a synthetic nitrate source signature, mixing of sources, or widespread denitrification. Results were examined with respect to general land-use classifications and, while nitrate concentrations followed the expected pattern of being higher in agricultural settings, δ18O-NO3−patterns are complicated by application of N-fertilizer in various forms, and subsequent N cycling in the soil zone. We found that the current understanding of oxygen isotope-fractionation mechanisms cannot yet explain the prevalence of oxygen-isotope compositions with higher than predicted δ18O values, but when paired with related data such as land use and indicators of denitrification, oxygen-isotope compositions of nitrate can help to assess nitrogen cycle dynamics.

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