δ2H Data Research Articles

Improved end-member characterisation of modern organic matter pools in the Ohrid Basin (Albania, Macedonia) and evaluation of new palaeoenvironmental proxies

Abstract. We present elemental, lipid biomarker and, in the supplement, compound-specific isotope (δ13C, δ2H) data for soils and leaf litter collected in the catchment of Lake Ohrid (Albania, Macedonia), as well as macrophytes, particulate organic matter and sediments from the lake itself. Lake Ohrid provides an outstanding archive of continental environmental change of at least 1.2 million years and the purpose of our study is to ground truth organic geochemical proxies that we developed in order to study past changes in the terrestrial biome. We show that soils dominate the lipid signal of the lake sediments rather than the vegetation or aquatic biomass. There is a strong imprint of suberin monomers on the composition of total lipid extracts and chain-length distributions of n-alkanoic acids, n-alcohols, ω-hydroxy acids and α, ω-dicarboxylic acids. Our end-member survey identifies that ratios of mid-chain length suberin-derived to long-chain length cuticular-derived alkyl compounds as well as their average chain length distributions can be used as new molecular proxies of organic matter sources to the lake. We tested these for the 8.2 ka event, a pronounced and widespread Holocene climate fluctuation. In SE Europe climate became drier and cooler in response to the event, as is clearly recognisable in the carbonate and organic carbon records of Lake Ohrid sediments. Our new proxies indicate biome modification in response to hydrological changes, identifying two phases of increased soil organic matter (OM) supply, first from soils with moderately degraded OM and then from more degraded soils. Our study demonstrates that geochemical fingerprinting of terrestrial OM should focus on the main lipid sources, rather than the living biomass. Both can exhibit climate-controlled variability, but are generally not identical.

Continuous monitoring of stream δ18O and δ2H and stormflow hydrograph separation using laser spectrometry in an agricultural catchment

AbstractA portable Wavelength Scanned‐Cavity Ring‐Down Spectrometer (Picarro L2120) fitted with a diffusion sampler (DS‐CRDS) was used for the first time to continuously measure δ18O and δ2H of stream water. The experiment took place during a storm event in a wet tropical agricultural catchment in north‐eastern Australia. At a temporal resolution of one minute, the DS‐CRDS measured 2160 δ18O and δ2H values continuously over a period of 36 h with a precision of ±0.08 and 0.5‰ for δ18O and δ2H, respectively. Four main advantages in using high temporal resolution stream δ18O and δ2H data during a storm event are highlighted from this study. First, they enabled us to separate components of the hydrograph, which was not possible using high temporal resolution electrical conductivity data that represented changes in solute transfers during the storm event rather than physical hydrological processes. The results from the hydrograph separation confirm fast groundwater contribution to the stream, with the first 5 h of increases in stream discharge comprising over 70% pre‐event water. Second, the high temporal resolution stream δ18O and δ2H data allowed us to detect a short‐lived reversal in stream isotopic values (δ18O increase by 0.4‰ over 9 min), which was observed immediately after the heavy rainfall period. Third, δ18O values were used to calculate a time lag of 20 min between the physical and chemical stream responses during the storm event. Finally, the hydrograph separation highlights the role of event waters in the runoff transfers of herbicides and nutrients from this heavily cultivated catchment to the Great Barrier Reef. Copyright © 2015 John Wiley & Sons, Ltd.

Groundwater Inflows Characterization in the Pahang-Selangor Raw Water Transfer Tunnel Using δ<sup>2</sup>H and δ<sup>18</sup>O as Tracers

Groundwater inflows represent a very important element in hydrological circulation. Water inflows in Pahang-Selangor Raw Water Transfer Tunnel have been analyzed for isotopes stable of δ2H and δ18O. 61 samples were collected, including Tunnel Seepage Water (TSW), surface water and hot spring water samples within the study area which to understand the effect of multi topographical scale and geological characteristic. Deuterium (δ2H) and Oxygen-18 (δ18O) contributes the understanding of the origin and flow paths of water in the mountainous region. The δ2H and δ18O data obtained from TSW samples ranging from-45.73%0to-54.68%0and-46.01%0to-58.49%0are clustered along the local meteoric water line (LMWL) indicating that the groundwater originated from meteoric water. δ2H and δ18O data, primarily indicate the recharge altitude from 100m–550m which control by the sub vertical flow path mainly from geological structures (i.e. fractures and faults) followed by the groundwater. The altitude effect is indicated by the relation between the stable isotope values and elevation in meters highlighting a depletion of the heavy stable isotope with the increase of the tunnel overburden. The general trend obtained is δ2H and δ18O decreased with the increase of the overburden. The deviation of the δ2H and δ18O data from the expected trends may reflect the recharges are coming from the sub-horizontal flow path such as rivers or water infiltration from the valley. The results show that environmental isotopes indicates a better understanding of the complex hydrogeological system in a mountainous region and interaction between groundwater in granitic and meta-sedimentary rock formation along the tunnel project.

Stable hydrogen isotopes identify leapfrog migration, degree of connectivity, and summer distribution of Golden Eagles in eastern North America

ABSTRACT Knowledge of the distribution and movements of populations of migratory birds is useful for the effective conservation and management of biodiversity. However, such information is often unavailable because of the difficulty of tracking sufficient numbers of individuals. We used more easily obtained feather stable hydrogen isotope ratios (δ2H) to predict the summer grounds of the small, threatened, and migratory population of Golden Eagles (Aquila chrysaetos) in eastern North America. We then identified summer locations and the extent of migratory connectivity for this population. We collected δ2H (δ2Hf), stable carbon isotope (δ13C), and stable nitrogen isotope (δ15N) data from the body feathers of 47 juvenile, subadult, and adult Golden Eagles. Values of δ13C and δ15N suggested that all but 2 birds obtained food from terrestrial-based food webs and therefore that δ2H data were appropriate for inferring the geographic region of molt for the majority of birds. There was relatively large interfeath...

Deuterium as a food source tracer: Sensitivity to environmental water, lipid content, and hydrogen exchange

Hydrogen stable isotopes (δ2H) are used for quantifying resources supporting food webs. However, application of δ2H in mixing models requires; (1) correction for environmental water (ω) in consumer tissues, (2) consideration of differential fractionation among biochemical constituents, and (3) consideration of differential H-exchange among samples and standards. We present data and sensitivity analyses addressing each of these issues and provide recommendations for future isotope food web studies. First, we determined from field data that maximum ω for aquatic consumers averaged 0.23 ± 0.03, similar to the median ω from a survey of published values (0.22 ± 0.02). Resource use estimates based solely on δ2H data were sensitive to the selected ω value. Second, to quantify the potential bias in bulk tissue analysis from differential tissue fractionation, we calculated the change in whole organism δ2H before and after lipid extraction for 61 aquatic samples. The average change in consumers' δ2H after lipid extraction was a positive shift of 11.8‰ relative to the pre-extraction value. This shift resulted in a minor change in resource use estimates when correcting for lipids. Finally, we evaluated the impact of correcting for H-exchange in samples using standards with dissimilar H-exchange portions. The impact of the correction factor for H-exchange on resource use estimates could be large if suitable standards are not used for comparison. From these analyses we conclude that despite these complicating factors, analysis of resource use is possible using whole organisms' δ2H, especially in combination with cautionary sensitivity analysis.

Stable isotope anatomy of tropical cyclone Ita, North-Eastern Australia, April 2014.

The isotope signatures registered in speleothems during tropical cyclones (TC) provides information about the frequency and intensity of past TCs but the precise relationship between isotopic composition and the meteorology of TCs remain uncertain. Here we present continuous δ18O and δ2H data in rainfall and water vapour, as well as in discrete rainfall samples, during the passage of TC Ita and relate the evolution in isotopic compositions to local and synoptic scale meteorological observations. High-resolution data revealed a close relationship between isotopic compositions and cyclonic features such as spiral rainbands, periods of stratiform rainfall and the arrival of subtropical and tropical air masses with changing oceanic and continental moisture sources. The isotopic compositions in discrete rainfall samples were remarkably constant along the ~450 km overland path of the cyclone when taking into account the direction and distance to the eye of the cyclone at each sampling time. Near simultaneous variations in δ18O and δ2H values in rainfall and vapour and a near-equilibrium rainfall-vapour isotope fractionation indicates strong isotopic exchange between rainfall and surface inflow of vapour during the approach of the cyclone. In contrast, after the passage of spiral rainbands close to the eye of the cyclone, different moisture sources for rainfall and vapour are reflected in diverging d-excess values. High-resolution isotope studies of modern TCs refine the interpretation of stable isotope signatures found in speleothems and other paleo archives and should aim to further investigate the influence of cyclone intensity and longevity on the isotopic composition of associated rainfall.

Contrasting assignment of migratory organisms to geographic origins using long‐term versus year‐specific precipitation isotope maps

Summary As a result of predictable large‐scale continental gradients in the isotopic composition of precipitation, stable isotopes of hydrogen (δ2H) are useful endogenous markers for delineating long‐distance movements of animals. Models to predict patterns of δ2H in precipitation (δ2Hp), and consequently determine likely geographic origin of migratory animals, have traditionally used static, amount‐weighted long‐term average values of δ2Hp over the growing season. However, animal tissues reflect H incorporated from food webs that integrate precipitation over a single year's growing season or portions thereof. Inter‐annual variation in precipitation and other climatic variables may lead to deviations from predictions derived from long‐term mean precipitation isotopic values and could therefore lead to assignment errors for specific years and locations that are atypical. We examined whether using biologically relevant short‐term δ2Hp isoscapes can improve estimates of geographic origin in comparison with long‐term isoscapes. Using δ2H data from known‐origin tissues of two migratory organisms in North America and Europe, we compared the accuracy, precision and similarity of assigned origins using both short‐ and long‐term δ2Hp isoscapes. Relative to long‐term δ2Hp isoscapes, using short‐term isoscapes for assignment often resulted in dissimilar regions of likely origin but did not significantly improve accuracy or precision. This was likely due to reduced spatial coverage in the data used to generate the short‐term δ2Hp isoscapes. We suggest that continued efforts to collect precipitation isotope data with a large spatiotemporal range will benefit future research on incorporating temporal variation in the amount and isotopic composition of precipitation into geospatial assignment models.

Understanding 2H/1H systematics of leaf wax n-alkanes in coastal plants at Stiffkey saltmarsh, Norfolk, UK

Interpretation of sedimentary n-alkyl lipid δ2H data is complicated by a limited understanding of factors controlling interspecies variation in biomarker 2H/1H composition. To distinguish between the effects of interrelated environmental, physical and biochemical controls on the hydrogen isotope composition of n-alkyl lipids, we conducted linked δ2H analyses of soil water, xylem water, leaf water and n-alkanes from a range of C3 and C4 plants growing at a UK saltmarsh (i) across multiple sampling sites, (ii) throughout the 2012 growing season, and (iii) at different times of the day. Soil waters varied isotopically by up to 35‰ depending on marsh sub-environment, and exhibited site-specific seasonal shifts in δ2H up to a maximum of 31‰. Maximum interspecies variation in xylem water was 38‰, while leaf waters differed seasonally by a maximum of 29‰. Leaf wax n-alkane 2H/1H, however, consistently varied by over 100‰ throughout the 2012 growing season, resulting in an interspecies range in the εwax/leafwater values of −79‰ to –227‰. From the discrepancy in the magnitude of these isotopic differences, we conclude that mechanisms driving variation in the 2H/1H composition of leaf water, including (i) spatial changes in soil water 2H/1H, (ii) temporal changes in soil water 2H/1H, (iii) differences in xylem water 2H/1H, and (iv) differences in leaf water evaporative 2H-enrichment due to varied plant life forms, cannot explain the range of n-alkane δ2H values we observed. Results from this study suggests that accurate reconstructions of palaeoclimate regimes from sedimentary n-alkane δ2H require further research to constrain those biological mechanisms influencing species-specific differences in 2H/1H fractionation during lipid biosynthesis, in particular where plants have developed biochemical adaptations to water-stressed conditions. Understanding how these mechanisms interact with environmental conditions will be crucial to ensure accurate interpretation of hydrogen isotope signals from the geological record.

Environmental isotopic and hydrochemical characteristics of groundwater from the Sandspruit Catchment, Berg River Basin, South Africa

The Sandspruit catchment (a tributary of the Berg River) represents a drainage system, whereby saline groundwater with total dissolved solids (TDS) up to 10,870 mg/l, and electrical conductivity (EC) up to 2,140 mS/m has been documented. The catchment belongs to the winter rainfall region with precipitation seldom exceeding 400 mm/yr, as such, groundwater recharge occurs predominantly from May to August. Recharge estimation using the catchment water-balance method, chloride mass balance method, and qualified guesses produced recharge rates between 8 and 70 mm/yr. To understand the origin, occurrence and dynamics of the saline groundwater, a coupled analysis of major ion hydrochemistry and environmental isotopes (δ(18)O, δ(2)H and (3)H) data supported by conventional hydrogeological information has been undertaken. These spatial and multi-temporal hydrochemical and environmental isotope data provided insight into the origin, mechanisms and spatial evolution of the groundwater salinity. These data also illustrate that the saline groundwater within the catchment can be attributed to the combined effects of evaporation, salt dissolution, and groundwater mixing. The salinity of the groundwater tends to vary seasonally and evolves in the direction of groundwater flow. The stable isotope signatures further indicate two possible mechanisms of recharge; namely, (1) a slow diffuse type modern recharge through a relatively low permeability material as explained by heavy isotope signal and (2) a relatively quick recharge prior to evaporation from a distant high altitude source as explained by the relatively depleted isotopic signal and sub-modern to old tritium values.

The groundwater recharge regime of some slightly metamorphosed neoproterozoic sedimentary rocks: an application of natural environmental tracers

AbstractIsotope data of precipitation and groundwater in parts of the Voltaian Basin in Northern Ghana were used to explain the groundwater recharge regime in the area. Groundwater recharge is an important parameter in the development of a decision support system for the management and efficient utilization of groundwater resources in the area. It is therefore important to establish the processes and sources of groundwater recharge. δ18O and δ2H data for local precipitation suggest enrichment relative to the Global Meteoric Water Line (GMWL) and indicate that precipitation takes place at a relative humidity less than 100%. The groundwater data plot on an evaporation line with a slope of 5, suggesting a high degree of evaporative enrichment of the precipitation in the process of vertical infiltration and percolation through the unsaturated zone into the saturated zone. This finding is consistent with the observation of high evapotranspiration rates in the area and ties in with the fact that significant clay fraction in the unsaturated zone limits vertical percolation and thus exposes the percolating rainwater to the effects of high temperatures and low humidities resulting in high evapotranspiration rates. Groundwater recharge estimates from the chloride mass balance, CMB, method suggest recharge in the range of 1.8–32% of the annual average precipitation in the form of rainfall. The highest rates are associated with areas where open wells encourage significant amount of groundwater recharge from precipitation in the area. In the northern parts of the study area, groundwater recharge is lower than 12%. The recharge so computed through the application of the CMB methodology takes on a spatial distribution akin to the converse of the spatial pattern of both δ18O and δ2H in the area. As such, the locations of the highest recharge are associated with the most depleted values of the two isotopes. This observation is consistent with the assertion that low vertical hydraulic conductivities slow down vertical percolation of precipitation down to the groundwater water. The percolating precipitation water thus gets enriched in the heavier isotopes through high evapotranspiration rates. At the same time, the amount of water that finally reaches the water table is considerably reduced. Copyright © 2013 John Wiley & Sons, Ltd.

Hydrochemistry of a complex volcano-sedimentary aquifer using major ions and environmental isotopes data: Dalha basalts aquifer, southwest of Republic of Djibouti

In the Republic of Djibouti (Horn of Africa), fractured volcanic aquifers are the main water resources. The country undergoes an arid climate. Alluvial aquifers exist in the wadis (intermittent streams) valleys and, in relation with volcanic aquifers, form complex volcano-sedimentary systems. Due to increasing water demands, groundwater resources are overexploited and require a rigorous management. This paper is focused on the Dalha basalts aquifer, located in the Dikhil area (Southwest of Djibouti). This aquifer is of vital importance for this area. Hydrochemical data and isotopic tracers (18O and 2H) were used to identify factors and phenomena governing the groundwater’s mineralization. The Piper diagram shows complex water types. Results from multivariate statistical analyses highlight three water families according to their locations: (1) groundwater characterized by low ionic concentrations located at the wadis zones; (2) groundwater characterized by moderate salinity and (3) highly mineralized waters mainly flowing in the eastern and central part of the study area, in volcanic aquifers. Results from scatter plots, especially Na versus Cl and Br versus Cl, suggest that the origin of more saline waters is not from dissolution of halite. The δ18O and δ2H data indicate that the groundwater flowing in the alluvial aquifer is of meteoric origin and fast percolation of rainwater occurs in the volcanic aquifers. These findings provide a preliminary understanding of the overall functioning of this complex volcano-sedimentary system. Additional investigations (pumping tests, numerical modeling) are in progress to achieve a more comprehensive understanding of this system.

Isotopic and Geochemical Study of the Vapor Dominated Geothermal System of Copahue, Neuquen, Argentine Republic

The first isotopic and geochemical data on samples of fresh waters, hot waters and vapor condensates from the geothermal system Copahue-Caviahue are presented. 3H, 2H and 18O analyses, suggest that the recharge of meteoric water in the deep seated reservoir occurs at around 2000 m a.s.l. In addition a shallower hot water reservoir shows a recent recharge at the same altitude. δ13C of the CO2 coming with vapor in one of the fumaroles ("Las Maquinitas") -6,80/oo vs PDB and the high gas-vapor ratio account for its magmatic origin and for the existence of a magmatic fed hydrothermally altered pipe. δ18O and δ2H data on vapor of the "Copahue-1", first drilled geothermal well, sampled recently and two years ago, show an evolution in the isotopic content as well as in the gas vapor ratio. This fact along with the geochemical and geophysical evidence allow the establishment of a preliminary model for the geothermal reservoir.

Isotopes of oxygen-18 and deuterium in precipitation in Slovakia / Izotopy kyslíka-18 A deutéria v zrážkach na Slovensku

The article synthesizes available information on isotopic composition of precipitation in Slovakia (the Western Carpathians). Monthly δ18O data from eleven stations and period 1988-1997 were used to investigate correlations among the stations, altitude, air temperature and precipitation amount effects. The mean annual altitude and air temperature gradients of δ18O in precipitation were 0.21‰/100 m and 0.36‰/1°C, respectively. Maps of spatial distribution of mean annual δ18O in precipitation based on both gradients were constructed. The two maps do not significantly differ for the majority of Slovakia. δ2H data were available for only three stations. Local meteoric water line derived for the station with the longest data series (δ2H = = 7.86δ18O + 6.99) was close to the Global Meteoric Water line. Its parameters in periods 1991-1993 and 1991-2008 did not change. The study indicates that a more detailed monitoring of isotopic composition of precipitation in mountains should be carried out in the future. The highest station exhibited very small seasonal variability of δ18O in precipitation compared to other Slovak stations. The second highest mountain station had significantly higher deuterium excess than the neighboring stations located in the valley. In some analyses the data from the nearest stations situated abroad (Vienna, Krakow) were used.

Isotopic and hydrochemical data as indicators of recharge areas, flow paths and water–rock interaction in the Caldas da Rainha–Quinta das Janelas thermomineral carbonate rock aquifer (Central Portugal)

Summary An updated conceptual circulation model for the Caldas da Rainha and Quinta das Janelas thermomineral waters was developed. These thermomineral waters (T ≈ 33 °C) are related to a huge syncline ascribed to the regional flow paths. Two diapiric structures were responsible for the uplift and subsequent folding of regional Jurassic carbonate rocks. Environmental isotopic (δ2H and δ18O) data indicates that the main recharge area of the thermomineral system is linked to the Jurassic limestones (Candeeiros Mountains, E border of the syncline). The thermomineral waters belong to the Cl–Na sulphurous-type, with a total mineralization of about 3000 mg/L. The thermomineral aquifer system seems to be “isolated” from anthropogenic contamination, which is typical for the local shallow groundwater systems, due to the existence of impermeable layers composed of a series of loamy and detritic rocks of the Upper Jurassic. The presence of 3H in some thermomineral borehole waters, not accompanied by an increase in SO 4 2 - and NO 3 - , could be ascribed to different underground flow paths and different mean residence time. The δ34S(SO4) and δ18O(SO4) values of dissolved sulphate of groundwaters of the Caldas da Rainha Spas indicate that the sulphate is the result of water–rock interaction with evaporitic rocks (e.g. gypsum and anhydrite) ascribed to the regional synclinal structure.

Identification of groundwater recharge sources and processes in a heterogeneous alluvial aquifer: results from multi‐level monitoring of hydrochemistry and environmental isotopes in a riverside agricultural area in Korea

AbstractWe evaluated sources and pathways of groundwater recharge for a heterogeneous alluvial aquifer beneath an agricultural field, based on multi‐level monitoring of hydrochemistry and environmental isotopes of a riverside groundwater system at Buyeo, Korea. Two distinct groundwater zones were identified with depth: (1) a shallow oxic groundwater zone, characterized by elevated concentrations of NO3− and (2) a deeper (>10–14 m from the ground surface) sub‐oxic groundwater zone with high concentrations of dissolved Fe, silica, and HCO3−, but little nitrate. The change of redox zones occurred at a depth where the aquifer sediments change from an upper sandy stratum to a silty stratum with mud caps. The δ18O and δ2H values of groundwater were also different between the two zones. Hydrochemical and δ18Oδ2H data of oxic groundwater are similar to those of soil water. This illustrates that recharge of oxic groundwater mainly occurs through direct infiltration of rain and irrigation water in the sandy soil area where vegetable cropping with abundant fertilizer use is predominant. Oxic groundwater is therefore severely contaminated by agrochemical pollutants such as nitrate. In contrast, deeper sub‐oxic groundwater contains only small amounts of dissolved oxygen (DO) and NO3−. The 3H contents and elevated silica concentrations in sub‐oxic groundwater indicate a somewhat longer mean residence time of groundwater within this part of the aquifer. Sub‐oxic groundwater was also characterized by higher δ18O and δ2H values and lower d‐excess values, indicating significant evaporation during recharge. We suggest that recharge of sub‐oxic groundwater occurs in the areas of paddy rice fields where standing irrigation and rain water are affected by strong evaporation, and that reducing conditions develop during subsequent sub‐surface infiltration. This study illustrates the existence of two groundwater bodies with different recharge processes within an alluvial aquifer. Copyright © 2009 John Wiley & Sons, Ltd.

Hydrogeologic controls on groundwater recharge and salinization: a geochemical analysis of the northern Hueco Bolson aquifer, Texas, USA

Identification of hydrogeologic controls on groundwater flowpaths, recharge, and salinization is often critical to the management of limited arid groundwater resources. One approach to identifying these mechanisms is a combined analysis of hydrogeologic and hydrochemical data to develop a comprehensive conceptual model of a groundwater basin. To demonstrate this technique, water samples were collected from 33 discrete vertical zone test holes in the Hueco Bolson aquifer, located within the Trans-Pecos Texas region and the primary water resource for El Paso, Texas, USA and Juarez, Mexico. These samples were analyzed for a suite of geochemical tracers and the data evaluated in light of basin hydrogeology. On the basis of δ2H and δ18O data, two regional recharge sources were recognized, one originating from western mountain-fronts and one from through-flow of the adjacent Tularosa aquifer. Chloride concentrations were strongly correlated with lithologic formations and both Cl/Br and 36Cl ratios suggested the primary chloride source is halite dissolution within a specific lithologic unit. In contrast, sulfur isotopes indicated that most sulfate originates from Tularosa basin Permian gypsum sources. These results yielded a more comprehensive conceptual model of the basin, which suggested that chloride salinization of wells is the result of upconing of waters from the Fort Hancock formation.

Hydrogeochemical and isotopic investigation of the Kolan geothermal field, southeastern Turkey

The Kolan geothermal field is located 24 km northwest of the Karakocan area of Elazig city in southeastern Turkey. The Keban crystallized limestone of Permo-Carboniferous age is the oldest unit in the area. This unit is overlain by the middle-upper Eocene Kirkgecit formation consisting of conglomerate, sandstone, limestone and marl alternations. The youngest unit in the area is the Upper Miocene-Lower Pliocene Karabakir formation consisting of basalt, andesite and tuffs. Thermal Springs in the Kolan field issue along two major fault zones. The temperature of the hot springs is between 38°C and 45°C. Thermal waters in the area are heated by the geothermal gradient. The waters are classified as “hot” or “very hot” and as “brackish” waters. On the basis of International Association of Hydrogeologists Classification (IAH), waters are grouped as “Ca–Na-HCO3–CO2-bearing thermal and mineral waters”. Chemical analyses indicate a chemical composition of Ca>(Na+K)>Mg - HCO3>SO4>Cl. Saturation calculations reveal that the waters are oversaturated with respect to calcite, dolomite and aragonite while undersaturated with respect to gypsum, anhydrite and halite minerals. On the basis of δ18O, δ2H and 3H isotope data, Kolan waters are of meteoric origin, recharged from high elevations and then circulated deeply.

STABLE HYDROGEN AND OXYGEN ISOTOPE COMPOSITION OF PRECIPITATION IN NORTHEASTERN COLORADO

ABSTRACT: Where data are available, hydrologic studies may use precipitation's stable oxygen and hydrogen isotope composition to investigate streamflow, ground water/surface water interaction, and ground water recharge. Paleoclimate studies utilize the δ18Oprecipitation-Tair relationship, in conjunction with lake sediments, fossils, or old ground waters, for example, to estimate pale-otemperatures. Ecological studies utilize precipitation and soil water isotope composition to track moisture uptake in plants, and to trace species migration patterns. Such studies require that the isotopic composition of precipitation be known. Oxygen-18 (δ18O) and deuterium (δ2H) data for precipitation are lacking in the semi-arid portion of the north-central U.S. Great Plains, and thus there is a need to establish additional meteoric water lines as isotope input functions across the region, as well as to develop better understanding of the isotopic climate linkages that control oxygen and hydrogen isotope ratios in precipitation. This study determined the δ18O and δ2H composition of precipitation in the Pawnee Grasslands of northeastern Colorado from 1994 through 1998 using archived National Atmospheric Deposition Program samples. The resulting local water line follows the relationship δ2H = 7.86 δ18O-7.66, and the data show a δ18Oweekly - Tweekly relationship of δ18O = 0.560-T (°C)-18.8.

Groundwater dating with3H and SF6 in relation to mixing patterns, transport modelling and hydrochemistry

A comprehensive study of a sandy aquifer of deltaic origin in southern Poland included water chemistry, isotopes, dissolved trace gases and transport modelling. Tritium, sulphur hexafluoride (SF6) and freons (F-11, F-12 and F-113) showed the presence of modern waters in the recharge areas and shallow confined parts of the aquifer. The presence of older Holocene waters farther from the recharge areas was indicated by lack of 3H, SF6 contents ≤0·02 fmol l−1 and relatively low 14C values. The discharge from the system is by upward seepage in the valley of a major river. Pre-Holocene waters of a cooler climate, identified on the basis of δ18O, δ2H, 14C, Ne and Ar data, were found in some distant wells. Concentrations of N2, Ne and Ar determined by gas chromatography were used for calculating the noble gas temperatures, air excess needed for correction of SF6, and nitrogen content released by denitrification process. The time series of 3H content available for some wells supplied quantitative information on age distributions and the total mean ages of flow through the unsaturated and saturated zones. The derived 3H age distributions turned out to be very wide, with mean values in the range of about 30 to 160 years. For each well with determined 3H age, the SF6 data showed either a lower age range or the possibility of a lower age as expected due to shorter travel times of SF6 through the unsaturated zone, which most probably also resulted in different types of age distributions of these tracers. Freons appeared to be of little use for individual age determinations. A quantitative estimation of two-component mixing from SF63H relations is not possible unless the travel time of 3H through the unsaturated zone is comparable to that of SF6. The ratio of integrals of the response function over the age range with tracer and the whole response function yields the ratio of water with tracer to total flow of water. That ratio is a tracer-dependent function of time. Transport modelling of SF6 tracer done with MT3D code yielded initially large discrepancies between calculated and measured tracer concentrations. Some discrepancies remained even after calibration of the transport model with SF6. Simulation of tritium contents with a calibrated transport model yielded reasonable agreement with measured contents in some wells and indicated a need for further investigations, particularly in the eastern part of the aquifer. The existence of distinct hydrochemical zones is consistent with the tracer data; young waters with measurable 3H and SF6 contents are aerobic and of HCO3Ca or HCO3SO4Ca types. Slightly elevated Na and Cl contents, as well as the highest concentrations of SO4 and NO3 within this zone are due to anthropogenic influences. Anaerobic conditions prevail in the far field, under the confining cover, where pre-bomb era Holocene waters dominate. In that zone, dissolved oxygen, NO3 and U contents are reduced, and Fe, Mn and NH4 contents increase. In the third zone, early Holocene and glacial waters occur. They are of HCO3CaNa or HCO3Na types, with TDS values higher than 1 g l−1 and Na content higher than 200 mg l−1, due to either small admixtures of ascending or diffusing older water or freshening of marine sediments, a process that is probably occurring till the present time. Copyright © 2005 John Wiley & Sons, Ltd.

Manufacture of silicon carbide reinforced steels by spray forming

Hydrochemical analysis and environmental isotopic tracing are successfully applied to study groundwater evolution processes. Located in eastern China, the Jiangsu Coastal Plain is characterized by an extensively exploited deep groundwater system, and groundwater salinization has become the primary water environmental problem. This paper provides a case study on the use of a hydrochemical and environmental isotopic approach to assess possible mixing and evolution processes at Yoco Port, Jiangsu Province, China. Hydrochemical and isotopic patterns of deep groundwater allow one to distinguish different origins in deep water systems. HCO3– is the dominant anion in the freshwater samples, whereas Na+ and Cl− are the dominant major ions in the saline samples. According to δ18O, δ2H and 14C dating, the fresh water is derived from precipitation under a colder climate during the Glacial Maximum (Dali Glacial), while the saline groundwater is influenced by glacial-interglacial cycles during the Holocene Hypsithermal. The δ18O, δ2H and 3H data confirm that deep groundwater in some boreholes is mixed with overlying saline water. The deep groundwater reservoir can be divided into a saline water sector and a fresh water sector, and each show distinct hydrochemical and isotopic compositions. The saline groundwater found in the deep aquifer cannot be associated with present seawater intrusion. Since the Last Glacial Maximum in the Late Pleistocene, the deep groundwater flow system has evolved to its current status with the decrease in ice cover and the rising of sea level. However, the hydraulic connection is strengthened by continuous overexploitation, and deep groundwater is mixed with shallow groundwater at some points.