Anthropogenic gadolinium as a microcontaminant in tap water used as drinking water in urban areas and megacities

Gadolinium chelates have been used since 1988 as contrast agents in magnetic resonance imaging (MRI), and produce positive anthropogenic Gd anomalies in rare earth element (REE) patterns of river and lake waters. These Gd compounds are not removed in wastewater treatment plants (WWTP) due to their high stabilities, and are transferred to surface waters with the clearwater discharge from WWTP. Through natural and induced bank filtration, the anthropogenic Gd is also transported into groundwater. To date, there are no related acute health risks known, but the potential long-term effects of exposure to low doses have not been studied.Here REE data is presented for tap water from the City of Berlin, Germany, a metropolitan area that is known for its anthropogenic Gd-rich rivers and groundwater. Natural and induced bank filtration play important roles in Berlin’s freshwater resource management. Therefore, the extent to which municipal tap water that is used as drinking water is affected by anthropogenic Gd was investigated. Large positive Gd anomalies were found in tap water samples from the western districts of Berlin, indicating the presence of up to 18 ng/L of anthropogenic Gd on top of a geogenic background of 0.54 ng/L. In marked contrast, the amount of anthropogenic Gd in tap water from the eastern districts of Berlin is negligible to minor (maximum of 0.18 ng/L on top of a geogenic background of 0.26 ng/L). This strong regional difference likely results from the specific historical situation of Berlin, where before the re-unification of Germany in 1990, natural and induced bank filtration were necessities in isolated West Berlin, but unimportant in East Berlin, a situation that has seen little change during the past 20 years. Thus, drinking water resources in the western part of Berlin are more strongly affected by anthropogenic Gd than those in the eastern part. The high anthropogenic Gd concentrations found in some tap waters in Berlin clearly show that the Gd initially used as contrast agent is removed neither during natural nor artificial water treatment. This is further evidence for the high stability and long environmental half-lives of these compounds. Considering that the amount of anthropogenic Gd in the Havel River in Berlin has increased more than 4-fold over the past 15 years and that water migration from the Havel River to the groundwater wells take years to decades, the amounts of anthropogenic Gd in West Berlin tap water will increase further over the next few years. Due to its presence in tap water that is consumed as drinking water, millions of people are exposed to low doses of these anthropogenic Gd chelates. Additional data for the City of London, UK, for example, indicate that this is not a local phenomenon confined to the City of Berlin, but rather a common feature of tap water in metropolitan areas and megacities in countries with highly developed health care systems. Hence, the REE distribution in tap waters used for human consumption should be monitored, especially since the anthropogenic Gd chelates can also be used as tracers for emerging microcontaminants such as steroids, pharmaceuticals and personal care products.     

High-technology metals as emerging contaminants: Strong increase of anthropogenic gadolinium levels in tap water of Berlin,Germany, from 2009 to 2012

The distribution of rare earth elements (REE) in tap water sampled in December 2012 in Berlin, Germany, is characterized by anomalously high levels of gadolinium (Gd). While the western districts of the city show strong anthropogenic positive Gd anomalies in REE distribution patterns, the eastern districts are (almost) unaffected. This contamination with anthropogenic Gd results from Gd-based contrast agents used in Magnetic Resonance Imaging, that enter rivers, groundwater and eventually tap water via the clear water effluent from wastewater treatment plants. While the spatial distribution of anthropogenic Gd in 2012 confirms results of an earlier study in 2009 (Kulaksiz and Bau, 2011a), anthropogenic Gd concentrations have increased between 1.5- and 11.5-fold in just three years. This confirms predictions based upon the increase of anthropogenic Gd concentrations in the Havel River over the past two decades and the time it takes the water to migrate from the Havel River to the groundwater production wells. Anomalously high levels of anthropogenic Gd in tap water, which are not confined to Berlin but have also been observed in London, U.K., and in German cities in the Ruhr area and along the Rhine River, reveal that high-technology metals have become emerging contaminants. While non-toxic at the observed concentrations, the anthropogenic Gd is a microcontaminant that may be used as a conservative pseudo-natural tracer for wastewater-derived xenobiotics such as pharmaceuticals, food additives and personal care products. Our results suggest that monitoring the concentrations of such substances in Berlin’s drinking water can be restricted to a few central and western districts of the city, demonstrating that implementation of anthropogenic Gd as a tracer in monitoring programs can contribute to significant cost savings.     

Seasonal evolution of the isotopic composition of atmospheric water vapour above a tropical lake: Deuterium excess and implication for water recycling

We present an analysis of the rainfall-evaporation-atmospheric moisture cycle in a semi-arid tropical zone (southwestern Madagascar) to quantify the recycling and mixing processes that occur above an endorheic lake system (Lake Ihotry) during an annual cycle. The study combines an isotope mass balance with a detailed field investigation of the lake system and a previously established daily time-step lake water balance model. The mass balance and Craig-Gordon equations are used to calculate the isotopic composition of the evaporative flux from the lake surface (δ_E) and to derive a daily time series of the ambient atmospheric water vapour composition above the lake (δ_AL) during a 8-month dry season. Calculated δ_AL results from a mixing between regional moisture (δ_AR) and locally evaporated water (δ_E), the latter representing 50% of δ_AL at the end of the dry season. The contribution of recycled moisture to on-lake precipitation during the wet season is estimated to ?16%. We show that, as expected, the deuterium excess is high in recycled precipitation and low in evaporated precipitation, but also that the recycled moisture in an endorheic system may have a low deuterium excess resulting from the low deuterium excess in regional precipitation. In case of a long evaporative season, the atmospheric moisture is not in isotopic equilibrium with the annual composition of precipitation because of the contribution of the recycled vapour to the local atmospheric pool. Our approach demonstrates the importance of water recycling on the atmospheric moisture cycle and precipitation in a tropical semi-arid system, and can be applied to other natural systems, enlarging the potential range of investigation of the atmospheric vapour cycle and rainfall sources in tropical lands. It may also represent a valuable complement to direct water vapour sampling, in yielding the long-term evolution of the atmospheric vapour composition with spatially averaged values and smoothed temporal variations.     

Origin of natural sulfur-metal chimney in the Tangyin hydrothermal field,Okinawa Trough: constraints from rare earth element and sulfur isotopic compositions

For the first time, we present the rare earth element (REE) and sulfur isotopic composition of hydrothermal precipitates recovered from the Tangyin hydrothermal field (THF), Okinawa Trough at a water depth of 1206 m. The natural sulfur samples exhibit the lowest ΣREE concentrations (ΣREE= 0.65×10^–6–4.580×10^–6) followed by metal sulfides (ΣREE=1.71×10^–6–11.63×10^–6). By contrast, the natural sulfur-sediment samples have maximum ΣREE concentrations (ΣREE=11.54×10^–6–33.06×10^–6), significantly lower than those of the volcanic and sediment samples. Nevertheless, the δEu, δCe, (La/Yb)_N, La/Sm, (Gd/Yb)_N and normalized patterns of the natural sulfur and metal sulfide show the most similarity to the sediment. Most hydrothermal precipitate samples are characterized by enrichments of LREE (LREE/HREE=10.09–24.53) and slightly negative Eu anomalies or no anomaly (δEu=0.48–0.99), which are different from the hydrothermal fluid from sediment-free mid-oceanic ridges and back-arc basins, but identical to the sulfides from the Jade hydrothermal field. The lower temperature and more oxidizing conditions produced by the mixing between seawater and hydrothermal fluids further attenuate the leaching ability of hydrothermal fluid, inducing lower REE concentrations for natural sulfur compared with metal sulfide; meanwhile, the negative Eu anomaly is also weakened or almost absent. The sulfur isotopic compositions of the natural sulfur (δ³⁴S=3.20‰–5.01‰, mean 4.23‰) and metal sulfide samples (δ³⁴S=0.82‰–0.89‰, mean 0.85‰) reveal that the sulfur of the chimney is sourced from magmatic degassing.     

Controls of δS and δO in dissolved sulphate: Learning from a detailed survey in the Llobregat River (Spain)

The S and O isotopic composition of dissolved SO₄, used as a tracer for SO₄ sources, was applied to the water of the Llobregat River system (NE Spain). The survey was carried out at 30 sites where surface water was sampled on a monthly basis over a period of 2a. The concentration of dissolved SO₄ varied from 20 to 1575 mg L⁻¹. Sulphur isotopic compositions clustered in two populations: one – 93% of the samples – had positive values with a mode of +9‰; the other had negative values and a mode of −5‰. Data for δ¹⁸O_SO4 showed a mean value of +11‰, with no bi-modal distribution, though lower values of δ¹⁸O corresponded to samples with negative δ³⁴S. These values can not be explained solely by the contribution of bedrock SO₄ sources: that is, sulphide oxidation and the weathering of outcrops of sulphates, though numerous chemical sediments exist in the basin. Even in a river with a high concentration of natural sources of dissolved SO₄, such as the Llobregat River, the δ³⁴S values suggest that dissolved SO₄ is controlled by a complex mix of both natural and anthropogenic sources. The main anthropogenic sources in this basin are fertilizers, sewage, potash mine effluent and power plant emissions. Detailed river water sampling, together with the chemical and isotopic characterisation of the main anthropogenic inputs, allowed determination of the influence of redox processes, as well as identification of the contribution of natural and anthropogenic SO₄ sources and detection of spatial variations and seasonal changes among these sources. For instance, in the Llobregat River the input of fertilisers is well marked seasonally. Minimum values of δ³⁴S are reported during fertilization periods – from January to March – indicating a higher contribution of this source. The dual isotope approach, δ³⁴S and δ¹⁸O, is useful to better constrain the sources of SO₄. Moreover, in small-scale studies, where the inputs are well known and limited, the mixing models can be enhanced and the contribution of the different sources can be quantified to some extent.     

A study of the interrelation between surface water and groundwater using isotopes and chlorofluorocarbons in Sanjiang plain,Northeast China

Surface water and groundwater are the main water resources used for drinking and production. Assessments of the relationship between surface water and groundwater provide information for water resource management in Sanjiang plain, Northeast China. The surface water (river, lake, and wetland) and groundwater were sampled and analyzed for stable isotopic (δD, δ ¹⁸O) composition, tritium, and chlorofluorocarbons concentrations. The local meteoric water line is δD = 7.3δ ¹⁸O–6.7. The tritium (T) and chlorofluorocarbon (CFC) contents in groundwater were analyzed to determine the groundwater ages. Most groundwater were modern water with the ages <50 years. The groundwaters in mountain area and near rivers were younger than in the central plain. The oxygen isotope (δ ¹⁸O) was used to quantify the relationship between surface water and groundwater. The Songhua, Heilongjiang, and Wusuli rivers were gaining rivers, but the shallow groundwater recharged from rivers at the confluence area of rivers. At the confluence of Songhua and Heilongjiang rivers, 88 % of the shallow groundwater recharged from Songhua river. The combination of stable isotopes, tritium, and CFCs was an effectively method to study the groundwater ages and interrelation between surface water and groundwater. Practically, the farmlands near the river and under foot of the mountain could be cultivated, but the farmlands in the central plain should be controlled.     

Anthropogenic gadolinium as a micropollutant in river waters in Pennsylvania and in Lake Erie, northeastern United States

“Anthropogenic” gadolinium, Gd, used in contrast agents in magnetic resonance imaging, is a micropollutant that enters river and lake waters with the discharge from wastewater treatment plants, WWTPs. Such discharge is also the source of other micropollutants, for example pharmaceuticals, such as steroids, antihistamins, and antibiotics. Together with the “natural” Gd, the anthropogenic Gd produces positive Gd anomalies in rare-earth element distribution patterns and is, therefore, easily detectable. This pilot study reports on the occurrence of anthropogenic Gd in rivers in Pennsylvania (Ohio, Beaver, Allegheny, Monongahela, Juniata, and Susquehanna) and in near-shore surface water from Lake Erie close to the city of Buffalo. Additional data are reported for the Delaware River and the headwaters of Spring Creek in Central Pennsylvania, and for Lake Ontario and Niagara River, all of which do not show significant anthropogenic Gd. Most pronounced impact of anthropogenic Gd discharged from WWTPs is observed in the Pittsburgh Metropolitan area. Such contamination is similar to that observed in densely populated areas with highly developed medical and healthcare systems in Europe and Japan. Its worldwide applicability adds to the promising potential of anthropogenic Gd as a cost-effective tracer for the presence of WWTP effluent in river, lake, ground, and drinking waters.     

Experimental Study on the Effects of Organic Acids on the Dissolution of REE in the Weathering Crust of Granite

The results of REE leached by some organic acids with various concentrations and water/rock ratios for different durations from a mixed samples of the weathering crust of a granite in Gonghe,Guangdong,China,showed that:1)the contents of REE leached increase with increasing concentrations of the organic acids;2) the contents of REE leached by 0.01mol/L organic acids increase with increasing water/rock ration;3) the interaction between the organic acids and the samples enhances the pH value of the medium and the contents of REE leached tend to increase with decreasing pH value;and 4) compared with those leached by ammonia sulfate,the REE leached by the organic acids are characterized by a weaker negative C e anomaly,a stronger negative Eu anomaly,and lower(La/Sm)N and (Gd/Yb)N ratios,indicating that the organic acids have made contributions to the fractionation of REE in the weathering crust.     

Plant growth and productivity along complex gradients in a Pacific northwest brackish intertidal marsh

Environmental characteristics were measured and recorded in the Skagit Marsh, a brackish intertidal marsh on Puget Sound, Washington. Four transects were placed perpendicular to a known gradient of increasing salinity which began with fresh water at the bank of one of the outlets of the Skagit River and reached a surface water salinity of 22‰ at a point alongshore 5 km north of the outlet. The environmental characteristics which were measured varied along gradients (soil texture, organic carbon in fines, soil column temperature, free soil water salinity) or had a patchy distribution (soil redox potential, soil macro-organic matter). Growth and production vary across the marsh. The maximum aboveground standing crop (1,742 g m^?2 dry weight) was measured at a site with 0–4‰ free soil water salinity, dominated by the sedgeCarex lyngbyei. In more saline areas (8–12‰), the bulrushScirpus americanus was dominant and standing crop values dropped to a third of the maximum. Species performance varied in a complex manner as did the environment.C. lyngbyei had diminished growth and decreased standing crop in areas where salinity was higher.S. americanus was equally productive in low elevation, high salinity sites and in high elevation, low salinity sites. An increase in shoot density for dominant species occurred in saline areas as individual shoot weights and leaf areas decreased. Because species responded differently, environmental variation was magnified in the population and community responses of the marsh vegetation.     

贵阳地表水-地下水的硫和氯同位素组成特征及其污染物示踪意义

喀斯特地表水和地下水的交换活跃,地下水系统容易受到地表污染物的污染。为了解喀斯特城市地表水—地下水系统污染特征和污染物质来源,对贵阳市地表水、地下水、雨水和城市排污污水的硫同位素和氯同位素组成变化进行了研究。贵阳市不同类型水体的δ³⁷Cl值在-4.07‰～+2.03‰之间变化,δ34SSO4值变化为-20.4‰～+20.9‰。大气输入物质和城市排污污水的δ³⁷Cl、δ³⁴S及Cl^-/SO₄^2-比值与地表水和地下水的不同,稳定硫和氯同位素的结合研究为示踪地下水污染物来源提供了有效研究手段。贵阳市地下水中的Cl^-和SO^₄2-至少有4种来源,人为活动通过城市排污和大气输入向地下水系统大量输入了硫酸盐和氯离子。      

Anomalies in rare earth distributions in seawater: Gd and Tb

We have measured profiles of the rare earth elements (REE) in Atlantic and Pacific Ocean waters. The data, normalized versus shales, exhibit a pronounced anomaly in Gd relative to its neighbors Eu and Tb in the REE series such that the Gd concentrations are high by 30–50%. Closer inspection reveals that the anomaly is made up of both elevated Gd and depressed Tb concentrations, likely associated with solution chemistry shifts in the transition from an exactly half filled 4f electron shell. Anomalies in Gd and Tb solution complexation are also indicated by the Turner-Whitfield-Dickson speciation model. The overall trend of heavy REE(III) enrichment in seawater and the $\text{Gd}\text{Tb}$ anomaly described here tend to support scavenging as an important removal mechanism for the REE from seawater.     

The interaction between surface water and groundwater and its effect on water quality in the Second Songhua River basin,northeast China

The relationship between surface water and groundwater not only influences the water quantity, but also affects the water quality. The stable isotopes (δD, δ ¹⁸O) and hydrochemical compositions in water samples were analysed in the Second Songhua River basin. The deep groundwater is mainly recharged from shallow groundwater in the middle and upper reaches. The shallow groundwater is discharged to rivers in the downstream. The runoff from upper reaches mainly contributed the river flow in the downstream. The CCME WQI indicated that the quality of surface water and groundwater was ‘Fair’. The mixing process between surface water and groundwater was simulated by the PHREEQC code with the results from the stable isotopes. The interaction between surface water and groundwater influences the composition of ions in the mixing water, and further affects the water quality with other factors.     

Evaporation pan isotopic behavior as an index of isotopic evaporation conditions

The stable isotope content of moisture (δ_E) removed by evaporation from a well mixed water body with no inflow is related to the isotopic content of the liquid (δ) by the equation m = (δ_E ? δ)/(δ ? δ_s). where δ_s is the isotopic 'steady state' of the liquid for given evaporation conditions, achieved as the liquid volume goes to zero, and m is a measure of the rate of approach of δ to δ_s. The parameters δ_s and m can be determined from simple isotopic and volume measurements of liquid water in an evaporation pan. If the mean daily surface water temperatures of such a pan and a nearby lake are equal, then with certain assumptions the pan-derived values of δ_s and m can be used to calculate δ_E for the lake surface from a knowledge of the isotopic content of the surface water. The method may be most useful in areas of low rainfall where evaporation pan observations can be conducted over long periods of time without interruption.     

Anthropogenic Rare Earth Element in rivers: Gadolinium and lanthanum. Partitioning between the dissolved and particulate phases in the Rhine River and spatial propagation through the Rhine-Meuse Delta (the Netherlands)

In this study, we report for the first time lanthanum and gadolinium anomalies at the catchment scale (Rhine-Meuse River system) together with the partitioning of their anthropogenic contents between the dissolved and the particulate phases. We compare the dissolved and total REE patterns of samples taken at 9 locations in the Rhine Branches including Lobith (situated at the German–Dutch border where the Rhine is not yet divided in three Branches), in surface water fed by the Rhine Branches (canals and lake IJsselmeer and Ketelmeer) and 3 locations where the water is derived from the river Meuse (originating from Belgium and France).We demonstrate that the anthropogenic input of lanthanum in the German part of the Rhine River identified by Kulaksiz and Bau (2011) can be traced in the complex Rhine-Meuse Delta up to the North Sea. In the Dutch Branches of the Rhine River, in contrast to the German part of the Rhine River, the anthropogenic lanthanum (La_ANTHRO) is mainly present in the particulate phase (SPM) and not in the dissolved phase (defined as the <0.45 μm fraction). In the Meuse River no anthropogenic lanthanum was found. The amount of La_ANTHRO transported by the Rhine River at the Lobith station (German–Dutch border) varies from 2008 to 2010 between 3.7 and 5.2 tons/y in the dissolved phase, and between 28.8 and 37.4 tons/y in the particulate phase. However, a big discrepancy is evidenced when we compare the La_ANTHRO load calculated on bases of the total water samples with the La_ANTHRO load calculated as the sum of the particulate and dissolved load: the total La_ANTHRO load is roughly 2 times larger than the La_ANTHRO load calculated as the sum of the dissolved and particulate La_ANTHRO load. The difference between the two calculated fluxes is most likely caused by not sampling the finest fraction of the particulate pool in the SPM samples with an overflow centrifuge.The anthropogenic gadolinium identified by high gadolinium anomalies in the REE patterns originates from numerous point sources (waste water treatment plant effluents) and can thus be considered as diffuse pollution when compared to anthropogenic lanthanum clearly resulting from a single source. The amount of anthropogenic gadolinium measured in the dissolved phase (main carrier of Gd) increases or decreases along the Rhine and Meuse Rivers depending whether or not the mixing water contains anthropogenic gadolinium, i.e. receives waste water effluents.     

Carbon and nitrogen pools in Padanian soils (Italy): Origin and dynamics of soil organic matter

Carbon and nitrogen elemental (C-N, wt%) and isotopic (δ¹³C-δ¹⁵N, ‰) investigation has been carried out on alluvial and deltaic soils from the Padanian plain (northern Italy), an area interested by intensive agricultural activities, to refine previous inferences on depositional facies, pedogenetic processes and anthropogenic influences. Soil analysis, carried out by EA-IRMS, have been focused on inorganic and organic fractions properly speciated by a thermally-based method, whereas further insights on the organic matter constituents have been obtained by sequential fractionation. The bulk EA-IRMS analyses reveal a remarkable compositional heterogeneity of the investigated soils (TC 0.89 to 11.93?wt%, TN 0.01 to 0.78?wt%, δ¹³C_TC -1.2 to -28.2‰, δ¹⁵N -1.2 to 10.0‰) that has to be explained as an integration between inorganic and organic pools. The latter have been subdivided in Non-Extractable Organic Matter (NEOM, δ¹³C -16.3 to -28.6‰) and in extractable fractions as Fulvic (FA, δ¹³C -24.7 to -27.5‰, δ¹⁵N 0.6 to 5.7‰) and Humic (HA, δ¹³C -24.6 to -27.0‰, δ¹⁵N 1.0 to 9.7‰) Acids, which have been used to infer soil dynamics and Soil Organic Matter (SOM) stability processes. Results indicate that SOM at depth of 100?cm was generally affected by microbial reworking, with the exception of clayey and peaty deposits in which biological activity seems inhibited. Peaty and clayey soils display an organic fraction loss of ca. 20% toward the surface, suggesting deterioration possibly induced by intensive agricultural activities. These latter may be the cause of the ubiquitous losses of organic fraction throughout the investigated area over the last seventy years, evaluated by the comparison with historical data on corresponding topsoils. The obtained insights are very important because these soils are carbon (and nitrogen) sinks that are vulnerable and can be degraded, loosing agricultural productivity and potentially contributing to greenhouse gases fluxes.     

Rare earth element behavior and Pb,Sr, Nd isotope systematics in a heavy metal contaminated soil

The aim of this study is to characterize the processes and phases which control migration and retention of rare earth elements (REE) in a heavy metal contaminated soil. In addition to concentration data, we used Pb, Sr and Nd isotopic compositions in order to distinguish between natural and anthropogenic trace metals and to characterize the phases leached away during the sequential extraction procedure.The samples were sequentially extracted in 3 steps with 1 N acetic acid (HAc), 1 N HCl and 1 N HNO₃. The Pb isotope data showed that anthropogenic Pb had mainly been retained in the uppermost 10 cm by the organic matter of the topsoil. The⁸⁷Sr/⁸⁶Sr ratios of the HAc extracts are almost constant and indicate that soil carbonate is derived from regionally outcropping carbonate-rich sediments. Most HCl and HNO₃ extracts have more radiogenic Sr isotopic compositions, but it is unclear whether this reflects a growing influence of anthropogenic or silicate-derived Sr.The depth distribution of the REE is mainly controlled by two different parameters: soil pH for the HAc extractable REE and FeMn oxides for the REE in the HCl and HNO₃ extracts. A part of the HNO₃ extractable REE was also bound to the organic matter of the topsoil. The REE concentrations in the HAc extractable phase increase with depth and increasing soil pH, which indicates that they are derived from the surface and hence are of anthropogenic origin. This is confirmed by¹⁴³Nd/¹⁴⁴Nd isotope ratios which show a mixing between a natural end-member at the top and an anthropogenic end-member at the base of the profile. We assume that the anthropogenic REE were transported in dissolved form as carbonate complexes and then precipitated during downward migration as soil pH increased.     

Biogeochemical implications of the isotopic equilibrium fractionation factor between the oxygen atoms of acetone and water

Carbonyl oxygens of organic molecules undergo isotopic exchange with water during reversible hydration reactions. The equilibrium isotopic fractionation factors between the carbonyl oxygen of acetone and water at 15°, 25°, and 35°C are 1.028, 1.028, and 1.026 respectively. The differences between the δ¹⁸O values of the carbonyl oxygen of acetone and of the water with which it is in equilibrium are similar to the differences that have been observed between the δ¹⁸O values of cellulose and the water used in its synthesis by a variety of aquatic plants and animals. Additionally, the identity of the acetone-water fractionation factors at 15° and 25°C parallels the observation that the difference between the δ¹⁸O values of cellulose and water shows no temperature dependence for individual species of plants grown over the same temperature range. These results are discussed in relation to the proposal that the oxygen isotopic relationship between cellulose and water is established by isotopic exchange occurring during the hydration of carbonyl groups of the intermediates of cellulose synthesis.     

Organic carbon isotope ratios of recent sediments from coastal lagoons of the Gulf of Mexico,Mexico

The stable carbon isotope composition sedimentary organic carbon was determined in the sediments of seven coastal lagoons of the Gulf of Mexico, Mexico. For most of the lagoons the δ¹³C values for sediments ranged from ?20.1 to ?23.9%. Anomalously low values, ?26.8 to 29.3%. were determined in sediments of two of the studied lagoons, probably due to the presence of organic carbon from anthropogenic sources, naturally absent in these environments. The δ¹³C values determined in the tissues of oysters collected at the same time in the different lagoons were very similar to those recorded in the sediments.     

Surface studies of water isotopes in Antarctica for quantitative interpretation of deep ice core data

Polar ice cores are unique climate archives. Indeed, most of them have a continuous stratigraphy and present high temporal resolution of many climate variables in a single archive. While water isotopic records (δD or δ¹⁸O) in ice cores are often taken as references for past atmospheric temperature variations, their relationship to temperature is associated with a large uncertainty. Several reasons are invoked to explain the limitation of such an approach; in particular, post-deposition effects are important in East Antarctica because of the low accumulation rates. The strong influence of post-deposition processes highlights the need for surface polar research programs in addition to deep drilling programs. We present here new results on water isotopes from several recent surface programs, mostly over East Antarctica. Together with previously published data, the new data presented in this study have several implications for the climatic reconstructions based on ice core isotopic data: (1) The spatial relationship between surface mean temperature and mean snow isotopic composition over the first meters in depth can be explained quite straightforwardly using simple isotopic models tuned to d-excess vs. δ¹⁸O evolution in transects on the East Antarctic sector. The observed spatial slopes are significantly higher (～ 0.7–0.8‰·°C^?1 for δ¹⁸O vs. temperature) than seasonal slopes inferred from precipitation data at Vostok and Dome C (0.35 to 0.46‰·°C^?1). We explain these differences by changes in condensation versus surface temperature between summer and winter in the central East Antarctic plateau, where the inversion layer vanishes in summer. (2) Post-deposition effects linked to exchanges between the snow surface and the atmospheric water vapor lead to an evolution of δ¹⁸O in the surface snow, even in the absence of any precipitation event. This evolution preserves the positive correlation between the δ¹⁸O of snow and surface temperature, but is associated with a much slower δ¹⁸O-vs-temperature slope than the slope observed in the seasonal precipitation. (3) Post-deposition effects clearly limit the archiving of high-resolution (seasonal) climatic variability in the polar snow, but we suggest that sites with an accumulation rate of the order of 40 kg.m^?2.yr^?1 may record a seasonal cycle at shallow depths.     

鄱阳湖流域赣江北支水体和沉积物中稀土元素的含量和分异特征

稀土的开发和广泛应用使得人们倍加关注其在环境中的分布及其环境地球化学行为。赣江作为鄱阳湖流域五大入湖河之一,发源于稀土资源富集的赣南地区,而其下游水体及周边地下水中稀土元素的含量和分异特征目前尚不完全清楚。以赣江北支水体及沉积物为研究对象,开展了稀土元素地球化学研究。结果表明,赣江北支水体中稀土元素总量在地表水中为230~1 146 ng/L(均值458.85 ng/L),地下水中为284~1 498 ng/L(均值634.94 ng/L),沉积物中稀土元素总量为177.9~270.7 mg/kg(均值226.99 mg/kg)。PHREEQC模拟计算表明,水体中的稀土元素主要以碳酸根络合物(REEC0₃⁺)的形式存在。地表水和地下水总体上均表现为重稀土元素相较于轻、中稀土元素富集,沉积物未表现出明显的富集特性;水体具有Ce、Eu负异常特点,而沉积物表现为Ce正异常和Eu负异常,指示氧化还原环境和水岩相互作用对稀土元素在水-沉积物系统中迁移转化的影响。地下水中稀土元素的含量沿流向具有上升趋势,而水体中重稀土元素的富集程度不断减弱,同时碳酸根络合物(REEC0₃⁺)的占比不断降低,反映水体中稀土元素的含量受到pH、胶体吸附、络合作用以及地下水-地表水相互作用的影响。水体中重稀土元素的富集受到碳酸根络合反应的影响,Ce、Eu负异常与Ce氧化沉淀和母岩特性相关。Gd异常值表明,研究区中下游水体中的Gd元素受到人为输入的影响。