Simplifying and improving the extraction of nitrate from freshwater for stable isotope analyses

Determining the isotopic composition of nitrate (NO3_) in water can prove useful to identify NO3_ sources and to understand its dynamics in aquatic systems. Among the procedures available, the ‘ionexchange resin method’ involves extracting NO3_ from freshwater and converting it into solid silver nitrate (AgNO3), which is then analysed for 15N/14N and 18O/16O ratios. This study describes a simplified methodology where water was not pre-treated to remove dissolved organic carbon (DOC) or barium cations (added to precipitate O-bearing contaminants), which suited samples with high NO3_ ($400 mM or 25 mg L_1 NO3_) and low DOC (typically <417 mM of C or 5 mg L_1 C) levels. % N analysis revealed that a few AgNO3 samples were of low purity (compared with expected % N of 8.2), highlighting the necessity to introduce quality control/quality assurance procedures for silver nitrate prepared from field water samples. Recommendations are then made to monitor % N together with % O (expected at 28.6, i.e. 3.5 fold % N) in AgNO3 in order to better assess the type and gravity of the contamination as well as to identify potentially unreliable data

Simplifying and improving the extraction of nitrate from freshwater for stable isotope analyses

Determining the isotopic composition of nitrate (NO3 ) in water can prove useful to identify NO3 sources and to understand its dynamics in aquatic systems. Among the procedures available, the `ion-exchange resin method? involves extracting NO3 from freshwater and converting it into solid silver nitrate (AgNO3), which is then analysed for 15N/14N and 18O/16O ratios. This study describes a simplified methodology where water was not pre-treated to remove dissolved organic carbon (DOC) or barium cations (added to precipitate O-bearing contaminants), which suited samples with high NO3 (<400 uM or 25 mgL-1 NO3) and low DOC (typically <417 uM of C or 5 mgL-1 C) levels. % N analysis revealed that a few AgNO3 samples were of low purity (compared with expected % N of 8.2), highlighting the necessity to introduce quality control / quality assurance procedures for silver nitrate prepared from field water samples. Recommendations are then made to monitor % N together with % O (expected at 28.6, i.e. 3.5 fold % N) in AgNO3 in order to better assess the type and gravity of the contamination as well as to identify potentially unreliable data

Evaluating the utility of 15N and 18O isotope abundance analyses to identify nitrate sources: A soil zone study

15N and 18O isotope abundance analyses in nitrate (NO3?) (expressed as ?15N-NO3? and ?18O-NO3? values respectively) have often been used in research to help identify NO3? sources in rural groundwater. However, questions have been raised over the limitations as overlaps in ? values may occur between N source types early in the leaching process. The aim of this study was to evaluate the utility of using stable isotopes for nitrate source tracking through the determination of ?15N-NO3? and ?18O-NO3? in the unsaturated zone from varying N source types (artificial fertiliser, dairy wastewater and cow slurry) and rates with contrasting isotopic compositions. Despite NO3? concentrations being often elevated, soil-water nitrate poorly mirrored the 15N content of applied N and therefore, ?15N-NO3? values were of limited assistance in clearly associating nitrate leaching with N inputs. Results suggest that the mineralisation and the nitrification of soil organic N, stimulated by previous and current intensive management, masked the cause of leaching from the isotopic prospective. ?18O-NO3? was of little use, as most values were close to or within the range expected for nitrification regardless of the treatment, which was attributed to the remineralisation of nitrate assimilated by bacteria (mineralisation-immobilisation turnover or MIT) or plants. Only in limited circumstances (low fertiliser application rate in tillage) could direct leaching of synthetic nitrate fertiliser be identified (?15N-NO3? 15 ?). Nevertheless, some useful differences emerged between treatments. ?15N-NO3? values were lower where artificial fertiliser was applied compared with the unfertilised controls and organic waste treatments. Importantly, ?15N-NO3? and ?18O-NO3? variables were negatively correlated in the artificial fertiliser treatment (0.001 ? p ? 0.05, attributed to the varying proportion of fertiliser-derived and synthetic nitrate being leached) while positively correlated in the dairy wastewater plots (p ? 0.01, attributed to limited denitrification). These results suggest that it may be possible to distinguish some nitrate sources if analysing correlations between ? variables from the unsaturated zone. In grassland, the above correlations were related to N input rates, which partly controlled nitrate concentrations in the artificial fertiliser plots (high inputs translated into higher NO3? concentrations with an increasing proportion of fertiliser-derived and synthetic nitrate) and denitrification in the dairy wastewater plots (high inputs corresponded to more denitrification). As a consequence, nitrate source identification in grassland was more efficient at higher input rates due to differences in ? values widening between treatments

Monitoring Deposited Dust in The Old Library, Trinity College Dublin

A study is currently being undertaken to characterise the accumulation rate, distribution, particle size, type and source of dust in the Old Library, Trinity College Dublin, in order to investigate its impact on the collection of more than 300,000 books and manuscripts held there. The majority (approximately 200,000 books, dating from 15th ? 19th century) are held on open shelves in the Long Room and Gallery. As well as being a research facility, the Old Library is an exhibition space, and a major tourist attraction as home to a renowned medieval manuscript (the Book of Kells, c.800). It is open to the public seven days a week, almost year-round

Neoproterozoic glaciation in the Proto-Andes: Tectonic implications and global correlation

The Chiquerío Formation in southern Peru records the only documented Neoproterozoic glacial episode in the entire Andean Belt. We present U-Th-Pb secondary ion mass spectrometry (SIMS) detrital zircon ages and C isotopic data from the tillite and its overlying dolomite cap, the San Juan Formation. Two prominent negative C isotopic excursions are documented: an older excursion (δ13C = −2‰) in the cap-carbonate unit overlying the tillite, and a younger excursion (δ13C = −8‰) in a laminated limestone unit 700 m up sequence. In both cases, δ13C values recover to 2‰. U-Th-Pb SIMS detrital zircon results from the tillite (both matrix and interbedded turbiditic sandstones) indicate a restricted age distribution of 950-1300 Ma. Turbiditic dolomitic sandstones overlying the younger (−8‰) carbon isotope excursion yield a similar 950-1300 Ma peak, but also contain grains dated as 1600-2000 Ma and 700-820 Ma. The detrital zircon geochronology and C isotope chemostratigraphy are consistent with the Chiquerío Formation being equivalent to the ca. 700 Ma Sturtian glacial. The younger negative C isotope excursion is delimited by the youngest detrital zircon (697 ± 11 Ma) in overlying strata. A correlation with the 635 Ma Marinoan glacial is inferred, although no unequivocal glaciogenic strata have been identifi ed. The detrital zircon data are consistent with derivation from the Proto-Andean margin, despite the Chiquerío Formation unconformably overlying basement gneisses of the 1800-2000 Ma Arequipa-Antofalla basement (AAB), which is exotic to Amazonia. This implies the Chiquerío Formation and AAB were proximal to the proto-Andean margin during Neoproterozoic glaciation, and supports paleogeographic reconstructions that favor AAB accretion to the Amazonian craton during the 1000-1300 Ma Grenville-Sunsas orogeny