Oxygen isotope exchange between O2 and CO2 over hot platinum: an innovative technique for measuring Δ17O in CO2.

The isotopic composition of carbon dioxide provides a powerful tool and has been widely used for constraining the sources and sinks of atmospheric CO2. In this work, we demonstrate a simple, rapid, and clean way for measuring the triple oxygen isotope ratio of carbon dioxide with high precision. The method depends on isotope exchange between O2 and CO2 in the presence of platinum at high temperature and allows rapid measurement of Δ(17)O of CO2. The method has been established and confirmed through several tests by using artificially made CO2 with known Δ(17)O values. The analytical precision obtained for determining Δ(17)O in CO2 is 0.045‰ (1 - σ standard deviation).

An improved CeO2 method for high-precision measurements of 17O/16O ratios for atmospheric carbon dioxide.

RATIONALE: The oxygen isotopic composition of carbon dioxide originating at the Earth's surface is modified in the stratosphere by interaction with ozone which has anomalous oxygen isotope ratio (Δ(17)O = 1000 * ln(1 + δ(17)O/1000) - 0.522 * 1000 * ln (1 + δ(18)O/1000) >0). The inherited anomaly provides a powerful tracer for studying biogeochemical cycles involving CO(2). However, the existing methods are either too imprecise or have difficulty in determining the small Δ(17)O variations found in the tropospheric CO(2). In this study an earlier published CeO(2) and CO(2) exchange method has been modified and improved for measuring the Δ(17)O values of atmospheric carbon dioxide with high precision. METHODS: The CO(2) fraction from air samples was separated by cryogenic means and purified using gas chromatography. This CO(2) was first analyzed in an isotope ratio mass spectrometer, then artificially equilibrated with hot CeO(2) to alter its oxygen isotopes mass-dependently and re-analyzed. From these data the (17)O/(16)O and (18)O/(16)O ratios were calculated and the Δ(17)O value was determined. RESULTS: The validity of the method was established in several tests by using artificially prepared CO(2) with zero and non-zero Δ(17)O values. The published value of the CO(2)-H(2) O equilibrium slope was also reproduced. CONCLUSIONS: The CO(2)-CeO(2) equilibration method has been improved to measure the oxygen isotope anomaly (Δ(17)O value) of atmospheric CO(2) with an analytical precision of ±0.12‰ (2σ).

Pollution and variation of stream nitrate in a protected high-mountain watershed of Central Taiwan: evidence from nitrate concentration and nitrogen and oxygen isotope compositions.

This study analyzed the concentration and stable nitrogen (δ(15)N) and oxygen (δ(18)O) isotopic compositions of water NO (3) (-) , as well as NO (3) (-) concentration and δ(15)N values of soils and manure-sourced fertilizers to assess pollution and variation in stream nitrate at the watershed of the Chi-Chia-Wan Stream (CCWS), a protected high-mountain stream in Central Taiwan. Results indicate a gully (G1) that contributes significantly high NO (3) (-) concentration water (up to 122 mg/L) to trunk water as the major pollution source of CCWS. The high NO (3) (-) concentration gully water has a close relationship with manure-sourced fertilizer with both having compatible enriched δ(15)N values. Results also indicate that water mixing over isotopic fractionation processes such as denitrification or assimilation is the major process accounting for variations in concentrations and isotopic values for stream NO (3) (-) . Incorporation of gully/tributary water of high NO (3) (-) concentration increases both the concentration and isotopic values of trunk water and vice versa for the incorporation of low NO (3) (-) concentration tributary water. Despite G1 contributing high NO (3) (-) concentration water to the trunk water of CCWS, the concentration of the trunk water is only slightly elevated and is still lower than the required water quality standard due to much lower drainage of the gully water compared to trunk water's runoff. In addition to gully or tributary water and rainwater, NO (3) (-) derived from soil is another important contributor to trunk water. The NO (3) (-) contribution of soil to trunk water is greater in summer than in winter. Additionally, NO (3) (-) concentrations in soil from ex-cultivated land are significantly lower than that in cultivated land. This means that NO (3) (-) contribution from ex-cultivated land soil to trunk water is small and demonstrates that the land-recovery plan that has been underway in the studied watershed for sometime is effective.

Detecting urbanization effects on surface and subsurface thermal environment--a case study of Osaka.

Tremendous efforts have been devoted to improve our understanding of the anthropogenic effects on the atmospheric temperature change. In comparison, little has been done in the study of the human impacts on the subsurface thermal environment. The objective of this study is to analyze surface air temperature records and borehole subsurface temperature records for a better understanding of the urban heat island effects across the ground surface. The annual surface air temperature time series from six meteorological stations and six deep borehole temperature profiles of high qualities show that Osaka has been undergoing excess warming since late 19th century. The mean warming rate in Osaka surface air temperature is about 2.0 degrees C/100a over the period from 1883 to 2006, at least half of which can be attributed to the urban heat island effects. However, this surface air temperature warming is not as strong as the ground warming recorded in the subsurface temperature profiles. The surface temperature anomaly from the Osaka meteorological record can only account for part of the temperature anomaly recorded in the borehole temperature profiles. Surface air temperature is conventionally measured around 1.5 m above the ground; whereas borehole temperatures are measured from rocks in the subsurface. Heat conduction in the subsurface is much less efficient than the heat convection of the air above the ground surface. Therefore, the anthropogenic thermal impacts on the subsurface can be more persistent and profound than the impacts on the atmosphere. This study suggests that the surface air temperature records alone might underestimate the full extent of urban heat island effects on the subsurface environment.

Erratum to "Temperature and hydrological variations of the urban environment in the Taipei metropolitan area, Taiwan".

In this study, the temperature, precipitation and groundwater level variations and changing patterns with varied time scales are presented for Taipei metropolitan area which consists of the capital city with neighboring counties. Along with the continuous city expansion during the past decades, global warming and heat island effect have generated perceivable negative impacts on environmental and reflect on the climatic and hydrological parameters. In addition to accelerating climate warming, hydrological extremity becomes more evident during the past decades and greatly elevates the risks of drought and floods in the study area. These observations in the Taipei metropolitan area support the common hypothesis that climate variability would increase as climate warms. The air temperature records, in conjunction with hydrological data, provide useful and invaluable information for the ongoing study of subsurface environmental changes resulting from nature and anthropogenic influences in Taipei metropolitan area. The continuing climatic warming and hydrological extremity would create observable impacts on the subsurface environment of Taipei metropolitan area and need to pursue in a fast and efficient pace.

Temperature and hydrological variations of the urban environment in the Taipei metropolitan area, Taiwan.

In this study, the temperature, precipitation and groundwater level variations and changing patterns with varied time scales are presented for Taipei metropolitan area which consists of the capital city with neighboring counties. Along with the continuous city expansion during the past decades, global warming and heat island effect have generated perceivable negative impacts on environmental and reflect on the climatic and hydrological parameters. In addition to accelerating climate warming, hydrological extremity becomes more evident during the past decades and greatly elevates the risks of drought and floods in the study area. These observations in the Taipei metropolitan area support the common hypothesis that climate variability would increase as climate warms. The air temperature records, in conjunction with hydrological data, provide useful and invaluable information for the ongoing study of subsurface environmental changes resulting from nature and anthropogenic influences in Taipei metropolitan area. The continuing climatic warming and hydrological extremity would create observable impacts on the subsurface environment of Taipei metropolitan area and need to pursue in a fast and efficient pace.

Difference in attenuation among Mn, As, and Fe in riverbed sediments.

We report, for the first time, a detailed study at river water and hyporheic zone systems through collection and analyses of shallow sediments and selected source rocks, pore water, and river water from forty-two locations at the Chianan Plain (CP), SW Taiwan. The study was focused to understand the possible changes in the river water and sediment chemistry as a consequence of high arsenic (mean±SD=71.28±16.24µg/L, n=46) groundwater discharge to three major rivers in the plain. The study shows, except few locations, As concentration in river sediments corresponds to average As concentration in soil and upper crustal abundance and of source rock. Sequential extraction indicates that As is mostly bound to FeOOH. No enrichment of arsenic in river sediments or depletion of aqueous As and iron in pore water was observed down to the maximum sampling depth of 1.7m although manganese is enriched in sediments. Dissolved As concentrations in the river sediments are much lower compared to the hotspots in the CP aquifers. This suggests that no As attenuation processes are active or they cannot be detected in this zone. Mn precipitates at higher redox level compared to Fe and As and thus attenuates in the studied zone.

Cyanophycin mediates the accumulation and storage of fixed carbon in non-heterocystous filamentous cyanobacteria from coniform mats.

Thin, filamentous, non-heterocystous, benthic cyanobacteria (Subsection III) from some marine, lacustrine and thermal environments aggregate into macroscopic cones and conical stromatolites. We investigate the uptake and storage of inorganic carbon by cone-forming cyanobacteria from Yellowstone National Park using high-resolution stable isotope mapping of labeled carbon (H(13)CO3 (-)) and immunoassays. Observations and incubation experiments in actively photosynthesizing enrichment cultures and field samples reveal the presence of abundant cyanophycin granules in the active growth layer of cones. These ultrastructurally heterogeneous granules rapidly accumulate newly fixed carbon and store 18% of the total particulate labeled carbon after 120 mins of incubation. The intracellular distribution of labeled carbon during the incubation experiment demonstrates an unexpectedly large contribution of PEP carboxylase to carbon fixation, and a large flow of carbon and nitrogen toward cyanophycin in thin filamentous, non-heterocystous cyanobacteria. This pattern does not occur in obvious response to a changing N or C status. Instead, it may suggest an unusual interplay between the regulation of carbon concentration mechanisms and accumulation of photorespiratory products that facilitates uptake of inorganic C and reduces photorespiration in the dense, surface-attached communities of cyanobacteria from Subsection III.

Linking geochemical processes in mud volcanoes with arsenic mobilization driven by organic matter.

The present study deals with geochemical characterization of mud fluids and sediments collected from Kunshuiping (KSP), Liyushan (LYS), Wushanting (WST), Sinyangnyuhu (SYNH), Hsiaokunshui (HKS) and Yenshuikeng (YSK) mud volcanoes in southwestern Taiwan. Chemical constituents (cations, anions, trace elements, organic carbon, humic acid, and stable isotopes) in both fluids and mud were analyzed to investigate the geochemical processes and spatial variability among the mud volcanoes under consideration. Analytical results suggested that the anoxic mud volcanic fluids are highly saline, implying connate water as the probable source. The isotopic signature indicated that δ(18)O-rich fluids may be associated with silicate and carbonate mineral released through water-rock interaction, along with dehydration of clay minerals. Considerable amounts of arsenic in mud irrespective of fluid composition suggested possible release through biogeochemical processes in the subsurface environment. Sequential extraction of As from the mud indicated that As was mostly present in organic and sulphidic phases, and adsorbed on amorphous Mn oxyhydroxides. Volcanic mud and fluids are rich in organic matter (in terms of organic carbon), and the presence of humic acid in mud has implications for the binding of arsenic. Functional groups of humic acid also showed variable sources of organic matter among the mud volcanoes being examined. Because arsenate concentration in the mud fluids was found to be independent from geochemical factors, it was considered that organic matter may induce arsenic mobilization through an adsorption/desorption mechanism with humic substances under reducing conditions. Organic matter therefore plays a significant role in the mobility of arsenic in mud volcanoes.

Assessment of renal function by the stable oxygen and hydrogen isotopes in human blood plasma.

Water (H(2)O) is the most abundant and important molecule of life. Natural water contains small amount of heavy isotopes. Previously, few animal model studies have shown that the isotopic composition of body water could play important roles in physiology and pathophysiology. Here we study the stable isotopic ratios of hydrogen (δ(2)H) and oxygen (δ(18)O) in human blood plasma. The stable isotopic ratio is defined and determined by δ(sample) = [(R(sample)/R(STD))-1] * 1000, where R is the molar ratio of rare to abundant, for example, (18)O/(16)O. We observe that the δ(2)H and the δ(18)O in human blood plasma are associated with the human renal functions. The water isotope ratios of the δ(2)H and δ(18)O in human blood plasma of the control subjects are comparable to those of the diabetes subjects (with healthy kidney), but are statistically higher than those of the end stage renal disease subjects (p<0.001 for both ANOVA and Student's t-test). In addition, our data indicate the existence of the biological homeostasis of water isotopes in all subjects, except the end stage renal disease subjects under the haemodialysis treatment. Furthermore, the unexpected water contents (δ(2)H and δ(18)O) in blood plasma of body water may shed light on a novel assessment of renal functions.

Regional scale high resolution δ18O prediction in precipitation using MODIS EVI.

The natural variation in stable water isotope ratio data, also known as water isoscape, is a spatiotemporal fingerprint and a powerful natural tracer that has been widely applied in disciplines as diverse as hydrology, paleoclimatology, ecology and forensic investigation. Although much effort has been devoted to developing a predictive water isoscape model, it remains a central challenge for scientists to generate high accuracy, fine scale spatiotemporal water isoscape prediction. Here we develop a novel approach of using the MODIS-EVI (the Moderate Resolution Imagining Spectroradiometer-Enhanced Vegetation Index), to predict δ(18)O in precipitation at the regional scale. Using a structural equation model, we show that the EVI and precipitated δ(18)O are highly correlated and thus the EVI is a good predictor of precipitated δ(18)O. We then test the predictability of our EVI-δ(18)O model and demonstrate that our approach can provide high accuracy with fine spatial (250×250 m) and temporal (16 days) scale δ(18)O predictions (annual and monthly predictabilities [r] are 0.96 and 0.80, respectively). We conclude the merging of the EVI and δ(18)O in precipitation can greatly extend the spatial and temporal data availability and thus enhance the applicability for both the EVI and water isoscape.

Biogeochemical cycling of arsenic in coastal salinized aquifers: Evidence from sulfur isotope study.

Arsenic (As) contamination of groundwater, accompanied by critical salinization, occurs in the southwestern coastal area of Taiwan. Statistical analyses and geochemical calculations indicate that a possible source of aqueous arsenic is the reductive dissolution of As-bearing iron oxyhydroxides. There are few reports of the influence of sulfate-sulfide redox cycling on arsenic mobility in brackish groundwater. We evaluated the contribution of sulfate reduction and sulfide re-oxidation on As enrichment using δ(34)S([SO(4)]) and δ(18)O([SO(4)]) sulfur isotopic analyses of groundwater. Fifty-three groundwater samples were divided into groups of high-As content and salinized (Type A), low-As and non-salinized (Type B), and high-As and non-salinized (Type C) groundwaters, based on hydro-geochemical analysis. The relatively high enrichment of (34)S([SO(4)]) and (18)O([SO(4)]) present in Type A, caused by microbial-mediated reduction of sulfate, and high (18)O enrichment factor (ε([SO(4)-H(2)O])), suggests that sulfur disproportionation is an important process during the reductive dissolution of As-containing iron oxyhydroxides. Limited co-precipitation of ion-sulfide increased the rate of As liberation under anaerobic conditions. In contrast to this, Type B and Type C groundwater samples showed high δ(18)O([SO(4)]) and low δ(34)S([SO(4)]) values under mildly reducing conditions. Base on (18)O mass balance calculations, the oxide sources of sulfate are from infiltrated atmospheric O(2), caused by additional recharge of dissolved oxygen and sulfide re-oxidation. The anthropogenic influence of extensive pumping also promotes atmospheric oxygen entry into aquifers, altering redox conditions, and increasing the rate of As release into groundwater.

Oxidation is Key for Black Carbon Surface Functionality and Nutrient Retention in Amazon Anthrosols.

Aims: Soil black carbon (BC) has been shown to possess large amounts of cation exchange sites and surface charge, and is viewed as a potential soil amendment to improve nutrient retention and for pollutant remediation. This study investigated the nanoscale distribution of reactive functional groups and the binding of cations on the surface of micron-size BC particles, identified the key processes, and explored the sources of surface functionality and their relative contribution to cation exchange capacity (CEC). Materials and Methods: Elemental microprobe and synchrotron-based Scanning Transmission X-ray Spectromicroscopy (STXM) coupled with Near Edge X-ray Absorption Fine Structure (NEXAFS) spectroscopy were used for nano-scale mapping of cations and reactive functional groups, and further distinction of the sources of reactive functional groups generated either by oxidation of BC surfaces or by adsorption of non- BC organic matter onto the BC surfaces. Their respective contribution to cation adsorption was obtained using a depth profile of a BC-rich Anthrosol from the central Amazon, Brazil. Results and Discussion: Adsorption of Non-BC organic matter is more dominant on the surface of BC particle in topsoil as evidenced by a stronger signal of microbial biomass and humic substances extracts. In comparison, a greater level of oxidation was found on the outerlayer of BC particles in subsoil horizons. Organic C in subsoils was found to generate 23-42% more CEC per unit C than topsoil. Based on CEC per unit C, the capacity of BC in creating CEC was 6-7 times higher than Non-BC, and the BC in deeper horizons had up to 20% higher CEC than the topsoil horizon. Near BC surfaces, higher ratios of Ca/C and K/C in subsoil than topsoil horizons reinforce the observation that BC in subsoil horizons had a higher capacity in binding cations and creating CEC than in the topsoil horizon. Conclusions: Oxidation of BC is suggested to be more efficient and important for creating CEC than the adsorption of non-BC onto BC surfaces, thus identified as being key for BC surface functionality and nutrient retention in Amazon Anthrosols.