Rubidium 87-strontium 87 age of carbonaceous chondrites
Rb 87-Sr 87 age determination of carbonaceous chondrites, showing agreement among petrological classification types
Kaushal, S. K.↗
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Ultra-High Resolution Elemental/Isotopic Mass Spectrometry (m/?m> 1,000,000): Coupling of the Liquid Sampling-Atmospheric Pressure Glow Discharge with an Orbitrap Mass Spectrometer for Applications in Biological Chemistry and Environmental Analysis
Many fundamental questions of astrophysics, biochemistry, and geology rely on the ability to accurately and precisely measure the mass and abundance of isotopes. Taken a step further, the capacity to perform such measurements on intact molecules provides insights into processes in diverse biological systems. Described here is the coupling of a combined atomic and molecular (CAM) ionization source, the liquid sampling-atmospheric pressure glow discharge (LS-APGD) microplasma, with a commercially available ThermoScientific Fusion Lumos mass spectrometer. Demonstrated for the first time is the ionization and isotopically-resolved fingerprinting of a long-postulated, but never mass-spectrometrically observed, bi-metallic complex Hg:Se-cysteine. Such a complex has been implicated as having a role in observations of Hg detoxification by selenoproteins/amino acids. Demonstrated as well is the ability to mass spectrometrically-resolve the geochronologically important isobaric 87Sr and 87Rb species (?m ~ 0.3 mDa, mass resolution m/?m ? 1,700,000). The mass difference in this case reflects the beta-decay of the 87Rb to the stable Sr isotope. These two demonstrations highlight what may be a significant change in bioinorganic and atomic mass spectrometry, with impact expected across a broad spectrum of the physical, biological and geological sciences.
Hoegg, Edward D.↗
Nuclear Data Sheets for A = 87
The evaluated experimental data are presented for 14 known nuclides of mass 87 (Ga, Ge, As, Se, Br, Kr, Rb, Sr, Y, Zr, Nb, Mo, Tc, Ru). New datasets have been added for {sup 87}Ga, {sup 87}Se, {sup 87}Kr, {sup 87}Rb, {sup 87}Sr, {sup 87}Nb, and {sup 87}Tc. The observation of and new lifetime measurements for {sup 87}As at the NSCL Coupled Cyclotron Facility and the Oak Ridge Isochronous Cyclotron at the HRIBF–ORNL Facility are included in the adopted levels for this isotope. The new evaluation also includes an isomeric level at unknown energy for {sup 87}Tc, changes to the adopted levels for {sup 87}Nb based on newly published data including an extension of the high spin levels and new lifetime measurements, and new heavy ion data for {sup 87}Kr. New high spin levels for {sup 87}Rb were observed, indicating possible neutron core excitations. In addition, the ground state lifetime of {sup 87}Rb has been revised and a new lifetime measurement for an excited level in {sup 87}Rb indicates a possible proton spin flip. New excitation levels have been observed for the first time in {sup 87}Se. New direct and precise measurement of atomic masses of {sup 87}Tc, {sup 87}Mo, {sup 87}Nb, {sup 87}Zr, {sup 87}Mo and {sup 87}Tc have greatly improved the Q value landscape in this mass region. This work supersedes the previous A=87 evaluation published in 2002He09, and Q values for all isotopes were updated to incorporate the mass evaluation in 2012Wa38.
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
Partitioning maternal and exogenous diet contributions to otolith 87 Sr/ 86 Sr in kokanee salmon ( Oncorhynchus nerka )
Strontium isotopes ( 87 Sr/ 86 Sr) recorded in the otoliths of Pacific salmon (Oncorhynchus spp.) are commonly used to identify natal origin. For species that migrate at or soon after emergence, the embryonic region of the otolith provides the only record of provenance. However, maternal contribution of Sr from the yolk can confound the isotopic signature of the natal site. We experimentally quantified maternal and exogenous diet contributions to otolith 87 Sr/ 86 Sr over embryonic development in kokanee salmon (Oncorhynchus nerka). Eggs from two populations in isotopically distinct lakes were incubated and reared in a common water source. Timing of developmental events and proportional contribution from yolk to otolith 87 Sr/ 86 Sr differed significantly between the two populations. We suggest that the magnitude of difference in 87 Sr/ 86 Sr between yolk and water, the relative concentrations of Sr and Ca in these isotopic sources, and population-specific effects on otolith growth and composition contribute to this variation. Furthermore, understanding how these factors affect otolith 87 Sr/ 86 Sr could extend the use of otolith geochemistry for determining provenance to species and populations in which natal site rearing is limited.
59 BASIC BIOLOGICAL SCIENCES↗
Strontium isoscape of sub-Saharan Africa allows tracing origins of victims of the transatlantic slave trade
Abstract Strontium isotope ( 87 Sr/ 86 Sr) analysis with reference to strontium isotope landscapes (Sr isoscapes) allows reconstructing mobility and migration in archaeology, ecology, and forensics. However, despite the vast potential of research involving 87 Sr/ 86 Sr analysis particularly in Africa, Sr isoscapes remain unavailable for the largest parts of the continent. Here, we measure the 87 Sr/ 86 Sr ratios in 778 environmental samples from 24 African countries and combine this data with published data to model a bioavailable Sr isoscape for sub-Saharan Africa using random forest regression. We demonstrate the efficacy of this Sr isoscape, in combination with other lines of evidence, to trace the African roots of individuals from historic slavery contexts, particularly those with highly radiogenic 87 Sr/ 86 Sr ratios uncommon in the African Diaspora. Our study provides an extensive African 87 Sr/ 86 Sr dataset which includes scientifically marginalized regions of Africa, with significant implications for the archaeology of the transatlantic slave trade, wildlife ecology, conservation, and forensics.
Science & Technology - Other Topics↗
Using stable isotopes (δD, δ{sup 18}O, δ{sup 34}S and {sup 87}Sr/{sup 86}Sr) to identify sources of water in abandoned mines in the Fengfeng coal mining district, northern China
With depleted coal resources or deteriorating mining geological conditions, some coal mines have been abandoned in the Fengfeng mining district, China. Water that accumulates in an abandoned underground mine (goaf water) may be a hazard to neighboring mines and impact the groundwater environment. Groundwater samples at three abandoned mines (Yi, Er and Quantou mines) in the Fengfeng mining district and the underlying Ordovician limestone aquifer were collected to characterize their chemical and isotopic compositions and identify the sources of the mine water. The water was HCO{sub 3}·SO{sub 4}-Ca·Mg type in Er mine and the auxiliary shaft of Yi mine, and HCO{sub 3}·SO{sub 4}-Na type in the main shaft of Quantou mine. The isotopic compositions (δD and δ{sup 18}O) of water in the three abandoned mines were close to that of Ordovician limestone groundwater. Faults in the abandoned mines were developmental, possibly facilitating inflows of groundwater from the underlying Ordovician limestone aquifers into the coal mines. Although the Sr{sup 2+} concentrations differed considerably, the ratios of Sr{sup 2+}/Ca{sup 2+} and {sup 87}Sr/{sup 86}Sr and the {sup 34}S content of SO{sub 4}{sup 2−} were similar for all three mine waters and Ordovician limestone groundwater, indicating that a close hydraulic connection may exist. Geochemical and isotopic indicators suggest that (1) the mine waters may originate mainly from the Ordovician limestone groundwater inflows, and (2) the upward hydraulic gradient in the limestone aquifer may prevent its contamination by the overlying abandoned mine water. The results of this study could be useful for water resources management in this area and other similar mining areas.
58 GEOSCIENCES↗
Groundwater mixing and mineralization processes in a mountain–oasis–desert basin, northwest China: hydrogeochemistry and environmental tracer indicators
Hydrogeochemistry and environmental tracers ({sup 2}H, {sup 18}O, {sup 87}Sr/{sup 86}Sr) in precipitation, river and reservoir water, and groundwater have been used to determine groundwater recharge sources, and to identify mixing characteristics and mineralization processes in the Manas River Basin (MRB), which is a typical mountain–oasis–desert ecosystem in arid northwest China. The oasis component is artificial (irrigation). Groundwater with enriched stable isotope content originates from local precipitation and surface-water leakage in the piedmont alluvial–oasis plain. Groundwater with more depleted isotopes in the north oasis plain and desert is recharged by lateral flow from the adjacent mountains, for which recharge is associated with high altitude and/or paleo-water infiltrating during a period of much colder climate. Little evaporation and isotope exchange between groundwater and rock and soil minerals occurred in the mountain, piedmont and oasis plain. Groundwater δ{sup 2}H and δ{sup 18}O values show more homogeneous values along the groundwater flow direction and with well depths, indicating inter-aquifer mixing processes. A regional contrast of groundwater allows the {sup 87}Sr/{sup 86}Sr ratios and δ{sup 18}O values to be useful in a combination with Cl, Na, Mg, Ca and Sr concentrations to distinguish the groundwater mixing characteristics. Two main processes are identified: groundwater lateral-flow mixing and river leakage in the piedmont alluvial–oasis plain, and vertical mixing in the north oasis plain and the desert. The {sup 87}Sr/{sup 86}Sr ratios and selected ion ratios reveal that carbonate dissolution and mixing with silicate from the southern mountain area are primarily controlling the strontium isotope hydrogeochemistry.
58 GEOSCIENCES↗
Excitation Function Calculations of Neutron-Induced Reactions of Some Zirconium Target Isotopes
Nuclear structures with high performance materials will be critical for the success of future fusion energy. Zirconium alloys are extensively used for nuclear reactor core materials as fuel cladding and guide tubes due to excellent radiation and corrosion resistant properties. In this paper, the excitation functions of {sup 90}Zr(n,2n){sup 89}Zr, {sup 90}Zr(n,α){sup 87}Sr, {sup 91}Zr(n,p){sup 91}Y and {sup 92}Zr(n,p){sup 92}Y nuclear reactions were calculated for energies up to 25 MeV. Besides, ALICE/ASH and TALYS 1.6 codes were used for the cross section calculations. The obtained calculations were compared with the experimental data in the literature.
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
Salinization of porewater in a multiple aquitard-aquifer system in Jiangsu coastal plain, China
Chemical and isotopic compositions were analyzed in porewater squeezed from a clayey aquitard in Jiangsu coastal plain, eastern China, to interpret the salinity origin, chemical evolution and water-mass mixing process. A strong geochemical fingerprint was obtained with an aligned Cl/Br ratio of 154 in the salinized aquitard porewater over a wide Cl{sup −} concentration range (396–9,720 mg/L), indicating that porewater salinity is likely derived from a mixing with old brine with a proportion of less than 20%. Very small contributions of brine exerted limited effects on water stable isotopes. The relationships between porewater δ{sup 18}O and δD indicate that shallow and intermediate porewaters could be original seawater and were subsequently diluted with modern meteoric water, whereas deep porewaters with depleted stable isotopic values were probably recharged during a cooler period and modified by evaporation and seawater infiltration. The cation–Cl relationship and mineralogy of associated strata indicate that porewater has been chemically modified by silicate weathering and ion-exchange reactions. {sup 87}Sr/{sup 86}Sr ratios of 0.7094–0.7112 further confirm the input source of silicate minerals. Numerical simulations were used to evaluate the long-term salinity evolution of the deep porewater. The alternations of boundary conditions (i.e., the third aquifer mixed with brine at approximately 70 ka BP, followed by recharge of glacial meltwater at 20–25 ka BP, and then mixing with Holocene seawater at 7–10 ka BP) are responsible for the shift in porewater salinity. These timeframes correspond with the results of previous studies on ancient marine transgression-regression in Jiangsu coastal plain.
58 GEOSCIENCES↗
Geochemical and isotopic evidence on the recharge and circulation of geothermal water in the Tangshan Geothermal System near Nanjing, China: implications for sustainable development
Geothermal resources are practical and competitive clean-energy alternatives to fossil fuels, and study on the recharge sources of geothermal water supports its sustainable exploitation. In order to provide evidence on the recharge source of water and circulation dynamics of the Tangshan Geothermal System (TGS) near Nanjing (China), a comprehensive investigation was carried out using multiple chemical and isotopic tracers (δ{sup 2}H, δ{sup 18}O, δ{sup 34}S, {sup 87}Sr/{sup 86}Sr, δ{sup 13}C, {sup 14}C and {sup 3}H). The results confirm that a local (rather than regional) recharge source feeds the system from the exposed Cambrian and Ordovician carbonate rocks area on the upper part of Tangshan Mountain. The reservoir temperature up to 87 °C, obtained using empirical as well as theoretical chemical geothermometers, requires a groundwater circulation depth of around 2.5 km. The temperature of the geothermal water is lowered during upwelling as a consequence of mixing with shallow cold water up to a 63% dilution. The corrected {sup 14}C age shows that the geothermal water travels at a very slow pace (millennial scale) and has a low circulation rate, allowing sufficient time for the water to become heated in the system. This study has provided key information on the genesis of TGS and the results are instructive to the effective management of the geothermal resources. Further confirmation and even prediction associated with the sustainability of the system could be achieved through continuous monitoring and modeling of the responses of the karstic geothermal reservoir to hot-water mining.
58 GEOSCIENCES↗
The integrated impacts of natural processes and human activities on groundwater salinization in the coastal aquifers of Beihai, southern China
Salinization in coastal aquifers is usually related to both seawater intrusion and water–rock interaction. The results of chemical and isotopic methods were combined to identify the origin and processes of groundwater salinization in Daguansha area of Beihai, southern China. The concentrations of the major ions that dominate in seawater (Cl{sup −}, Na{sup +}, Ca{sup 2+}, Mg{sup 2+} and SO{sub 4}{sup 2–}), as well as the isotopic content and ratios ({sup 2}H, {sup 18}O, {sup 87}Sr/{sup 86}Sr and {sup 13}C), suggest that the salinization occurring in the aquifer of the coastal plain is related to seawater and that the prevailing hydrochemical processes are evaporation, mixing, dissolution and ion exchange. For the unconfined aquifer, groundwater salinization has occurred in an area that is significantly influenced by land-based sea farming. The integrated impacts of seawater intrusion from the Beibuwan Gulf and infiltration of seawater from the culture ponds are identified in the shallowest confined aquifer (I) in the middle of the area (site BBW2). Leakage from this polluted confined aquifer causes the salinization of groundwater in the underlying confined aquifer (II). At the coastal monitoring site (BBW3), confined aquifer I and lower confined aquifer II are heavily contaminated by seawater intrusion. The weak connectivity between the upper aquifers, and the seaward movement of freshwater, prevents saltwater from encroaching the deepest confined aquifer (III). A conceptual model is presented. Above all, understanding of the origin and processes of groundwater salinization will provide essential information for the planning and sustainable management of groundwater resources in this region.
58 GEOSCIENCES↗
Isotopes and genes reveal freshwater origins of Chinook salmon Oncorhynchus tshawytscha aggregations in California’s coastal ocean
The ability of salmon to navigate from the ocean back to their river of origin to spawn acts to reinforce local adaptation and maintenance of unique and heritable traits among salmon populations. Here, the extent to which Chinook salmon Oncorhynchus tshawytscha from the same freshwater breeding groups associate together in the ocean at regional and smaller-scale aggregations prior to homeward migration is evaluated. Natural variation in salmon otolith daily growth bands, strontium isotopes ( 87 Sr/ 86 Sr), and microsatellite DNA were used as intrinsic tags to link the distributions of fish caught in the ocean with their freshwater origins. Adults were caught from vessels by hook and line in small aggregations (7-18 ind.) at the same geographic location (1-24 km of coastline) and time (4-36 h) from 3 ocean regions along central California, USA. Salmon caught together in aggregations were from the same genetic group, and to a lesser extent, of the same natal origin (individual rivers or hatcheries). However, at regional scales, adult salmon mixed. Central Valley winter-run Chinook salmon caught together in the ocean varied in the duration of freshwater rearing for up to 2-3 mo prior to seaward migration, suggesting associations within the group were not established in freshwater or maintained over the lifetime of the fish. Our findings are consistent with coarser information indicating stocks are distributed differently in time and space, but larger sample sizes are required to evaluate the consistency of patterns at smaller spatial scales. This study uncovers freshwater associations prior to homeward migration, a principle and undocumented prerequisite of the collective navigation hypothesis.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Detecting inter-aquifer leakage in areas with limited data using hydraulics and multiple environmental tracers, including {sup 4}He, {sup 36}Cl/Cl, {sup 14}C and {sup 87}Sr/{sup 86}Sr
The investigation of regionally extensive groundwater systems in remote areas is hindered by a shortage of data due to a sparse observation network, which limits our understanding of the hydrogeological processes in arid regions. The study used a multidisciplinary approach to determine hydraulic connectivity between the Great Artesian Basin (GAB) and the underlying Arckaringa Basin in the desert region of Central Australia. In order to manage the impacts of groundwater abstraction from the Arckaringa Basin, it is vital to understand its connectivity with the GAB (upper aquifer), as the latter supports local pastoral stations and groundwater-dependent springs with unique endemic flora and fauna. The study is based on the collation of available geological information, a detailed analysis of hydraulic data, and data on environmental tracers. Enhanced inter-aquifer leakage in the centre of the study area was identified, as well as recharge to the GAB from ephemeral rivers and waterholes. Throughout the rest of the study area, inter-aquifer leakage is likely controlled by diffuse inter-aquifer leakage, but the coarse spatial resolution means that the presence of additional enhanced inter-aquifer leakage sites cannot be excluded. This study makes the case that a multi-tracer approach along with groundwater hydraulics and geology provides a tool-set to investigate enhanced inter-aquifer leakage even in a groundwater basin with a paucity of data. A particular problem encountered in this study was the ambiguous interpretation of different age tracers, which is attributed to diffusive transport across flow paths caused by low recharge rates.
58 GEOSCIENCES↗
Spatial changes in trace element and strontium isotope water chemistry in a temperate river system with application to sturgeon movement
Understanding patterns in trace element concentrations and water quality within river systems provides a foundation to evaluate retrospective movements and habitat use of fish. Because trace elements are incorporated into calcified structures of fishes relative to water concentrations, baseline maps have application for fisheries management, including for rare species such as sturgeons. Therefore, trace elements [strontium (Sr), barium (Ba), manganese (Mn), zinc (Zn), and magnesium (Mg)], strontium isotopes ( 87 Sr/ 86 Sr), dissolved oxygen and salinity were measured in the Pearl River and Lake Pontchartrain watersheds, within Mississippi and Louisiana, USA for application in assessing riverine use by Gulf Sturgeon Acipenser oxyrinchus desotoi. Water samples were collected during the summer-fall period when juvenile Gulf Sturgeon were anticipated to be present and analyzed by solution and multi-collector inductively coupled plasma mass spectrometry. Trace element to calcium (Ca) ratios in Sr, Ba, Zn, and Mg were distinguishable between the upper Pearl River and the Bogue Chitto River tributary, and the upper Pearl River and lower Pearl River. For most trace elements and 87 Sr/ 86 Sr, there was a gradual increase from upper river regions to lower river regions, and large differences between freshwater and saline areas. Lake Pontchartrain watershed rivers were not easily differentiated, but regions of low dissolved oxygen concentrations in the lower reaches suggest available Gulf Sturgeon habitat may be seasonally limited. Therefore, maps of water microchemistry in the Pearl River watershed allow for retrospective analyses of fish watershed use.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
The incorporation of environmentally derived 87 Sr / 86 Sr and Sr/Ca in early otolith formation of Chinook salmon
Abstract Effective species management often requires understanding patterns of movement and habitat use. A common approach in identifying where individuals reside relies upon chemical tracers from the environment that are incorporated into an individual's tissues. For fish, isotopes in their otoliths, specifically the portion of their otolith formed during their larval stage, have been used to identify the natal origin. Complicating this work, however, is the fact that during this life stage, there is a shift in the source of isotopes deposited onto the growing otolith from maternally to environmentally derived. The objective of this study was to identify the portion of the otolith representing this transition to environmentally derived isotopes so as to accurately investigate questions of natal origin for a threatened population of fall Chinook salmon ( Oncorhynchus tshawytscha ). We exposed developing larvae to four treatments that differed in terms of their water strontium isotope ratio ( 87 Sr/ 86 Sr) and used change‐point analysis of otolith 87 Sr/ 86 Sr and strontium to calcium ratio (Sr/Ca) to identify the otolith radius corresponding to the transition to environmentally derived isotopes. Our results indicated this transition occurred, on average, at 132 μm ( 87 Sr/ 86 Sr; ±50 μm standard deviation) and 127 μm (Sr/Ca; ±29 μm) from the otolith core, which corresponded to the developmental time between hatching and exogenous feeding. A substantial proportion of our otoliths (i.e., 61%) did not show convergence between otolith and water 87 Sr/ 86 Sr by the end of the 113‐day experiment, which was likely due to the dietary contribution of marine‐based feed. Therefore, we were unable to recommend an otolith radius to target for the purposes of reconstructing natal origin apart from being beyond approximately 130 μm.
Chittaro, Paul↗
Otolith 87 Sr / 86 Sr identifies natal origin, movement and life history of Burbot Lota lota in the Kootenai River following 45 years of impoundment
Abstract Hydropower has long been an effective form of renewable energy, but the development of the resource has negatively impacted fishes throughout the world. Formulating recovery plans to mitigate these effects requires a firm understanding of species‐specific provenance, life history and life stage habitat requirements. However, the importance of this information is often only recognised after a substantial population decline, when obtaining it becomes demographically challenging. We provide a case study for this scenario and present a post hoc approach to gain insight into these critical data gaps for Burbot Lota lota in the upper Kootenai River in Montana and British Columbia. The population once supported a robust tribal and recreational harvest but declined following impoundment and these fisheries have remained closed or curtailed for nearly 20 years. The reasons for the decline are unknown and actions to assist recovery have been constrained by limited information regarding natal origin, life history and habitat use. We addressed this issue using strontium isotope ratios ( 87 Sr/ 86 Sr) in otoliths collected over four decades in Lake Koocanusa, the reservoir on the Kootenai River above Libby Dam. Due to the geologic heterogeneity of the basin and resulting variation in water 87 Sr/ 86 Sr, the assignment probability for Burbot to their region of natal origin approached unity. Otolith 87 Sr/ 86 Sr also indicated the population was comprised of mainstem‐ and tributary‐origin forms and their relative abundance changed over time. Mainstem Burbot was most abundant during the 1970s and 2000s, whereas tributary forms dominated between these periods. We suggest ecosystem changes following impoundment contributed to this shift in life history forms and the overall decline of the population. Our findings underscore the need for additional investigations of these impacts to guide restoration efforts.
Dunnigan, James L.↗
Geographic source attribution of honey by strontium isotope analyses: Latvia and India measurements compared to model predictions in a feasibility study
Strontium isotope ratios ( 87 Sr/ 86 Sr) can be used to determine the geographic origin of agricultural products. Here, in this study, we measured the 87 Sr/ 86 Sr of honey samples from Richland, WA, USA, Latvia, and India, and compared the results to published 87 Sr/ 86 Sr from surrounding areas and values predicted based upon a random forest isoscape model (Bataille et al., 2020). While the 87 Sr/ 86 Sr of the honey samples compared well with previously published data, the model did not accurately predict the 87 Sr/ 86 Sr of the honey samples, demonstrating that further refinement of the model would be beneficial. Because Sr cycling in terrestrial ecosystems is complex, the 87 Sr/ 86 Sr of honey is likely to reflect several sources (e.g., nectar, surface water, dust) and may change over time. In order to accurately predict the 87 Sr/ 86 Sr of honey, models must consider local geology, ecology, and bee behavior. Additional research examining how Sr is incorporated into honey is needed to inform models.
60 APPLIED LIFE SCIENCES↗
A dendritic strontium river isoscape for fisheries applications in the Sacramento River basin, California, USA
Objective Understanding the origins and movements of fish is fundamental to effective conservation and fisheries management. Strontium isotope ratios ( 87 Sr/ 86 Sr) in otoliths provide a powerful tracer of natal origin and migratory pathways. However, existing 87 Sr/ 86 Sr isoscapes for the Sacramento River basin, an ecosystem that supports ecologically and economically important salmon populations, rely on discrete classification approaches that overlook unsampled habitats and do not incorporate spatial uncertainty. Our objective was to develop a continuous, network-explicit 87 Sr/ 86 Sr isoscape with quantified uncertainty to fill in data gaps and enable probabilistic assignments of fish origin and movement. Methods We used river water 87 Sr/ 86 Sr data from 106 sites (1997–2021) to develop spatial stream network models that use dendritic connectivity and watershed characteristics (lithology, bedrock age, and land cover) to predict river water 87 Sr/ 86 Sr throughout the basin. Models were fitted using maximum and restricted likelihood and were evaluated via Akaike’s information criterion and leave-one-out cross validation. We produced both historical (pre-dam) and present-day (below-dam) isoscapes, delineated uncertainty-informed isotopic ranges using k -means clustering, and applied a proof-of-concept Bayesian assignment to estimate natal origins and early rearing habitats for two endangered winter-run Chinook Salmon Oncorhynchus tshawytscha. Results Cross validation indicated strong performance of the 87 Sr/ 86 Sr model (leave-one-out cross validation: R 2 = 0.91; root mean square error = 0.0005). Uncertainty-informed clustering identified 19 isotopic “suites” (reaches with indistinguishable 87 Sr/ 86 Sr values) in present-day anadromous habitats and 25 suites in the historical network. Example natal and early rearing assignments included predictions that challenged expectations for juvenile salmon migration based on predicted river 87 Sr/ 86 Sr compositions. Conclusions This study developed a continuous, network-explicit 87 Sr/ 86 Sr isoscape that integrates existing river data to predict 87 Sr/ 86 Sr in unsampled reaches and the likely achievable range and resolution of otolith-based origin and life history inference. The resulting river isoscape provides a valuable tool to predict salmon movements and identify habitats supporting their survival and growth that otherwise might remain undetected. Coupling these predictions with complementary approaches that ground-truth juvenile presence (e.g., targeted fish surveys) represents an important step toward science-informed restoration and management of critical habitats throughout the Sacramento River basin.
Environmental sciences↗