Tracer Approach Research Articles

Natural Asphalt Seeps Are Potential Sources for Recalcitrant Oceanic Dissolved Organic Sulfur and Dissolved Black Carbon.

Natural oil seepages contribute about one-half of the annual petroleum input to marine systems. Yet, environmental implications and the persistence of water-soluble hydrocarbons from these seeps are vastly unknown. We investigated the release of oil-derived dissolved organic matter (DOM) from natural deep sea asphalt seeps using laboratory incubation experiments. Fresh asphalt samples collected at the Chapopote asphalt volcano in the Southern Gulf of Mexico were incubated aerobically in artificial seawater over 4 weeks. The compositional changes in the water-soluble fraction of asphalt-derived DOM were determined with ultrahigh-resolution mass spectrometry (Fourier-transform ion cyclotron resonance mass spectrometry, FT-ICR-MS) and by excitation-emission matrix spectroscopy to characterize fluorescent DOM (FDOM) applying parallel factor (PARAFAC) analysis. Highly reduced aliphatic asphalt-derived DOM was readily biodegraded, while aromatic and sulfur-enriched DOM appeared to be less bioavailable and accumulated in the aqueous phase. A quantitative molecular tracer approach revealed the abundance of highly condensed aromatic molecules of thermogenic origin. Our results indicate that natural asphalt and potentially other petroleum seepages can be sources of recalcitrant dissolved organic sulfur and dissolved black carbon to the ocean.

Evaluating the use of an Unmanned Aerial Vehicle (UAV)-based active AirCore system to quantify methane emissions from dairy cows

Enteric fermentation and manure methane emissions from livestock are major anthropogenic greenhouse gas emissions. In general, direct measurements of farm-scale methane emissions are scarce due to the source complexity and the limitations of existing atmospheric sampling methods. Using an innovative UAV-based active AirCore system, we have performed accurate atmospheric measurements of CH4 mole fractions downwind of a dairy cow farm in the Netherlands on four individual days during the period from March 2017 to March 2019. The total CH4 emission rates from the farm were determined using the UAV-based mass balance approach to be 1.1–2.4 g/s. After subtracting estimated emission factors of manure onsite, we derived the enteric emission factors to be 0.20–0.51 kgCH4/AU/d (1 AU = 500 kg animal weight) of dairy cows. We show that the uncertainties of the estimates were dominated by the variabilities in the wind speed and the angle between the wind and the flight transect. Furthermore, nonsimultaneous sampling in the vertical direction of the plume is one of the main limiting factors to achieving accurate estimate of the CH4 emissions from the farm. In addition, a N2O tracer release experiment at the farm was performed when both a UAV and a mobile van were present to simultaneously sample the N2O tracer and the CH4 plumes from the farm, improving the source quantification with a correction factor of 1.04 and 1.22 for the inverse Gaussian approach and for the mass balance approach, respectively. The UAV-based active AirCore system is capable of providing useful estimates of CH4 emissions from dairy cow farms. The uncertainties of the estimates can be improved when combined with accurate measurements of local wind speed and direction or when combined with a tracer approach.

CPExtract, a Software Tool for the Automated Tracer-Based Pathway Specific Screening of Secondary Metabolites in LC-HRMS Data.

The use of stable isotopically labeled tracers is a long-proven way of specifically detecting and tracking derived metabolites through a metabolic network of interest. While the recently developed stable isotope-assisted methods and associated, supporting data analysis tools have greatly improved untargeted metabolomics approaches, no software tool is currently available that allows us to automatically and flexibly search liquid chromatography coupled with high-resolution mass spectrometry (LC-HRMS) chromatograms for user-definable isotopolog patterns expected for the metabolism of labeled tracer substances. Here, we present Custom Pattern Extract (CPExtract), a versatile software tool that allows for the first time the high-throughput search for user-defined isotopolog patterns in LC-HRMS data. The patterns can be specified via a set of rules including the presence or absence of certain isotopologs, their relative intensity ratios as well as chromatographic coelution. Each isotopolog pattern satisfying the respective rules is verified on an MS scan level and also in the chromatographic domain. The CPExtract algorithm allows the use of both labeled tracer compounds in nonlabeled biological samples as well as a reversed tracer approach, employing nonlabeled tracer compounds along with globally labeled biological samples. In a proof-of-concept study, we searched for metabolites specifically arising from the malonate pathway of the filamentous fungi Fusarium graminearum and Trichoderma reesei. 1,2,3-13C3-malonic acid diethyl ester and native malonic acid monomethyl ester were used as tracers. We were able to reliably detect expected fatty acids and known polyketides. In addition, up to 46 and 270 further, unknown metabolites presumably including novel polyketides were detected in the F. graminearum and T. reesei culture samples, respectively, all of which exhibited the user-predicted isotopolog patterns originating from the malonate tracer incorporation. The software can be used for every conceivable tracer approach. Furthermore, the rule sets can be easily adapted or extended if necessary. CPExtract is available free of charge for noncommercial use at https://metabolomics-ifa.boku.ac.at/CPExtract.

In-situ catalytic upgrading of tar from integrated process of coal pyrolysis with steam reforming of methane over carbon based Ni catalyst

In order to improve the tar quality by decreasing the heavy tar content and ensuring high tar yield, in-situ catalytic upgrading of tar from the integrated process of coal pyrolysis coupled with steam reforming of methane was conducted over carbon (KD-9) based Ni catalyst. The results show that at 650 °C, the tar yield of CP-SRM over 5Ni/KD-9 is 24.4%, which is a little lower than that of without catalyst, while the light tar yield (i.e., 18.9%) is 1.4 times higher than that of without catalyst, and the content of C2, C3 and C4 alkyl used as a substitute for benzene significantly increases tar yields by 0.5, 0.6 and 4.0 times, respectively. The content of phenols and naphthalenes in tar also increases dramatically after upgrading. Isotope tracer approach combined with the mass spectra of typical components was employed in exploring the mechanism of the upgrading process. The results show that 5Ni/KD-9 catalyzes coal tar cracking and SRM at the same time. Small free radicals such as ·CHx, ·H and ·OH generated by SRM can combine with free radicals from tar cracking, thus avoiding excessive cracking of tar.

Biochar amendment benefits 15N fertilizer retention and rhizosphere N enrichment in a maize-soil system

Biochar amendments regulate fertilizer nitrogen (N) transformation in soil and crop N uptake. To elucidate the effect of biochar amendment on the translocation of fertilizer N in a crop-soil system during crop growth, a maize pot experiment was conducted using an isotope tracer approach. The treatments were: without N application; 15N-labelled urea; and 15N-labeled urea plus biochar. During maize growth, biochar amendment increased root biomass, total crop N uptake, and urea N retention in soil. In bulk and rhizospheric soils, biochar amendment significantly (P < 0.05) increased urea N retention in soil total N (TN), microbial biomass N (MBN), particulate organic N (PON) and mineral associated total N (MTN) from the eighth leaf stage (V8) to physiological maturity (R6) and decreased fertilizer N retention in inorganic N and dissolved organic N from stages V8 to silking (R1). Relative to bulk soil, rhizospheric soil promoted urea N retention in TN, inorganic N, MBN, and MTN under both fertilizer treatments, and biochar application enlarged this difference for MBN; rhizospheric soil enhanced PON mineralization resulting in a significantly (P < 0.05) lower PON from stages R1 to R6 when compared with bulk soil, and biochar application retarded this mineralization. These findings unveiled that biochar application increased fertilizer N retention by increasing MBN, PON, and MTN and that biochar application benefited the enrichment of fertilizer N in rhizospheric soil.

Reworking activity of the thalassinidean shrimp Trypaea australiensis Dana, 1852 (Decapoda: Pleocyemata: Callianassidae) in an Australian estuary: A pilot study

Abstract Trypaea australiensis Dana, 1852 is the predominant bioturbating thalassinidean shrimp on the east coast of Australia. It is, like other large bioturbators, generally considered an important ecosystem engineer. The sediment particle reworking rate of thalassinideans, a key parameter in benthic biogeochemical modelling, nevertheless remains unknown. We have for the first time quantified particle reworking by a population of T. australiensis living in fine estuarine sand. The particle reworking rate was monitored for 18 days using coarse sand as a new tracer approach followed by analyses of grain-size distribution in the sediment to a depth of 24 cm. Burial depth (BD, cm) over time (t, days) followed the relationship BD = 0.3002 × t for an average population density of 96 individuals m–2, equivalent to a sediment displacement of 1.1 m3 m–2 yr–1 (11.4 liters individual–1 yr–1). The individual-specific particle reworking by this thalassinidean is higher than that reported for most other key bioturbators, and its engineering impact on estuarine sediments therefore has potentially large consequences for biodiversity and ecosystem functioning.

The student tracer, an innovative approach in training institutes

The quality approach allows an institution to analyse and improve its internal organisation in order to satisfy its clients or users regarding their expectations. For nursing training institutes, which have been included in higher education since July 2009, a quality approach of the training must be implemented. Like the patient tracer, a study has shown that the transfer of this method to training facilities is possible via the student tracer approach.

The role of fluorescent and hybrid tracers in radioguided surgery in urogenital malignancies.

The increasing availability of new imaging technologies and tracers has enhanced the application of nuclear molecular imaging in urogenital interventions. In this context, preoperative nuclear imaging and radioactivity-based intraoperative surgical guidance have become important tools for the identification and anatomical allocation of tumor lesions and/or suspected lymph nodes. Fluorescence guidance can provide visual identification of the preoperatively defined lesions during surgery. However, the added value of fluorescence guidance is still mostly unknown. This review provides an overview of the role of fluorescence imaging in radioguided surgery in urogenital malignancies. The sentinel node (SN) biopsy procedure using hybrid tracers (radioactive and fluorescent component) serves as a prominent example for in-depth evaluation of the complementary value of radio- and fluorescence guidance. The first large patient cohort and long-term follow-up studies show: 1) improvement in the SN identification rate compared to blue dye; 2) improved detection of cancer-positive SNs; and 3) hints towards a positive effect on (biochemical) recurrence rates compared to extended lymph node dissection. The hybrid tracer approach also highlights the necessity of a preoperative roadmap in preventing incomplete resection. Recent developments focus on receptor-targeted approaches that allow intraoperative identification of tumor tissue. Here radioguidance is still leading, but fluorescent and hybrid tracers are also finding their way into the clinic. Emerging multiwavelength approaches that allow concomitant visualization of different anatomical features within the surgical field may provide the next step towards even more refined procedures.

Addition of base cations increases microbial carbon use efficiency and biomass in acidic soils

The leaching of base cations in acidic soils can result in calcium (Ca2+) and magnesium (Mg2+) deficiencies, which are important for microbial cell function. We aimed to determine if microbial carbon use efficiency (CUE) and microbial biomass carbon (MBC) were limited in acidic soils due to a lack of base cations. Microbial CUE across a range of agricultural soils (n = 970; pHCa 3.4–7.9) treated with either deionised H2O (control) or a solution of 300 mM CaCl2 + 300 mM MgCl2 (+Base cations) was determined using a14C radioisotope tracer approach. Our results showed that the addition of base cations significantly increased microbial CUE (by up to 20%) at pHCa < 4.7; which coincided with a steep increase in exchangeable acidity. Base cation addition significantly increased MBC in nil-limed soils (pHCa 4.6) from 494 mg C kg−1 to 769 mg C kg−1 when plant residue was added, but not in limed soils (pHCa 6.2). Our findings indicate that the addition of base cations to highly acidic soils can increase microbial growth, thus aiding with carbon sequestration in these agricultural soils.

Priming effect varies with root order: A case of Cunninghamia lanceolata

Plant litter inputs can influence soil organic carbon (SOC) decomposition via the priming effect. However, our understanding of the priming effect and underlying mechanisms is primarily from studies with leaf litter addition, while little is known about root litter effects, particularly of woody plants. Here, using a13C natural tracer approach, we conducted a 12-week incubation experiment to investigate litter decomposition and priming effect of mature-tree root orders (1st to 5th) of Cunninghamia lanceolata (Lamb.) Hook. We explored how litter decomposition and the priming effect were related to microbial biomass of main groups, enzyme activities, and root tissue chemistry. Root litter decomposition rates increased with increasing root order, especially during the first 4 weeks, which was likely due to higher non-structural C and lower tannin concentrations for higher order roots. A negative priming effect occurred at this initial intensive stage when microbes may have preferred utilizing litter-derived labile C. Subsequently, the priming effect switched to positive, and showed larger priming effects for the higher order roots than the lower order ones. Higher order roots also showed higher fungi to bacteria ratios and enzyme activities than the lower order roots. These patterns of fungi to bacteria ratios and enzyme activities and thus the priming effect could be attributed to the difference in carbon:nitrogen ratio among root orders. Overall, we for the first time provide strong evidence for the effect of root order on the priming effect, and thus highlight that separating root litter based on root order is necessary for accurately evaluating its influence on SOC decomposition.

Effects of no-tillage and stover mulching on the transformation and utilization of chemical fertilizer N in Northeast China

Microbial immobilization-remineralization of nitrogen (N) and mineral fixation-release of ammonium play essential roles in the retention of fertilizer N in the soil and the subsequent crop N uptakes. No-till farming with stover mulching leaves a significant amount of crop residues on the soil that provide carbon (C) substrates for microbes and regulate soil N availability to crops. However, crop residue removal, especially maize stover, for bioenergy feedstocks may threaten ecological benefits of no-till farming with stover mulching on N retention in the soil. Thus, it is of great importance to understand whether no-till farming should come with different levels of stover mulching to regulate N transformation to three main N pools as well as crop yields. With the help of a 15N-labeled tracer approach, we conducted a long-term maize cropping field study in the black soil of Northwest China with the following five treatments: (1) ridge tillage (RT); (2) no-tillage with 0 % mulching (NT-0); (3) no-tillage with 33 % mulching (NT-33); (4) no-tillage with 67 % mulching (NT-67); (5) no-tillage with 100 % mulching (NT-100). Our research showed that stover mulching (NT-33, NT-67, and NT-100) significantly increased maize yields from averaging 12038–13904 kg ha−1 and crop N uptakes by averaging 16 % than RT. In the seedling stage, compared to RT, residual 15N-labeled N decreased by 13 % in the topsoil of NT-0, NT-67 and NT-100, but increased by 15 % in all no-till treatments at 20−40 cm soil layer. Further assessment of three soil N pools revealed that at top 20 cm soil layer, maize stover mulching significantly reduced 15N-labeled mineral N by 33 % and 52 % compared to RT and NT-0 in the seedling and tasseling stages, respectively, but increased 15N-labeled fixed NH4+ and organic N in the seedling stage, potentially enhancing the fertilizer N transformation from mineral N to fixed NH4+ and organic N reserves. At 20–40 cm soil layer, 15N-labeled fixed NH4+ increased in NT-67 and NT-100 than NT-0 in the seedling stage. Our results suggest that no-till farming should accompany crop residue mulching to enhance fertilizer N processes to more stable N reserves of fixed NH4+ and organic N rather than labile mineral N pool. Thus, indiscriminate harvesting of crop residues for biofuel feedstocks may deteriorate soil nutrient cycling to reduce N use efficiency in the soil-crop system, leading to a decline of crop N uptakes and yields.

Dew water-uptake pathways in Negev desert plants: a study using stable isotope tracers.

Dew is an important water resource for plants in most deserts. The mechanism that allows desert plants to use dew water was studied using an isotopic water tracer approach. Most plants use water directly from the soil; the roots transfer the water to the rest of the plant, where it is required for all metabolic functions. However, many plants can also take up water into their leaves and stems. Examining the dew water uptake pathways in desert plants can lend insight on another all water-use pathways examination. We determined where and how dew water enters plants in the water limited Negev desert. Highly depleted isotopic water was sprayed on three different dominant plant species of the Negev desert-Artemesia sieberi, Salsola inermis and Haloxylon scoparium-and its entry into the plant was followed. Water was sprayed onto the soil only, or on the leaves/stems only (with soil covered to prevent water entry via root uptake). Thereafter, the isotopic composition of water in the roots and stems were measured at various time points. The results show that each plant species used the dew water to a different extent, and we obtained evidence of foliar uptake capacity of dew water that varied depending on the microenvironmental conditions. A. sieberi took up the greatest amount of dew water through both stems and roots, S. inermis took up dew water mainly from the roots, and H. scoparium showed the least dew capture overall.

Groundwater discharge rates and uncertainties in a coastal lagoon using a radon mass balance

Coastal lagoons face anthropogenic pressures worldwide, and understanding groundwater discharge to these sensitive environments can enable better management of water budgets and nutrient inputs. The main objective of the study was to quantify groundwater seepage into a large and shallow coastal lagoon using a detailed radon (222Rn, a natural groundwater tracer) mass balance. To assess and reduce uncertainty, three wind-speed scenarios were modelled in two seasons using two 222Rn-in-groundwater endmembers. Groundwater discharge to the lagoon ranged between 5.2 ± 5.8 m3/s to 18.7 ± 19.6 m3/s during summer and 0.9 ± 2.2 m3/s to 8.1 ± 10.5 m3/s during winter. Wind-driven radon evasion was the most influential component of the radon mass balance. Higher summer wind speeds resulted in groundwater discharge estimates 3.5 times greater than those during winter. We carried out an in-depth uncertainty analysis of the radon mass balance results, which confirmed the importance of accounting for individual uncertainties, particularly the most sensitive parameters of the model. Overall, results from the radon mass balance revealed groundwater discharge to the lagoon was 1–2 orders of magnitude greater than previous localised seepage meter estimates. This is likely because radon tracer approaches quantify both one-directional discharge and bi-directional porewater exchange at a larger spatial scale than traditional seepage meter methods. In spite of large uncertainties, the possible range of reasonable estimates revealed groundwater seepage as an important component of the water budget at this site. This study highlights the benefits of broad-scale tracer-based mass balances for quantifying groundwater discharge to coastal lagoons and the value of in-depth uncertainty analysis to increase confidence in seepage flux estimates.

In Vivo Estimation of Ketogenesis Using Metabolic Flux Analysis-Technical Aspects and Model Interpretation.

Ketogenesis occurs in liver mitochondria where acetyl-CoA molecules, derived from lipid oxidation, are condensed into acetoacetate (AcAc) and reduced to β-hydroxybutyrate (BHB). During carbohydrate scarcity, these two ketones are released into circulation at high rates and used as oxidative fuels in peripheral tissues. Despite their physiological relevance and emerging roles in a variety of diseases, endogenous ketone production is rarely measured in vivo using tracer approaches. Accurate determination of this flux requires a two-pool model, simultaneous BHB and AcAc tracers, and special consideration for the stability of the AcAc tracer and analyte. We describe the implementation of a two-pool model using a metabolic flux analysis (MFA) approach that simultaneously regresses liquid chromatography-tandem mass spectrometry (LC-MS/MS) ketone isotopologues and tracer infusion rates. Additionally, 1H NMR real-time reaction monitoring was used to evaluate AcAc tracer and analyte stability during infusion and sample analysis, which were critical for accurate flux calculations. The approach quantifies AcAc and BHB pool sizes and their rates of appearance, disposal, and exchange. Regression analysis provides confidence intervals and detects potential errors in experimental data. Complications for the physiological interpretation of individual ketone fluxes are discussed.

Principles of stable isotope research – with special reference to protein metabolism

SummaryThe key to understanding the mechanisms regulating disease stems from the ability to accurately quantify the dynamic nature of the metabolism underlying the physiological and pathological changes occurring as a result of the disease. Stable isotope tracer technologies have been at the forefront of this for almost 80 years now, and through a combination of both intense theoretical and technological development over these decades, it is now possible to utilise stable isotope tracers to investigate the complexities of in vivo human metabolism from a whole body perspective, down to the regulation of sub-nanometer cellular components (i.e organelles, nucleotides and individual proteins). This review therefore aims to highlight; 1) the advances made in these stable isotope tracer approaches – with special reference given to their role in understanding the nutritional regulation of protein metabolism, 2) some considerations required for the appropriate application of these stable isotope techniques to study protein metabolism, 3) and finally how new stable isotopes approaches and instrument/technical developments will help to deliver greater clinical insight in the near future.

Anatomical projections to the dorsal tegmental nucleus and abducens nucleus arise from separate cell populations in the nucleus prepositus hypoglossi, but overlapping cell populations in the medial vestibular nucleus.

Specialized circuitry in the brain processes spatial information to provide a sense of direction used for navigation. The dorsal tegmental nucleus (DTN) is a core component of this circuitry and utilizes vestibular inputs to generate neural activity encoding the animal's directional heading. Projections arising from the nucleus prepositus hypoglossi (NPH) and the medial vestibular nucleus (MVe) are thought to transmit critical vestibular signals to the DTN and other brain areas, including the abducens nucleus (ABN), a component of eye movement circuitry. Here, we utilized a dual retrograde tracer approach in rats to investigate whether overlapping or distinct populations of neurons project from the NPH or MVe to the DTN and ABN. We report that individual MVe neurons project to both the DTN and ABN. In contrast, we observed individual NPH neurons that project to either the DTN or ABN, but rarely to both structures simultaneously. We also examined labeling patterns in other structures located in the brainstem and posterior cortex and observed (1) complex patterns of interhemispheric connectivity between the left and right DTN, (2) projections from the supragenual nucleus, interpeduncular nucleus, and retrosplenial cortex to the DTN, (3) projections from the lateral superior olive to the ABN, and (4) a unique population of cerebrospinal fluid-contacting neurons in the dorsal raphe nucleus. Collectively, our experiments provide valuable new information that extends our understanding of the anatomical organization of the brain's spatial processing circuitry.

Stoichiometric imbalance and microbial community regulate microbial elements use efficiencies under nitrogen addition

Microbial elements use efficiencies are the important parameters in regulating soil carbon (C) and nitrogen (N) mineralization processes. Microbial C use efficiency (CUE) describes the proportion of C used for growth relative to the total organic C uptake. As such, high CUE values mean relatively less CO2 emission and more C retention in microbial biomass. Similarly, a higher microbial N use efficiency (NUE) indicates efficient biomass N sequestration and less N mineralization. However, very little is known how the microbial CUE and NUE are affected by N enrichment in forest soils. Here, we studied soil microbial CUE and NUE simultaneously using 18O-water tracer approach in a long-term N addition experiment comprising control (atmospheric N deposition, 2.7 g N m−2 yr−1), low N addition (atmospheric N deposition + 2.5 g N m−2 yr−1) and high N addition (atmospheric N deposition + 7.5 g N m−2 yr−1) in a temperate forest. We found microbial CUE responses to N addition were dependent on N addition rates and soil horizons. Specifically, low N addition significantly increased the microbial CUE by 45.12% while high N addition significantly reduced it by 27.84% in organic soil. Further, mineral soil microbial CUE did not change under low N addition but significantly increased by 133.18% under high N addition. We also found microbial NUE decreased with increasing N addition rate in organic soil but showed an opposite pattern in mineral soil. The stoichiometric imbalances associated with phosphorus between microbial biomass and resources and the microbial community changes under N addition were correlated with microbial CUE and NUE. Further, N addition decreased microbial biomass turnover in organic soil but accelerated it in mineral soil. Altogether, our results indicated that N addition could control soil C and N cycling processes by affecting microbial elements use efficiencies (i.e. CUE and NUE), which may consequently impact C and N sequestration in this temperate forest soil.

Human activity intensity controls the relative importance of denitrification and anaerobic ammonium oxidation across subtropical estuaries

Human activities are dramatically increasing estuarine nitrogen (N) loads, further altering N processes. However, relative importance of denitrification and anaerobic ammonium oxidation (anammox) in response to human activities intensity gradient remains poorly understood for estuaries. In this study, we used a 15N isotope tracer approach to characterize the variations in sediment denitrification and anammox rates and determined the crucial factors controlling the partitioning of N2 production and regulating N2O production across five subtropical estuaries in southeast China. Denitrification rates increased significantly from 8.82 ± 3.89 nmol N g−1h−1 (low human activity intensity) to 41.2 ± 11.5 nmol N g−1h−1 (high human activity intensity) across the studied estuaries. Anammox rates not varied significantly between low (2.37 ± 0.66 nmol N g−1h−1), moderate (3.96 ± 0.91 nmol N g−1h−1), and high (4.04 ± 1.09 nmol N g−1h−1) human activity intensity estuaries. Relative contribution of anammox to total N2 production (Ra) decreased toward estuary mouth within each estuary. The Ra was also significantly lower in the estuaries characterized by high N loads and low DO. N2O production rates were in a range of 0.192–1.92 nmol N2O g−1h−1 across the estuaries and controlled by water NO2–, salinity and TOC. DO, NH4+, and NO3– were the best predictors of the partitioning of N2 production between denitrification and anammox. The high human activities intensity increased NH4+ and NO3– loads and further enhanced denitrification, leading to the decrease in Ra and increase in N2O production. These findings suggest that low DO and high N loads estuaries can increase denitrification and N2O emissions, whereas not affect anammox substantially under the higher intensity of human activities.

Identification of groundwater conditions in the recharge zone of regionally extended aquifer system with use of water chemistry and isotopes (Lwowek region, Poland)

Study regionThe studied recharge zone of regionally extended Quaternary aquifers - Lwówek region (Wielkpolska, Poland) is located in a region where Quaternary aquifers are the principal source of drinking water. A visible water quality deterioration trend was observed, manifested mainly by increase of nitrate concentration. Study focusThe main objective of the presented study is to examine groundwater flow patterns and vertical difference of groundwater chemistry using a multicomponent chemical tracers approach and groundwater isotopic compositions (stable isotopes, tritium and radiocarbon). New hydrological insights for the regionThis study documented the influence of water extraction on groundwater contamination. The contamination plume that moves to the deepest parts of the aquifer in the region, where water extraction is performed, was documented. As a consequence, in deep parts of the aquifer, nitrates appear, and the groundwater chemistry is very similar to that observed in the shallow part. Meanwhile, in regions where natural gradients exist (without water extraction) the contamination in the shallow part is also evident, but recently infiltrating water does not reach the deeper parts of the aquifer. A stagnation point exists in the deep part of the aquifer, with completely different groundwater chemistry in the deep and shallow parts of the aquifer. This work shown how groundwater chemistry can help to investigate groundwater flow systems.

Gut amino acid absorption in humans: Concepts and relevance for postprandial metabolism

<h2>Summary</h2> Dietary amino acid absorption kinetics are an important determinant of protein quality. The term "amino acid digestibility" is commonly used to refer to the amount of ingested amino acids that become available following absorption. However, one should differentiate between the subsequent processes of converting protein into smaller constituents (protein digestion) and luminal amino acid uptake (amino acid absorption). Amino acid "absorbability" or "bioavailability" is assessed by quantifying the disappearance of amino acids across (part of) the gastrointestinal tract. The assessment of fecal, apparent ileal (AID), standardized ileal (SID), and true ileal disappearance (TID), reflect amino acid absorbability with increasing accuracy, due to correction for microbial metabolism in the large intestine, basal gut endogenous amino acid losses, and total gut endogenous amino acids losses, respectively. A substantial amount of absorbed amino acids undergo first-pass splanchnic extraction, but the majority is immediately released in the circulation and becomes available for peripheral tissues. The assessment of amino acid "bioavailability" or "absorbability" is used in protein quality ranking systems such as the Digestible Indispensable Amino Acid Score (DIAAS). However, such scores neglect that the rate of absorption is also an important determinant of postprandial metabolism. In addition, amino acid absorption and/or its rate are highly dependent on factors such as the duration of the postprandial assessment period. Therefore, amino acid absorption kinetics should be assessed under the relevant experimental conditions. To this end, an oral-intravenous dual tracer approach can be applied to assess dietary protein derived amino acid release into the circulation and allows the assessment of the subsequent impact on postprandial whole-body protein metabolism.