Strontium Isotope Analysis Research Articles

Residential Mobility and Dental Decoration in Early Medieval Spain: Results from the Eighth Century Site of Plaza del Castillo, Pamplona

Excavations at Plaza del Castillo in Pamplona (northern Spain) revealed a large Islamic necropolis dating to the eighth century A.D., including the skeleton of an adult female showing intentional dental modification (PLA-159). While the practice of dental decoration was virtually absent in Medieval Spain, it is common in Africa and suggests that this individual was born in Africa and brought to Spain later in life. The historically documented occupation of Pamplona by Muslim groups from northern Africa between ca. 715 and 799 A.D. also supports an African origin. As an additional line of evidence, we investigated the geographic origins of two individuals from the cemetery, including PLA-159, via radiogenic strontium and stable oxygen isotope analyses on enamel hydroxyapatite. The human isotopic signatures were measured following established methodologies and compared to the local geochemical composition and modern precipitation values. The data analysis showed a non-local isotopic signature for both individuals, suggesting that they moved to Pamplona following childhood, probably from northern Africa, during the Islamization of the city. Stable carbon isotope analysis revealed a diet heavily based on C3 terrestrial plants. Overall, this preliminary data set exemplifies the use of biogeochemistry as an analytical tool, and provides unique insight about the diffusion of Muslim groups into the Early Medieval Iberian Peninsula.

Case studies on the utility of sequential carbonate leaching for radiogenic strontium isotope analysis

Radiogenic strontium isotopes (87Sr/86Sr) have been extensively used as a tool to explore a diversity of Earth system problems, including long-term global weathering rates and global sequence correlation. Strontium isotopes are measured on a range of geological materials (e.g., calcite fossils, barites, limestone micrites), but whole-rock limestones are by far the most abundant of these materials within the geological record for paleo-seawater 87Sr/86Sr work. Whole-rock limestones, however, have a poor track record of recording primary seawater 87Sr/86Sr values. Alteration of the limestone during diagenesis and contamination from detrital aluminosilicate phases during carbonate extraction have been consistent problems. Various preparation and quality control methods have been applied to whole-rock 87Sr/86Sr work, yet there remains no consistent framework used to separate and identify both contamination and alteration simultaneously. The lack of consistent and systematic methods has made it difficult to gauge the accuracy and fidelity of much of the previously generated whole rock limestones 87Sr/86Sr data, especially for Precambrian sequences. Building on previous work, we explore a sequential leaching method designed to systematically isolate least-altered carbonate phases from detrital aluminosilicate Sr contamination and present several case studies that demonstrate the advantages of this approach. In the first case study, we use the Mid-Carboniferous Bird Spring Formation to empirically validate the accuracy of this sequential leaching method. Comparing least-altered sequentially leached whole-rock 87Sr/86Sr values with well-preserved calcite brachiopod 87Sr/86Sr values from the same section, we find near identical values. Following this first case, we studied the Neoproterozoic Dhaiqa Formation and the mid-Proterozoic Jixian Group and Muskwa Assemblage to outline a framework for identifying least-altered leachate fractions in Proterozoic carbonate samples. As a whole, we find that with this method it is possible to better identify whole-rock samples primary or least-altered carbonate fractions, and better account for alteration, providing a means to back-calculate a samples primary and least-altered marine 87Sr/86Sr value.

Isotopic Evidence for Landscape use and the Role of Causewayed Enclosures During the Earlier Neolithic in Southern Britain

The nature of landscape use and residence patterns during the British earlier Neolithic has often been debated. Here we use strontium and oxygen isotope analysis of tooth enamel, from individuals buried at the Hambledon Hill causewayed enclosure monument complex in Dorset, England to evaluate patterns of landscape use during the earlier Neolithic. Previous analysis suggests that a significant proportion of the artefacts found at the site may originate from lithology of Eocene and Upper to Middle Jurassic age that the enclosures overlook to the immediate west and south. The excavators therefore argued that the sector of landscape visible from Hambledon Hill provides an approximate index for the catchment occupied by the communities that it served. Most of the burial population exhibit isotope ratios that could be consistent with this argument. Connections between Hambledon Hill and regions much further afield are also hypothesised, based on the presence of artefacts within the assemblage that could have been sourced from lithology in Somerset, Devon, and Cornwall in south-west England. However, few of the sampled individuals have strontium isotope ratios consistent with having obtained the majority of their diet from such areas during childhood. The individuals who exhibit the highest strontium isotope ratios are all adult males, whom the excavators suggest to have died during one or more episodes of conflict, following the burning and destruction of surrounding defensive outworks built during the 36th centurybc. At least one of these individuals, who was found with an arrowhead amongst his ribs, did not obtain his childhood diet locally and has87Sr/86Sr values that could be comparable to those bioavailable in the south-west peninsula.

Strontium isotope analysis on cremated human remains from Stonehenge support links with west Wales

Cremated human remains from Stonehenge provide direct evidence on the life of those few select individuals buried at this iconic Neolithic monument. The practice of cremation has, however, precluded the application of strontium isotope analysis of tooth enamel as the standard chemical approach to study their origin. New developments in strontium isotopic analysis of cremated bone reveal that at least 10 of the 25 cremated individuals analysed did not spend their lives on the Wessex chalk on which the monument is found. Combined with the archaeological evidence, we suggest that their most plausible origin lies in west Wales, the source of the bluestones erected in the early stage of the monument’s construction. These results emphasise the importance of inter-regional connections involving the movement of both materials and people in the construction and use of Stonehenge.

Water uncertainty, ritual predictability and agricultural canals at Chaco Canyon, New Mexico

The Pueblo population of Chaco Canyon during the Bonito Phase (AD 800–1130) employed agricultural strategies and water-management systems to enhance food cultivation in this unpredictable environment. Scepticism concerning the timing and effectiveness of this system, however, remains common. Using optically stimulated luminescence dating of sediments and LiDAR imaging, the authors located Bonito Phase canal features at the far west end of the canyon. Additional ED-XRF and strontium isotope (87Sr/86Sr) analyses confirm the diversion of waters from multiple sources during Chaco’s occupation. The extent of this water-management system raises new questions about social organisation and the role of ritual in facilitating responses to environmental unpredictability.

Social differences in Neolithic/Bronze Age Myanmar: 87Sr/86Sr in skeletal remains from Oakaie 1 and Nyaung'gan

Here we begin to investigate prehistoric kinship and social differentiation in ancient Myanmar, through analyses of strontium isotopes in human tooth samples from excavated skeletal remains of 18 individuals from the archaeological sites of Oakaie 1 and Nyaung'gan, in Sagaing Division, central Myanmar. The archaeological deposits at these sites span the Late Neolithic and Early Bronze Age (approximately 12th to 8th c. BCE). These isotopic data are interpreted in association with bioarchaeological, material culture and stratigraphic data. These preliminary results suggest a differentiation in mean strontium signatures between the sites, which are <3 km apart, but with sex-based patterns within the sites. This indicates kinship was a strong organizing principle, with little long-distance migration, despite apparently considerable long-distance exchange networks active by the early Bronze Age in Myanmar.

Strontium isotope evidence for human mobility in the Neolithic of northern Greece

Strontium isotope ratios are widely used in archaeology to differentiate between local and non-local populations. Herein, strontium isotope ratios of 36 human tooth enamels from seven archaeological sites spanning the Early to Late Neolithic of northern Greece (7th–5th millennia B.C.E.) were analysed with the aim of providing new information relating to the movement of humans across the region. Local bioavailable 87Sr/86Sr signals were established using tooth enamel from 26 domestic animals from the same Neolithic sites. 87Sr/86Sr values of faunal enamel correlate well with predicted strontium isotope ratios of the local geology. This is consistent with animal management occurring at a local level, although at Late Neolithic sites strontium isotope values became more varied, potentially indicating changing herding practices. The strontium isotope analysis of human tooth enamel likewise suggests limited population movement within the Neolithic of northern Greece. Almost all individuals sampled exhibited 87Sr/86Sr values consistent with having spent their early life (during the period of tooth mineralisation) in the local area, although movement could have occurred between isotopically homogeneous areas. The strontium isotope ratios of only three individuals lay outside of the local bioavailable 87Sr/86Sr range and these individuals are interpreted as having spent their early lives in a region with a more radiogenic biologically available 87Sr/86Sr. Mobility patterns determined using Sr isotope analysis supports the current evidence for movement and exchange observed through studies of pottery circulation. Suggesting limited movement in the Early and Middle Neolithic and greater movement in the Late Neolithic.

Provenance analysis of human cremations by 87Sr/86Sr isotopic ratios: migration into an Iron Age mining region in North-Rhine Westphalia

The Siegerland (North-Rhine Westphalia, FRG) is famous for its early mining industry and ore exploitation. The archaeological context of cremated burials as well as grave goods indicate parallels to today's Wetterau (Hesse), suggesting migration into the Siegerland. After morphological examination of the cremations augmented by a histological age-at-death determination, provenance analysis by use of stable strontium isotope analysis was carried out. 60 individuals from the burial mound at Netphen-Deuz in the Siegerland were available for anthropological examination. The 87Sr/86Sr isotopic ratio was measured in 29 dentine and 15 bone samples. At least 19 individuals exhibited a non-local isotopic signal which was compatible with a provenance from the Wetterau region. Since 87Sr/86Sr isotopic ratios in the bioapatite are thermally stable, provenance analysis of cremated finds is thus possible, whereby a testable archaeological hypothesis is prerequisite. Histological examination of cremated bones proved indispensable for the age-at-death estimation.

Revisiting the potential of carbonized grain to preserve biogenic 87Sr/86Sr signatures within the burial environment

Strontium (Sr) isotope analysis of archaeological crops is a potential method of provenancing and identifying the movement of crops in the past, but there remains uncertainty about whether original 87Sr/86Sr values can be obtained from carbonized buried grains. We have determined that hydrochloric acid (HCl) leaching removes some, but not all, exogenous Sr from carbonized cereal grains buried in soil for up to one year. We conclude that while further work could refine the leaching method, Sr isotope analysis of archaeological cereal grains can distinguish crops sourced from outside a particular (e.g., local) area if it can be shown that leaching moves grain 87Sr/86Sr values significantly away from the expected Sr signature.

The llama's share: Highland origins of camelids during the Late Paracas period (370 to 200 BCE) in south Peru demonstrated by strontium isotope analysis

This article contributes to the debate on the habitat of “New World” camelids in pre-Colonial South America and provides new insights into the breeding and herding strategies developed by Andean societies. The case discussed here refers to the Late Paracas period (370 to 200 BCE) in the Palpa valleys of the western Andes in south Peru. Tooth enamel, which is formed only in the first years of life in mammals such as camelids, from 30 camelid individuals is examined through strontium isotope analysis. The camelid remains were excavated by the Palpa Archaeological Project (PAP) at the Paracas sites of Jauranga, Collanco, and Cutamalla, which are situated at distinct ecological levels. The data displays similar isotopic signatures for Jauranga on the coast, Collanco in the western yunga, and Cutamalla in the highlands. These results largely correspond with strontium isotope compositions for the highland of the Ayacucho region in the research area, as proved by recent environmental and archaeological reference samples. Therefore, it is assumed that the camelids utilized by Paracas people originated in highland areas, where the rearing of the animals took place. However, the possibility that a limited portion of camelids were raised in ecosystems at lower altitudes, including the coast, is not excluded. The results also indicate major exchange and mobility of camelids, camelid commodities, and other products that were transported along the western slopes of the Andes, to a great extent with the help of camelids as pack animals in caravans. Finally, our case study demonstrates the variety of camelid husbandry practices in pre-Hispanic South America.

Multi-isotope evidence for cattle droving at Roman Worcester

Tooth enamel from six cattle mandibles excavated from Roman deposits at The Hive development site, Worcester (mid-2nd to early 4th century AD) was subjected to strontium, oxygen and carbon isotope analyses (87Sr/86Sr, δ18O and δ13C) to investigate the movement of cattle into Worcester, a purported regional cattle market, during the Roman period. Strontium isotope ratios show that none of the cattle were born and bred in close proximity to Worcester and arrived as mature beasts some time before death. Whilst two are consistent with origins in the region of Old Red Sandstone of Herefordshire to the west, the unusually high strontium isotope ratios of four of the cattle (i.e. >0.714) show that they originated in a region of ancient or radiogenic rocks such as granites which are found only in the west and north of Britain (e.g. Wales, the Lake District and northern Scotland) based on the currently available biosphere data. Comparison of the oxygen and carbon isotope values also suggests that the cattle were not from the same herd, but interpretation is complicated by the lack of comparative cattle data for the Roman period as well as other time periods. The severe wear of the molars from the aged cattle in this study also limits the interpretation of the results. More isotopic analyses are needed from other British sites in order to fully understand the implications of cattle movement into urban centres during the Roman period.

Diet and mobility of fauna from Late Neolithic–Chalcolithic site of Perdigões, Portugal

Perdigões is located in the Alentejo region of south-eastern Portugal, with occupational phases dating from the Late Middle Neolithic to Late Chalcolithic/Early Bronze Age (middle 4th and 3rd millennium BCE) periods. It is a complex site that can be considered as a centre of social aggregation and a part of a larger settlement network. In this study, the nature of animal subsistence patterns as well as husbandry management practices and mobility are examined using stable carbon and nitrogen isotopic values from bone collagen of 35 archaeological faunal samples (Canis familiaris, Bos taurus, Bos primigenius, Sus sp., Ovis/Capra, Cervus elaphus, O. cuniculus, Equus sp.) and strontium isotope (87Sr/86Sr) analysis of 23 enamel samples. To provide necessary biological 87Sr/86Sr baseline data, the strontium isotopic composition of 14 modern plant samples were measured. The stable carbon and nitrogen isotope data shows that animals subsisted on a selection of C3 terrestrial resources, with subtle differences in animal husbandry practices in domesticated animals, while strontium isotope analysis shows that <5% of analysed fauna is consistent with the local bioavailable strontium isotopic range. Other animals can be divided into two clusters – those having strontium isotope values either lower or higher than the bioavailable range, showing that most of the fauna browsed and grazed within 10 km of the site's surrounding landscape, which is not such an unusual practice during prehistoric times.

Isotopic analysis of burials from the early Anglo-Saxon cemetery at Eastbourne, Sussex, U.K.

The transition from Roman Britain to early Anglo-Saxon England, traditionally described as the Adventus Saxonum and associated with a large-scale invasion by Germanic peoples, has been the subject of much debate. The archaeological record does not support a replacement of the local Romano-British population with Germanic incomers, and alternative explanations for the transition argue for a much smaller contribution of Germanic immigrants. As a contribution to this debate and to address the question of the number of immigrants, we have applied strontium and oxygen isotope analysis to study residential mobility in a sample of 19 individuals from the early Anglo-Saxon cemetery at Eastbourne, Sussex, on the southern English coast. Local variation in bio-available strontium isotope ratios was established by sampling soils from different geological substrates within 19 km of the cemetery and from a small sample of domestic animals recovered from the graves. Four individuals are likely continental immigrants, three others could be, but could also originate elsewhere in the British Isles, and two women are likely immigrants from nearby communities. The identified immigrants at Eastbourne show a temporal spread and lack of wealth expressed as grave goods. This pattern is not consistent with simple models of mass invasion, elite takeover or acculturation. Our results, together with other recent findings, imply that the Adventus Saxonum involved diverse migratory and demographic processes.

THE ORIGINS OF TRADESCANT’S ‘INDIA OCCIDENTALI’ WOODEN CLUBS:14C DATING, MATERIAL IDENTIFICATION AND STRONTIUM ISOTOPE STUDIES

This paper focuses on the material study (radiocarbon dating, wood identification and strontium isotope analyses) of four large ‘India occidentali’ clubs, part of the founding collections of the Ashmolean Museum, in Oxford, and originally part of John Tradescant’s ‘Ark’, in Lambeth (1656). During the seventeenth century, the term ‘India occidentali/occidentales’ referred not only to the ‘West Indies’ (its literal translation), but to the Americas as a whole; hence, the Ashmolean clubs and, indeed, thecforty examples of similarly large, decorated clubs known in international museum collections had no firm provenance and lacked even the most basic information. Previous attempts at attribution, based on stylistic comparisons with nineteenth- to twentieth-century Brazilian and Guyanese clubs, have proved inconclusive given the unique features of this club style, raising the intriguing possibility that these may be exceptionally rare examples of ‘Island Carib’ (Kalinago) material culture, particularly as images of such clubs appear in seventeenth-century ethnographic accounts from the Lesser Antilles. This paper provides new data for these poorly known objects from early collections, revealing not only the type of wood from which they were carved (Platymisciumsp. andBrosimumcfguianense) and their probable dates of manufacture (c AD1300–1640), but also their possible provenance (strontium results are consistent with a possible range from Trinidad south to French Guiana).

Amorphous glass fragments from archaeological surface surveys: Potential chronological use of ion beam and isotopic analytical characterization

Analytical techniques have been used to implement the archaeological information from surface surveys. We have shown that the compositional comparison of amorphous samples, e.g. glass, can provide important chronological information when compared with findings from other sites. A group of 61 glass fragments, recovered from an archaeological surface survey at the site of the Roman city of Duratón (1st to 3rd century AD), near Segovia, Spain, have been analysed by combined Particle Induced X-ray/Gamma-ray Emission (PIXE-PIGE) techniques and by isotope dilution mass spectrometry. Four groups of objects were identified. The largest group by far, corresponds to the typical sodium-rich natron-made Roman glass. Compared with data reported in previous studies, including a few on the Iberian Peninsula, the composition of Duratón natron glass is similar to that of the widespread Roman 1st–3rd century AD glasses. The glasses of the nearby Patones, six of which have been analysed in this study, belong, on the contrary, to the so-called HIMT glass. This is compatible with the soda-lime-silica glass pattern observed in the Western Mediterranean. HIMT glass is dominant in this area from the 4th century onward. HIMT glass products are much easier to make and less expensive. Strontium and neodimium isotope analysis confirms the compositional proximity of the Duratón glasses to three groups of 1st–3rd century samples from Barcino, Lyon and the Iulia Felix wreck and point to a production of the glass in the Eastern Mediterranean. Pliny the Elder in his Naturalis Historia had specifically mentioned the glass production of Hispania and Gallia, which should hopefully be confirmed by the findings in the corresponding regional sites. This is the case for Gallia but not yet for the Iberian Peninsula, where few Roman glass analyses have been completed.

Unravelling biocultural population structure in 4th/3rd century BC Monterenzio Vecchio (Bologna, Italy) through a comparative analysis of strontium isotopes, non-metric dental evidence, and funerary practices.

The 4th century BC marks the main entrance of Celtic populations in northern Italy. Their arrival has been suggested based on the presence of Celtic customs in Etruscan mortuary contexts, yet up to now few bioarchaeological data have been examined to support or reject the arrival of these newcomers. Here we use strontium isotopes, non-metric dental traits and funerary patterns to unravel the biocultural structure of the necropolis of Monterenzio Vecchio (Bologna, Italy). Subsamples of our total sample of 38 individuals were analyzed based on different criteria characterizing the following analyses: 1) strontium isotope analysis to investigate migratory patterns and provenance; 2) non-metric dental traits to establish biological relationships between Monterenzio Vecchio, 13 Italian Iron age necropolises and three continental and non-continental Celtic necropolises; 3) grave goods which were statistically explored to detect possible patterns of cultural variability. The strontium isotopes results indicate the presence of local and non-local individuals, with some revealing patterns of mobility. The dental morphology reveals an affinity between Monterenzio Vecchio and Iron Age Italian samples. However, when the Monterenzio Vecchio sample is separated by isotopic results into locals and non-locals, the latter share affinity with the sample of non-continental Celts from Yorkshire (UK). Moreover, systematic analyses demonstrate that ethnic background does not retain measurable impact on the distribution of funerary elements. Our results confirm the migration of Celtic populations in Monterenzio as archaeologically hypothesized on the basis of the grave goods, followed by a high degree of cultural admixture between exogenous and endogenous traits. This contribution shows that combining different methods offers a more comprehensive perspective for the exploration of biocultural processes in past and present populations.

Earliest isotopic evidence in the Maya region for animal management and long-distance trade at the site of Ceibal, Guatemala

This study uses a multiisotope (carbon, nitrogen, oxygen, and strontium) approach to examine early animal management in the Maya region. An analysis of faunal specimens across almost 2,000 years (1000 BC to AD 950) at the site of Ceibal, Guatemala, reveals the earliest evidence for live-traded dogs and possible captive-reared taxa in the Americas. These animals may have been procured for ceremonial functions based on their location in the monumental site core, suggesting that animal management and trade began in the Maya area to promote special events, activities that were critical in the development of state society. Isotopic evidence for animal captivity at Ceibal reveals that animal management played a greater role in Maya communities than previously believed.

The Effects of Differences in Vegetation on Calcium Dynamics in Headwater Streams

Although organisms can alter dynamics of elements in ecosystems via physiological results, the effects of tree species on ecosystem nutrient dynamics are highly uncertain. A four-fold variation in the calcium concentrations of streams, soils and leaf litters were caused by the planting of Cryptomeria japonica in south-central Japan. In this study, we examined how the calcium dynamics were affected by the planting of C. japonica through strontium isotope analysis. We predicted the planting of C. japonica would result in the calcium concentration increasing because of the significant dissolution of calcium from bedrock. In a forest ecosystem, calcium is usually derived from precipitation and bedrock weathering, and their relative contributions can be estimated using a strontium isotope mixing model. Therefore, we collected stream water, litter, soil, precipitation and bedrock samples from 17 sites in catchments dominated by C. japonica plantation or evergreen broad-leaved forest; after collection, we analyzed the sample chemical compositions and strontium isotope ratios. The calcium concentrations in the stream water and the water-soluble calcium in the soil were significantly higher at sites dominated by C. japonica than at broad-leaved forest sites. Strontium isotope analysis indicated that there was more calcium from the bedrock present in stream water at sites dominated by C. japonica than in stream water at broad-leaved forest sites. Our results showed that watershed-scale dynamics of calcium and other cations can be altered by the type of vegetation in a catchment due to the effects of vegetation on the supply of calcium from bedrock.

What is left behind: Advancing interpretation of pastoral land-use in Harappan Gujarat using herbivore dung to examine biosphere strontium isotope (87Sr/86Sr) variation

The analysis of strontium isotopes in archaeologically preserved biological tissues is most productive when these can be compared to naturally occurring variation in strontium isotope ratios across the physical landscape. Such work is in its infancy in South Asia. Here, we report on the first attempt to monitor 87Sr/86Sr variation across the Indian state of Gujarat using herbivore dung. As it incorporates plant material from throughout an individual animal's grazing range, herbivore dung averages local isotopic variation in palatable vegetation and is therefore an ideal material for use in studies involving domestic livestock. In our analysis of 125 dung samples from 38 sampling locations across the study area, 87Sr/86Sr values and geographic variation are commensurate with expectations based on regional geology. The values that we report are significantly different from those reported for both ecosystem elements and archaeological humans and livestock that have been published for other regions of the Indus Civilization (2600–1900 BC). No individual humans or livestock in these studies appear to have their origins in Gujarat. The present study further allows for more detailed interpretations of our previously published study of strontium isotope ratios in faunal remains from the walled Indus manufacturing center of Bagasra in Gujarat (Chase et al., 2014b). Specifically, it is now clear that while most livestock show very little movement within the period of enamel formation, their places of origin were scattered throughout central Saurashtra, adjacent to the site, suggesting that a portion of the livestock consumed at Bagasra were initially raised in the many small unexcavated villages in the area. There is little evidence for the procurement of livestock from further afield within the region and none for livestock originating outside the region. These results demonstrate that monitoring geographic 87Sr/86Sr variation using herbivore dung has the potential to significantly advance archaeological interpretation of livestock mobility in the past and is applicable anywhere that modern livestock graze on natural vegetation.

Strontium isotope ratios of human hair record intra-city variations in tap water source

The oxygen (18O/16O) isotope analysis of hair is commonly applied to reconstruct an individual’s residence history. However, region-of-origin as determined from oxygen isotope values (δ18O) alone is often spatially indistinct. Adding additional geochemical recorders can refine region-of-origin estimates. In this capacity, strontium (87Sr/86Sr) isotope analysis has attracted increased interest. While 87Sr/86Sr reflects the influences of local geology, 87Sr/86Sr of hair includes both external environmental signals as well as the internal dietary indicators. To better understand the impact of these contributions to the spatial signal encoded within 87Sr/86Sr of hair, human hair was collected from three locations within Salt Lake City, Utah along with the donor’s sex. The 87Sr/86Sr and δ18O of hair and local tap water were measured. There were no significant relationships between sex and either δ18O or 87Sr/86Sr of hair, nor between collection location and the δ18O of hair. However, we found significant associations between collection location and 87Sr/86Sr of hair. These findings suggest that interactions with local water may be an important source of Sr to human hair and that the 87Sr/86Sr of hair may have the capacity to record differences in 87Sr/86Sr of tap waters on small spatial scales.