Clumped isotopes reveal relationship between mussel growth and river discharge.

Freshwater mussels preserve valuable information about hydrology, climate, and population dynamics, but developing seasonal chronologies can be problematic. Using clumped isotope thermometry, we produced high-resolution reconstructions of modern and historic (~ 1900) temperatures and δ18Owater from mussel shells collected from an impounded river, the Brazos in Texas, before and after damming. We also performed high-resolution growth band analyses to investigate relationships between mussel growth rate, rainfall, and seasonal temperature. Reconstructed δ18Owater and temperature vary little between the modern (3R5) and historic shell (H3R). However, a positive relationship between reconstructed δ18Owater and growth rate in H3R indicates that aside from diminished growth in winter, precipitation and flow rate are the strongest controls on mussel growth in both modern and pre-dam times. Overall, our results demonstrate (1) the impact, both positive and negative, of environmental factors such as flow alteration and temperature on mussel growth and (2) the potential for clumped isotopes in freshwater mussels as a paleohydrology and paleoclimate proxies in terrestrial environments.

Finding balance: Tree-ring isotopes differentiate between acclimation and stress-induced imbalance in a long-term irrigation experiment.

Scots pine (Pinus sylvestris L.) is a common European tree species, and understanding its acclimation to the rapidly changing climate through physiological, biochemical or structural adjustments is vital for predicting future growth. We investigated a long-term irrigation experiment at a naturally dry forest in Switzerland, comparing Scots pine trees that have been continuously irrigated for 17 years (irrigated) with those for which irrigation was interrupted after 10 years (stop) and non-irrigated trees (control), using tree growth, xylogenesis, wood anatomy, and carbon, oxygen and hydrogen stable isotope measurements in the water, sugars and cellulose of plant tissues. The dendrochronological analyses highlighted three distinct acclimation phases to the treatments: irrigated trees experienced (i) a significant growth increase in the first 4 years of treatment, (ii) high growth rates but with a declining trend in the following 8 years and finally (iii) a regression to pre-irrigation growth rates, suggesting the development of a new growth limitation (i.e. acclimation). The introduction of the stop treatment resulted in further growth reductions to below-control levels during the third phase. Irrigated trees showed longer growth periods and lower tree-ring δ13 C values, reflecting lower stomatal restrictions than control trees. Their strong tree-ring δ18 O and δ2 H (O-H) relationship reflected the hydrological signature similarly to the control. On the contrary, the stop trees had lower growth rates, conservative wood anatomical traits, and a weak O-H relationship, indicating a physiological imbalance. Tree vitality (identified by crown transparency) significantly modulated growth, wood anatomical traits and tree-ring δ13 C, with low-vitality trees of all treatments performing similarly regardless of water availability. We thus provide quantitative indicators for assessing physiological imbalance and tree acclimation after environmental stresses. We also show that tree vitality is crucial in shaping such responses. These findings are fundamental for the early assessment of ecosystem imbalances and decline under climate change.

Isotopic biographies reveal horse rearing and trading networks in medieval London.

This paper reports a high-resolution isotopic study of medieval horse mobility, revealing their origins and in-life mobility both regionally and internationally. The animals were found in an unusual horse cemetery site found within the City of Westminster, London, England. Enamel strontium, oxygen, and carbon isotope analysis of 15 individuals provides information about likely place of birth, diet, and mobility during the first approximately 5 years of life. Results show that at least seven horses originated outside of Britain in relatively cold climates, potentially in Scandinavia or the Western Alps. Ancient DNA sexing data indicate no consistent sex-specific mobility patterning, although three of the five females came from exceptionally highly radiogenic regions. Another female with low mobility is suggested to be a sedentary broodmare. Our results provide direct and unprecedented evidence for a variety of horse movement and trading practices in the Middle Ages and highlight the importance of international trade in securing high-quality horses for medieval London elites.

Regional heterothermies recorded in the oxygen isotope composition of harbour seal skeletal elements.

Regional heterothermy is a strategy used by marine mammals to maintain a high and stable core body temperature, but its identification needs in situ measurements difficult to set up in extant wild organisms and inapplicable to extinct ones. We have analysed the oxygen isotope composition of bioapatite phosphate (δ18Op) from one permanent tooth and from thirty-six skeletal elements of one adult male harbour seal (Phoca vitulina) from the Baie de Somme (Hauts-de-France, France). We propose that the observed intra-skeletal δ18Op variability reflects tissue temperature heterogeneities typical of the pinniped regional heterothermy strategy. Our δ18Op data indicate that bone hydroxylapatite from harbour seal autopod skeletal elements (metacarpals, metatarsals, and phalanxes) mineralises at a lower temperature than that of the bone from the axial skeleton (e.g. vertebrae, ribs, and girdle bones). The results suggest that it is possible to locate a history of regional heterothermies in amphibious marine vertebrates using the δ18Op values of their mineralised tissues. This enables direct evaluation of the thermophysiology of both modern and fossil Pinnipedia from their skeletons opening perspectives on understanding their thermal adaptation to the marine environment in the fossil record. In addition to thermophysiology, oxygen isotope data from the permanent teeth of Pinnipedia, which are formed during the in utero phase from body fluid of the mother and at a stable temperature, could be valuable for locating the geographical areas inhabited by existing Pinnipedia females during their gestation period.

Evaluation of Phosphorus Enrichment in Groundwater by Legacy Phosphorus in Orchard Soils with High Phosphorus Adsorption Capacity Using Phosphate Oxygen Isotope Analysis.

Long-term phosphorus (P) fertilization results in P accumulation in agricultural soil and increases the risk of P leaching into water bodies. However, evaluating P leaching into groundwater is challenging, especially in clay soil with a high P sorption capacity. This study examined whether the combination of PO4 oxygen isotope (δ18OPO4) analysis and the P saturation ratio (PSR) was useful to identify P enrichment mechanisms in groundwater. We investigated the groundwater and possible P sources in Kubi, western Japan, with intensive citrus cultivation. Shallow groundwater had oxic conditions with high PO4 concentrations, and orchard soil P accumulation was high compared with forest soil. Although the soil had a high P sorption capacity, the PSR was above the threshold, indicating a high risk of P leaching from the surface orchard soil. The shallow groundwater δ18OPO4 values were higher than the expected isotopic equilibrium with pyrophosphatase. The high PSR and δ18OPO4 orchard soil values indicated that P leaching from orchard soil was the major P enrichment mechanism. The Bayesian mixing model estimated that 76.6% of the P supplied from the orchard soil was recycled by microorganisms. This demonstrates the utility of δ18OPO4 and the PSR to evaluate the P source and biological recycling in groundwater.

Quantifying isotope parameters associated with carbonyl-water oxygen exchange during sucrose translocation in tree phloem.

Stable oxygen isotope ratio of tree-ring α-cellulose (δ18Ocel) yields valuable information on many aspects of tree-climate interactions. However, our current understanding of the mechanistic controls on δ18Ocel is incomplete, with a knowledge gap existent regarding the fractionation effect characterizing carbonyl-water oxygen exchange during sucrose translocation from leaf to phloem. To address this insufficiency, we set up an experimental system integrating a vapor 18O-labeling feature to manipulate leaf-level isotopic signatures in tree saplings enclosed within whole-canopy gas-exchange cuvettes. We applied this experimental system to three different tree species to determine their respective relationships between 18O enrichment of sucrose in leaf lamina (Δ18Ol_suc) and petiole phloem (Δ18Ophl_suc) under environmentally/physiologically stable conditions. Based on the determined Δ18Ophl_suc-Δ18Ol_suc relationships, we estimated that on average, at least 25% of the oxygen atoms in sucrose undergo isotopic exchange with water along the leaf-to-phloem translocation path and that the biochemical fractionation factor accounting for such exchange is c. 34‰, markedly higher than the conventionally assumed value of 27‰. Our study represents a significant step toward quantitative elucidation of the oxygen isotope dynamics during sucrose translocation in trees. This has important implications with respect to improving the δ18Ocel model and its related applications in paleoclimatic and ecophysiological contexts.

The Pleistocene high-elevation environments between 2.02 and 0.6 Ma at Melka Kunture (Upper Awash Valley, Ethiopia) based upon stable isotope analysis.

Pleistocene environments are among the most studied issues in paleoecology and human evolution research in eastern Africa. Many data have been recorded from archaeological sites located at low and medium elevations (≤ 1500 m), whereas few contexts are known at 2000 m and above. Here, we present a substantial isotopic study from Melka Kunture, a complex of prehistoric sites located at 2000-2200 m above sea level in the central Ethiopian highlands. We analyzed the stable carbon and oxygen isotopic composition of 308 faunal tooth enamel samples from sites dated between 2.02 and 0.6 Ma to investigate the animal diets and habitats. The carbon isotopic results indicate that the analyzed taxa had C4-dominated and mixed C3-C4 diets with no significant diachronic changes in feeding behavior with time. This is consistent with faunal and phytolith analyses, which suggested environments characterized by open grasslands (with both C3 and C4 grasses), patches of bushes and thickets, and aquatic vegetation. However, palynological data previously documented mountain forests, woodlands, and high-elevation grasslands. Additionally, the carbon isotopic comparison with other eastern African localities shows that differences in elevation did not influence animal feeding strategies and habitat partitioning, even though plant species vary according to altitudinal gradients. In contrast, the oxygen isotopic comparison suggests significant differences consistent with the altitude effect. Our approach allows us to detect diverse aspects of animal behavior, habitat, and vegetation that should be considered when reconstructing past environments.

Effects of particle size, storage conditions, and chemical pretreatments on carbon and oxygen isotopic measurements of modern tooth enamel.

Isotopic analysis of human tooth enamel can provide life history information useful in forensic identification. These applications depend on the availability of reference data documenting isotopic values for individuals with known life history and on the comparability of data from reference and case work samples. Here we build on previous methodological research, which has largely focused on paleontological and archaeological samples, and conduct experiments using enamel from modern human teeth targeting three sample preparation variables (sample particle size, storage conditions, and chemical pretreatments). Our results suggest that differences in particle size affect the efficiency of sample reactions during pretreatment and analysis, with coarse particles giving reduced loss of enamel carbonate during acid pretreatments but producing slightly higher oxygen isotope values than fine particles during analysis. Data for samples stored in dry and ambient environments following pretreatment were indistinguishable, suggesting no exchange of oxygen between samples and ambient water vapor. Finally, chemical pretreatments with a range of commonly used reactants and conditions showed a pervasive, moderate oxygen isotope shift associated with acetic acid treatment, which may be caused by exchange of enamel hydroxyl groups with reagents or rinse waters. Collectively, the results emphasize the importance of methodological standardization to improve comparability and reduce potential for bias in the forensic application of tooth enamel isotope data.

The stable isotope hydrology of Sable Island, Nova Scotia, Canada with implications for evaluating the water budget of wild horses.

We investigated the stable isotope hydrology of Sable Island, Nova Scotia, Canada over a five year period from September, 2017 to August, 2022. The δ2H and δ18O values of integrated monthly precipitation were weakly seasonal and ranged from -66 to -15 ‰ and from -9.7 to -1.9 ‰, respectively. Fitting these monthly precipitation data resulted in a local meteoric water line (LMWL) defined by: δ2H = 7.22 ± 0.21 · δ18O + 7.50 ± 1.22 ‰. Amount-weighted annual precipitation had δ2H and δ18O values of -36 ± 11 ‰ and -6.1 ± 1.4 ‰, respectively. Deep groundwater had more negative δ2H and δ18O values than mean annual precipitation, suggesting recharge occurs mainly in the winter, while shallow groundwater had δ2H and δ18O values more consistent with mean annual precipitation or mixing of freshwater with local seawater. Surface waters had more positive values and showed evidence of isolation from the groundwater system. The stable isotopic compositions of plant (leaf) water, on the other hand, indicate plants use groundwater as their source. Fog had δ2H and δ18O values that were significantly more positive than those of local precipitation, yet had similar 17O-excess values. δ2H values of horsehair from 4 individuals lacked seasonality, but had variations typical to those of precipitation on the island. Differences in mean δ2H values of horsehair were statistically significant and suggest variations in water use may exist between spatially disparate horse communities. Our results establish an important initial framework for ongoing isotope studies of feral horses and other wildlife on Sable Island.

Effects of sampling time and location on the geographical origin traceability of protected geographical indication (PGI) Hongyuan yak milk: Based on stable isotope ratios.

Hongyuan yak milk is a protected geographical indication (PGI) product of rich nutritional value, which is popular among consumers. Stable isotope ratio analysis (SIRA) is an effective way to protect the authenticity of the geographical origin of PGI products, and it is crucial to study the factors affecting stable isotopes. Firstly, we proved that the SIRA could be used to identify the geographical origin of Hongyuan yak milk, and that the identification accuracy in combination with δ13C and δ18O was 100 %. Secondly, we analyzed the effect of sampling selection on the stable isotopes of Hongyuan yak milk in practical applications, which showed that sampling time influenced the δ13C, δ2H, and δ18O, while the sampling locations did not. There were interactions between the effect of sampling time and location on δ2H and δ18O. These results provide a reliable method for identifying PGI products and also provide new guidance on sampling models.

The determining factors of hydrogen isotope offsets between plants and their source waters.

A fundamental assumption when using hydrogen and oxygen stable isotopes to understand ecohydrological processes is that no isotope fractionation occurs during plant water uptake/transport/redistribution. A growing body of evidence has indicated that hydrogen isotope fractionation occurs in certain environments or for certain plant species. However, whether the plant water source hydrogen isotope offset (δ2 H offset) is a common phenomenon and how it varies among different climates and plant functional types remains unclear. Here, we demonstrated the presence of positive, negative, and zero offsets based on extensive observations of 12 plant species of 635 paired stable isotopic compositions along a strong climate gradient within an inland river basin. Both temperature and relative humidity affected δ2 H offsets. In cool and moist environments, temperature mainly affected δ2 H offsets negatively due to its role in physiological activity. In warm and dry environments, relative humidity mainly affected δ2 H offsets, likely by impacting plant leaf stomatal conductance. These δ2 H offsets also showed substantial linkages with leaf water 18 O enrichment, an indicator of transpiration and evaporative demand. Further studies focusing on the ecophysiological and biochemical understanding of plant δ2 H dynamics under specific environments are essential for understanding regional ecohydrological processes and for conducting paleoclimate reconstructions.

Topographic influence on ecohydrology in volcanic watersheds of the western Pacific monsoon area: evidence from water stable isotope composition of meteoric water, thermal water, and plants.

In Taiwanese volcanic watersheds, we investigated stable water isotopes in meteoric water, plants, and thermal water. Meteoric water exhibited a seasonal cycle, with heavier isotopes in winter and lighter ones in summer, especially in the southern region. The northern monsoon signal lagged the south by two weeks. In the Tatun mountains, young water fractions indicated prevalent old water sources. In the northern watershed, streamwater mainly came from the winter monsoon, while the southern one was influenced by alternating monsoons. Both indices indicated that winter plants depended on summer rainfall. Streamwater and plants had distinct sources in winter, supporting ecohydrological separation. Thermal spring water's d-excess helped identify water-rock interactions, with low d value signaling such interactions. The topographic wetness index showed a higher summer monsoon contribution to southern streamwater but a lower one to plants. The mean linear channel direction significantly affected the monsoon contribution fraction, with northeast-oriented channels vulnerable to northeastward winter monsoons. Finally, we developed a model illustrating hydrological processes on short and long timescales. Our findings enhance our understanding of hydrological disturbances' impact on water resources and ecosystems.

Determination of the water-use patterns for two xerophyte shrubs by hydrogen isotope offset correction.

The stable hydrogen and oxygen isotope technique is typically used to explore plant water uptake; however, the accuracy of the technique has been challenged by hydrogen isotope offsets between plant xylem water and its potential source water. In this study, the soil hydrogen and oxygen isotope waterline was used to correct the hydrogen isotope offsets for Salix psammophila and Caragana korshinskii, two typical shrub species on the Chinese Loess Plateau. Five different types of isotopic data [(i) δ18O, (ii) δ2H, (iii) combination δ18O with δ2H, (iv) corrected δ2H and (v) combination δ18O with corrected δ2H] were separately used to determine the water-use patterns of the two shrubs. The δ2H offset values of S. psammophila and C. korshinskii did not show significant temporal variation among the sampling months (May, July and September) but showed notable differences between the two shrubs (-0.4 ± 0.5‰ in S. psammophila vs -4.3 ± 0.9‰ in C. korshinskii). The obtained water absorption proportion (WAP) of S. psammophila in the different soil layers (0-20, 20-60 and 60-200 cm) did not differ significantly among the five different input data types. However, compared with the input data types (iii) and (v), the data types (i), (ii) and (iv) overestimated the WAP of C. korshinskii in the 0-20 cm soil layer and underestimated that in the 60-200 cm layer. The data type (iii) overestimated the WAP of C. korshinskii in 0-20 cm soil layer (25.9 ± 0.8%) in July in comparison with the WAP calculated based on data type (v) (19.1 ± 1.1%). The combination of δ18O and corrected δ2H, i.e., data type (v), was identified as the best data type to determine the water use patterns of C. korshinskii due to the strong correlation between the calculated WAP and soil water content and soil sand content. In general, S. psammophila mainly used (57.9-62.1%) shallow soil water (0-60 cm), whereas C. korshinskii mainly absorbed (52.7-63.5%) deep soil water (60-200 cm). We confirm that the hydrogen isotope offsets can cause significant errors in determining plant water uptake of C. korshinskii, and provide valuable insights for accurately quantifying plant water uptake in the presence of hydrogen isotope offsets between xylem and source water. This study is significant for facilitating the application of the stable hydrogen and oxygen isotope technique worldwide, and for revealing the response mechanism of shrub key ecohydrological and physiological processes to the drought environment in similar climate regions.

Modeling the response of Norway spruce tree-ring carbon and oxygen isotopes to selection harvest on a drained peatland forest.

Continuous cover forestry (CCF) has gained interest as an alternative to even-aged management particularly on drained peatland forests. However, relatively little is known about the physiological response of suppressed trees when larger trees are removed as a part of CCF practices. Consequently, studies concentrating on process-level modeling of the response of trees to selection harvesting are also rare. Here, we compared, modeled and measured harvest response of previously suppressed Norway spruce (Picea abies) trees to a selection harvest. We quantified the harvest response by collecting Norway spruce tree-ring samples in a drained peatland forest site and measuring the change in stable carbon and oxygen isotopic ratios of wood formed during 2010-20, including five post-harvest years. The measured isotopic ratios were compared with ecosystem-level process model predictions for ${\kern0em }^{13}$C discrimination and ${\kern0em }^{18}$O leaf water enrichment. We found that the model predicted similar but lower harvest response than the measurements. Furthermore, accounting for mesophyll conductance was important for capturing the variation in ${\kern0em }^{13}$C discrimination. In addition, we performed sensitivity analysis on the model, which suggests that the modeled ${\kern0em }^{13}$C discrimination is sensitive to parameters related to CO2 transport through stomata to the mesophyll.

Global scale identification of catchments phosphorus source shifts with urbanization: A phosphate oxygen isotope and Bayesian mixing model approach.

Different scenarios of urban expansion can influence the dynamic characteristics of catchments in terms of phosphorus (P). It is important to identify the changes in P sources that occur during the process of urbanization to develop targeted policies for managing P in catchments. However, there is a knowledge gap in quantifying the variations of potential P sources associated with urbanization. By combining phosphate oxygen isotopes from global catchments with a Bayesian model and the urbanization process, we demonstrate that the characteristics of potential P sources (such as fertilizers, urban wastewater, faeces, and bedrock) change as urban areas expand. Our results indicate that using phosphate oxygen isotopes in conjunction with a Bayesian model provides direct evidence of the proportions of potential P sources. We classify catchment P loadings into three stages based on shifts in potential P sources during urban expansion. During the initial stage of urbanization (urban areas < 1.5 %), urban domestic and industrial wastewater are the main contributors to P loadings in catchments. In the mid-term acceleration stage (1.5 % ≤ urban areas < 3.5 %), efforts to improve wastewater treatment significantly reduce wastewater P input, but the increase in fertilizer P input offsets this reduction in sewage-derived P. In the high-level urbanization stage (urban areas ≥ 3.5 %), the proportions of the four potential P sources tend to stabilize. Remote areas bear the burden of excessive P loadings to meet the growing food demand and improved diets resulting from the increasing urban population. Our findings support the development of strategies for water quality management that better consider the driving forces of urbanization on catchment P loadings.

Effects of season and slope orientation on stable isotopes of different water bodies in the subalpine shrub zone of the eastern Qilian Mountains in China.

The subalpine shrub zone of the Qilian Mountains is an important water-retaining area, and it is crucial to clarify the processes of its hydrological cycle. Therefore, based on the stable isotope values of different water bodies in the subalpine shrub zone of the eastern Qilian Mountains from May to October 2019, the characteristics of δD and δ18O of different water bodies and their hydraulic relationships with each other were studied. The results showed that the stable isotope values of precipitation exhibited the largest fluctuations, while they were the most stable for groundwater. Plant transpiration was stronger than the evaporation of other water bodies. The stable isotope of precipitation was enriched in high temperature and low humidity environments. Isotopic values of plant and soil water were higher and more stable on the semi-sunny slope than on the semi-shady slope. According to the stable isotopes, there was a strong hydraulic relationship between the different water bodies in the study area, and precipitation was the ultimate source of all of them. Precipitation replenished soil water through infiltration. Part of the soil water was absorbed by plants, while the rest continued to infiltrate to replenish groundwater. Groundwater and precipitation replenished the river water.

BITACORA: An isotopic database of modern human tissues (keratin, teeth) for Argentina.

As a consequence of the recent history of Argentina related to crimes against humanity, the country has positioned itself as a leader on Forensic Anthropology in human rights contexts. To some extent it can even be argued that Forensic Genetics for human identification had its origins in human rights work in the early 1980s in Argentina. However, there are still hundreds of unidentified human remains recovered from the dictatorial regimes' crimes. Additionally, every year there are dozens of unidentified deceased buried in public cemeteries. Thus, there is an urgent need to adopt new techniques that could increase the biological profile of a person, and therefore increase the chances of positive identifications. One of such initiatives is the development of isotopic databases and models that can provide information on the population and region of origin of unidentified victims. We present the development of an isotopic database of modern human tissues named BITACORA (from its name in Spanish: Base de Información Isotópica de Tejidos Actuales Como Referencia Argentina). BITACORA holds isotopic data (δ18O, δ2H, δ13C, δ15N and δ34S values) from teeth (enamel and dentine) and keratin tissues (scalp hair, beard and fingernails) obtained from volunteers of known origin, as well as individual information of the donors (age, gender, biometrics, dietary preferences, and relocation history). BITACORA is associated with a tap water isotope database. Currently, we have 345 keratin, 273 teeth and 287 tap water samples gathered from across the country. We present preliminary analyses on the geographic distribution of these isotopic markers, and provide an overall discussion of the current status and future development of the databases.

Oxygen isotope variation in drinking water in Oaxaca, Mexico and its implications for forensic provenancing efforts.

Forensic anthropologists have used oxygen isotopic analyses (δ18O) in recent decades because of its ability to help estimate probable regions of origin of unidentified individuals based on isotopic composition of bodily tissues. Prior research has found that drinking water is geographically patterned and that tap water is often representative of drinking water in assessing these links between human tissues and geography. Researchers have begun applying the method in a variety of global contexts. This research critically assesses the assumption that tap water is isotopically representative of drinking water in Oaxaca, Mexico. Drinking water samples from Oaxaca were analyzed and compared with predicted δ18O values from a previously constructed tap water isoscape of Mexico. Hair samples from Oaxaca were also analyzed to compare against various water sources. Tap water δ18O values do not reliably reflect drinking water δ18O in sampled regions of Oaxaca, Mexico. Further, the models relating hair keratin to drinking water, built on this assumption, fail to hold predictive power. With an incomplete understanding of tap water's ability to represent drinking water isotopically, researchers need to study the role of other key factors in δ18O values. If the individual's being identified with δ18O are from non-Western communities, forensic practitioners run the risk of incorrectly predicting region of origin because of the method's assumptions. Recognizing the varying sociocultural realities of the communities forensic practitioners seek to aid is paramount as we grow and develop our methods moving forward.

Optimization of phosphate oxygen isotope pretreatment measurement method based on phosphate in situ enrichment blanket.

Phosphate oxygen isotope analysis is an effective tool for investigating phosphorus migration and transformation in water bodies. Unfortunately, current pretreatment methods for this technology are significantly limited due to their demanding sample amount requirements, complex operation, and limited scope of application. In order to enhance the efficiency of the pretreatment process, hydrated zirconia was synthesized through liquid-phase precipitation. Zeolite, D001 macroporous resin, activated carbon, and ceramsite were chosen as possible candidate materials for loading purposes. The optimal zirconium loading material was identified through a combination of field enrichment and laboratory elution experiments. The ideal in situ enrichment duration, material dosages, and elution time were ascertained using response surface methodology. The findings showed that D001 resin exhibited superior selective adsorption and elution capacity for phosphate. The response surface optimization yielded the optimal parameters for the in situ phosphate-enrichment blanket: a mass of 13 g for zirconium-loaded D001 resin, an enrichment period of 360 min, and an elution period of 853 min. The attainment of a bright yellow Ag3PO4 solid after purification served as proof of the reliability of the optimization method. The obtained results provide a fundamental basis for the preparation and application of phosphate oxygen isotope analysis in freshwater ecosystem.

Large-scale surface water-groundwater origins and connectivity in the Ordos Basin, China: Insight from hydrogen and oxygen isotopes.

The sustainability of water resources is a major challenge for the Ordos Basin and Loess Plateau of China. The basis of effective water management is an understanding of the water cycle process. This study investigated the surface water-groundwater origins and connectivity using stable isotopes (δD and δ18O) of surface water and groundwater in 11 river basins in the Ordos Basin. It was found that the surface water-groundwater origins and hydraulic connection were characterized by regional differences, mainly induced by climatic characteristics, hydrogeological conditions and human activities. Specifically, the impact of thick loess deposits caused surface water and groundwater to take long time to produce a hydraulic connection. In contrast, areas with thin loess deposits and frequent human activities showed a good connectivity between surface water and groundwater. As for water origins, summer precipitation was a common source of surface water and groundwater in the study area, and groundwater discharge was another source of surface water. However, surface water and groundwater were subjected to different degrees of evaporation during receiving precipitation recharge. Notably, thick loess deposits had an impact on groundwater evaporation because both the recharge of precipitation to groundwater and the discharge of groundwater to surface water took a long time. In addition, it was found that frequent human activities (mining, irrigation and urban construction) could weaken the impact of evaporation. This large-scale analysis provided new insights into the origins and connectivity of surface water and groundwater in areas with thick unsaturated zones for water resources management.