Recharge source and hydrogeochemical evolution of shallow groundwater in a complex alluvial fan system,southwest of North China Plain

Many cities around the world are developed at alluvial fans. With economic and industrial development and increase in population, quality and quantity of groundwater are often damaged by over-exploitation in these areas. In order to realistically assess these groundwater resources and their sustainability, it is vital to understand the recharge sources and hydrogeochemical evolution of groundwater in alluvial fans. In March 2006, groundwater and surface water were sampled for major element analysis and stable isotope (oxygen-18 and deuterium) compositions in Xinxiang, which is located at a complex alluvial fan system composed of a mountainous area, Taihang Mt. alluvial fan and Yellow River alluvial fan. In the Taihang mountainous area, the groundwater was recharged by precipitation and was characterized by Ca–HCO₃ type water with depleted δ¹⁸O and δD (mean value of −8.8‰ δ¹⁸O). Along the flow path from the mountainous area to Taihang Mt. alluvial fan, the groundwater became geochemically complex (Ca–Na–Mg–HCO₃–Cl–SO₄ type), and heavier δ¹⁸O and δD were observed (around −8‰ δ¹⁸O). Before the surface water with mean δ¹⁸O of −8.7‰ recharged to groundwater, it underwent isotopic enrichment in Taihang Mt. alluvial fan. Chemical mixture and ion exchange are expected to be responsible for the chemical evolution of groundwater in Yellow River alluvial fan. Transferred water from the Yellow River is the main source of the groundwater in the Yellow River alluvial fan in the south of the study area, and stable isotopic compositions of the groundwater (mean value of −8.8‰ δ¹⁸O) were similar to those of transferred water (−8.9‰), increasing from the southern boundary of the study area to the distal end of the fan. The groundwater underwent chemical evolution from Ca–HCO₃, Na–HCO₃, to Na–SO₄. A conceptual model, integrating stiff diagrams, is used to describe the spatial variation of recharge sources, chemical evolution, and groundwater flow paths in the complex alluvial fan aquifer system.     

Determining Spatial and Temporal Inputs of Freshwater,Including Submarine Groundwater Discharge,to a Subtropical Estuary Using Geochemical Tracers,Biscayne Bay,South Florida

Geochemical mixing models were used to decipher the dominant source of freshwater (rainfall, canal discharge, or groundwater discharge) to Biscayne Bay, an estuary in south Florida. Discrete samples of precipitation, canal water, groundwater, and bay surface water were collected monthly for 2 years and analyzed for salinity, stable isotopes of oxygen and hydrogen, and Sr²⁺/Ca²⁺ concentrations. These geochemical tracers were used in three separate mixing models and then combined to trace the magnitude and timing of the freshwater inputs to the estuary. Fresh groundwater had an isotopic signature (δ ¹⁸O = −2.66‰, δD −7.60‰) similar to rainfall (δ ¹⁸O = −2.86‰, δD = −4.78‰). Canal water had a heavy isotopic signature (δ ¹⁸O = −0.46‰, δD = −2.48‰) due to evaporation. This made it possible to use stable isotopes of oxygen and hydrogen to separate canal water from precipitation and groundwater as a source of freshwater into the bay. A second model using Sr²⁺/Ca²⁺ ratios was developed to discern fresh groundwater inputs from precipitation inputs. Groundwater had a Sr²⁺/Ca²⁺ ratio of 0.07, while precipitation had a dissimilar ratio of 0.89. When combined, these models showed a freshwater input ratio of canal/precipitation/groundwater of 37%:53%:10% in the wet season and 40%:55%:5% in the dry season with an error of ±25%. For a bay-wide water budget that includes saltwater and freshwater mixing, fresh groundwater accounts for 1–2% of the total fresh and saline water input.     

Spatio-temporal variations of δ<Superscript>2</Superscript>H and δ<Superscript>18</Superscript>O in precipitation and shallow groundwater in the Hilly Loess Region of the Loess Plateau,China

Groundwater is of utmost significance to socio-economic development and ecological recovery for the Loess Plateau. However, studies regarding the mechanism governing groundwater recharge over this area appear to be inadequate. This study is to examine the spatio-temporal variations of δ²H and δ¹⁸O in precipitation and shallow groundwater. On the basis of this, the mechanisms governing shallow groundwater recharge were explored. Precipitation and groundwater were sampled monthly from May to October during the period 2004–2006 at 13 sites in the Chabagou Catchment (187 km²). In the Caopingxigou Experimental Watershed (0.1 km²), meteorological variables were observed and rainfall larger than 5 mm was sampled immediately after each rain event. Across the area, 90% of the precipitation occurred from May to September primarily in the form of heavy rains or rainstorms with great spatial variability. There were about 30 localized rains in each year. It was indicated that there existed notable seasonality and pronounced spatial variability in precipitation isotopic compositions. Contributing factors and indications of isotopic compositions, as well as their climatic indications such as monsoon intensities and mixing processes of water vapor, were investigated. The δ²H–δ¹⁸O relation of groundwater was found to be δ²H = 3.22 × δ¹⁸O − 38.1, deviating from the local meteoric water line δ²H = 7.57 × δ¹⁸O + 3.9. The range of δ values in groundwater is shrunken to be 15–21% of that in individual precipitations, and groundwater in the middle reaches shows a wider range of δ values. Isotopic results showed that groundwater originates from precipitation with hydrogen and oxygen isotopic compositions being −69 and −9.7‰, respectively, and most groundwater experiences serious evaporation and adequate mixing with old water during infiltration or percolation in the aerated zone. It was also founded that obvious fluctuations of isotopic compositions in groundwater mainly appear in the middle reaches especially at sites that are close to valleys, suggesting varying sources of groundwater from precipitation, precipitation runoff, isotopically enriched surface water and/or lateral recharge of adjacent groundwater.     

Shallow groundwater dynamics and origin of salinity at two sites in salinated and water-deficient region of North China Plain,China

Large salinated areas are distributed in the middle and east of the North China Plain (NCP), where the fresh water shortage is serious. In this study, two sites in Cangzhou (CZ) and Hengshui (HS) of Hebei Province were selected to study the dynamics of shallow groundwater level and salinity. Electrical conductivity (EC) of groundwater was combined with the isotope compositions of δ¹⁸O and δ²H to identify the origin of salinity. Results showed that the dynamics of groundwater level at both sites were mainly controlled by precipitation and evaporation. Soil texture and structure played a significant role in the dynamics of salinity. The summer precipitation diluted the EC of groundwater at the HS site with homogeneous soil of sand loam, suggesting the larger infiltration rate; however, it did not dilute the EC at the CZ site with heterogeneous soil of sand loam and silt loam, suggesting that the summer precipitation could not recharge the groundwater directly. In winter, the EC decreased rapidly due to the temperature gradient underground if the groundwater was above the threshold level (at least 3 m below the ground surface) after the rainy season. Isotopes of δ¹⁸O and δ²H showed that precipitation was the major recharge source for the groundwater at the two sites. The salt mainly comes from the dissolution of soil or rock at the CZ site. While, the evaporation effect was strong at the HS site leading to the increase of the salt concentration.     

Relationships between precipitation,soil water and groundwater at Chongling catchment with the typical vegetation cover in the Taihang mountainous region,China

Vegetation cover plays an important role in the process of evaporation and infiltration. To explore the relationships between precipitation, soil water and groundwater in Taihang mountainous region, China, precipitation, soil water and water table were observed from 2004 to 2006, and precipitation, soil water and groundwater were sampled in 2004 and 2005 for oxygen-18 and deuterium analysis at Chongling catchment. The soil water was sampled at three sites covered by grass (Carex humilis and Carex lanceolata), acacia and arborvitae respectively. Precipitation is mainly concentrated in rainy seasons and has no significant spatial variance in study area. The stable isotopic compositions are enriched in precipitation and soil water due to the evaporation. The analysis of soil water potential and isotopic profiles shows that evaporation of soil water under arborvitae cover is weaker than under grass and acacia, while soil water evaporation under grass and acacia showed no significant difference. Both δ¹⁸O profiles and soil water potential dynamics reveal that the soil under acacia allows the most rapid infiltration rate, which may be related to preferential flow. In the process of infiltration after a rainstorm, antecedent water still takes up over 30% of water in the topsoil. The soil water between depths of 0–115 cm under grass has a residence time of about 20 days in the rainy season. Groundwater recharge from precipitation mainly occurs in the rainy season, especially when rainstorms or successive heavy rain events happen.     

Isotopic and hydrochemical data to restrict the origin of the groundwater in the Badain Jaran Desert,Northern China

Despite its extreme aridity, the Badain Jaran Desert is rich in groundwater. In the southeastern part of the desert, it is characterized by coexistence of high megadunes and a great number of lakes. Deuterium and oxygen 18 isotope compositions as well as hydrochemistry of groundwater, lake water, soil water and river water were investigated in detail to gain an insight into their relationships and the origin of the ground-water. The results show that the groundwater and the lake water are genetically related, but unrelated to local precipitation and the leakage of Heine River at northern slope of Qilian mountain. δD and δ¹⁸O values of deep soil water (lower than 40 cm) and groundwater plot on the same evaporation line E11, which shows that they have the same recharge source. The point of intersection between E11 and LMWL suggests that the groundwater originates from the water resource which has a weighted mean value that is lighter by some 6‰ δ¹⁸O than the local precipitation in Badain Jaran Desert. ³H data of water samples shows that the groundwater in Badain Jaran Desert originates from the water recharged after the nuclear test. The deep fault zone underground maybe the water circulation channel based on Helium analysis of groundwater. The result has guiding significance to rational exploitation and utilization of the local groundwater.     

Oyster and Macroalgae Bioindicators Detect Elevated δ<Superscript>15</Superscript>N in Maryland’s Coastal Bays

Nitrogen loading from anthropogenic sources, including fertilizer, manure, and sewage effluents, has been linked with declining water quality in coastal lagoons worldwide. Freshwater inputs to mid-Atlantic coastal lagoons of the USA are from terrestrially influenced sources: groundwater and overland flow via streams and agricultural ditches, with occasional precipitation events. Stable nitrogen isotopes ratios (δ¹⁵N) in bioindicator species combined with conventional water quality monitoring were used to assess nitrogen sources and provide insights into their origins. Water quality data revealed that nutrients derived from terrestrial sources increased after precipitation events. Tissues from two bioindicator species, a macroalgae (Gracilaria sp.) and the eastern oyster (Crassostrea virginica) were analyzed for δ¹⁵N to determine spatial and temporal patterns of nitrogen sources. A broad-scale survey assessment of deployed macroalgae (June 2004) detected regions of elevated δ¹⁵N. Macroalgal δ¹⁵N (7.33 ± 1.15‰ in May 2006 and 6.76 ± 1.15‰ in July 2006) responded quickly to sustained June 2006 nutrient pulse, but did not detect spatial patterns at the fine scale. Oyster δ¹⁵N (8.51 ± 0.89‰) responded slowly over longer time periods and exhibited a slight gradient at the finer spatial scale. Overall, elevated δ¹⁵N values in macroalgae and oysters were used to infer that human and animal wastes were important nitrogen sources in some areas of Maryland’s coastal bays. Different nitrogen integration periods across multiple organisms may be used to indicate nitrogen sources at various spatial and temporal scales, which will help focus nutrient management.     

A comparative study on isotopic composition of precipitation in wet tropic and semi-arid stations across southern India

Isotopic composition of monthly composite precipitation samples from Kozhikode (n = 31), a wet tropic station and Hyderabad (n = 25), a semi-arid station across southern India were studied for a period of four years from 2005 to 2008. During the study period, the Kozhikode station recorded an average rainfall of 3500 mm while the Hyderabad station showed an average rainfall of 790 mm. The average stable isotope values in precipitation at the Kozhikode station were δ ¹⁸O = −3.52‰, d-excess = 13.72‰; δ ¹⁸O = −2.94‰, d-excess = 10.57‰; and δ ¹⁸O = −7.53‰, d-excess = 13.79‰, respectively during the pre-monsoon (March–May), monsoon (June–September) and post-monsoon (October–February) seasons. For the Hyderabad station, the average stable isotope values were δ ¹⁸O = −5.88‰, d-excess = 2.34‰; δ ¹⁸O = −4.39‰, d-excess = 9.21‰; and δ ¹⁸O = −8.69‰, d-excess = 14.29‰, respectively for the three seasons. The precipitation at the two stations showed distinctive isotopic signatures. The stable isotopic composition of precipitation at the Hyderabad station showed significant variations from the global trend while the Kozhikode station almost followed the global value. These differences are mainly attributed to the latitudinal differences of the two stations coupled with the differences in climatic conditions.     

Using stable isotopes of nitrogen to study its source and transformation in a heavily farmed watershed

Twenty private wells and ten stream locations were sampled to assess the source and fate of dissolved nitrate in the Cedar River watershed of Iowa, USA. The average levels of nitrate in groundwater decreased from 39.5 mg/L in May, to 38 mg/L in July, to 30 mg/L in September. Although several surface water samples exceeded MCL in May, most values dropped to below 20 mg/L by July and September. The decreasing N levels were attributed to the gradual uptake of nitrate by growing crops as well as the cyanobacterial growth in the aquatic systems. The δ¹⁵N values of dissolved nitrate in groundwater ranged from +0.45 to +5.35‰, whereas those in surface water ranged from +1.48 to +5.16‰. The results suggested that commercial fertilizers and soil organic nitrogen were probably mixed up in their transport pathways. A fertilizer-only source would provide much lower delta values, whereas soil nitrogen would provide higher than observed delta values. Denitrification was considered unlikely because of the low δ¹⁵N values, high nitrate concentrations, and moderately high DO content in groundwater. Animal wastes were not found as a possible source of nitrate in the water. This is supported by the low chloride concentrations and lower than 10‰ delta values in the water samples. The study demonstrates that nitrogen isotope data in coordination with the dissolved nitrate levels and land use can be effectively used in nitrogen source identification and its transformation studies.     

Nitrogen isotope indicators of seasonal source variability to groundwater

 A nitrogen isotope study of soil water and groundwater in southern Indiana, USA, in 1991–1992 demonstrated considerable variations in nitrate degradation processes compared to an earlier investigation in 1986–1987. Although N-fertilizers were applied in May 1991, the δ¹⁵N values in soil water decreased in February 1992, indicating its delayed release into the system after substantial rainfall. The δ¹⁵N values of groundwater decreased from +12.3‰ in November 1991 to +11.3‰ in February 1992, and to +7.5‰ in March 1992. The increased residence time of nitrate in the soil resulted in increased denitrification, ammonia volatilization and plant uptake, and reduced threat to the groundwater quality. The 1986–1987 study in the area reported that excessive rainfall during the summer rapidly transported the nitrate to deeper horizons and drastically reduced volatilization and microbial reduction of nitrate, thus increasing the immediate threat to the groundwater quality in the area. The present study demonstrated that nitrogen isotopic signatures can be used to determine the effects of local soil type, rainfall, and land-use practices on the fate of nitrate in the subsurface. Received: 18 February 1997 · Accepted: 17 June 1997     

Study on Modern Plant C－13 in Western China and Its Significance

Organic carbon isotopic composition(δ^13C) is one of the important proxies in paleoenvironment studies.In this paper modern plant δ^13C in the arid areas of China and Tibetan Plateau is studied.It is found that most terrestrial plant species in western China are C3 plants with δ^13C values ranging from -32.6‰ to -23.2‰ and only few species are C4 plants with δ^13C values from -16.8‰ to -13.3‰.The δ^13C is closely related to precipitation (or humidity),i.e., light δ^13C is related to high precipitation(or humid climate),while heavy δ^13C to low precipitation (or dry climate),but there is almost no relation between plant δ^13C and temperature.Submerged plants have δ^13C values ranging from -22.0‰ to -12.7‰,like C4 plants,while merged plants have δ^13C values ranging from -28.1‰ to -24.5‰，like C3 C4 plants,while marged plants have δ^13C values ranging from -28.1‰ to -24.5‰,like C3 plants.It can then be concluded that organic δ^13C variations in terrestrial sediments such as loeas and soil in western China can indicate precipitation changes,but those in lake sediments can reflect organic sources and the productivity of different types of aquatic plants.     

A Geochemical study of the groundwater in the Misli basin and environmental implications

The aim of this study was to determine geochemical properties of groundwater and thermal water in the Misli Basin and to assess thermal water intrusion into shallow groundwater due to over-extraction. According to isotope and hydrochemical analyses results, sampled waters can be divided into three groups: cold, thermal, and mixed waters. Only a few waters reach water–rock chemical equilibrium. Thermal waters in the area are characterized by Na⁺–Cl⁻–HCO₃⁻, while the cold waters by CaHCO₃ facies. On the basis of isotope results, thermal waters in the Misli basin are meteoric origin. In particular, δ¹⁸O and δ²H values of shallow groundwater vary from −10.2 to −12.2‰ and −71.2 to −82‰, while those of thermal waters range from −7.8 to −10.1‰ and from −67 to −74‰, respectively. The tritium values of shallow groundwater having short circulation as young waters coming from wells that range from 30 to 70 m in depth vary from 10 to 14 TU. The average tritium activity of groundwater in depths more than 100 m is 1.59 ± 1.16, which indicates long circulation. The rapid infiltration of the precipitation, the recycling of the evaporated irrigation water, the influence of thermal fluids and the heterogeneity of the aquifer make it difficult to determine groundwater quality changes in the Misli Basin. Obtained results show that further lowering of the groundwater table by over-consumption will cause further intrusion of thermal water which resulted in high mineral content into the fresh groundwater aquifer. Because of this phenomenon, the concentrations of some chemical components which impairs water quality in terms of irrigation purposes in shallow groundwaters, such as Na⁺, B, and Cl⁻, are highy probably expected to increase in time.     

Hydrogeochemical controls and usability of groundwater in the semi-arid Mayo Tsanaga River Basin: far north province,Cameroon

Deuterium, δ ¹⁸O, major ions and dissolved silica in groundwater from semi-arid Mayo-Tsanaga river basin in the Far North Province, Cameroon were used to trace hydrogeochemical processes that control their concentrations and to explore for usability of the water. Electrical conductivity ranges from 57–2,581 μs/cm with alternating low and high values along the hydraulic gradient. Waters from piedmont alluvium show low concentrations in major cations, which peak in Mg within basalt, Na within plain alluvium, and Ca within basalt and the sandy Limani-Yagoua ridge. The initial dominant groundwater composition is CaHCO₃, which did not evolve within the basalt and piedmont alluvium, but evolved to NaHCO₃ in the granite and plain alluvium. The main processes controlling the major ions composition include the following: (1) dissolution of silicates and fluorite; (2) precipitation of fluorite and carbonate; (3) cation exchange of Ca in water for Na in clay; (4) and anthropogenic activities. The δD and δ ¹⁸O ratios vary from −35 to 0.7 and −5.3 to 1.1‰, respectively. The lowest and highest isotope ratios are observed in groundwater within the downstream sandy Limani-Yagoua ridge and the upstream graintes respectively. Variation in isotope ratios depends on altitude effect of −0.48‰ per 100 m between 600 and 850 m asl, and on evaporation, which had insignificant effect on the water salinity. Seventy percent of the groundwater shows poor drinking quality and 90% is suitable for irrigation. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Sources and transformations of N in reclaimed coastal tidelands: evidence from soil δ<Superscript>15</Superscript>N data

Electrical conductivity of saturated soil extracts (EC_e) in three reclaimed tideland (RTL) soils on the west coast of Korea decreased with time since reclamation, indicating natural desalinization through leaching of salts by precipitation water. Soil N concentration increased with decreasing EC_e. With the increase in soil N concentration, the δ¹⁵N decreased, likely caused by the input of ¹⁵N-depleted N sources. As N₂-fixing plant species were found in the oldest RTL, atmospheric N₂ fixation likely contributed to the increase in soil N concentration in the oldest RTL. Negative δ¹⁵N (−7.1 to −2.0‰) of total inorganic N (NH₄ ⁺+NO₃ ⁻) and published data on N deposition near the study area indicate that atmospheric N deposition might be another source of N in the RTLs. Meanwhile, the consistently negative δ¹⁵N of soil NO₃ ⁻ excluded N input from chemical fertilizer through groundwater flow as a potential N source, since NO₃ ⁻ in groundwater generally have a positive δ¹⁵N. The patterns of δ¹⁵N of NH₄ ⁺ (+2.3 to +5.1‰) and NO₃ ⁻ (−9.2 to −5.0‰) suggested that nitrification was an active process that caused ¹⁵N enrichment in NH₄ ⁺ but denitrification was probably minimal which would otherwise have caused ¹⁵N enrichment in NO₃ ⁻. A quantitative approach on N budget would provide a better understanding of soil N dynamics in the studied RTLs.     

Isotopic constraints on the origin of groundwater in the Ordos Basin of northern China

Despite its extreme aridity, the Ordos Basin in northern China is rich in groundwater. Many artesian wells or springs with large fluxes are utilized for drinking, irrigation and industrial production. In a search for the origin of the groundwater, a detailed investigation of the stable isotopes of oxygen and hydrogen in the local precipitation, the river water, the springs, the well water, as well as the soil water extracted from six soil profiles in the Ordos Basin, was carried out. The data show that δD, δ¹⁸O and TDS values of the river water are similar to those of groundwater, while the TDS values of the soil water are about ten times greater than those of groundwater. Furthermore, the mean isotopic compositions of the local precipitation are significantly higher than those of river water and groundwater. Based on the chloride mass balance method, the estimated recharge rates range from 5.2 to 17.2 mm/year, with a mean value of 10.5 mm/year. The results show that the main source of recharge of the groundwater in the Ordos Basin is not the local precipitation, but must come from a region where the precipitation is characterized by much lower δD and δ¹⁸O values. In addition, the groundwater in the Ordos Basin contains a component of mantle-derived ³He and crust-derived ⁴He suggesting that the groundwater may partly derive from flows through basement faults beneath the Ordos Basin.     

Sulphate Sources in the Sava and Ljubljanica Rivers, Slovenia, Inferred from Sulphur and Oxygen Isotope Compositions

Measurements were made of sulphur and oxygen isotope ratios of sulphate in some Slovenian rivers, lakes and tap waters. δ³⁴S ranged from −0.2 to + 13.3‰, δ¹⁸O ranged from +4.9 to + 13.6‰, and the sulphate content varied from 0.8 to 41.4 mg/L. Rivers flowing from the Julian Alps contain a very low amount of sulphate that is leached from a thin horizon of soil by rain. As confirmed by their low δ¹⁸O values, these sulphates do not enter the rivers directly in rain, but arise from biochemical cycling in the soil. The low δ³⁴S of this sulphate indicates that it originates from the oxidation of sedimentary sulphides. The evolution of sulphates along the river course was investigated for the Sava and Ljubljanica rivers. The variations observed in sulphate from the waters studied result from variations in the contribution of sulphates of different origin. Downstream the Sava River sulphate is depleted in the heavy isotopes of both sulphur and oxygen, with δ-values gradually tending toward the δ-values of groundwater sulphates in the watershed. In contrast, the δ-values of sulphate in the Ljubljanica River are almost constant and similar to those of sulphate in local groundwater. Introduction of water from Italian and Slovenian mines was recorded in the Soča River, where the lowest δ³⁴S value of sulphate sulphur (−0.2‰) was observed. In addition, the influence of sulphate from the oxidation of sedimentary sulphides was recorded in the Sotla River. No evidence was found for introduction of sulphate from factories.     

Detrital,metamorphic and metasomatic tourmaline in high-pressure metasediments from Syros (Greece): intra-grain boron isotope patterns determined by secondary-ion mass spectrometry

The boron isotopic composition of zoned tourmaline in two metasediments from the island of Syros, determined by secondary-ion mass spectrometry (SIMS), reflects the sedimentary and metamorphic record of the rocks. Tourmaline from a silicate-bearing marble contains small (≤20 μm) detrital cores with highly variable δ ¹¹B values (−10.7 to +3.6‰), pointing to a heterogeneous protolith derived from multiple sources. The sedimentary B isotopic record survived the entire metamorphic cycle with peak temperatures of ∼500°C. Prograde to peak metamorphic rims are homogeneous and similar among all analysed grains (δ ¹¹B ≈ +0.9‰). The varying δ ¹¹B values of detrital cores in the siliceous marble demonstrate that in situ B isotope analysis of tourmaline by SIMS is a potentially powerful tool for provenance studies not only in sediments but also in metasediments. A meta-tuffitic blueschist bears abundant tourmaline with dravitic cores of detrital or authigenic origin (δ ¹¹B ≈ −3.3‰), and prograde to peak metamorphic overgrowth zones (−1.6‰). Fe-rich rims, formed during influx of B-bearing fluids under retrograde conditions, show strongly increasing δ ¹¹B values (up to +7.7‰) towards the margins of the grains. The δ ¹¹B values of metamorphic tourmaline from Syros, formed in mixed terrigenous–marine sediments, reflect the B signal blended from these two different sources, and was probably not altered by dehydration during subduction.     

Stable water isotope climate archives in springs from the Olympic Mountains,Washington

The ¹⁸O and ²H (HDO) compositions are summarized for sampled springs (n = 81) within the Elwha watershed (≈692 km²) on the northern Olympic Peninsula. Samples, collected during 2001–2009, of springs (n = 158), precipitation (n = 520), streams (n = 176), and firn (n = 3) assisted the determinations for meteoric composition of recharge waters. The local mean water line (LMWL) is defined as δ²H = 8.2δ¹⁸O − 9.3 for the watershed. Recharge history is surmised from groundwater ages ranging from 5 ± 3 years (apparent ⁸⁵Kr) to 9,490 ± 420 ¹⁴C cal years BP. About 56% of the springs were recharged over the last 1,000 years while 13% of springs were recharged over 5,000 years ago. Spring HDO values fluctuate between −11.8 to −15.6‰ δ¹⁸O and −90.9 to −119.4‰ δ²H. Deuterium excess values predominate around 4–6‰. The HDO proxy records from springs suggest a pronounced paleoclimate shift in air masses near 5,000 year BP on the Peninsula.     

Spatio-temporal variation of stable isotopes in precipitation in the Heihe River Basin,Northwestern China

An intensive investigation of the spatial and temporal variations of δD and δ ¹⁸O in precipitation was conducted during 2002–2004 in six sites in the Heihe River Basin, Northwestern China. The δD and δ ¹⁸O values for 301 precipitation samples ranged from +59 to −254 and +6.5 to −33.4‰, respectively. The relationship between δD and δ ¹⁸O defines a well-constrained line given by dD = 7.82d¹⁸\textO + 7.63 \delta D = 7.82\delta {}^{18}{\text{O}} + 7.63 , which is nearly identical to the meteoric water line in the Northern China. This wide range indicates that stable isotopes in precipitation were primarily controlled by different condensation mechanisms as a function of air temperature and varying sources of moisture. The results of backward trajectory of each precipitation day at Xishui show that the moisture of the precipitation in cold season (October–March) mainly originated from the west while the moisture source was more complicated in warm season (April–September). The simulation of seasonal δ ¹⁸O variation shows that the stable isotope composition of precipitation tended to a clear sine-wave seasonal variation. The spatial variation of δ ¹⁸O shows that the weighted average δ ¹⁸O values decreases with the increasing altitude of sampling sites. The great difference of air temperature which led to the differences of condensation mechanisms and local recycled continental moisture may have influence upon the isotopic composition of rain events in different sites.