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Chapter 18. Tracing of Weathering Reactions and Water Flowpaths: A Multi-isotope Approach
Abstract
This chapter discusses the importance of using isotopes in a complementary manner, primarily to constrain and enrich models developed from hydrologic and chemical data. Isotopes are viewed as tools for testing rather than developing hypotheses, particularly in studies operating under tight budgetary constraints. Water isotopes are very useful tools for determining water sources in catchments. Chemical tracers are very useful for understanding the reactions along flowpaths. The potential application of Fe isotopes to catchment studies lies in the assumption that Fe mobilized inorganically from minerals under either reducing or low-pH conditions will have a different isotopic composition than microbially-reduced Fe. To the extent that certain zones or flowpaths in the catchment can be characterized by microbial cycling of labile Fe, the Fe isotopes may provide an effective tracer of contributions from these pathways. The solute isotopes, for example, strontium, carbon, and lead are as yet under-utilized in catchment research compared to the water isotopes.
... Le rapport isotopique du strontium 87 Sr/ 86 Sr est un traceur utile pour distinguer les sources de Sr car il n'est pas significativement affecté ou fractionné par des processus naturels tels que la séparation de phases, la spéciation chimique, l'évaporation ou les processus biologiques (Bullen et al., 1996;Bullen and Kendall, 1998;Rachold et al., 1997). Ainsi, chaque compartiment de la zone critique sont marqués par une signature des ratios isotopiques du Sr spécifique. ...
... It is tightly linked to water flow, which 44 brings reactive species from the surface to the subsurface and sustains chemical disequilibrium 45 by removing products of dissolution (Maher, 2011;Maher and Druhan, 2014). As a result, 46 hydrologic processes and particularly fluid residence times exert a major control on chemical 47 weathering rates (Mulholland and Hill, 1997;Bullen and Kendall, 1998;Shand et al., 2007;48 Peters and Aulenbach, 2009;Jin et al., 2011). 49 ...
... 107 We characterized the evolution of water chemistry along the river by analysing major cations 116 and anions, dissolved silica concentrations and the isotopic ratio of strontium 86 Sr / 87 Sr. The 117 latter is a useful tracer to distinguish between sources of Sr since it is not significantly affected 118 or fractionated by natural processes such as phase separation, chemical speciation, evaporation, 119 or biological processes (Bullen et al., 1996;Rachold et al., 1997;Bullen and Kendall, 1998). (Figure 1, a.). ...
Les réactions chimiques souterraines jouent un rôle crucial dans la dynamique de la zone critique. La cinétique des réactions chimique est généralement déterminée à partir d’expériences dans un milieu homogène. Pourtant, le milieu naturel est caractérisé par des gradients chimiques multi-échelles qui pourraient avoir des conséquences majeures sur l’efficacité des réactions. Cette thèse porte donc sur l’origine, la dynamique et les conséquences des gradients chimiques sur les réactions. Dans un premier temps, nous développons une approche pluridisciplinaire pour comprendre les mécanismes à l’origine d’un fort gradient géochimique observé le long d’une rivière au niveau d’une rupture topographique sur un bassin versant instrumenté en Guadeloupe (SNO OBSERA, OZCAR). Des mesures géophysiques, hydrologiques et géochimiques sont couplées avec un modèle hydrogéologique représentant les circulations profondes et l’altération des roches. Notre étude montre que l’altération active est limitée aux zones d’intersection des flux descendants et du front d’altération. La zone d’export est localisée dans les zones de convergence des flux ascendants. Dans un deuxième temps, nous menons une étude théorique et numérique sur l’effet de l’évolution temporelle des gradients chimiques par diffusion sur la cinétique effective d’une réaction non-linéaire. Nous démontrons que la dynamique spatio-temporelle des gradients chimiques entraine des lois de cinétique effectives jusqu’à plusieurs ordres de grandeur supérieures ou inférieures aux cinétiques déterminées en milieu homogène, en fonction de l’ordre de la réaction. Une théorie analytique des cinétiques effectives est validée par des simulations numériques. Ces travaux offrent de nouvelles perspectives pour observer et comprendre l’origine des gradients chimiques souterrains, et modéliser leurs effets sur les dynamiques réactives de la zone critique, par l’apport de nouveaux concepts de transport réactif.
... Isótopos estáveis também têm sido empregados em estudos de contaminação de fluoreto na água subterrânea, como é o caso dos trabalhos realizados por Datta et al. (1996), com isótopos de oxigênio, Travi & Chernet (1998), com isótopos de oxigênio, hidrogênio e carbono, e Tirumalesh et al. (2007), com isótopos de oxigênio e hidrogênio. Os isótopos de estrôncio, por sua vez, são em geral empregados como traçadores da interação entre água e arcabouço geológico (Bierman et al. 1998, Bullen & Kendall 1998, Frost & Toner 2004, embora haja trabalhos em que isótopos de estrôncio são usados como traçadores de contaminação antrópica (Capo et al. 1998, Vilomet et al. 2001. Assim, ambos os sistemas isotópicos -radiogênico e estávelfornecem informações importantes e complementares para estudos hidrogeológicos (Bullen & Kendall 1998, Banner 2004. ...
... Os isótopos de estrôncio, por sua vez, são em geral empregados como traçadores da interação entre água e arcabouço geológico (Bierman et al. 1998, Bullen & Kendall 1998, Frost & Toner 2004, embora haja trabalhos em que isótopos de estrôncio são usados como traçadores de contaminação antrópica (Capo et al. 1998, Vilomet et al. 2001. Assim, ambos os sistemas isotópicos -radiogênico e estávelfornecem informações importantes e complementares para estudos hidrogeológicos (Bullen & Kendall 1998, Banner 2004. Tal relação é bem exemplificada pelo trabalho de Petelet-Giraud et al. (2007), que investigaram a contaminação de um aqüífero em uma área fortemente industrializada na Alemanha: as razões isotópicas de hidrogênio e oxigênio foram importantes para determinar distintas fontes de água, inclusive misturas de águas; enquanto as de estrôncio foram essenciais na identificação das águas contaminadas. ...
... Desse modo, a composição isotópica da água subterrânea tende a refletir a dos minerais solúveis capazes de realizar trocas químicas com a água (Voerkelius, no prelo). Em solução, o estrôncio comporta-se de maneira semelhante ao cálcio (Bullen & Kendall 1998). ...
... Strontium isotopes ( 87 Sr/ 86 Sr ratios) have been widely used for provenance analysis because they cannot be significantly affected by many natural processes, such as chemical speciation, phase separation, biological assimilation, water evaporation or diagenesis (Bullen & Kendall, 1998;Gierlowski-Kordesch et al., 2008;Smith et al., 2009). 87 Sr in natural environments is mainly sourced from the radioactive beta decay of 87 Rb and element Rb has a high affinity with element K; consequently, K-bearing siliciclastic materials (such as K-feldspar and illite) contain much more 87 Sr than carbonates and evaporites. ...
... 87 Sr in natural environments is mainly sourced from the radioactive beta decay of 87 Rb and element Rb has a high affinity with element K; consequently, K-bearing siliciclastic materials (such as K-feldspar and illite) contain much more 87 Sr than carbonates and evaporites. Therefore, for mixed sediments accumulating in lakes, the 87 Sr/ 86 Sr ratios are controlled by the relative proportions of allogenic siliciclastic materials to authigenic carbonate and evaporite materials (Bullen & Kendall, 1998). Siliciclastic rocks, such as mudstone, siltstone and sandstone, represent the allogenic endmember of lake deposition. ...
Palustrine‐lacustrine carbonates of the well‐dated Xichagou section (ca. 43 to ca. 13 Ma) next to the active Altyn Tagh Fault (ATF) are investigated in terms of abundance, lithofacies, strontium, carbon and oxygen isotopes, to differentiate tectonic and climatic controls on the evolution of intermontane lakes in the Tibetan Plateau. Volumetrically dominant siliciclastic strata document five depositional stages: mid‐Eocene alluvial fan (onshore), late Eocene fan delta (nearshore), Oligocene semi‐deep lake (offshore), early Miocene braided fluvial delta (nearshore) and mid‐Miocene fluvial plain (onshore). Carbonates are most abundant in the middle three lacustrine stages and contain various lithofacies, including calcretes, microbialites, grainstones and marlstones. Oxygen isotopes show two positive excursions (−1.17‰ and −2.59‰) at the first nearshore and late offshore stages, indicating two relatively saline stages linked to the Eocene and late Oligocene global warming climates. Carbon isotopes show a positive excursion (from −4.0‰ to +2.9‰) at the middle semi‐deep lake stage and meanwhile strontium isotopes of carbonates show a large negative excursion (from 0.7120‰ to 0.7113‰), both in response to the early Oligocene global humid and cooling climate and resultant lake expansion at the Qaidam Basin. Except for this lake expansion event, the first‐order lake transgressing, shallowing and regressing evolution at the Xichagou section were not consistent with Cenozoic global climatic change trends. Instead, the two‐stage strike‐slip faulting of the ATF probably induced the northeastward and eastward migration of basin depocenter and resulted in the lake transgression‐regression at the Xichagou section. The widespread presence and relatively minor variation in oxygen isotopes (from −7.5‰ to −7.0‰) of early Miocene microbialites in the northern Tibetan Plateau suggest a warm climate and a low relief before ca. 15 Ma.
... Only 204 Pb is not a radiogenic isotope. Therefore, the variability of lead isotopic ratios in rocks is far higher than for 87 Sr/ 86 Sr (Bullen and Kendall 1998). Just as in the case of 87 Sr/ 86 Sr, stationary and bioavailable lead and its respective isotopic ratios need to be distinguished from each other. ...
... Consequently, the assessment of a typical "local" stable lead isotopic ratio is much more difficult. In addition to the lithological sources, the atmospheric introduction of lead into a certain catchment area is also of crucial importance (Bullen and Kendall 1998). While such airborne lead is concentrated in the topsoil layers, lead and its respective isotopic ratios in groundwater are largely a function of rock weathering. ...
The term “isotopic landscape” or “isoscape” is used to indicate a map depicting isotopic variation in the environment. The spatial distribution of isotopic ratios in environmental samples is an indispensable prerequisite for generating an isotopic landscape yet represents more than simply an assessment of this distribution. An isotopic landscape also includes the fundamental parameters of prediction and modelling, thus providing estimated isotopic signatures at sites for which no values are known. When calibrated, such models are very helpful in assessing the origin of geological and biological materials. Reconstructing the place of origin of primarily non-local archaeological finds is a major topic in bioarchaeology because it gives clues to major driving forces for population development through time such as mobility, migration, and trade. These are fundamental aspects of the past human behaviour. For decades, stable isotope analysis has been the method of choice, but still has its limitations. Bioarchaeological sciences have adopted “isoscapes” mainly as a term, but not as a contextual concept. This chapter briefly introduces the research substrate of bioarchaeology, which mainly consists of human and animal skeletal finds, provides a concise overview of selected stable isotopic ratios in these remains, and explains their research potential for migration research. State of the art in bioarchaeology, including efforts towards the generation of predictive models, is discussed within the framework of existing isotopic maps and landscapes relevant to bioarchaeology. The persisting challenges in this field of research, which gave rise to research efforts summarized in this book, are also addressed.
... Strontium is known to have a hydrogeochemical behavior similar to that of calcium (McNutt, 2000). It occurs in nature as positively charged solutes, and is therefore affected by cationic exchange processes (Bullen and Kendal, 1998;Fidelibus, 2003;Faure and Mensing, 2005). In addition, the 87 Sr and 86 Sr isotope ratio is not affected by fractionation processes, because of their minor difference in atomic weight (Ingraham et al., 1998). ...
... According to Bullen and Kendal (1998), an equilibrium between the dissolved strontium and the strontium present in the exchange pool may be achieved given enough time. Under this scenario, the strontium available in the exchange pool has the same isotopic composition as that in the dissolved phase due to negligible fractionation processes in strontium geochemistry. ...
The La Paz aquifer system (Baja California Sur, Mexico) is under severe anthropogenic pressure because of high groundwater abstraction for urban supply (city of La Paz, around 222,000 inhabitants) and irrigated agriculture (1900ha). In consequence, seawater has infiltrated the aquifer, forcing the abandonment of wells with increased salinity. The objective of this study was to assess seawater intrusion, understand the hydrogeochemical processes involved and estimate the contribution of seawater in the wells tested. The aquifer comprises mainly the alluvial filling and marine sediments of a tectonic graben oriented north-south, in contact with the Gulf of California. Groundwater samples were collected in 47 locations and analyzed for major constituents. A subset of 23 samples was analyzed for strontium and boron concentrations and isotopic signatures (⁸⁷Sr/⁸⁶Sr and δ¹¹B). Results were interpreted using standard hydrochemical plots along with ad hoc plots including isotopic data. Seawater intrusion was confirmed by several hydrogeochemical indicators, such as the high salinity in areas of intense pumping or the Na⁺-Ca²⁺ exchange occurring in sediments that were previously in chemical equilibrium with fresh water. However, seawater contribution was not sufficient to explain the observed concentrations and isotopic signatures of Sr and B. According to the isotopic data, desorption processes triggered by a modification in chemical equilibrium and an increase in ionic strength by seawater intrusion significantly increased Sr and probably B concentrations in groundwater. From a calculation of seawater contribution to the wells, it was estimated that one-third of the sampled abstraction wells were significantly affected by seawater intrusion, reaching concentrations that would limit their use for human supply or even irrigated agriculture. In addition, significant agricultural pollution (nitrates) was detected. Planned management of the aquifer and corrective measures are needed in order to invert the salinization process before it severely affects water resources in the long term.
... In many carbonate-poor watersheds, waters along shallow flowpaths in the soil zone have characteristically light δ 13 C values reflecting carbonic-acid weathering of silicates. Waters along deeper flowpaths within less weathered materials have intermediate δ 13 C values characteristic of carbonic-acid weathering of carbonates (Bullen and Kendall, 1998). Other processes that may complicate the interpretation of the δ 13 C values of surface waters and groundwater include CO 2 degassing, input of soil gas CO 2 from bacteria respiration, carbonate precipitation, exchange with atmospheric CO 2 , carbon uptake by aquatic organisms, methanogenesis, and methane oxidation (Bullen and Kendall, 1998). ...
... Waters along deeper flowpaths within less weathered materials have intermediate δ 13 C values characteristic of carbonic-acid weathering of carbonates (Bullen and Kendall, 1998). Other processes that may complicate the interpretation of the δ 13 C values of surface waters and groundwater include CO 2 degassing, input of soil gas CO 2 from bacteria respiration, carbonate precipitation, exchange with atmospheric CO 2 , carbon uptake by aquatic organisms, methanogenesis, and methane oxidation (Bullen and Kendall, 1998). ...
Understanding the origin of groundwater flow to fractured-rock aquifers provides a mechanism to assess the vulnerability of residential-supply wells to capture contaminants from known contamination areas. For this study, although concentrations of tetrachloroethylene (PCE) have yet to be detected in samples from nearby residential-supply wells, concerns over future changes in hydraulic stresses (pumpage) or modifications to remedial operations at operable units provided motivation to characterize groundwater from the residential–supply wells. The interpretation of geochemical and isotopic data helped researchers assess the origin of flowpaths to each well.
... Trace elements in coal provide valuable indicators of palaeoenvironmental sedimentary conditions of coal formation because of their coherent geochemical behaviour and predictable nature of fractionation. The trace element Sr has a global average concentration of 110 ppm in coal (Ketris and Yudovich, 2009) and strontium isotopes are increasingly used as geological and environmental tracers (Bullen and Kendall 1998;Qing et al., 1998;Hermann et al., 2011;Wang et al., 2018). A large number of these studies are on the reconstruction of the chronology of geological events in marine environments globally. ...
... Carbon isotopes help us to assess the origin of dissolved inorganic carbon (DIC), the main component in waters draining carbonate systems. The isotope composition of dissolved inorganic carbon (δ 13 C DIC ) is used to understand the biogeochemical reactions controlling alkalinity and to trace the origin of the bicarbonate ion, which is the dominant anion in the shallow groundwater (Bullen & Kendall, 1998). ...
The groundwater characteristics of the Učja aquifer were investigated using geochemical and isotopic data. The water discharge and physico-chemical properties of the groundwater and the Učja River reflect the climate that is characteristic of the area. The mixed snow/rainfall regime is characteristic for the Učja Valley, with the highest discharges appearing during the spring snowmelt and autumn precipitation, and the lowest discharges in the winter and especially summer months. The temperature of the groundwater and the Učja River is lower in winter and higher in summer. The specific electrical conductivity values indicate a very permeable carbonate aquifer. Higher conductivity values were observed in spring and autumn at all sampling sites, which is related to snowy and rainy periods. The groundwater from the Učja aquifer indicates a uniform type of water (Ca-Mg-HCO3), with Ca2+, Mg2+ and HCO3– the most abundant ions. Differences in Ca2+ and Mg2+ concentrations and in the Mg2+/Ca2+ molar ratio between sampling sites were observed. Those springs with lower Mg2+ and lower Mg2+/Ca2+ molar ratios indicate limestone recharge areas, and those springs with higher Mg2+ and molar ratios indicate interaction with the dolomite hinterland. The pH values confirm alkaline waters characteristic of carbonate aquifers. The hydrogen (δ2H) and oxygen (δ18O) isotope values suggest the main source of water is from precipitation from a complex mixing of maritime and continental air masses. An altitude isotopic effect is observed with minor δ18O and δ2H depletion at higher altitude sampling sites compared to those springs at lower altitudes. The altitude isotopic effect is most prominent in spring. The δ13CDIC values indicate the dissolution of carbonates and the degradation of organic matter.
... The alkaline earth metal Sr is present in nature with four stable, naturally occurring isotopes: 88 Sr, 87 Sr, 86 Sr and 84 Sr, whereby the isotope composition varies according to the βdecay of 87 Rb, which decays into stable 87 Sr with a half-life decay time of 4.7 Â 10 10 years. The Rb-Sr combination generates different 87 Sr/ 86 Sr, reflecting only the variations in the amount of radiogenic 87 Sr present in the sample, depending on the geological ages and the geochemical characteristics of the rock where they naturally occur, namely their geographical origin (Bullen and Kendall, 1998). If Rb and Sr are integrated into a mineral or rock at its formation, the amount of 87 Sr rises over time as radioactive 87 Rb decays to 87 Sr. ...
This study uses conventional ⁸⁷ Sr/ ⁸⁷ Sr and ⁸⁷ Nd/ ⁸⁷ Nd isotope and interelement ratios of Ca, Sr, K, Mn, Mg, and Ti as fingerprints for ordinary Portland cements (OPC) provenancing. Herein, the first database of Sr and Nd isotope ratios investigated in OPCs stemming from twenty-nine cement plants located worldwide was created. The results show that the Sr isotope ratios of OPCs are higher than those of seawater from the observed geological period. The spread of ⁸⁷ Nd/ ⁸⁷ Nd in OPCs is not as large as the spread for ⁸⁷ Sr/ ⁸⁷ Sr isotope ratios. However, the combination of both Sr and Nd isotope ratios provides the potential for distinguishing between cements of different production sites. Most of the investigated OPCs have measurable differences in their ⁸⁷ Sr/ ⁸⁷ Sr and ⁸⁷ Nd/ ⁸⁷ Nd isotope ratios, which can be employed as a valuable analytical fingerprinting tool. In the case of equivocal results, Divisive Hierarchical Clustering was employed to help overcome this issue. The construction of geochemical profiles allowed computing suitably defined distances between cements and clustering them according to their chemical similarity. By applying this methodology, successful fingerprinting was achieved in 27 out of 29 analysed ordinary Portland cements.
... For example, Miller et al. (1993) used the difference in isotopic composition between strontium in rainfall and soil parent material to partition cation loss from a North American catchment into components derived from weathering and the exchangeable cation pool. There is potential for increased use of isotopic tracers like strontium to explore weathering and the flow pathways of dissolved cations and anions in catchments (Bullen and Kendall 1998). Another productive approach is that of modelling weathering rates. ...
Soil acidification is one of Australia's major land degradation problems. About half of the more intensively used agricultural land in Australia is acidic, and the area is expanding. The gross value of agricultural production lost nationally each year due to soil acidity has been estimated at $1585 million, compared to $187 million for dryland salinity. For NSW alone the corresponding estimates are $378 million for soil acidity and $6 million for dryland salinity. The rate of spread of soil acidity is not known with any degree of certainty. One estimate is that, in the absence of remedial action, an additional 2.7 to 6 million hectares of Australian agricultural land could reach the strongly acidic threshold (pHCa = 4.8) each year.Although it has been known for over 60 years that Australian agricultural practices can cause soil acidification, recognition of its significance has been slow. Currently farmers perceive soil acidity to be not much more of a problem than dryland salinity. Soil acidity has been managed mainly as an agronomic, paddock scale problem, and there has been considerable research into liming and plant adaptation to acidic soils. These areas will continue to be important. However the great extent of the problem, limitations to the economic viability of liming on more extensive grazing land, and the occurrence of off-site and long term effects, indicate that additional work is needed to address the problem from a broader natural resource management perspective. The causes of soil acidification have features in common with those of salinity and erosion, in that all are associated with increased leakage of water and nutrients from agricultural systems compared to pre-European landscapes. There has been little integration of research and management of soil acidification with other hydrologically based soil degradation problems.
... The isotope ratio 87 Sr/ 86 Sr is used to express the abundance of radiogenic isotope ( 87 Rb) compared to the stable ( 86 Sr). In the case of lead, 204 Pb can be considered stable, while 206 Pb, 207 Pb and 208 Pb constitute products of the radioactive decay of 238 U, 235 U and 232 Th, respectively (Bullen and Kendall 1998). ...
Urbanization and agriculture increase the risk of water contamination in watersheds. A special concern arises when this water is used for public supply. Conventional hydrochemical methods have been applied to identify contaminants in bulk water; however, there is lack of investigation of their origins. Environmental isotopes can be used to address such knowledge gap by tracking the harmful substance back to its origins. This study evaluates the interference of urbanization as well as inorganic fertilizers in the suspended sediments of the tributaries of two impoundments, whose water supplies 72% of the municipality of Caxias do Sul, Southern Brazil. To achieve this goal, the isotopic ratios 87Sr/86Sr, 208Pb/204Pb, 206Pb/204Pb, 207Pb/204Pb, 208Pb/206Pb and 207Pb/206Pb were selected as geochemical tracers, showing promising results to evaluate sources of contamination in source water. The results of strontium isotopes showed two distinct groups, one marked by the geogenic origin of the sediment and the other by inorganic fertilizers. Lead isotopes indicated that suspended sediments have signatures compatible with the rocks that occur in the region and are in a range of isotopic ratios different from fertilizers or copper sulfate.
... However, more groundwater with sufficient lixiviation enters the conduit in the low water period. Under the strong hydrodynamic conditions in groundwater, soluble minerals continue to dissolve and are transported with groundwater, resulting in the codissolution of calcite and dolomite (Bullen et al. 1998). Furthermore, the role of hydrodynamic change has not drawn enough attention in the previous studies of hydrogeochemical processes in karst areas. ...
The Qingjiang River is the second largest tributary of the Yangtze River in Hubei Province and is also a typical karst catchment. Eighty-two important groundwater samples were collected during the high and low water periods of 2019. The results show the following. (1) The major hydrochemical types are Ca + Mg-HCO 3 and Ca-HCO 3 , indicating that carbonate weathering is the main factor controlling the groundwater chemistry. (2) The results of inverse hydrochemical modeling reveal two kinds of groundwater-carbonate rock interactions. One is the codissolution of calcite and dolomite, and the other is dedolo-mitization, which is widespread in the dolomite aquifers. Furthermore, gypsum has a tendency to dissolve in each aquifer, and the common ion effect of Ca 2+ caused by gypsum dissolution promotes dedolomitization. The modeling results suggest that major elements can be effectively used to trace the material source of the groundwater. (3) The chemical weathering of carbonate rock is mainly affected by carbonic acid, sulfuric acid, and nitric acid. After accounting for the impacts of evapo-rites and atmospheric input, the calculations show that the contribution of carbonic acid involved in carbonate weathering is 70.9% in the high water period and 70.0% in the low water period. Statistical analysis of karst spring discharge and the contributions of the acids involved in carbonate weathering reveals that the two are positively related. This result reflects the behaviors of sulfuric acid and nitric acid under the hydrodynamic conditions in different seasons. Therefore, carbonate weathering should be carefully evaluated in karst areas with abundant groundwater, and the role of groundwater in carbonate weathering is worthy of further study.
... 3 H compositions in groundwater can be differentiated in waters that were produced relative to the 1950's atmospheric testing of nuclear bombs (Clark and Fritz, 1997 Sr/ 86 Sr of dissolved Sr in water was analyzed at the MIT Isotope Laboratory, using multi-collector thermal ionization mass spectroscopy (MC-TIMS). Stontium-87/86 ( 87 Sr/ 86 Sr) has negligible fractionation during mineral-water interactions, it is used as an environmental tracer to trace strontium due to weathering from specific geologic settings and strontium-bearing minerals (Bullen and Kendall, 1998). Strontium isotopic compositions from the Cretaceous, Pennsylvanian and Permian minerals in the study area and surrounding areas are not documented in the literature, therefore it is difficult to draw any kind of conclusion from the results ( Figure 37). ...
... The use of hydrochemistry and isotopic investigation can provide new insight to classical investigation. For example, groundwater dissolved 87 Sr/ 86 Sr ratios have proven to be useful in determining the sources of solutes in natural waters (Négrel and Deschamps, 1996, Négrel et al., 2001, Dotsika et al., 2010, investigating mineral weathering reactions (Brass, 1975;Åberg et al., 1989;Bullen et al., 1996;Clow and Drever, 1996;Bullen and Kendall, 1998), and identifying mixing processes involving groundwaters of different sources (Woods et al., 2000;Frost and Toner, 2004;Singleton et al., 2006) also inside an unstable context (Deiana et al., 2018). Values of groundwater dissolved d 34 S-SO4 2have also been used in aquifer studies to identify sulfate sources (Moncaster et al., 2000;Cortecci et al., 2002;Gammons et al., 2013). ...
Les risques gravitaires sont à l’origine de catastrophes importantes pouvant engendrer des dégâts matériels et humains, ils sont aussi l’un des mécanismes principaux de dénudation des chaines de montagne. Il est maintenant clairement établi qu’il existe un lien entre l’instabilité gravitaire et l’eau qu’elle reçoit. La compréhension du fonctionnement des aquifères de milieux instables est d’une importance fondamentale dans l’étude de ces structures complexes dont la déstabilisation implique des enjeux considérables. C’est dans cet esprit que cette thèse s’intéresse à la relation entre le milieu instable et les écoulements souterrains du versant de Séchilienne (Isère, France). Ce travail vise à caractériser dans un premier temps le fonctionnement hydrogéologique de l’aquifère du milieu instable au travers de l’analyse de deux exutoires au sein de l’instabilité. L’utilisation de données hydrogéologiques recueillies sur le long terme permet une analyse temporelle fournissant de bonnes informations sur le fonctionnement, le dynamisme et la recharge de l’aquifère à plusieurs échelles allant du cycle hydrologique à l’année. Les analyses corrélatoires se révèlent être un bon outil quant à la compréhension du fonctionnement hydrodynamique de l’aquifère. L’apport de la chimie des eaux, est essentielle à l’identification des signatures hydrochimiques caractérisant le versant. Elle permet par ailleurs d’obtenir des informations sur l’état d’altération du versant, la composition chimique des eaux dépendant des interactions eau-roche. L’analyse comparative des deux exutoires au sein de l’instabilité couplée à l’analyse d’un exutoire de la zone stable reflète l’hétérogénéité des milieux instables et fracturés. Ce travail s’axe dans une deuxième partie, sur le couplage entre traceurs isotopiques et chimie des éléments majeurs, afin de préciser l’amplitude des réactions d’altération chimique des phases minérales induites par les interactions eau-roches à l’intérieur du versant. L’utilisation d’un modèle de mélange permet d'attribuer les différents éléments majeurs à différentes sources et de quantifier l'implication des acides sulfurique et carbonique comme source de protons. Les résultats montrent que l'instabilité crée des conditions favorables et durables au sein de la rupture, par l'ouverture de nouvelles fractures apportant des surfaces fraîches et réactives permettant la production d'acide sulfurique par oxydation de la pyrite. Les résultats obtenus permettent d’autre part d’affiner le modèle hydrogéologique préexistant par la mise en évidence de la contribution de la dissolution du gypse au budget sulfate des eaux. L’originalité de ce travail réside également dans nos résultats qui montrent le comportement du glissement de terrain de Séchilienne qui, malgré son rôle dans l'accélération de l'altération chimique et physique des roches, agit à l’échelle des temps géologiques (c'est-à-dire à des échelles de temps plus longues que les précipitations de carbonate dans l'océan) comme une source de CO2 dans l'atmosphère.
... Whereas, more groundwater with su cient lixiviation enters the conduit in low water period. Under the circumstance of strong groundwater hydrodynamic, soluble minerals continue to dissolve and transport with groundwater, results in codissolution of calcite and dolomite (Bullen et al. 1998). Furthermore, the role of hydrodynamics change still has not drawn enough attention in previous studies of hydrogeochemical process in karst area. ...
Qingjiang river is the second largest tributary of the Yangtze River in Hubei province, it’s also a typical karst catchment. Eighty-two important groundwater samples were collected during high and low water period of 2019. The results show that: (1) The major hydrochemistry types are Ca+Mg-HCO 3 and Ca-HCO 3 , indicate that carbonate weathering is the main source of groundwater chemistry; (2) The results of inverse hydrochemical modeling show that there are two kinds of groundwater-carbonate rock interactions. One is co-dissolution of calcite and dolomite, the other is dedolomitization, and thereinto, dedolomitization is widespread in dolomite aquifers. Furthermore, gypsum has a tendency to dissolve in each aquifer, and the common ion effect of Ca ²⁺ caused by gypsum dissolution promotes dedolomitization. The modeling results suggest that major elements have a good traceability effect on the material source of groundwater. (3) The chemical weathering of carbonate rock is mainly affected by carbonic acid, sulfuric acid and nitric acid. After modifying the impact of evaporite and atmospheric input, the calculations show that the contribution of carbonic acid involved in carbonate weathering is 70.9% (high water period) and 70.0% (low water period). Through statistics of karst springs discharge and contribution of acid involved in carbonate weathering, the two are in a positive relationship. The result can reflect the laws of sulfuric acid and nitric acid under the hydrodynamic condition in different seasons. Therefore, the carbonate weathering should be carefully evaluated in karst areas which have abundant groundwater and the role of groundwater in carbonate weathering is worthy of further study.
... 9 Indeed, the 87 Sr/ 86 Sr ratio of horticultural products like apples is directly related to that of the strontium (Sr)-bioavailable fraction in the soil, which mainly depends and varies according to the geo-lithological features of the growing area. [26][27][28] Its high potential as soil-derived traceability marker to distinguish different types of horticultural products according to their origin has been demonstrated in several studies. [29][30][31][32] A multi-chemical approach is rather promising to detect the origin of agricultural products, especially when data are analysed through chemometric methods. ...
BACKGROUND
The use of PDO (protected designation of origin) and PGI (protected geographical indication) labels allows to protect and promote agricultural products characterized by unique features related to the place of origin and traditional know‐how. However, the presence of non‐authentic products in the market represents a fraud that can be tackled applying analytical techniques combined with chemometric analysis. In this study, we applied multi‐element and multi‐isotope analysis to characterize PDO and PGI apples cultivated in northern Italy, comparing them with Italian apples without labels of geographical indications.
RESULTS
The multi‐element and multi‐isotope approach allowed to characterize the apples cultivated in northern Italy. Despite a significant effect of the sampling sites on the apple composition, the comparison of the multi‐chemical fingerprint of the apples significantly varied among cultivation areas. Results of this characterization were used to classify samples according to their cultivation area applying a linear discriminant analysis (LDA). Outputs of the LDA showed that correct sample classification can be successfully achieved (balanced accuracy > 96%). Moreover, using a selection of variables, it was possible to correctly classify samples also at regional level.
CONCLUSION
The presented evidences indicate that the multi‐element and multi‐isotope fingerprint can be successfully applied to traceability studies. The combination of this characterization with chemometric tools allows the classification of Italian apples based on their origin both on a national and regional scale. This approach represents an interesting tool to enhance and protect PDO and PGI Italian products.
© 2021 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.
... The dominant form of DIC present in aquatic ecosystems is determined by pH and alkalinity (Stumm & Morgan, 1981;Gray et al., 2011) which also influence the ratio of heavy to light isotopes of carbon ( 13 C) of the DIC (Bade et al., 2004). The 13 C of the DIC can also be affected by salinity or nutrient limitation (Lin & Sternberg, 1992;McKee et al., 2002), pressure of CO2 as a result of terrestrial respiration of organic material (Striegl et al., 2001), ecosystem area and metabolism (Finlay, 2003;Bade et al., 2004), geology and hydrology (Bullen & Kendall, 1998), and basin geochemistry . Subsequently, the factors that determine the 13 C of primary producers are complex because of the influences of spatial heterogeneity at multiple scales, such as local habitat, reach, watershed, hydrology and geochemistry (Doi et al., 2007;Casey & Post, 2011;Costas & Pardo, 2014). ...
Stable isotopes analyses have become a popular tool among ecologists. Carbon, nitrogen, hydrogen and sulfur stable isotopes are used to analyze many ecological attributes of populations, communities and ecosystems. The more commonly employed isotopes by freshwater ecologists are δ13C and δ15N, which are utilized as natural “markers” of biotic and abiotic molecules and are applied to reconstruct ecological processes or to trace ecological activities. Among the numerous freshwater ecosystems, river-floodplain systems are remarkable for being extremely complex ecosystems, with high biodiversity and high habitat heterogeneity, which makes these environments suitable to elucidate patterns and processes with stable isotopes. Thus, it is extremely important to recognize the factors that affect the variability of C and N isotopes, since the isotopic mapping of natural environments (isotopic landscape/isoscapes) has proven to be a great tool to elucidate migratory animal movement patterns, as well as the origin and fate of organic matter, including that of anthropogenic origin. Besides the isotopic landscapes, the elucidation of trophic niches through stable isotopes (e.g. isotopic niche) has also been widely used, especially when it comes to competition for food resources between native and non-native species. Therefore, the use of stable isotopes goes beyond the application of ecological theories, thus becoming an important tool for decision making when incorporated anthropogenic factors to the analysis. That being said, this thesis is divided into two themes: the first one assesses the factors that affect the variation of δ13C and δ15N of carbon sources in four Neotropical floodplains (Paraná, Pantanal, Amazon and Araguaia), highlighting local (limnological factors) and regional (basin identity) patterns. The second evaluates the trophic interactions of the population of an invasive fish species (Serrasalmus marginatus) and a native species (S. maculatus), through the analysis of stable isotopes in two floodplains (Pantanal, wherein the two species are native; and Paraná, where S. marginatus is non-native and potential competitor of S. maculatus). Due to the relatively greater heterogeneity within versus among systems in our study highlights that the spatial scale of sampling for control of baseline heterogeneity should be explicitly considered. As for the piranhas’ trophic interactions, we found no evidence of niche overlap between the species, indicating that the coexistence of the species in the non-native co-occurrence environment is modulated by the niche segregation.
... Groundwater that has dissolved carbonate minerals is expected to have low 87 Sr/ 86 Sr ratios and relatively high δ 13 C-TDIC values (Figures 6 and 7) [65][66][67][68]. On the other hand, although it is expected that plutonic rocks will have higher 87 Sr/ 86 Sr ratios (>0.715) [64], the Sr isotope ratio of sample M0012 is due to albite containing the least radiogenic type of Sr [69]. ...
Fluxes between fractured-karstified and detritic aquifers are commonly poorly understood in many environments. These two types of aquifers are in contact in the southeastern Pampean region in the Argentine Buenos Aires province, and the aim of this work is to analyze their relationship contributing to improve the hydrological model. A joint application of hydrochemical and multi-isotope (δ2H, δ18O, δ13C-TDIC, δ18O-TDIC, 87Sr/86Sr) tools was used. TDIC, δ2H, δ18O and δ13C-TDIC allowed differentiating
two main end members. Water in the Pampeano aquifer (PA) which is transferred from the fractured-karstic aquifer (F-KA) is characterised by high TDIC around 500–700 mg/L, isotopically depleted in 18O (about −5.5 ‰) and high δ13C-TDIC (around −10.0 ‰). The other end member is direct recharge water infiltrated into the PA with TDIC ranging from 400 to 500 mg/L, slightly enriched in 18O (δ18O=−4.8 ‰), and δ13C-TDIC in the range of soil CO2 as a result of reactions with calcrete concretions (from −20.0 to −9.0 ‰). Dolomite dissolution is the main process controlling the chemistry of the low-mineralized (Mg–Ca-HCO3) waters, whereas high-mineralized (Na-HCO3) waters are strongly
influenced by ion-exchange reactions with adsorbed Ca2+ and Mg2+ and by evaporation.
... However, landslides constitute very 430 heterogeneous media due to their intense fracturation, which makes hydrogeological investigation complicated. The use of hydrochemistry and isotopic investigation is a good substitute to classical investigation since the groundwaters 87 Sr/ 86 Sr ratios have proved to be useful in determining the sources of solutes in natural waters (Négrel and deschamps, 1996, Négrel et al., 2001, Dotsika et al., 2010 and investigating mineral weathering reactions (Brass, 1975;Åberg et al., 1989;Bullen et al., 1996;Clow and Drever, 1996;Bullen and Kendall, 1998) and identifying mixing processes involving groundwaters of 435 different sources (Woods et al., 2000;Frost and Toner, 2004;Singleton et al., 2006) also inside an unstable context (Deiana et al., 2018). In groundwaters, d 34 S values of dissolved SO4 2are used in aquifer studies to identify sulfate sources (Cortecci et al., 2002;Gammons et al., 2013;Moncaster et al., 2000). ...
This study makes use of a highly instrumented active landslide observatory (9 years of data) in the French Alps, the Séchilienne slope. Using a combination of major element chemistry and isotopes ratios (87Sr / 86Sr, δ34S) measured in different water types of the stable and unstable part of the Séchilienne instability to assess the contribution of the different lithologies of the slope and the chemical weathering mechanisms. Chemical and isotopic ratios appear useful to characterize weathering processes and the origin of waters and their flowpaths through the massif. A mixing model allows us to allocate the different major elements to different sources and quantify the involvement sulfuric and carbonic acids as a source of protons. As a consequence of the model, we are able to show that the instability creates favorable and sustained conditions for the production of sulfuric acid by pyrite oxidation by supplying reactive surfaces. We clearly identify the contribution of gypsum dissolution to the sulfate budget in the landslide. We are also able to refine the pre-existing hydrogeological views on the local water circulation and water flow paths in the instability but showing the hydrological connectivity of the different zones. Overall, our results show that the Séchilienne landslide, despite its role in accelerating rock chemical and physical weathering, acts, at a geological time scale (i.e. at timescales longer that carbonate precipitation in the ocean) as a source of CO2 to the atmosphere. If generalizable to other instable zones in mountain ranges, this study illustrates the complex coupling between physical and chemical erosion and climate. The study also highlights the importance of deciphering between sulfite oxidation and gypsum dissolution as a source of sulfate ions to rivers, particularly in mountain ranges.
... 4,5 The 87 Sr/ 86 Sr ratio of a crop is directly related to that of the Sr-bioavailable fraction in the soil, which mainly depends and varies according to the geolithological features of the growing area. [6][7][8] Its high potential as soil-derived traceability marker to distinguish different types of horticultural products according to their origin, either alone or coupled with other analytical methods has been demonstrated in several studies. [9][10][11][12][13] The present study aimed at applying 87 Sr/ 86 Sr analysis to characterize the Italian PDO and PGI Golden Delicious apples in comparison with fruits of the same variety from other areas of Northern Italy where no GIs for apples are registered (non-GI apples from Emilia Romagna, Lombardia, Piemonte and Veneto). ...
BACKGROUND
Apples have a leading role in the Italian fruit sector, and high‐quality apples, including the Golden Delicious variety, are cultivated mainly in the Northern mountain districts. In the present study, Golden Delicious apples from PDO (Protected Designation of Origin) and PGI (Protected Geographical Indication) cultivation districts were characterized according to their Sr isotope composition and compared with apples from other Northern Italian districts.
RESULTS
Apples collected in two consecutive years (2017 and 2018) confirmed the low annual variability of the ⁸⁷Sr/⁸⁶Sr ratio. The isotope ratio of apples was highly correlated with that of the soil extracts of the respective orchards. Statistical differences were highlighted between cultivation districts. However, because similar geological features characterized some areas, their ratios overlapped and a complete separation of the districts was not possible.
CONCLUSION
The ⁸⁷Sr/⁸⁶Sr ratio is an excellent marker for studies of food traceability because it retains the information about the place of origin. However, its strength is limited when comparing products from cultivation areas sharing similar geological features. In the perspective of geographical traceability, a multichemical characterization can overcome the limits of single‐parameter approach. © 2020 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.
... The importance of isoscape research has been noted not only in environmental, biological, agricultural, and archeological studies but also in societal applications such as food security and forensic investigations (Kelly et al., 2005). The stable isotope ratio of Sr ( 87 Sr/ 86 Sr) in freshwater has been used as a hydrogeological tracer, as it reflects the characteristic 87 Sr/ 86 Sr of regional rocks (Bullen and Kendall, 1998;Négrel, 1999;McNutt, 2000;Rose and Fullagar, 2005;Tripathy et al., 2012). Freshwater has generally stable 87 Sr/ 86 Sr, but groundwater is more stable in this respect compared to river water, in which 87 Sr/ 86 Sr is affected by changes in discharge from tributaries with different 87 Sr/ 86 Sr values (Voss et al., 2014). ...
The geographic distribution of the stable isotope ratio of Sr (87Sr/86Sr) is useful for identifying the provenance of drinking water, organisms, and agricultural products. To explore how environmental factors influence this ratio, we determined the 87Sr/86Sr, sulfur isotope ratio (δ34S), and elemental composition of 208 commercially available bottled waters in Japan, and compared them with the 87Sr/86Sr values of groundwater, rainwater, rocks, and vegetables from similar localities. We classified the bottled waters into seven categories based on the geology of their source aquifers. The 87Sr/86Sr and concentrations of several elements (Ca, K, Si, Rb, and Ba) of the bottled waters differed with the aquifer rock type and were well correlated with the 87Sr/86Sr of reported spring waters, indicating that bottled water, like other groundwater, reflects the lithology and chemistry of its aquifer. The 87Sr/86Sr of bottled water, taken as a proxy for groundwater, showed regional variations consistent with those of rocks and vegetables, demonstrating that an 87Sr/86Sr map of water and agricultural products has value for determining the production areas of these substances. However, the value and range of 87Sr/86Sr differed among these three materials, and the degree of the difference between groundwater and rock depended on the rock type. An analysis of geochemical data from rocks and rainwater suggests that groundwater contains Sr and additional S derived from atmospheric sources such as rainwater and sea salt aerosols. The atmospheric contribution of Sr to groundwater is greatest in areas of siliceous sedimentary rocks with low Sr concentrations and high resistance to weathering. A weak correlation of δ34S of bottled waters with 87Sr/86Sr indicates the usefulness of maps of combined Sr and S isotope ratios for groundwater provenance. This study shows that for accurate provenance determinations of groundwater, organisms, and agricultural products, it is essential to better quantify the contributions of Sr and S from the atmosphere as well as from rocks and human activities.
... The δ 13 C values for the peat grass were found to be 0.5‰ more negative than those for the pastures in the mineral soil. Additionally, the plants in the swampy area are submitted to less water stress (Bullen & Kendall, 1998;Clark & Fritz, 1997), which should be reflected by lower amplitude of seasonal variations. Alternatively, low values of δ 13 C could also be explained by the consumption of forest resources. ...
The arrival of early farmers and their livestock in the Western Mediterranean during the Early Neolithic marked a new way of life for the northeast Iberian Peninsula. Given the permanence of the introduced economic strategies, which are still practiced today, and their apparently momentous outcome, this process has generally been explained as a success. The introduction of livestock must have played a fundamental role but we know little about how these newly‐arrived domestic animals were managed. In this sense, the management of food habits of domestic animals could be a key factor to understand the success of different herding systems during the introduction and adaptation of domesticates in the Iberian Peninsula. Sequential analyses of δ13C and δ18O values in tooth enamel crowns are here used to provide detailed information about dietary inputs of early caprine and bovine herds introduced into the Iberian Peninsula. Our study was carried out at La Draga (5314‐5209 cal BC), a site on the eastern side of Lake Banyoles (Girona, NE Iberian Peninsula). Data shows that caprine and bovine herds were fed with variable foddering strategies. Sheep reflect feeding in the swamps or on forest resources all year round with reduced seasonal dietary changes. Goat and cattle herds display food habits that could involve foddering on stored agricultural by‐products during specific‐season times, probably linked to reproductive and productive strategies. This information helps to reconstruct how these early Neolithic communities found the way to success in the new territories of the Western Mediterranean.
... Lead isotopic composition is commonly discussed as a ratio of radiogenic Pb nuclides to primordial 204 Pb nuclides (e.g. 206 Pb/ 204 Pb) in geologic and earth science investigations (Kendall & McDonnell 1998 (Bullen & Kendall 1998). ...
Water is both a crucial resource for the mining industry, as well as the primary pathway for the spread of mining related contamination to the environment. Knowledge and characteriza-tion of hydrogeological parameters at a mine site are crucial for establishing baseline hydro-logical conditions and for predicting the release and transport of contamination related to mine drainage. This report provides a consolidation literature based information on how and why different geochemical and isotopic analytes may contribute to characterization of mine water-environment interactions.
First the report describes the background information on the geochemical settings common to mine areas. Contaminant mobility is discussed in the context of how geochemical monitoring can be applied to understand mine water-environment interactions. Also a review of the prin-ciples of environmental isotope tracer applications as they relate to mine water-environment interactions is presented. The report also concludes with a review of case studies demonstrat-ing the application of the discussed principles and of isotope system applications.
Water is both a crucial resource for the mining industry, as well as the primary pathway for the spread of mining related contamination to the environment. Knowledge and characteriza-tion of hydrogeological parameters at a mine site are crucial for establishing baseline hydro-logical conditions and for predicting the release and transport of contamination related to mine drainage. This report provides a consolidation literature based information on how and why different geochemical and isotopic analytes may contribute to characterization of mine water-environment interactions.
First the report describes the background information on the geochemical settings common to mine areas. Contaminant mobility is discussed in the context of how geochemical monitoring can be applied to understand mine water-environment interactions. Also a review of the prin-ciples of environmental isotope tracer applications as they relate to mine water-environment interactions is presented. The report also concludes with a review of case studies demonstrat-ing the application of the discussed principles and of isotope system applications.
Available at: http://tupa.gtk.fi/raportti/arkisto/92_2018.pdf
... Additional insight into lake evolution can be gained by using novel isotopic tools, such as δ 37 Cl and δ 81 Br (Eggenkamp 2014), in combination with more traditional geochemical and isotopic analyses (δ 18 O, δ 2 H, 3 H, δ 34 S/δ 18 O (SO4), and 87 Sr/ 86 Sr). Use of these isotopic parameters has been applied elsewhere to provide increased understanding of evaporation (Gibson, Birks, and Yi 2016;Leng and Anderson 2003), glaciation/ deglaciation (Blum and Erel 1997), weathering (Anderson, Drever, and Humphrey 1997;Blum and Erel 1997;Sharp, Creaser, and Skidmore 2002), aeolian transport (Hanlon 2015;Hanlon et al. 2017), marine inputs (McArthur et al. 1989;Negrel and Roy 1998;Wood and Sanford 1995), groundwater-surface water interaction (Bohlke and Denver 1995;Bullen and Kendall 1998;Hagerty and Webb 2008;Kendall and McDonnell 1998;Lyons et al. 1995;Negrel et al. 2003), and microbial processes (van Everdingen and Krouse 1985) in glaciated areas. ...
In west Greenland, an approximate chronosequence of landscape evolution and weathering exists between the coast, which has been ice free for long periods, and more recently deglaciated areas along the present day ice margin. Traditional geochemical and isotopic analyses (δ¹⁸O, δ²H, ³H, δ³⁴S/δ¹⁸O (SO4), and ⁸⁷Sr/⁸⁶Sr) along with novel isotopic tools, such as δ³⁷Cl and δ⁸¹Br, were used to provide new insights into lake geochemical processes along a transect of lakes from the coast to the ice margin in the Kangerlussuaq region. Evaporation was found to be a key process impacting lake chemistry and isotopic signatures in the ice marginal area, with decreasing importance toward the coast. Evaporative processes were apparent in the δ³⁷Cl and δ⁸¹Br isotopic signatures of lake-water chemistry. Consistent with previous work elsewhere (e.g., Blum and Erel, 1995) on increased biotite weathering in glaciated environments, ⁸⁷Sr/⁸⁶Sr isotopic ratios were found to be more radiogenic (>0.73) in lakes found in more recently glaciated terrain. Sulfide oxidation was the main source of sulfur (as sulfate) in lakes in the ice marginal area, while the influence of marine aerosols and bacterial sulfate reduction increased further away from the ice sheet around the fjord Kangerlussuaq. Groundwater discharge significant enough to impact lake chemistry was not observed in any of the lakes studied, suggesting that little groundwater–surface water interaction occurs in the study area or that recharge conditions are present in the majority of the lakes studied.
... Provenancing metal objects by use of lead isotopes has a long history in archaeometry, and likewise no isotopic fractionation is evidenced in the course of the mining and metal working processes. 13 Since radiogenic lead is the product of three different decay series ( 238 14 According to Price and coworkers, 15 contemporary animal bone finds are also suitable for the definition of local ratios because the animals will "fingerprint" the nearest lead source. Lead stable isotopes in mammalian skeletons can thus be used as a georeferencing tool just as 87 Sr/ 86 Sr ratios, and it is highly recommended that all four isotopes should be measured, including the least abundant 204 Pb, to avoid information loss. ...
RATIONALE
Due to the spatial heterogeneity of stable isotope ratios of single elements measured in attempts to georeference bioarchaeological finds, multi‐isotope fingerprints are frequently employed under the assumption that similar isotopic signatures are indicative of similar shared environments by the individuals studied. The extraction of the spatial information from multi‐isotope datasets, however, is challenging.
METHODS
Gaussian mixture clustering of six‐ to seven‐dimensional isotopic fingerprints measured in archaeological animal and human bones was performed. Uncremated animal bones served for an isotopic mapping of a specific reference area of eminent archaeological importance, namely the Inn‐Eisack‐Adige passage across the European Alps. The fingerprints consist of ⁸⁷Sr/⁸⁶Sr, ²⁰⁸Pb/²⁰⁴Pb, ²⁰⁷Pb/²⁰⁴Pb, ²⁰⁶Pb/²⁰⁴Pb, ²⁰⁸Pb/²⁰⁷Pb, ²⁰⁶Pb/²⁰⁷Pb ratios, and δ¹⁸Ophosphate values in uncremated bone apatite, while the thermally unstable δ¹⁸O values of human cremations from this region were discarded.
RESULTS
The bone finds were successfully decontaminated. Animal and human isotope clusters not only reflect individual similarities in the multi‐isotopic fingerprints but also permit a spatial allocation of the finds. This holds also for cremated finds where the δ¹⁸Ophosphate value is no longer informative. To our knowledge, for the first time Pb stable isotopes have been systematically studied in cremated skeletal remains and proved significant in a region that was sought after for its ore deposits in prehistory.
CONCLUSIONS
Gaussian mixture clustering is a promising method for the interpretation of multi‐isotopic fingerprints aiming at detecting and quantifying migration and trade.
... Overall, bivalve shells from both sites were found to have a high potential to reconstruct discharge patterns, but high discharge conditions were difficult to capture due to growth cessation (as suggested for the Oubangui River) and due to the logarithmic relationship between Q and δ 18 O w . C DIC values in river systems are known to be a result of a range of different processes, including changes in the importance of silicate and carbonate weathering (linked to the main water sources supplying the river discharge, i.e. groundwater versus surface runoff), and seasonality of in situ primary production and mineralization (Probst et al., 1994;Bullen and Kendall, 1998;Bouillon et al., 2012). For the Oubangui River, the more 13 C−depleted values during high discharge conditions have been linked to an increased relative importance of silicate weathering, while during low discharge, in situ production by phytoplankton production is thought to leave the DIC pool more enriched in 13 C (Bouillon et al., 2012(Bouillon et al., , 2014. ...
Freshwater bivalve shell oxygen and carbon stable isotope ratios (δ18O, δ13C) may act as recorders of
hydroclimate (e.g., precipitation−evaporation balance, discharge) and aquatic biogeochemistry. We
investigate the potential of these hydroclimate proxies measured along the growth axis of shells collected
from the Oubangui River (Bangui, Central African Republic) and the Niger River (Niamey, Niger).
Biweekly water samples and in−situ measurements collected over several years, along with daily
discharge data from both sites allowed a direct comparison with proxies recorded in the shells. Data from
a total of 14 unionid shells, including three species (Chambardia wissmanni, Aspatharia dahomeyensis,
and A. chaiziana), confirmed that shells precipitate carbonate in oxygen isotope equilibrium with ambient
water. Because water temperature variations were small, shell δ18O values (δ18Oshell) also accurately
record the seasonality and the range observed in water δ18O (δ18Ow) values when calculated using an
average temperature. Calculated δ18Ow values were in good agreement over the entire record of
measured δ18Ow values, thus δ18Oshell records can be reliably used to reconstruct past δ18Ow values.
Discharge and δ18Ow values from both rivers fit a logarithmic relationship, which was used to attempt
reconstruction of past hydrological conditions, after calculating δ18Ow values from δ18Oshell values. A
comparison with measured discharge data suggests that for the two rivers considered, δ18Oshell data are
good proxies for recording discharge conditions during low(er) discharge levels, but that high discharge
values cannot be accurately reconstructed due to the large scatter in the discharge−δ18Ow relationship.
Moreover, periods of bivalve shell growth cessation due to high turbidity or air exposure should be taken
into account. While δ13C values of dissolved inorganic carbon in both rivers showed clear seasonality and
correlated well with discharge, most of the shells analyzed did not record these variations adequately,
likely due to the complication of vital effects including the variable contribution of metabolic CO2. Thus,
tropical African unionid δ18Oshell values can be used to reconstruct δ18Ow values with high confidence to
provide insight on past hydroclimate such as precipitation−evaporation balance and periods of low
discharge.
... Radon is present in high concentrations in groundwater due to the continuous decay of uranium in soils, making it ideal for estimates of groundwater input. The conservative and inert nature of radon gives it some advantage over other geochemical groundwater tracers commonly used such as conductivity, alkalinity, methane (CH 4 ), and stable isotopes of lead, strontium, and carbon, which can be affected by biological and chemical transformations [Bullen and Kendall, 1998; Kalbus et al., 2006; Santos et al., 2008]. Chloride (CI) is one of the most widely used conservative tracers for estimating groundwater discharge. ...
The water balance of drained floodplains is highly dynamic with complex groundwater-surface water interactions operating over varying spatial and temporal scales. Here, we hypothesise that the majority of groundwater discharge will follow flood events in a modified wetland. To test this hypothesis, we developed a detailed water balance that quantifies the contribution of groundwater discharge to the annual water budget of an extensively drained agricultural floodplain. A clear relationship between surface water radon measurements and groundwater level indicated alternating connection-disconnection dynamics between the drains and shallow groundwater. This relationship was used to develop a radon mass balance to quantitatively model groundwater discharge continuously throughout the year. Groundwater discharge varied by four orders of magnitude over the study period, with daily average rates ranging from 0 to 27,200 m3 d−1, peaking just a few hours after floods receded. Flood events occurred only 12% of the time yet contributed 72 to 76% of the total groundwater discharge. During flood recession periods, aerial groundwater discharge rates reached up to 325 cm d−1 which were some of the highest rates ever estimated. We proposed that the high drainage density of this site (12.4 km constructed drains km−2 catchment area) enhanced groundwater discharge during wet periods due to increased connectivity with the soil. Overall, groundwater discharge contributed 30-80% to the total surface water discharge. This study offers insight into the dynamic behaviour of groundwater within an extensively drained floodplain, and the importance of capturing flood events to quantify total groundwater contribution to floodplain water balances. This article is protected by copyright. All rights reserved.
... Strontium isotopic ratios ( 87 Sr/ 86 Sr) vary depending on bedrock composition and age (Albarède, 1995) and they are not fractionated by natural processes (Bullen & Kendall, 1998). 87 Sr/ 86 Sr ratios measured in suspended sediment are representative of 87 Sr/ 86 Sr ratios of their eroded parent material and have been used to identify suspended sediment sources in riverine, estuarine and marine environments (Asahara, et al., 2006;Douglas, et al., 1995;Wasson, et al., 2002). ...
In Brazil, agricultural expansion has increased soil erosion and sediment supply to waterways. As elevated sediment loads often degrade freshwater environments, sediment fingerprinting techniques are increasingly used to identify the sources supplying sediment to riverine and lacustrine environments. In this study, the contribution of various soil types to sediment was investigated in the Guaporé catchment (2,032 km2) in southern Brazil. Soil samples (n = 75) were collected to characterize five soil types: Ferralsols (n = 26), Nitisols (n = 13), Acrisols (n = 8), Leptosols (n = 6), and Luvisols (n = 22). Sediment samples (n = 7) were collected in a trap installed at the catchment outlet. Sediment source contributions were modelled according to soil types with elemental geochemistry and 87Sr/86Sr ratios. 87Sr/86Sr ratios, K, Ti, Co, As, Ba and Pb were selected as the optimal suite of properties discriminating between soil types. Sediment samples were modelled to mainly originate from downstream Acrisols (mean 41%, SD 2%), Leptosols (mean 34%, SD 4%) and Luvisols (mean 17%, SD 4%). In contrast, contributions of upstream Ferralsols (mean 4%, SD 2%) and Nitisols (mean 4%, SD 6%) were low. These results suggest that soils found in lower parts of the catchment, cultivated with conventional agriculture on steep slopes, were the main source of sediment to the river network. In contrast, soils found in upper parts of the catchment, cultivated with soybean under direct sowing, were less eroded or deposited before reaching the sediment sampling location at the outlet. These findings demonstrate that the management of local and degraded soil sources is important for reducing sediment loads.
... Strontium isotope ratio ( 87 Sr/ 86 Sr) analysis of groundwater systems is a well-established method of identifying water sources, degree of water-rock interactions, and in many cases mixing relationships between the sources of dissolved constituents in water (Bullen and Kendall, 1998;Shand et al., 2009). The most common mixing is between dissolved constituents in rainfall (usually dominated by sea spray) and those arising from aquifer mineral weathering. ...
... Stable isotopes of hydrogen and oxygen are also useful tools for determining residence time (Vitvar and Balderer 1997;Rodgers et al. 2005), to indicate the potential water inputs to the system and to determine the mixing of waters with different origins within the system (Clark and Fritz 1997;Glynn and Plummer 2005). The isotope composition of dissolved inorganic carbon is used to understand the biogeochemical reactions controlling alkalinity in the watershed and to trace the origin of bicarbonate ion, which is the dominant anion in the shallow groundwater (Bullen and Kendall 1998). ...
In order to investigate stream water, spring waters and water from a borehole facies, weathering processes, residence times and average recharge altitudes in the Radovna River valley were analysed for their concentrations of dissolved Ca2+, Mg2+, K+, Na+, HCO3−, Cl−, NO3−, SO42− and for the isotope compositions of hydrogen, oxygen and dissolved inorganic carbon (DIC). All water samples show a Ca2+–HCO3− water facies with low contents of K+, Na+, Cl−, NO3− and SO42−. Water–rock interaction and carbonate weathering are the significant contributors to water geochemistry. Analysis of the water chemistry indicates that waters drain a monolithological terrain and non-anthropogenically influenced watershed. The δ2H and δ18O values are seasonally dependent on the snowmelt, precipitation and evaporation. The average recharge altitudes for all sampling locations are between 1120 and 2130 m. The average residence time for the stream water is 2.4 years and for karst springs 1.2 years. The δ13CDIC values in all samples are influenced by dissolution of carbonates, degradation of organic matter and by equilibrium with atmospheric CO2. All geochemical and isotope analyses show changes in stream water in the downstream direction and are highly dependent on the inflow of karstic spring. Based on hydrogeological mapping, geochemical and stable isotope results, a conceptual hydrogeological model of the Radovna system, in which karstic and alluvial aquifers are in contact, was determined.
... Further, CO 2 exchange with atmosphere, in stream dissolution or precipitation of carbonate/silicate minerals, primary production (P ) and community respiration (R) are the additional in-stream processes impacting DIC dynamics (McConnaughey et al., 1994; Amiotte-Suchet et al., 1999; Abril et al., 2003; Finlay and 20 Kendall, 2007). The strength of each of these processes depends on the size of the river, its productivity (Finlay, 2003) as well as the geology and hydrology of the basin (Bullen and Kendall, 1998), and varies seasonally as a function of temperature and discharge. The complexity of all these processes and their interplay makes it difficult to constrain the sources of riverine DIC. ...
A basin-wide study was conducted in the Tana River Basin (Kenya), in February 2008 (dry season), September–November 2009 (wet season), and June–July 2010 (end of the wet season) to assess the dynamics and sources of dissolved inorganic carbon (DIC) as well as to quantify CO2 fluxes, community respiration (R), and primary production (P). Samples were collected along the altitudinal gradient (from 3600 m to 8 m) in several headwater streams, reservoirs (Kamburu and Masinga), and main Tana River. DIC concentrations ranged from 0.2 mmol L–1 to 4.8 mmol L–1 but with exceptionally high values (3.5 ± 1.6 mmol L–1) in Nyambene Hills tributaries. The wide range of δ13CDIC values (−15.0‰ to −2.4‰) indicate variable sources of DIC with headwater streams recording higher signatures compared to main Tana River. With few exceptions, the entire riverine network was supersaturated in CO2, implying the system is a net source of CO2 to the atmosphere. pCO2 values were generally higher in the lower main Tana River compared to headwater tributaries, opposite to the pattern typically observed in other river networks. This was attributed to high suspended sediment in the main Tana River fuelling in-stream community respiration and net heterotrophy. This was particularly evident during 2009 wet season campaign (median pCO2 of 1432 ppm) compared to 2010 end of wet season (1002 ppm) and 2008 dry season (579 ppm). First-order estimates show in-stream community respiration was responsible for the bulk of total CO2 evasion (59% to 89%) in main Tana River while in tributaries respiration accounted for 4% to 52% of total CO2 evasion, suggesting CO2evasion in tributaries was sustained by processes than respiration, such as CO2-oversaturated groundwater input. While sediment loads increase downstream and thus light availability decreases in the water column, both chlorophyll a (0.2 μg L–1 to 9.6 μg L–1) and primary production (0.004 μmol L–1 h–1 to 7.38 μmol L–1 h–1) increased consistently downstream. Diurnal fluctuations of biogeochemical processes were examined at three different sites along the river continuum (headwater, reservoir, and mainstream), and were found to be substantial only in the headwater stream, moderate in the reservoir and not detectable at main Tana River. The pronounced diurnal fluctuations observed in the headwater stream were largely regulated by periphyton as deduced from the low chlorophyll a in the water column.
... As the surface-water-fed seasonal stream had a contemporary 14 C signature and the local soils do not contain carbonate , the fossil carbonate contribution likely originates from weathering of carbonate minerals in the bed rock that enter the aquatic systems via groundwater flow. Further, the correlations observed between [DIC], [Ca] and δ 13 C DIC are consistent with the influx of carbon from carbonate weathering (Doctor et al., 2008; Bullen and Kendall, 1998). As dilution of [DIC] is observed during event flow, the aged carbon is likely to enter the perennial New Colpita Stream in groundwater . ...
Knowing the rate at which carbon is cycled is crucial to understanding the
dynamics of carbon transfer pathways. Recent technical developments now
support measurement of the 14C age of evaded CO2 from fluvial
systems, which provides an important "fingerprint" of the source of C. Here
we report the first direct measurements of the 14C age of effluxed
CO2 from two small streams and two rivers within the western Amazonian
Basin. The rate of degassing and hydrochemical controls on degassing are also
considered. We observe that CO2 efflux from all systems except for the
seasonal small stream was 14C-depleted relative to the contemporary
atmosphere, indicating a contribution from "old" carbon fixed before
~ 1955 AD. Further, "old" CO2 was effluxed from the perennial
stream in the rainforest; this was unexpected as here connectivity with the
contemporary C cycle is likely greatest. The effluxed gas represents all
sources of CO2 in the aquatic system and thus we used end-member
analysis to identify the relative inputs of fossil, modern and
intermediately aged C. The most likely solutions indicated a contribution
from fossil carbon sources of between 3 and 9% which we interpret as
being derived from carbonate weathering. This is significant as the currently
observed intensification of weather has the potential to increase the future
release of old carbon, which can be subsequently degassed to the atmosphere,
and so renders older, slower C cycles faster. Thus 14C fingerprinting of
evaded CO2 provides understanding which is essential to more accurately model the
carbon cycle in the Amazon Basin.
... One option to separate out the contribution of weathering to stream pCO 2 would be to combine the sampling of CO 2 from stream water with stable isotope analysis, namely d 13 C and d 87 Sr. Their combined use has shown some potential to identify the sources of stream water CO 2 in catchments underlain by calcareous rocks in the past (Bullen and Kendall 1998). Nevertheless, the observed spatial patterns in pCO 2 are consistent with the general idea that aquatic CO 2 concentrations depend on catchment productivity (Demars and Tr emolières 2009;Maberly et al. 2013) which is decreasing with elevation (Sundqvist et al. 2013). ...
Surface waters contribute substantially to carbon dioxide (CO2) emissions to the atmosphere. However, global estimates remain uncertain due to methodological difficulties, such as in precisely estimating gas transfer in steep upland streams. Here, we addressed the question of what drives CO2 evasion from steep mountainous stream network of the European Alps by assessing the spatial and temporal variation of partial pressure of CO2 (pCO2) for 148 streams and the gas transfer coefficient for CO2 (kCO2) for 88 locations within this 254 km2 watershed. Results show that log kCO2 can be predicted reasonably well (r2=0.71, p<0.001, n=88) using a statistical model based on slope, average width, flow velocity and stream discharge. Also, most sites were supersaturated in CO2 with significant variation in pCO2 due to season (September vs. December) and time of day (day vs. night), but not stream order. Resulting median CO2 evasion rates were 145, 119, 46, 43, and 50 mg C m-2 h-1 at 1st to 5th order streams, respectively. CO2 evasion was dependent on season and time of day, with the highest evasion (184.0 kg C h-1) during growing season at nighttime, followed by 124.6 kg C h-1 during daytime. Dormant season nighttime evasion was 30.9 kg C h-1 and daytime evasion only 17.1 kg C h-1. Overall we conclude that CO2 evasion of steep mountainous streams depends on seasonal and diurnal variation in pCO2 and reach-specific variability in kCO2. These controls strongly alter landscape-scale CO2 evasion estimates, with implications for regional to global carbon budgets. © 2016 Association for the Sciences of Limnology and Oceanography.
... Geochemical and isotopic tracing methods have also demonstrated their usefulness to answer these questions. In addition to the commonly used tracer approaches based on major and trace elements and radiogenic and traditional stable isotopes (e.g., Aubert et al., 2001;Négrel et al., 2010;Stille et al., 2009Stille et al., , 2011Bullen and Kendall, 1998;Blum and Erel, 2005;Kendal and Doctor, 2005), new isotope tools have been developed based on the isotopic shifts in metals (e.g., Li, Mg, Ca, Fe, etc.) and metalloids (e.g., B and Si) in the environment (e.g., Bullen and Eisenhauer, 2009;Lemarchand et al., 2010;Cividini et al., 2010;Opfergelt and Delmelle, 2012;Opfergelt et al., 2014;Schmitt et al., 2003Schmitt et al., , 2012Bouchez et al., 2013;Akerman et al., 2014). These studies clearly highlight the importance of coupling various geochemical tracers to identify the biogeochemical processes involved in the CZ function. ...
... Geochemical and isotopic tracing methods have also demonstrated their usefulness to answer these questions. In addition to the commonly used tracer approaches based on major and trace elements and radiogenic and traditional stable isotopes (e.g., Aubert et al., 2001; Négrel et al., 2010; Stille et al., 2009 Stille et al., , 2011 Bullen and Kendall, 1998; Blum and Erel, 2005; Kendal and Doctor, 2005), new isotope tools have been developed based on the isotopic shifts in metals (e.g., Li, Mg, Ca, Fe, etc.) and metalloids (e.g., B and Si) in the environment (e.g., Bullen and Eisenhauer, 2009; Lemarchand et al., 2010; Cividini et al., 2010; Opfergelt and Delmelle, 2012; Opfergelt et al., 2014; Schmitt et al., 2003 Schmitt et al., , 2012 Bouchez et al., 2013; Akerman et al., 2014). These studies clearly highlight the importance of coupling various geochemical tracers to identify the biogeochemical processes involved in the CZ function . ...
... Geochemical and isotopic tracing methods have also demonstrated their usefulness to answer these questions. In addition to the commonly used tracer approaches based on major and trace elements and radiogenic and traditional stable isotopes (e.g., Aubert et al., 2001; Négrel et al., 2010; Stille et al., 2009 Stille et al., , 2011 Bullen and Kendall, 1998; Blum and Erel, 2005; Kendal and Doctor, 2005), new isotope tools have been developed based on the isotopic shifts in metals (e.g., Li, Mg, Ca, Fe, etc.) and metalloids (e.g., B and Si) in the environment (e.g., Bullen and Eisenhauer, 2009; Lemarchand et al., 2010; Cividini et al., 2010; Opfergelt and Delmelle, 2012; Opfergelt et al., 2014; Schmitt et al., 2003 Schmitt et al., , 2012 Bouchez et al., 2013; Akerman et al., 2014). These studies clearly highlight the importance of coupling various geochemical tracers to identify the biogeochemical processes involved in the CZ function . ...
... Geochemical and isotopic tracing methods have also demonstrated their usefulness to answer these questions. In addition to the commonly used tracer approaches based on major and trace elements and radiogenic and traditional stable isotopes (e.g., Aubert et al., 2001;Négrel et al., 2010;Stille et al., 2009Stille et al., , 2011Bullen and Kendall, 1998;Blum and Erel, 2005;Kendal and Doctor, 2005), new isotope tools have been developed based on the isotopic shifts in metals (e.g., Li, Mg, Ca, Fe, etc.) and metalloids (e.g., B and Si) in the environment (e.g., Bullen and Eisenhauer, 2009;Lemarchand et al., 2010;Cividini et al., 2010;Opfergelt and Delmelle, 2012;Opfergelt et al., 2014;Schmitt et al., 2003Schmitt et al., , 2012Bouchez et al., 2013;Akerman et al., 2014). These studies clearly highlight the importance of coupling various geochemical tracers to identify the biogeochemical processes involved in the CZ function. ...
This study presents the results of a geochemical and isotope (U and Sr) study of soil solutions from two experimental sites in the Strengbach catchment, one under spruce trees and the other under beech trees. The soil solution data, combined with the data from soil and vegetation samples, indicate that the "dissolved" U (filtered to 0.45. μm) in the soil solutions is primarily of lithogenic origin, implying that the colloidal U is secondarily associated with organic matter or organo-metallic complexes present in the soil solutions. The uranium activity ratios and Sr isotope ratios of soil solutions are used to decipher the nature of the minerals that control the lithogenic contribution to the soil solutions. A comparison of soil solution data collected over the period 2004-2006 with those collected over the period 1993-2010 indicates a decrease in the Ca and K exported by the soil solutions between 1998 and 2004 at the spruce site and a significantly smaller decrease at the beech site. In addition, the Sr isotope ratios of the soil solutions vary significantly between these two periods at the spruce site but not or much less at the beech site. Such observations suggest that the forest ecosystem at the spruce site is in a transient state associated with recent changes in weathering reactions. The data also suggest that the comparison of U and Sr isotopes in soil solutions and plant samples could be a relevant method for determining whether a forest ecosystem is in a steady or transient state.
... Dissolved 87 Sr/ 86 Sr ratios have often been used to trace weathering patterns, water flow paths, erosion sources, and biological processes in groundwater, watershed/lake, riverine, and oceanic systems Edmond, 1989, 1992;Yang et al., 1996;Bullen and Kendall, 1998;Chesney et al., 1998;Leung and Jiao, 2006). The 87 Sr/ 86 Sr ratio in sediments and suspended matter has also been used to identify sediment provenance in freshwater, estuarine, and marine systems (Faure, 1986;Rachold et al., 1997;Négrel et al., 2000;Ingramand Lin, 2002;Singh and France-Lanord, 2002;Douglas et al., 2003;Bayless et al., 2004). ...
The objective of this thesis was to study element speciation and migration in the boreal environments (Karelia and Central Russia). Specific goals were to i) characterize the molecular weight distribution of trace elements and organic matter (OM) in various types of natural waters, ii) reveal the TE colloidal forms dependence in the continuum soil solution - bog - stream - feeding and terminal lakes in the surface waters of boreal watersheds, and iii) quantify the dependence of stable and radiogenic element isotopic composition on the size fraction, element speciation and physico-chemical conditions of surface waters. The main originality of the work is to apply the method of cascade filtration to study the molecular weight distribution of trace elements in surface waters and to combine the geochemical and isotope techniques, for the first time on the same natural objects, and particularly within the watershed continuum soil solution - bog - stream - feeding and terminal lakes, in order to better understand the factors that control biogeochemical cycling of elements in the subarctic region. The first part is devoted to general introduction and the insight into the problems. The second chapter is aimed at studying natural organic matter size distribution in the natural waters with different redox and hydrodynamic conditions in the continuum soil solution - bog - stream - feeding and terminal lakes for a small watershed with homogeneous bedrock composition. In particular, we investigate organic matter concentrations, weight-average molecular weights, optical properties and carbon/nitrogen ratios to get the information about the origin of DOM (autochthonous / allochthonous), its aromaticity, and its hydrophility / hydrophobicity. The third chapter describes the study the molecular weight distribution of trace elements and it provides quantitative characterization of TE colloidal speciation in pristine, organic-rich rivers and surface waters. We demonstrate that, using TE correlations with iron and OM in the filtrates, one can characterize colloids distribution and compare partition coefficients in the continuum soil solution - bog - stream - feeding and terminal lakes, and also compare natural and modeling data. The fourth chapter describes the results of variations of stable (Cu, Mg) and radiogenic (Sr, Nd) isotopic composition in filtrates and ultrafiltrates of various size fraction in the different types of natural waters of south and north of European Russia boreal zone allowing to identify the factors influencing the isotopic composition variation along the landscape continuum in different size fractions. Finally, the fifth part is devoted to study the variations of iron isotopic composition of different water types and colloidal size fractions. In particular, we investigate the dependence of isotopic composition of filtrates and ultrafiltrate son iron and OM concentrations, pH and other physico-chemical factors. The sixth chapter presents the main conclusions and perspectives. Investigations carried out in this study should contribute to the prediction of TE and OM behavior in the Arctic and boreal regions due to climate warming mostly pronounced in these latitudes.
... Such relations can be used to deduce the flow path of water for a particular region or catchment area (e.g. Bullen and Kendall, 1998), but more information about the environment of the sampling sites (like soil, its mineral content, etc.), is required. One possible interpretation would imply that the increasing trend of the radiogenic Sr (higher δ 87 Sr) with the Sr concentration points to a higher residence time of those samples with more 87 Sr. ...
Human activities in urban areas disturb the natural landscape upon which they develop, disrupting pedogenic processes and ultimately limiting the ecosystem services urban soils provide. To better understand the impacts on and resiliency of urban soils in response to urban development, it is essential to understand the processes by which and degree to which soil physical and chemical properties are altered in urban systems. Here, we apply the source-tracing capabilities of Sr isotopes (87Sr/86Sr) to understand the impacts of urban processes on the composition of soils in eight watersheds in Austin, Texas. We evaluate natural and anthropogenic Sr sources in watersheds spanning a wide range of urbanization, comparing soils by variations in their natural (including mineralogy, thickness, soil type, and watershed) and anthropogenic (including irrigation, soil amendments, and fertilization) characteristics. A strong positive correlation between soil thickness and 87Sr/86Sr is observed among unirrigated soils (R2 = 0.83). In contrast, this relationship is not observed among irrigated soils (R2 = 0.004). 95 % of 42 irrigated soil samples have 87Sr/86Sr values approaching or within the range for municipal supply water. These results indicate soil interaction with municipal water through irrigation and/or water infrastructure leakage. Soils irrigated with municipal water have elevated 87Sr/86Sr values relative to unirrigated soils in seven of eight watersheds. We propose that original soil 87Sr/86Sr values are partially to completely reset by irrigation with municipal water via ion exchange processes. Our results demonstrate that in urban systems, Sr isotopes can serve as an environmental tracer to assess the overprint of urbanization on natural soil characteristics. In the Austin region, resetting of natural soil compositions via urban development is extensive, and the continued expansion of urban areas and irrigation systems may affect the ability of soils to retain nutrients, filter contaminants, and provide other ecosystem services that support environmental resilience.
This study makes use of a highly instrumented active
landslide observatory (9 years of data) in the French Alps, the
Séchilienne slope. Here, we use a combination of major element chemistry
and isotopes ratios (87Sr / 86Sr, δ34S) measured in
different water types of the stable and unstable part of the Séchilienne
instability to assess the contribution of the different lithologies of the
slope and the chemical weathering mechanisms. Chemical and isotopic ratios
are used to characterize weathering processes and the origin of waters and
their flow paths through the massif. A mixing model allows us to allocate the
different major elements to different sources, to identify secondary
carbonate formation as a major process affecting solutes in the subsurface
waters of the instability, and to quantify the involvement of sulfuric and
carbonic acids as a source of protons.
We show that the instability creates favorable and sustained conditions for
the production of sulfuric acid by pyrite oxidation, by opening new
fractures and supplying fresh reactive surfaces. We clearly identify the
contribution of the dissolution of each mineral phase to the chemistry of
the waters, with a clear role of remote gypsum dissolution to the sulfate
budget in the sampled waters. We are also able to refine the preexisting
hydrogeological views on the local water circulation and water flow paths in
the instability by showing the hydrological connectivity of the different
zones. Overall, our results show that the Séchilienne landslide, despite
its role in accelerating rock chemical and physical weathering, acts as a
geological source of CO2 to the atmosphere. If generalizable to other
large instabilities in mountain ranges, this study illustrates the complex
coupling between physical and chemical erosion and their impact on the
carbon cycle and global climate. The study also highlights the importance of
distinguishing between sulfite oxidation and gypsum dissolution as a source
of sulfate ions to rivers, particularly in mountain ranges.
In drought-sensitive lowland catchments, ecohydrological feedbacks to climatic anomalies can give valuable insights into ecosystem functioning in the context of alarming climate change projections. However, the dynamic influences of vegetation on spatio-temporal processes in water cycling in the critical zone of catchments are not yet fully understood. We used water stable isotopes to investigate the impacts of the 2018 drought on dominant soil–vegetation units of the mixed land use Demnitz Millcreek (DMC, north-eastern Germany) catchment (66 km2). The isotope sampling was carried out in conjunction with hydroclimatic, soil, groundwater, and vegetation monitoring. Drying soils, falling groundwater levels, cessation of streamflow, and reduced crop yields demonstrated the failure of catchment water storage to support “blue” (groundwater recharge and stream discharge) and “green” (evapotranspiration) water fluxes. We further conducted monthly bulk soil water isotope sampling to assess the spatio-temporal dynamics of water soil storage under forest and grassland vegetation. Forest soils were drier than the grassland, mainly due to higher interception and transpiration losses. However, the forest soils also had more freely draining shallow layers and were dominated by rapid young (age 2 months), though the lack of deep percolation produced water ages >1 year under forest. We found the displacement of any “drought signal” within the soil profile limited to the isotopic signatures and no displacement or “memory effect” in d-excess over the monthly time step, indicating rapid mixing of new rainfall. Our findings suggest that contrasting soil–vegetation communities have distinct impacts on ecohydrological partitioning and water ages in the sub-surface. Such insights will be invaluable for developing sustainable land management strategies appropriate to water availability and building resilience to climate change.
Detailed hydrogeochemical and isotopic data of groundwaters from Jerba unconfined aquifer are used to provide a better understanding of the natural and anthropogenic processes that control the groundwater mineralization as well as the sources of different groundwater bodies. The total dissolved solid contents of groundwaters are highly variable (0.5–20.3 g.L⁻¹). Groundwaters with Na-K-Cl and Ca-Mg-Cl-SO4 facies, are mainly influenced by the dissolution of evaporites (especially in the central area of the island, where the substrate is mainly made of gypsum), the cation-exchange process in the southern parts of the study area, and seawater intrusion due to overexploitation of the aquifer, especially in the northern, western and southwestern coastal areas where the topographic and piezometric levels are the lowest, and complementary by anthropogenic processes in relation with sewage waters and uncontrolled tanks (in the northern part of Jerba island). Hydrogeochemical characteristics based on bivariate diagrams of major and minor ions show that changes in the chemical composition of groundwater are mainly controlled by the salinization process followed by cation-exchange reactions. Molar Li⁺/SO4²⁻ and Sr²⁺/Cl⁻ ratios for the analysed samples strongly suggest that the source of salinity is seawater intrusion coupled to the dissolution of evaporites. The isotopic signatures permit to classify the studied groundwaters into two different groups. Evaporated groundwaters with enriched δ¹⁸O and δ²H, are mainly encountered in the central areas of the Island Jerba. Saline water, from coastal areas, results from mixing of groundwater with seawater.
This study presents U-Th-Ra isotope data for soils, soil grain size fractions, soil solutions, throughfall, rainwater and tree samples from two experimental plots under spruce and beech trees, in the Strengbach catchment (France) that highlight the importance of the ²³⁸U-²³⁴U-²³⁰Th-²²⁶Ra nuclides and the (²³⁰Th/²³²Th) for the tracing of biogeochemical cycles in the plant-soil-water system of the critical zone (CZ).
The results underscore the very contrasting impact of trees on the U-Th and Ra (Ba) budgets in forest ecosystems with Ra-Ba being strongly and U-Th very little cycled by vegetation, leading to high (²²⁶Ra/²³⁰Th) and (²²⁶Ra/²³⁸U) in trees. Thorium-Ra(Ba) fractionations in soil solutions and soils are therefore strongly influenced by tree uptake and litter decay but U-Th fractionations are little influenced. Compared to other classical isotope systems such as Sr or Nd that are routinely used in the study of the CZ and significantly affected by vegetation cycling, U-Th isotopes are probably among the few tracers to be specific tracers of water-rock interactions in the CZ. The Th activity ratios of soil minerals, especially of minor and secondary mineral phases, show a large range of variation, from 0.7 to 5 in the Strengabch case. These different characteristics give Th activity ratio an important role for tracing the sources of chemical fluxes in soils, soil solutions and vegetation that is currently under-exploited. The Strengbach study illustrates the utility of this approach and the methodology is further strengthened by the combination of U, Th activity ratios and Sr isotope ratios, which also provides additional constraints on the weathering processes affecting the Strengbach bedrocks and the nature of the reservoirs involved in the plant-soil-water transfers. The results emphasize that minor mineral phases such as zircon, sulfate and phosphate are important sources of the U-Th fluxes circulating in soil solutions and significantly control the U and Th budget of the Strengbach soil samples and their Th activity ratios. Furthermore, the comparison of the U-Th-Sr isotopic characteristics of soil solutions and soil grain size fractions allows the recognition of two stages of weathering of the bedrock i.e. 1- dissolution of the primary minerals and formation of the secondary ones in the deep soil horizons, and 2- dissolution of both primary and secondary minerals mainly from the finest soil grain size fractions in the nearest surface soil horizons. The latter might be related to recent modifications of the weathering processes in the catchment, stronger and older under the spruce than the beech plot. We propose that degree of weathering modification is related to the nature of tree cover because spruce plantations have caused an increase of soil acidity and hence of weathering intensity of some minerals and likely also of Ca leaching from the Ca-poor Strengbach soils over the past decades. The U-Th-Sr results of this study also point to the occurrence of isotopically different reservoirs of these elements for trees and gravity soil solutions collected by lysimetric plates. This further suggests that for the Strengbach watershed the gravity soil solutions cannot be the main tree nutrient reservoir.
In December 2008, the Kingston coal ash spill led to contamination of the Emory, Clinch, and Tennessee rivers with toxic metals and metalloids (e.g., arsenic, cadmium, chromium, mercury, vanadium). At present, it is unclear whether the surface waters are impacted by releases from the coal ash residing in the bottom river sediments. Therefore, in April 2016 we collected new samples from several depths of the water column (0, 4, 6, 10 m) from seven impacted and three non-impacted sites along these river systems. The sampled water was analyzed for trace metal and metalloid concentrations and carbon-sulfur-hydrogen-oxygen (C-S-H-O) isotope compositions. The obtained results show that most trace metals and metalloids were below detection limit in the water column (<0.002 mg/L) with only manganese (0.11–0.29 mg/L) exceeding the Environmental Protection Agency drinking water guideline (0.05 mg/L) in two locations. The studied river waters are of local meteoric origin (δ¹⁸O of −6.4 to −5.6‰ and δ²H of −37.4 to −32.4‰) and classified as mainly calcium-bicarbonate (Ca-HCO3) type originating from dissolution of local carbonate bedrock. The latter likely increases the buffering capacity of the studied rivers resulting in pH at neutral to moderately alkaline levels (6.5–8.5) where trace metals and metalloids are most likely to be found adsorbed onto sediments. At the sediment-water interface, however, the Emory River water had the lowest pH (6.6), DO (5.0 mg/L), alkalinity (15–60 mg/L), and δ¹³C of DIC (−13.7‰), suggesting some acidification occurring due to organic matter decomposition in the river sediments. Given that elevated acid-leachable metals and metalloids from coal ash spill are still present at elevated concentrations in the shallow sediments of Emory River, the decreasing pH might be a concern as it could lead to their releases into the water column. Moreover, S isotopes appear to be useful tracers of coal ash and bioremediation of arsenic via microbial sulfide reduction. In the most impacted sediments, the highest δ³⁴S of +4 to +12‰ at depth of ∼5–15 cm points to the raw coal ash enriched in heavier ³⁴S isotopes. In less impacted sediments, the negative δ³⁴S of sulfides (−8 to −6‰) were accompanied by higher leachable arsenic concentrations suggesting that microbial sulfate reduction might be involved in formation of arsenic-rich biogenic sulfides.
From a biogeochemical perspective, catchments can be regarded as reactors that transform the input of various substances via precipitation, deposition, or human activities as they pass through soils and aquifers towards receiving streams. Understanding and modeling the variability of solute concentration in catchment waters require the identification of prevailing processes, determining their respective contributions to the observed transformation of substances, their interplay with hydrological processes, and the determination of anthropogenic impacts. However, numerous biogeochemical processes often interact in a highly non-linear way and vary on temporal and spatial scales, resulting in temporally and spatially varying water chemistry in catchments. This is particularly true for riparian wetlands. Processes in this catchment area often superimpose the influence of the hill slope (and largest) area of the catchment on surface water quality. Accordingly, the first part of this thesis (Study 1 and 2), focuses on the temporal and spatial variability of biogeochemical processes at the catchment scale. Therefore, the first aim was to identify the prevailing biogeochemical processes which affect the quality of catchment waters in two forested granitic catchments. Based on these results, (i) the long-term behavior of these processes was determined (Study 1) and (ii) hot spots of these processes at the catchment scale along different flow paths were identified (Study 2). The second part (Study 3) focuses on the interplay between hydrological and biogeochemical processes in a riparian wetland, with the aim of systematically tracing back the temporal patterns of stream water chemistry to different biogeochemical processes and antecedent hydrological boundary conditions in the wetland. The third part (Study 4 and 5) focuses on weathering processes with the goal (i) of identifying the mineralogical sources of the groundwater’s buffer capacity against acid atmospheric deposition in a forested granitic catchment and (ii) determining the mineralogical sources of the high cation loads in surface water, induced by intensive agricultural activities in two agricultural granitic catchments. To reach these aims, multivariate statistical methods of dimensionality reduction (linear Principal Component Analysis, non-linear Isometric Feature Mapping), a low-pass filtering of time-series, a Cluster analysis, and major and trace element ratios and strontium isotopes were used. A small number of biogeochemical process bundles explained 94% and 89% of the variance of the data set in Study 1 and 2, respectively. In Study 1, redox and topsoil processes, road salt and sulfate contamination were identified as predominating processes influencing water chemistry in the respective catchments. Low-pass filtered time series of component scores revealed a different long-term behavior at different sampling sites in both catchments, which could be traced back to the fraction of wetland area in the respective subcatchments as well as by the varying thickness of the regolith. Study 2 revealed that the upper 1 m topsoil layer could be considered as a biogeochemical hot spot for redox processes, acid-induced podsolization, and weathering processes along different flow paths. Up to 97% of the biogeochemical transformation of the chemical composition of soil solution, groundwater and stream water in the Lehstenbach catchment was restricted to this soil layer representing less than 2% of the catchment’s regolith. Wetland stream water, mobilized in the topsoil layer being considered a biogeochemical hot spot, showed a highly dynamic temporal pattern of component scores. Study 3 revealed four different types of wetland stream water chemical status, depending on the interplay between discharge dynamics, biological activity, and the water table position in the wetland. The sequence of different stream water types roughly followed a seasonal pattern, albeit being heavily modified by the respective hydrological boundary conditions for different years. Extended periods of low groundwater level in the second half of the growing season drastically changed the chemical boundary conditions, becoming evident in a drastic reoxidation of reduced species like sulfides and corresponding effects. Weathering processes are one of the predominating biogeochemical process bundles influencing water chemistry in forested catchments. Study 4 showed that the mineralogical sources of the groundwater’s buffer capacity against acid atmospheric deposition were dominated by the release of base cations from apatite dissolution, preferential cation release from feldspars and biotite, and feldspars weathering. In Study 5, determining the mineralogical sources of the high cation loads in surface water induced by intensive agricultural activities revealed a dominant manure contribution in the topsoil, and enhanced mineral dissolution (plagioclase and biotite) by fertilizer application in subsoils, becoming the unique source of base cations in the saprolite. Stream water chemistry differed from that of soil water, suggesting that stream water chemistry was dominated by elements issued from enhanced mineral and rock weathering. Soil acidification induced by agriculture allows the mobilization of cations stored in soil layers, enhances the rock weathering and accelerates plagioclase dissolution, which can highly influence stream water quality. Numerous biogeochemical, hydrological, and anthropogenic processes were found to interact with each other, mostly with non-linear patterns, influencing catchment water chemistry. The integral approach used in this thesis would be a useful prerequisite to develop accurate and parsimonious models commonly used for water management purposes by distinguishing between short- term and long-term shifts, reducing the number of processes to the predominating ones ultimately to be included in the model, focusing on hot spots and including spatial patterns where necessary and appropriate.
1. Study region
The Clare Valley region of South Australia.
2. Study focus
Continuing extraction of groundwater threatens pools in seasonal and permanent streams. In order to determine this groundwater dependence, the pools and groundwater from corresponding fractured rock aquifers were investigated using environmental tracers (δD, δ18O, 87Sr/86Sr, and major and minor elements). For the 11 paired pool-groundwater sites in the four different catchments, groundwater dependence was evaluated over a four season sampling period.
3. New hydrological insights
In this Mediterranean climate with cool wet winters and dry hot summers strong salinity changes (up to 2.5 times) due to seasonal cycles of wetting and drying were observed in surface water. Oxygen and hydrogen isotope values from pool sites showed strong evaporative enrichment during the dry season with up to 50% net evaporation calculated. Water isotopes from groundwater, however, cluster at the depleted end of the local meteoric water line and most do not show change despite significant seasonal salinity changes. Strontium isotope values and concentrations from the pools over the one year period do not define a mixing relationship. Instead, most pool sites have unchanging strontium isotope values despite the large seasonal change in salinity indicating strong evaporation of groundwater fed pools during this drought year.
The technique of using nitrogen and oxygen isotopic compositions to identify nitrogen sources and assess the nitrogen cycle process has been extensively applied in freshwater research in the last few decades. Nitrate pollution in freshwater has caused concern worldwide: if nitrate sources could be identified, this major form of pollution could be combated. Thus, this technique provides much-needed scientific help with the remediation of freshwater. As the method of determining nitrogen and oxygen isotopic ratios has become more precise, many deficiencies in earlier methods of determination have been overcome. Moreover, each kind of nitrate source and some isotopic fractionation processes have also been well studied; all these factors play an important role in research into the use of isotopic tools in tracing nitrate sources. The joint use dual isotopes with water chemistry are indeed providing very detailed and useful information relating to the identification of nitrate sources and the tracking of nitrate transformation in freshwater systems. Recently, some other stable isotopic tools, which are not affected by biogeochemical processes, have been incorporated into dual-isotope research. These tools are better able to respond to the complexities of environments containing multiple potential nitrate sources coexisting in freshwater system, as well as the mixing of point and nonpoint sources in freshwater systems. At the end of this chapter, two actual researches on surface and groundwater were cited as examples for the better comprehension about the dual-isotope work. © 2013 Springer Science+Business Media Dordrecht. All rights are reserved.
Depletion of Ca in forests and its effects on forest health are poorly
quantified. Depletion has been difficult to document due to limitations
in determining rates at which Ca becomes available for ecosystem
processes through weathering, and difficulty in determining changes in
ecosystem storage. We coupled a detailed analysis of Sr isotopic
composition with a mass balance at Cone Pond Watershed, New Hampshire,
in order to further constrain estimates of these processes. Strontium
acted as an analog for Ca in most processes except translocation of
nutrients within forest vegetation. Variability in mineralogic and Sr
isotopic composition of bedrock and soils complicated assessment of the
87Sr/86Sr ratio released to solution by weathering
reactions. By conducting a mass balance on atmospherically derived Ca,
it is possible to distinguish Ca weathering losses from Ca leached from
ecosystem pools. The calcium weathering rate estimated by this method
was less than half of that determined by mass balance assuming steady
state conditions.
Sr isotopic ratios of atmospheric deposition, surface and subsurface water, and geologic materials were measured in an alpine/subalpine watershed to characterize weathering reactions and identify sources of dissolved Ca in stream water. Previous studies have noted an excess of Ca in stream water above that expected from stoichiometric weathering of the dominant bedrock minerals. Mixing calculations based on 87Sr/86Sr indicate that on an annual basis, 26 ± 7% of Ca export in streams is atmospherically derived, 23 ± 1% is from weathering of plagioclase, and the remainder is from weathering of calcite present in trace amounts in the bedrock. A potential source of error when applying Sr isotopes in catchment studies is determination of the 87Sr/86Sr of Sr released by mineral weathering, which is complicated by the wide range of mineral isotopic compositions, particularly in older rocks, and the variable rates at which the minerals weather. In this study, base-flow stream chemistry was used to represent the 87Sr/86Sr of Sr derived from mineral weathering because it effectively integrates the potentially variable isotopic composition of Sr released by weathering in the alpine environment.
Leakage from sinkhole lakes significantly influences recharge to the
Upper Floridan aquifer in poorly confined sediments in northern Florida.
Environmental isotopes (oxygen 18, deuterium, and tritium),
chlorofluorocarbons (CFCs: CFC-11, CCl3F; CFC-12,
CCl2F2; and CFC-113,
C2Cl3F3), and solute tracers were used
to investigate groundwater flow patterns near Lake Barco, a seepage lake
in a mantled karst setting in northern Florida. Stable isotope data
indicated that the groundwater downgradient from the lake contained
11-67% lake water leakage, with a limit of detection of lake water in
groundwater of 4.3%. The mixing fractions of lake water leakage, which
passed through organic-rich sediments in the lake bottom, were directly
proportional to the observed methane concentrations and increased with
depth in the groundwater flow system. In aerobic groundwater upgradient
from Lake Barco, CFC-modeled recharge dates ranged from 1987 near the
water table to the mid 1970s for water collected at a depth of 30 m
below the water table. CFC-modeled recharge dates (based on CFC-12) for
anaerobic groundwater downgradient from the lake ranged from the late
1950s to the mid 1970s and were consistent with tritium data.
CFC-modeled recharge dates based on CFC-11 indicated preferential
microbial degradation in anoxic waters. Vertical hydraulic
conductivities, calculated using CFC-12 modeled recharge dates and
Darcy's law, were 0.17, 0.033, and 0.019 m/d for the surficial aquifer,
intermediate confining unit, and lake sediments, respectively. These
conductivities agreed closely with those used in the calibration of a
three-dimensional groundwater flow model for transient and steady state
flow conditions.
A quantitative understanding of the factors controlling the variation of dissolved organic carbon (DOC) in headwater streams is of scientific concern for at least two reasons. First, quantifying the overall carbon budgets of lotic systems is needed for a fundamental understanding of these systems. Second, DOC interacts strongly with other dissolved substances (heavy metals in particular) and plays an important role in the transport of contaminants.
In the Snake River near Montezuma, Colorado, measurements of DOC from 1980 to 1986 show rapid decreases in concentration from a peak very early in the snowmelt period. Peak DOC concentrations occur approximately one month prior to peak discharge in the stream. The decline in DOC with time is approximately exponential, suggesting that a simple flushing mechanism can explain the response. We examined hydrological mechanisms to explain the observed variability of DOC in the Snake River by simulating the hydrological response of the catchment using TOPMODEL and routing the predicted flows through a simple model that accounted for temporal changes in DOC. Conceptually the DOC model represents a terrestrial (soil) reservoir in which DOC builds up during low flow periods and is flushed out by infiltrating meltwaters. The model reproduces the main features of the observed variation in DOC in the Snake River and thus lays the foundation for quantitatively linking hydrological processes with carbon cycling through upland catchments. Model results imply that a significant fraction of the soils in the Snake River catchment contribute DOC to the stream during peak discharge. Our work represents one of the first attempts to quantitatively describe the hydrological controls on DOC dynamics in a headwater stream. These controls are studied through the model by imposing mass balance constraints on both the flux of water through the various DOC source areas and the amount of DOC that can accumulate in these areas.
The recent literature on the kinetics of water-rock interactions is reviewed. The data are then extended to provide a quantitative framework for the description of weathering and alteration. The available experimental data on dissolution of silicates verifies quantitatively the usual mineral stability series in sedimentary petrology. The rate of hydration of carbonic acid is shown to be a possible limiting factor in water-rock interactions. The framework is developed to enable use of laboratory dissolution experimental results and thermodynamics to arrive at a rate law applicable up to equilibrium and therefore applicable to natural systems. The kinetic justification for the significance of a water-rock ratio is discussed. With a proper treatment of fluid flow, the equations are applied to the weathering profile leading to the development of bauxites from nepheline syenites.
Recent measurements of the carbon isotopic abundance of atmospheric methane give a value of sigma(C-13/C-12) = -47.0 within 0.3 parts per thousand, which is significantly different from earlier values measured between 1950 and 1970. The isotopic composition of various sources and the possibility of a temporal trend are discussed. The average methane concentration measured was 1.66 ppm, which is in accord with the increase in concentration since 1965-1970 observed in other studies.
Stable isotopes of strontium provide a unique quantification of ecosystem processes because organisms do not differentiate between them. For landscapes with contrasting geologies, these isotopes can identify atmospheric source material from local weathered material. This study quantified the input of strontium, distribution within the ecosystem, canopy capture versus leaf leachate, canopy loss, and Sr increment in biomass from an atmospheric origin. Forest ecosystems were studied along an elevational gradient in New Mexico. Spruce forests had a much greater capacity for capturing atmospheric Sr than aspen forests; however, aspen contained more total atmospheric Sr in their tissues because of greater uptake rates and the ability to utilize atmospheric deposited Sr before the initiation of the aspen forest. This technique has excellent capabilities for estimating the relative importance of atmospheric and weathering inputs to certain ecosystems.
Granitoid rocks of the compositionally zoned Late Cretaceous Toulumne Intrusive Suite in the central Sierra Nevada, California, have initial87Sr/86Sr values (Sri) and143Nd/144Nd values (Ndi) that vary from 0.7057 to 0.7067 and from 0.51239 to 0.51211 respectively. The observed variation of both Sri and Ndi and of chemical composition in rocks of the suite cannot be due to crystal fractionation of magma solely under closed system conditons. The largest variation in chemistry, Ndi, and Sri is present in the outer-most equigranular units of the Tuolumne Intrusive Suite. Sri varies positively with SiO2, Na2O, K2O, and Rb concentrations, and negatively with Ndi, Al2O3, Fe2O3, MgO, FeO, CaO, MnO, P2O5, TiO2, and Sr concentrations. This covariation of Sri, Ndi and chemistry can be modeled by a process of simple mixing of basaltic and granitic magmas having weight percent SiO2 of 48.0 and 73.3 respectively. Isotopic characteristic of the mafic magma are Sri=0.7047, Ndi=0.51269 and
18O=6.0, and of the felsic magma are Sri=0.7068, Ndi=0.51212 and
18O=8.9. The rocks sampled contain from 50 to 80% of the felsic component. An aplite in the outer equigranular unit of the Tuolumne Intrusive Suite apparently was derived by fractional crystallization of plagioclase and hornblende from magma with granudiorite composition that was a product of mixing of the magmas described above. Siliceous magmas derived from the lower crust, having a maximum of 15 percent mantle-derived mafic component, are represented by the inner prophyritic units of the Tuolumne Intrusive Suite.