2H Values Research Articles

Exploring hydrogen isotope fractionation in lipid biomolecules of freshwater algae: implications for ecological and paleoenvironmental studies

ABSTRACT Understanding the stable hydrogen isotope (δ 2H) composition and fractionation in lipid biomolecules of primary producers, such as terrestrial and aquatic plants, is crucial for deciphering past environmental conditions, as well as applying compound-specific stable isotope analysis for the study of metabolic and ecological processes. We conducted a new tracer experiment to explore the δ 2H composition of algal fatty acid biomarkers, focusing on freshwater algae, which form the base of aquatic food webs. We selected a range of algal species widely found in freshwater ecosystems and cultivated them under controlled conditions. First, we added 2H2O to ambient water as a tracer to investigate the net hydrogen isotope fractionation during algal lipid synthesis at isotopic equilibrium, which is particularly informative for paleo-geochemical studies. Then, we conducted kinetic experiments to quantify the time needed for algal fatty acids to achieve isotopic steady-state conditions in response to the change in ambient water δ 2H values. Our findings revealed substantial variability in hydrogen isotope fractionation among different algal taxa and various fatty acids. Based on taxa, different fatty acids exhibited faster integration of water hydrogen than others, but they were not necessarily in the order of the biosynthetic pathway. This experiment underscores the complexity of hydrogen isotope fractionation and the requirement for controlled laboratory studies to properly apply compound-specific stable H isotope analysis techniques in ecological and paleo-environmental studies.

Morphology of the Buluus, Ulakhan-Taryn aufeis, conditions of its occurrence and stable oxygen and hydrogen isotope variations in the lower part

Aufeis is one of the most dangerous natural phenomena. The negative impact of aufeis is determined by the unexpected flooding of the territory and subsequent freezing of water, the formation of ice barriers, the icing of underground structures and communications (mines, tunnels, culverts, and sewer wells), as well as the icing of roads and railways, coastal hydraulic structures, etc. There are cases when explosions of aufeis mounds produce catastrophic disturbances within a few seconds. The aufeis that forms annually in the valley of the Buluus Creek is one of the most famous and studied aufeis of Central Yakutia. The aufeis was sampled from a vertical section. The aufeis is layered, and the thickness of the layers is 3-10 cm. In the upper part of the aufeis, the ice layers are thicker than in the lower. Sampling from the aufeis ice was carried out using a 5.1-cm-diameter steel crown driven by a Bosch electric drill. Measurements of the isotopic composition of oxygen and hydrogen in ice were performed using a Picarro L 2130-i laser isotope analyzer. The isotopic composition of the Buluus ice varies in a narrow range: δ18O values vary from −20.2 to −21.9‰, δ2H values vary from −159.5 to −173.7‰. Generally, the ice is isotopically slightly enriched compared to the surface water of the Ulakhan-Taryn creek, where the δ18O value is −22.18‰ and the δ2H value is −175.1%. Groundwater is isotopically close to the creek water; its isotope composition is also isotopically enriched compared to the ice of the aufeis, with δ18O values varying from −22.17 to −22.25‰ and δ2H values varying from −173.7 to −175.1‰.

Stable isotope hydrology of surface and ground waters in King George Island, Antarctica

ABSTRACT The region around the tip of the Antarctic Peninsula is warming fast, a situation that will lead to widespread changes in local hydrological cycles. King George Island (KGI) hosts a complex network of lakes and rivers, fed by glaciers, snow and rain, and underlain by thick permafrost. We present here the first study of the stable isotope composition of the surface waters in the ice-free southern peninsulas of KGI. Permafrost samples had the highest δ 18O and δ 2H values (–6.7 and –50 ‰, respectively), and river waters the lowest (–9.1 and –70 ‰, respectively), with groundwater (–8.2 and –62.7 ‰, respectively), lakes (–8.6 and –66.8 ‰, respectively) and (summer) meltwater (–9 and –69.5 ‰, respectively) having intermediary values. Our results suggest that a clear separation of the various water bodies (permafrost, snow, meltwater, lakes) based on the δ 18Owater and δ 2Hwater is possible. Further, water in lakes on a W–E transect (i.e. with increased distance from the Bellingshausen Sea) have a general tendency towards lower δ 18O (and δ 2H) values. The results allow for the establishment of a baseline against which ongoing and future changes of the hydrological cycle could be analysed, and past climate changes be reconstructed.

Using 81Kr and isotopic tracers to characterise old groundwater in the Bangkok metropolitan and vicinity areas

ABSTRACT Krypton-81 was applied to investigate the age of groundwater in the aquifer system in the Bangkok metropolitan and vicinity areas. Stable (2H, 18O and 13C) and radioactive (3H, 85Kr and 14C) isotopes and noble gases were applied in parallel. Low levels of 14C and significant radiogenic 4He confirm that groundwater in the deep aquifers is older than 30 ka. 81Kr analysis identified groundwater with ages ranging from 17 to 300 ka. At some sites, large age discrepancies between 81Kr and 14C indicated that inter-aquifer mixing is likely occurring. The interpretation of the noble gases suggests that groundwaters in the deeper aquifers, with apparent ages of 300 to 10 ka, have recharged in slightly colder and wetter climates than those found in the upper aquifers with apparent ages < 10 ka. Degradation of water quality from seawater intrusion was identified in the upper four aquifers. This was also evidenced by higher δ 18O and δ 2H values, typical of seawater. The four deeper aquifers contain high quality water characterised by less enriched 18O and 2H. This work presents new findings of very old groundwater in the Bangkok aquifer system.

Insights into the influence of morphology on the hydrological processes of river catchments using stable isotopes

ABSTRACT Water isotopes (δ18O, δ2H) were systematically monitored in two river catchments to investigate the isotopic spatiotemporal variation and the differences between them. The Pinios River Basin (PRB) exhibited lower average δ 18O and δ 2H values (−7.9‰ and −50.8‰, respectively) compared to the Evrotas River Basin (ERB) (−6.5‰ and −38.2‰, respectively) but higher in range (3.3‰ vs 1.2‰ for δ18O, respectively). The Bayesian modelling results showed higher groundwater contribution in the PRB (25–50%) than in the ERB (15–35%) relative to precipitation during the wet period. The isotopic spatial variability was attributed to the influence of local precipitation, evaporation and additional flow pathways (e.g. soil water). The correlation analysis showed that the isotopic composition is controlled by the catchment altitude, slope and discharge. This study highlights the catchment physiographic control on the isotopic composition of rivers, which can support strategies for better water resources management.

The Spatiotemporal Variability of Snowpack and Snowmelt Water 18O and 2H Isotopes in a Subarctic Catchment

AbstractThis study provides a detailed characterization of spatiotemporal variations of stable water 18O and 2H isotopes in both snowpack and meltwater in a subarctic catchment. We performed extensive sampling and analysis of snowpack and meltwater isotopic compositions at 11 locations in 2019 and 2020 across three different landscape features: (a) forest hillslope, (b) mixed forest, and (c) open mires. The vertical isotope profiles in the snowpack's layered stratigraphy presented a consistent pattern in all locations before snowmelt, and isotope profiles homogenized during the peak melt period; represented by a 1–2‰ higher 18O value than prior to melting. Our data indicated that the liquid‐ice fractionation was the prime reason that caused the depletion of heavy isotopes in initial meltwater samples prior to the peak melt period. The liquid‐ice fractionation was influenced by snowmelt rate, with higher fractionation during slow melt. The kinetic liquid‐ice fractionation was evident only in close examination of meltwater lc‐excess values, not 18O values alone. Meltwater was isotopically heavier and more variable than the depth‐integrated snowpack; the weighted mean of meltwater isotope values was higher by 0.62–1.33‰ 18O than the weighted mean of snowpack isotope values in forest hillslope and mixed forest areas, and 1.51–6.37‰ 18O in open mires. Our results reveal close to 3.1‰ 18O disparity between the meltwater and depth‐integrated snowpack isotope values prior to the peak melt period, suggesting that proper characterization of meltwater 18O and 2H values is vital for tracer‐based ecohydrological studies and models.

Stable oxygen and hydrogen isotope ratios of the aufeis of the Viluy River valley

The object of the study is the isotope composition of three aufeis (icing) in the Viluy River basin. Two of the three tested icing were located in the wide valleys of the streams-tributaries of the Viluy River, one on the flat bottom of the thermosuffusion sinkholes. The areas of studied icings did not exceed 30 sq. m., their thickness ranges from 45 to 100 cm. Stratification is recorded in the icings. The co-isotope diagram &amp;#948;2H-&amp;#948;18O shows that icing ice was formed from spring water and generally is isotopically “lighter” compared to the water of Kysyl-Yurekh stream and Viluy River. The isotope composition of the icing ice varies in a very narrow range: a) for icing 1 &amp;#948;18O values vary from –19.3 to –20.9‰, &amp;#948;2H values vary from –156.5 to –162.9‰; b) for icing 2 &amp;#948;18O values vary from –19.7 to –22.4‰, &amp;#948;2H values vary from –153.2 to –173.1‰; c) for icing 3 &amp;#948;18O values vary from –19.8 to –22.7‰, &amp;#948;2H values vary from –162.9 to –181.3‰. The similarity of the isotope profiles of icing 2 on Viluy and icing IB93-5 on Baylot Island and isotope profiles of icing 3 on Viluy and icing F192-6 on Baylot Island was noted, however, the scale of isotopic variations for icings on Baylot Island are 5-6 times greater than that of Viluy icings.

Effects of phenotypic variability on the oxygen and hydrogen isotope compositions of grains in different winter wheat varieties

ABSTRACT Stable isotope analyses are the leading method for geographic origin determination, especially of plant-based agricultural products. Origin analysis is typically done by comparing a suspicious sample to reference materials with known geographic origin. Reference materials are usually collected at the species level, assuming different varieties of a species to have comparable isotope compositions within a given location. We evaluated whether different phenotypes that are expressed in different varieties of winter wheat (Triticum aestivum L.) influence the oxygen (δ 18O) and hydrogen (δ 2H) isotope composition of plant tissue water and organic compounds. We found that mean δ 18O and δ 2H values among winter wheat varieties did not differ significantly in leaf water, however, differed significantly in bulk dried grain tissue. The differences in bulk dried grain δ 18O and δ 2H values among varieties can be related to differences in phenotypic trait expression among varieties. Despite this substantial phenotypic variability, the overall variability of bulk dried grain δ 18O and δ 2H values among varieties was small (SD 0.54 ‰ for oxygen, 3.60 ‰ for hydrogen). We thus conclude that reference materials collected at the species level should be sufficient for geographic origin analysis of winter wheat and possibly other cereals using δ 18O and δ 2H values.

Comparative study on water structures of poly(tetrahydrofurfuryl acrylate) and poly(2-hydroxyethyl methacrylate) by nuclear magnetic resonance spectroscopy

It is well known that poly(2-methoxyethyl acrylate) (PMEA) has good blood compatibility and its performance is attributed to its water structure. Recently, we applied solution nuclear magnetic resonance spectroscopy (solution-NMR) for analyzing the water structure in PMEA at ambient temperature and concluded that this method is useful because of the clear observation of the resonance peaks at low and high magnetic field (downfield and upfield, respectively) areas indicating the existence of more than two types of water. The present study was performed to compare the water structure of poly(tetrahydrofurfuryl acrylate) (PTHFA) and poly(2-hydroxyethyl methacrylate) (PHEMA) using solution 2H-NMR and deuterium oxide as water at the temperature range 15–45 °C. It was found that PTHFA has a different water structure from that of PHEMA. Water in PTHFA clearly showed two resonance peaks at downfield and upfield areas, with different spin-lattice relaxation times, T1 2H (high and low values, respectively). These observations are similar to those of PMEA. In contrast, PHEMA showed only one broad resonance peak (at downfield) with a low T1 2H value. Based on these observations, this study discusses the effect of water structures on the blood compatibility of these polymers.

Hydrochemistry and environmental isotopes (18O, 2H, 3H, 3He/4He) of groundwater and floodwater in the great area of Hurghada, Eastern Desert of Egypt

Porous and fractured aquifers exist in the area of Hurghada, Eastern Desert of Egypt, whose recharge processes through the common flash floods are not identified. Hydrochemical parameters, stable isotopes 18O, 2H and tritium in floodwater and groundwater were applied in the area subject to study. Additionally, He isotopes were investigated in the deep wells in the faulted zone at the Abu Shaar Plateau. 3H activity in all sampled points lies below the detection limit excluding a recent recharge component in groundwater. However, the hydrochemical ratios and the stable isotope signature confirm that the shallow wells and springs (Red Sea Hills group) are being recharged from modern precipitation. The hydrochemical parameters of the deep wells at the Abu Shaar Plateau (coastal plain group) confirm another origin for the ions rather than the modern precipitation. Together with the 18O and 2H values, the Br/Cl ratio of this group confirms the absence of seawater intrusion component and the role of the fault as a hydraulic barrier. These 18O and 2H values deviate from the GMWL confirming an evaporation effect and colder infiltration conditions and reveal strongly a possible mixing with the Nubian Sandstone in the region. The 3He/4He ratio confirms a mantle contribution of 2% from the total He components.

Spatial distribution of stable isotopes (18O and 2H) in precipitation and groundwater in Iran

ABSTRACT Iran is a semi-arid and arid country which always faces a water shortage crisis. Thus, the water resources in Iran should be studied by accurate methods such as stable isotope techniques. In precipitation sampling stations across Iran, the δ 18O (ranges from −16.3 to −0.3 ‰, −4.9 ‰ average), δ 2H (−114 to –13 ‰, −24.2 ‰ average) and d-excess (−2.1 to –22.7, 16.5 ‰ average) values are higher compared to δ 18O (ranges from −10.9 to −3.1 ‰, −6.7 ‰ average), δ 2H (−71 to −6 ‰, −37.4 ‰ average) and d-excess (1.0 to –21.6 ‰, 14.9 ‰ average) values in groundwater stations. Stable isotope distribution maps in precipitation and groundwater were also developed for Iran. The stepwise technique was used to study the role of parameters influencing stable isotopes in Iran precipitation. Results show the dominant role of temperature, elevation and latitude as well as ‘cP and MedT’ air masses mixture on stable isotope values in precipitation. Furthermore, the contribution percentage of each air mass which influences Iran in groundwater resources recharge was studied using ‘Simmr’ package in R programming language. Finally, the accuracy of the developed stable isotope distribution maps was validated.

Measurement of \u03b418O and \u03b42H of water and ethanol in wine by Off-Axis Integrated Cavity Output Spectroscopy and Isotope Ratio Mass Spectrometry

There are two officially approved methods for stable isotope analysis for wine authentication. One describes δ18O measurements of the wine water using Isotope Ratio Mass Spectrometry (IRMS), and the other one uses Deuterium-Nuclear Magnetic Resonance (2H-NMR) to measure the deuterium of the wine ethanol. Recently, off-axis integrated cavity output (laser) spectroscopy (OA-ICOS) has become an easier alternative to quantify wine water isotopes, thanks to the spectral contaminant identifier (SCI). We utilized an OA-ICOS analyser with SCI to measure the δ18O and δ2H of water in 27 wine samples without any pre-treatment. The OA-ICOS results reveal a wealth of information about the growth conditions of the wines, which shows the advantages to extend the official δ18O wine water method by δ2H that is obtained easily from OA-ICOS. We also performed high-temperature pyrolysis and chromium reduction combined with IRMS measurements to illustrate the “whole wine” isotope ratios. The δ18O results of OA-ICOS and IRMS show non-significant differences, but the δ2H results of both methods differ much more. As the δ2H difference between these two methods is mainly caused by ethanol, we investigated the possibility to deduce deuterium of wine ethanol from this difference. The results present large uncertainties and deviate from the obtained 2H-NMR results. The deviation is caused by the other constituents in the wine, and the uncertainty is due to the limited precision of the SCI-based correction, which need to improve to obtain the 2H values of ethanol as alternative for the 2H-NMR method.

Possible changes of the isotopic composition of ice wedge as a result of self-diffusion

&amp;nbsp; The subject of this research is the assessment of changes of the isotopic composition of ice wedge as a result of self-diffusion. The author offers a relatively simple method of considering the impact of the process of self-diffusion upon redistribution of paleo-isotopic composition that allows accurately and quickly estimating the changes in the values&amp;nbsp;&amp;delta;18О and &amp;delta;2H values in ice wedges at different periods of the quaternary (1000 years, 10,000 years, 100,000 years, and 1,000,000 years). The patterns of diffusion process in physico-chemical systems&amp;nbsp;are described by two differential forms of Fick's diffusion laws, which are transformed into Gaussian integral, using six-digit Chambers&amp;nbsp;charts for calculation of the&amp;nbsp;threshold values&amp;nbsp;&amp;delta;18О. The article applies the experimentally determined real values of&amp;nbsp;self-diffusion coefficient in the ice &amp;ndash;&amp;nbsp;D=(2&amp;ndash;10)&amp;times;10-15 m2/s. The values of the Gaussian integral are calculated for time intervals, at different distances between samples with different concentration; for the period of 1,000 years its values in all cases&amp;nbsp;exceed 0.99. For longer time intervals, these values change significantly. The calculated probabilistic values of changes in the concentration of heavy oxygen isotopes in ice wedge&amp;nbsp;under the impact&amp;nbsp;of&amp;nbsp;self-diffusion at different distances and concentration gradients are noticeable only for&amp;nbsp;the time period&amp;nbsp;of over 100,000 years. &amp;nbsp;

Isotopic partitioning of evapotranspiration in a mesic grassland during two wetting–drying episodes

Evapotranspiration (ET) is the dominant water loss flux in mesic tallgrass prairie. Partitioning of ET into its two components—soil evaporation (E) and plant transpiration (T)—is challenging but critical for unraveling biophysical processes underlying ecosystem functioning and sustainability in a changing environment. Because of the pulsed nature of ecophysiological processes in this water-limited ecosystem, we carried out two field campaigns during wetting–drying episodes following precipitation pulses. We applied a two-source isotopic mixing model for ET partitioning. The isotopic compositions of ET, E, and T (δET, δE, and δT) were determined by the Keeling-plot method, the Craig–Gordon model, and midday plant xylem water, respectively. We found that the ET partitioning results (T/ET) could be more accurately quantified with 2H than with 18O, because of (1) the better performance of 2H in Keeling-plot regressions of high-temporal-frequency isotopic measurements of water vapor, and (2) the stronger sensitivity of 2H to the equilibrium fractionation. Using 2H values, we found that the mean ± standard deviation of T/ET was 0.84 ± 0.05 and 0.92 ± 0.06 during two field campaigns. Soil water near the surface (especially the top 10 cm) responded actively during these two wetting–drying episodes and was the major source for the total ET flux during the initial drying periods. Only after shallow soil moisture had become substantially exhausted did deeper soil layers (up to 1 m) increasingly become the major source for the T flux, while the E flux declined progressively to a negligible level.

Groundwater Circulation in the Xianshui River Fault Region: A Hydrogeochemical Study

Water samples from rainfall, river, springs, and wells in the Xianshui River fault region near Xialatuo, China were collected during two sampling campaigns to investigate the complex groundwater circulation in the region. The major ions, stable isotopes, and four natural radium isotopes of the water samples were analyzed, and the results were utilized to identify different groundwater circulation depths. Most water samples excluding the one at a hot spring and the one at a borehole possess similar hydrochemical compositions and lower total dissolved solids (TDS), implying that their circulation depth is relatively shallow or that residence time is short. The sample at the hot spring has high TDS and high temperature as well as the high F concentration, inferring that it may circulate at a deeper depth. The sample at the borehole contains mixed hydrochemical characteristics of other samples. Three groundwater flow systems may exist in the study area: the shallow groundwater system recharged by precipitations and local groundwater flow, the deep groundwater system recharged by the regional groundwater flow, and the intermediate one between the above two systems. The finding of the three flow systems is supported by the δ2H and δ18O as well as the apparent radium ages of the samples. The δ2H and δ18O values at the intercept of the line formed by the shallow groundwater samples and the local meteoric water line (LMWL) are similar to those of modern precipitations. The δ2H and δ18O values at the intercept of the line formed by the deep groundwater samples and the LMWL show that it is probably recharged by relatively older precipitations. The 2H and 18O values of the borehole samples are between the above two intercept points. The deep-circulated groundwater with high temperature has longer apparent radium age than other water samples. The apparent radium ages of the shallow groundwater are similar but less than that of the deep groundwater. Groundwater at the borehole may circulate at a depth between the above two. The results of this study improve our understanding of the complex groundwater circulation and enable us to better protect and manage the groundwater resources in the region.

Geographic variations in the slope of the δ 2 H – δ 18 O meteoric water line over Europe: a record of increasing continentality

Abstract δ 2 H and δ 18 O values of precipitations follow an empirical linear relationship at the global scale that is called the Global Meteoric Water Line (GMWL) and characterized by a slope of 8. However, Local Meteoric Water Lines (LMWLs) may have different slopes S depending on their geographic situation. Monthly δ 2 H and δ 18 O of precipitation have been compiled from European International Atomic Energy Agency (IAEA) stations. Those data allowed the calculation of the slopes S of the δ 2 H– δ 18 O LMWL determined for each station. S increases with longitude ϕ from c. 5 (Portugal) to c. 9 (Russia) – they are positively correlated with relative humidity (RH), negatively with temperature and positively with the mean intra-annual amplitude of temperatures, which is a proxy of continentality. Slopes of 5–6, recorded in SW Europe, reflect mean RH (70–75%) and sea surface temperatures ( c. 25°C) of the Central Atlantic Ocean where the main flux of moisture is formed before being transported by the westerlies. In addition, falling water droplets within an air column with a high RH (&gt;80%) and low temperature are expected to escape sub-cloud evaporation. Therefore, slopes with values close to 9 are considered to reflect isotopic equilibrium conditions during the condensation of water vapour in clouds.

Geochemistry of groundwater and saltwater intrusion in a coastal region of an island in Malacca Strait, Indonesia

Most people in Bengkalis island use groundwater as their primary resource, but brackish water discovered in the wells located near the shore as well as in the distance. A hydrogeology study through geochemistry and isotope aspect conducted for the first time to identify the effect of saltwater intrusion (SWI) on groundwater. Na &gt; Mg &gt; K &gt; Ca were the most dominant cation sequence in groundwater, while Cl &gt; HCO3 &gt; SO4 was the most dominant for anion. NaCl is the main type of groundwater in shallow aquifer and NaCl &amp; NaHCO3 both became the most dominant type of groundwater in the deeper aquifer system. Most of the groundwater samples from dug wells indicating the weak acid exceeding strong acid. Meanwhile, the groundwater samples from bore wells dominated by alkalis exceeding alkaline earth. SWI analysis shows 36.4% of groundwater samples from dug wells and 40% of bore water samples experiencing the salinization process. From isotope analysis, the groundwater samples found to be originated from the higher elevation or distance source. Meanwhile, there are lighter 2H values in the samples that are indicating the groundwater flown in the deeper part of the aquifer.

Terrestrial contributions to Afrotropical aquatic food webs: The Congo River case.

Understanding the degree to which aquatic and terrestrial primary production fuel tropical aquatic food webs remains poorly understood, and quantifying the relative contributions of autochthonous and allochthonous inputs is methodologically challenging. Carbon and nitrogen stable isotope ratios (δ 13C, δ 15N) can provide valuable insights about contributions of terrestrial resources and trophic position, respectively, but this approach has caveats when applied in typical complex natural food webs.Here, we used a combination of C, N, and H (δ 2H) stable isotope measurements and Bayesian mixing models to estimate the contribution of terrestrial (allochthonous) and aquatic (autochthonous) inputs to fish and invertebrate communities in the Congo River (and some tributaries).Overall, our results show that we gained power to distinguish sources by using a multiple tracer approach and we were able to discriminate aquatic versus terrestrial sources (esp. including hydrogen isotopes). Fish δ 2H values were clearly correlated with their food preferences and revealed a high level of variation in the degree of allochthony in these tropical aquatic communities.At the community level, it is clear that terrestrial C3 plants are an important source fueling the Congo River food web. However, in order to better constrain source contribution in these complex environments will require more robust constraints on stable isotope values of algal and methane‐derived C sources.

Rapid and Accurate Assessment of Diuretic Response: Validation of an Equation to Predict Diuretic Induced Sodium Output Using a Spot Urine Sample

Introduction Diuretic response is generally assessed using crude measures such as fluid or weight loss which are usually reported in a delayed manner (e.g. the change in weight from one day to the next). This in turn restricts clinicians’ ability to titrate diuretics. These established metrics have poor correlation with one another and they do not predict outcomes as well as cumulative sodium excretion. However, a 24h urine collection is difficult to perform even in a clinical trial, much less in routine clinical practice. It also does not address the lag time between diuretic administration and assessment of response. We previously reported proof of concept results on an equation to estimate sodium excretion based on a post-diuretic spot urine sample. Our current objective was to validate this equation in a real-world sample of patients undergoing IV diuretic therapy. Hypothesis Cumulative sodium output from a loop diuretic can be predicted using a spot urine sample. Methods The validation cohort consisted of 286 hospitalized patients receiving IV diuretics. Our equation is shown below (Figure). The validation cohort consisted of 286 hospitalized patients receiving IV diuretics. Urine collections were performed under intense supervision by a study coordinator. A spot urine was obtained at 1h, 2h post diuretic administration, and a cumulative 6h urine collection was used to determine total sodium. We used the 2h value for the equation. We defined a poor diuretic response as Results The predicted sodium equation had the best receiver operating characteristics (AUC = 0.92, 95% CI = 0.88 to 0.96, p Conclusions Our natriuretic response equation provides a faster and more accurate estimation of sodium excretion following a diuretic dose than either net fluid loss or weight change. This may aid in more rapid assessment of diuretic response and ultimately dose titration.

Marking mosquitoes in their natural larval sites using 2H-enriched water: a promising approach for tracking over extended temporal and spatial scales.

1.Tracking mosquitoes using current methods of mark-release-recapture are limited to small spatial and temporal scales exposing major gaps in understanding long-range movements and extended survival. Novel approaches to track mosquitoes may yield fresh insights into their biology which improves intervention activities to reduce disease transmission.Stable isotope enrichment of natural mosquito breeding sites allows large-scale marking of wild mosquitoes absent human handling. Mosquito larvae that develop in 2H-enriched water are expected to be detectable for over four months using tissue mass-fraction 2H measurements, providing opportunities for long-term mark-capture studies on a large scale. 2.A laboratory study followed by a field experiment of mosquito larval habitat 2H-enrichment was conducted in Mali, to evaluate potential labeling of wild mosquitoes. Twelve natural larval sites were enriched using [2H]-Deuterium-oxide (D2O, 99%). Enrichment level was maintained by supplementation following dilution by rains. Availability of 2H to mosquito larvae was enhanced by locally collected and cultured microorganisms (i.e. protozoa, algae and bacteria) reared in deuterated water, and provided as larval diet. Putative natural predators were removed from the larval sites and first instar larvae Anopheles gambiae s.l. larvae were added every other day. Emergence traps enabled collection of eclosing adults. Adult mosquitoes were kept at laboratory conditions for analysis of label attrition with age. 3.Deuterium enrichment of wild mosquitoes above background levels (maximum = 143.1 ppm) became apparent 5-6 days after initial exposure, after which 2H values increased steadily until ~24 days later (to a mean of approx. 220 ppm). Anopheles and Culex mosquitoes showed significantly different 2H values (211 and 194.2 ppm respectively). Both genera exhibited exponential label attrition (e (-x)) amounting to 21.6% by day 30 post emergence, after which attrition rate continuously decreased. Males of both taxa exhibited a higher mean 2H value compared to females. 4.Deuterium-oxide proved useful in marking mosquitoes in their natural larval sites and although costly, may prove valuable for studies of mosquitoes and other aquatic insects. Based on our field study, we provide a protocol for marking mosquito larval sites using deuterium-oxide.