Study on Oxygen Isotope Fractionation in RE Oxide Minerals

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Geochemical characteristics of the Yufuin outflow plume, Beppu hydrothermal system, Japan

Thermal water at Yufuin (Kyushu Island, Japan) is tapped through about 820 shallow wells and used mainly for hot-spring bathing purposes. Chemical and isotopic data for fluids from wells and fumaroles in Yufuin and Beppu indicate that the thermal activity at Yufuin represents a dilute, westward-flowing hydrothermal outflow plume from the Beppu hydrothermal system. Two other (eastward-flowing) outflow plumes have long been recognized at Beppu, but the Yufuin outflow plume is first recognized here. The Yufuin outflow plume is apparently a mixture of two end-member fluids: (1) deep high-temperature (250–300°C) fluid from the Beppu system having high chloride concentration (1400–1600 mg/L) and a δ¹⁸O value near −6.0%, and (2) meteoric water having low chloride concentration (≤7 mg/L) and a δ¹⁸O value near −9.2%.A permeable conduit for the vertical and lateral transport of deep fluid from the Beppu system is provided by the Yufuin Fault zone, which extends westward from the southern flank of Mt. Tsurumi volcano to the town of Yufuin. Stable isotope ratios and chloride concentrations for shallow groundwaters near the eastern end of the fault, at an elevation near 700 m, are consistent with those required for the low-chloride meteoric end-member of the Yufuin thermal waters. Recharge of this meteoric water, as well as mixing with the Beppu deep fluid, may occur along the Yufuin Fault. Enthalpy-chloride relations indicate additional conductive heating of the Yufuin waters, in the amount of 350–500 kJ/kg beyond that which can be accounted for by mixing between Beppu deep fluid and meteoric water. This could be a result of conductive heating with convection to a depth of 1–2 km. Estimates of the magnitude of the heat source for the Beppu hydrothermal system should take into account the heat being discharged at Yufuin.     

The use of the stable isotope 44Ca in studies of calcium incorporation into dentin

The incorporation into rat incisor dentin of two calcium isotopes, the stable ⁴⁴Ca and the radioactive ⁴⁵Ca, was studied using secondary ion mass spectrometry (SIMS) stepscanning and imaging, and autoradiography, respectively. The results demonstrated a time-dependent incorporation of the calcium isotopes into the mineral phase of dentin. With the SIMS step-scanning, detecting ⁴⁴Ca, the ion yield was high in the odontoblasts 2 min after intravenous injection. After 10 min a marked increase in signal intensity was found at the dentin mineralization front. This result was consistent with those obtained by ⁴⁵Ca autoradiography; a peak of incorporation occurred 10 min after injection of the isotope. Likewise, localization of ⁴⁴Ca to the mineralization front could be demonstrated 10 min after injection by SIMS imaging. In images obtained at earlier intervals, no such increase in ion yield could be detected. The results show that the nonradioactive, stable isotope ⁴⁴Ca can be used as a marker for biomineralization in a similar way to radioactive ⁴⁵Ca.     

PdY8．5Ru0．19合金吸放氢氘特性

在25℃～100℃的温度范围内,测定了PdY8.5Ru0.19合金吸放氢、氘的P-C-T曲线.与纯钯相比,合金的P-C-T曲线坪区变窄,坪压降低,有显著的同位素效应,但迟滞效应较小.合金吸放氢氘的P-C-T曲线可拟合成p=A(er/B-1)形式.吸氘热焓为-13.9 kJ/mol·D2,熵变为-9.4 J/mol K·D2.进行了25℃下合金吸氢、氘速率的测量,合金吸氢、氘速率常数分别为KH=2.39×10-4 mol·s-1,KD=1.16×10-4 mol·s-1.而且合金的氢化过程用渐进转化模型描述.     

Chemical and Isotopic Tracer Evaluation of Water Mixing and Evaporation in a Dammed Texas River During Drought

The interaction between drought and river regulation is monitored to better understand river flow mixing, evaporation and surface‐groundwater exchange in changing regional climates and in increasingly regulated waterways. This study compared Brazos River stable isotope (δ¹⁸O and δD) and electrical conductivity values with reservoir, creek and aquifer samples in the Brazos watershed, the largest watershed in Texas. The combination of tributaries, rainfall and the Brazos River Alluvium Aquifer, on the one hand, and the Lake Whitney reservoir, on the other hand, represent endmembers of dilute run‐off water and evaporated saline water, respectively. A simple isotope mixing model that uses monthly river discharge, Lake Whitney discharge, historical monthly precipitation δ¹⁸O and pan evaporation accurately reconstructs river δ¹⁸O (±0.5‰ on average). Data and isotope balance modelling support continued evaporation of ¹⁸O‐enriched Lake Whitney water as it flows downstream, although the most evaporation took place in Lake Whitney. The difference between river and precipitation δ¹⁸O, or Δ¹⁸O_RIV‐_PPT, here a measurement of degree of evaporation, ranged from ?0.1‰ for a small creek, to 1.7‰ for the Brazos River, to at least 2.7‰ in Lake Whitney. This study indicates that drought in regulated rivers may enhance reservoir discharge dominance in river flows during peak drought conditions when combined run‐off and baseflow dominance would be expected in a similar undammed river. Copyright © 2016 John Wiley & Sons, Ltd.     

Preparation and Characterization of 17O-Enriched Alumina for Nuclear Fusion Damage Experiments

Alumina enriched in ¹⁷O was successfully fabricated from aluminum isopropoxide and water containing the ¹⁷O isotope. This material was necessary for an experiment to study the radiation damage expected in alumina exposed to a nuclear fusion reactor environment. The enrichment levels of specimens subjected to different preparation schedules were measured using a nuclear reaction analysis technique. Replacement of the ¹⁷O isotope in the ceramic by atmospheric oxygen occurred readily. Therefore, successful fabrication of suitably enriched alumina specimens required that all processing steps be performed under vacuum or inertgas environments. The optimum fabrication procedure produced enriched alumina specimens of >99.5% of theoretical density, ∽10-μm grain size, and a flexural strength of 280 MPa.     

Subsoil <Superscript>15</Superscript>N-N<Subscript>2</Subscript>O Concentrations in a Sandy Soil Profile After Application of <Superscript>15</Superscript>N-fertilizer

Studies on emissions of nitrous oxide (N₂O) from agricultural soils mostly focus on fluxes between the soil and the atmosphere or are limited to the atmosphere in the topsoil. However, in soils with shallow water tables, significant N₂O formation may occur closer to the groundwater. The aims of this study were (i) to determine the importance of subsoil N₂O formation in a sandy soil; and (ii) to obtain a quantitative insight in the contribution of subsoil N₂O to the overall losses of N₂O to the environment. We applied ¹⁵N labeled fertilizer at a rate of 5.22 kg ¹⁵N ha⁻¹; 50% as Ca(NO₃)₂ and 50% as NH₄Cl, on a mesic typic Haplaquod seeded with potatoes (Solanum tuberosum L.), and traced soil N₂O concentrations and fluxes over a one-year period. Throughout the year, total N₂O and the amount of ¹⁵N recovered in soil N₂O were highest in the subsoil, with a maximum concentration at 48 cm depth in mid-February of 19900 μl m⁻³ and 24 μg ¹⁵N m⁻³, respectively. The maximum concentration coincided with the highest water-filled pore space of 71%. The cumulative flux of N₂O was 446 g N₂O-N ha⁻¹, the recovery of ¹⁵N in this flux was 0.06%. During the summer, maximum fluxes followed high soil N₂O concentrations. During winter, no such relation was found. We concluded that the formation of N₂O was the highest in the subsoil, largely controlled by water-filled pore space rather than NO₃⁻ concentration or temperature. Although high subsoil N₂O concentrations did not lead to high surface fluxes of N₂O in the winter, artificial draining may lead to high indirect N₂O emissions through supersaturated drainage water.     

渭北西部中奥陶统碳酸盐岩地球化学特征及古环境恢复

通过对渭北西部中奥陶统马家沟组碳酸盐岩C、O同位素和微量元素的测试分析和对C、O同位素原始性的评估与校正,分析该地区马家沟期的古环境。对古沉积环境的盐度、温度、气候及氧化还原性进行了定性与定量分析。分别采用公式法与最小二乘法对古温度与古气候进行了定量分析,并比较其差异,研究认为综合这2种算法可有效反映古环境的气候与温度等信息。     

Establishing spatial trends in water chemistry and stable isotopes (δ15N and δ13C) in the Elwha River prior to dam removal and salmon recolonization

Two high‐head dams on the Elwha River in Washington State (USA) have changed the migratory patterns of resident and anadromous fish, limiting Pacific salmon to the lower 7.9 km of a river that historically supported large Pacific salmon runs. To document the effects of the dams prior to their removal, we measured carbon and nitrogen stable isotope ratios of primary producers, benthic macroinvertebrates, and fish, and water chemistry above, between and below the dams. We found that δ¹⁵N was significantly higher in fish, stoneflies, black flies, periphyton and macroalgae where salmon still have access. Fish and chloroperlid stoneflies were enriched in δ¹³C, but the values were more variable than in δ¹⁵N. For some taxa, there were also differences between the two river sections that lack salmon, suggesting that factors other than marine‐derived nutrients are structuring longitudinal isotopic profiles. Consistent with trophic theory, macroalgae had the lowest δ¹⁵N, followed by periphyton, macroinvertebrates and fish, with a range of 6.9, 6.2 and 7.7‰ below, between, and above the dams, respectively. Water chemistry analyses confirmed earlier reports that the river is oligotrophic. Phosphorous levels in the Elwha were lower than those found in other regional rivers, with significant differences among regulated, unregulated and reference sections. The removal of these dams, among the largest of such projects ever attempted, is expected to facilitate the return of salmon and their marine‐derived nutrients (MDN) throughout the watershed, possibly altering the food web structure, nutrient levels and stable isotope values that we documented. Published in 2010 by John Wiley & Sons, Ltd.     

Delivery of nutrients and seston from the Muskegon River Watershed to near shore Lake Michigan

Drowned river mouth lakes are major features of coastal Great Lakes habitats and may influence nutrient and organic matter contributions from watersheds to near shore coastal zones. In May through October 2003, we measured loads of nutrients, surficial sediment, and seston to track the delivery of riverine-derived materials from the lower Muskegon River Watershed (MRW) into the near shore area of southeast Lake Michigan. Nutrient flux data indicated that seasonal loads of 1800 metric tons (MT) of particulate organic carbon, 3400 MT of dissolved organic carbon, and 24 MT of total phosphorus were discharged from the lower Muskegon River, with approximately 33% of TP load and 53% of the POC load intercepted within the drowned river mouth terminus, Muskegon Lake. Carbon: phosphorus molar ratios of seston in Muskegon River (C:P = 187) and Muskegon Lake (C:P = 176) were lower than in Lake Michigan (C:P = 334), indicating phosphorus limitation of phytoplankton in near shore Lake Michigan. Isotopic signatures of seston collected in Muskegon Lake were depleted in δ¹³C (− 30.8 ± 1.6‰) relative to the isotope signatures of seston from Lake Michigan (− 26.2 ± 1.3‰) or the mouth of the Muskegon River (− 28.1 ± 0.5‰), likely due to the presence of biogenic methane in Muskegon Lake. Seston δ¹⁵N increased on a strong east-to-west gradient within Muskegon Lake, indicating significant microbial processing of nutrients. The extent of nutrient uptake in Muskegon Lake altered the chemical and isotopic characterization of seston flowing into Lake Michigan from Muskegon River.