Origin and type of rainfall for recharge of a karstic aquifer in the western Mediterranean: a case study from the Sierra de Gador–Campo de Dalias (southeast Spain)

Isotope signatures in precipitation from the Global Network for Isotopes in Precipitation around the Mediterranean basin and literature data are compared with isotopic data from a large karstic aquifer in southeast Spain to explain the origin and type of the precipitation events dominating recharge. Analysis of the deuterium excess d at the scale of the Mediterranean basin and at the regional scale allows us to understand the isotopic context of the study area: Campo de Dalias and the Sierra de Gador (Almería province). The origin of precipitation can be determined from its d value. The d value changes as a function of the initial evaporation condition. It depends on the relative humidity and temperature during the evaporation producing the water vapour of the clouds. The water vapour, which dominates the study area, is generated in two areas: the Atlantic Ocean (d = 10‰) and the western Mediterranean basin (d = 15‰). With increasing precipitation volume, the western Mediterranean character dominates. These heavier storms contribute mainly to recharge, as illustrated by the d value of 13·6‰ in deep groundwater of the Campo de Dalias. Weighted d values increase with the volume of precipitation, giving a significant relationship for the southern and eastern coasts of the Iberian Peninsula. This selectivity of d to monthly precipitation was used to estimate the return period of precipitation leading to aquifer recharge at 0·9–4·9 years. Moderate rainfall, which occurs more frequently, still represents ～60–90% of the total precipitation. One of the challenges to meet ever‐growing water demands is to increase recharge from moderate events yielding intermediate quantities per event, but forming the bulk of the annual precipitation. Copyright © 2006 John Wiley & Sons, Ltd.     

中国大陆夏季水汽稳定同位素空间特征

大气降水的水汽来源主要是海洋,而借助降水稳定同位素空间分布格局可以反演水汽输送路径,进而示踪水汽来源。利用全球降水同位素监测网数据,基于GIS平台完成了中国大陆夏季大气降水δD、δ¹⁸O和过量氘空间格局表征。中国大陆夏季氢氧稳定同位素空间分布存在着地域分异,其成因与不同水汽源及诸多环境效应密切相关。非季风区内的西北内陆高值中心与欧亚大陆自蒸发及经由西风带输送的大西洋水汽相关,青藏高原高值则是由高程效应所造成。季风区内大气降水稳定同位素总体呈现出自东南向西北递减趋势,多由纬度效应、大陆效应共同作用而形成;我国西南地区氢氧稳定同位素明显低于同纬度东南地区的,西南地区地形复杂和气流暖湿造成的雨量效应应该是主因。过量氘空间格局则与中国大陆三大气候带分界线基本吻合,区分了西北内陆低值区、青藏高原高值区及东部的自西南向东北递减趋势显著区。依据季风区内大气降水过量氘空间分布特征,大体推断出中国大陆西南夏季风与东南夏季风的区域影响分界可能在"长沙—西安"一线附近。     

Using stable isotopes to determine the water sources in alpine ecosystems on the east Qinghai‐Tibet plateau,China

To investigate the water circulation of eastern Qinghai‐Tibet plateau during rainy season, water samples of precipitation, throughfall, fog, soil, litter and xylem were collected for stable isotope analysis. The results showed that precipitation mainly originated as a result of the East Asian Monsoon, and the secondarily evaporated water from subalpine ecosystem was an important part in local atmospheric water cycle. The deuterium excess of rainfall in the alpine meadow was evidently higher than the precipitation in the Dengsheng stations. This suggests that a large part of precipitation in alpine meadow was derived from secondarily evaporated water and the mean contribution was 39·57%, about 3·65 mm produced shortly after rain events. Through the contrast of delta (d)‐excess value in different water samples, it could be concluded that the water in subalpine shrubland and transpiration of subalpine dark coniferous forest were the main source of secondarily evaporated water that transferred to alpine meadow. Hence, the precipitation on the east Qinghai‐Tibet plateau was doubly controlled by monsoon and local water circulation in alpine ecosystems. Copyright © 2010 John Wiley & Sons, Ltd.     

The controls on boreal peatland surface water chemistry in Northern Alberta,Canada

Spatial and temporal variability in surface water chemistry, organic soil chemistry and hydrologic indicators were investigated at three poor‐fen complexes in two boreal catchments in Northern Alberta to provide insight into the dominant controls on surface water chemistry. Improved understanding of these controls is required to enable prediction of runoff chemistry in the region under changing atmospheric deposition conditions. Surface water chemistry exhibited considerable variability; within each fen conductivity, dissolved organic carbon (DOC), and Cl⁻ tended to decrease and pH tended to increase with increasing distance from the lake edge. Variations in evaporative isotopic enrichment in ²H and ¹⁸O, expressed as deuterium excess, were used to distinguish between throughflow waters and those that were more evaporatively enriched. Throughflow surface waters were more acidic primarily due to higher concentrations of DOC and NO₃⁻. Exchangeable base saturation and pH of organic soils were strongly related to surface water chemistry at two of the fen complexes, demonstrating the capacity for cation exchange to influence surface water chemistry. Fen surface water concentrations of most elements and DOC increased during the summer period (between June and August), while pH of water decreased. Evaporative concentration of the surface waters was a dominant driver, with surface water temperature increasing at both catchments. Localized groundwater discharge was an important contributor of base cations to the fens, while the organic soils are sinks for atmospherically deposited SO₄²⁻, N and Cl⁻. Copyright © 2010 John Wiley & Sons, Ltd.     

基于氢氧同位素与水化学的潮白河流域地下水水循环特征

为了研究变化环境下潮白河流域地下水水循环规律,通过现场调查,结合环境同位素及水化学应用,对潮白河流域浅层和深层地下水采样,测定其氢、氧环境同位素及水化学成分,通过分析其变化特征判明地下水的补给来源以及各含水层的相互联系。降水和地下水中的环境同位素δD和δ¹⁸O组成分析表明,降水是山前地下水的主要补给源,山区浅层地下水受蒸发影响非常强烈。水化学研究结果表明,山区地下水水质以 Ca²⁺和 HCO^-₃为主,属Ca²⁺-Mg²⁺-HCO^-₃型地下水。山前地下水类型为Ca²⁺-Mg²⁺-HCO^-₃、 Na⁺-K⁺-HCO^-₃、Mg²⁺-Ca²⁺-HCO^-₃和 Ca²⁺-Mg²⁺-Cl^--SO^2-₄。平原区地下水为Mg²⁺, Na⁺和HCO^-₃。滨海冲积海积平原为Ca²⁺-Mg²⁺-HCO^-₃型和Ca²⁺-Mg²⁺-Cl^--SO^2-₄型地下水。水化学分析证实了越流补给的存在。Ca²⁺ 和 HCO^-₃离子均呈山区高、山前和平原低、而滨海增高的趋势。沿潮白河流向地下水类型变化为:Ca²⁺-Mg²⁺-HCO^-₃ Na⁺＝K⁺-HCO^-₃ Ca²⁺-Mg²⁺-HCO^-₃。     

Seasonality of stable isotope composition of atmospheric water input at the southern slopes of Mt. Kilimanjaro,Tanzania

To understand the moisture regime at the southern slopes of Mt. Kilimanjaro, we analysed the isotopic variability of oxygen (δ¹⁸O) and hydrogen (δD) of rainfall, throughfall, and fog from a total of 2,140 samples collected weekly over 2 years at 9 study sites along an elevation transect ranging from 950 to 3,880 m above sea level. Precipitation in the Kilimanjaro tropical rainforests consists of a combination of rainfall, throughfall, and fog. We defined local meteoric water lines for all 3 precipitation types individually and the overall precipitation, δD_prec = 7.45 (±0.05) × δ¹⁸O_prec + 13.61 (±0.20), n  = 2,140, R ² = .91, p  < .001. We investigated the precipitation‐type‐specific stable isotope composition and analysed the effects of amount, altitude, and temperature. Aggregated annual mean values revealed isotope composition of rainfall as most depleted and fog water as most enriched in heavy isotopes at the highest elevation research site. We found an altitude effect of δ¹⁸O_rain = ?0.11‰ × 100 m^?1, which varied according to precipitation type and season. The relatively weak isotope or altitude gradient may reveal 2 different moisture sources in the research area: (a) local moisture recycling and (b) regional moisture sources. Generally, the seasonality of δ¹⁸O_rain values follows the bimodal rainfall distribution under the influences of south‐ and north‐easterly trade winds. These seasonal patterns of isotopic composition were linked to different regional moisture sources by analysing Hybrid Single Particle Lagrangian Integrated Trajectory backward trajectories. Seasonality of d excess values revealed evidence of enhanced moisture recycling after the onset of the rainy seasons. This comprehensive dataset is essential for further research using stable isotopes as a hydrological tracer of sources of precipitation that contribute to water resources of the Kilimanjaro region.     

ISOTOPE STUDIES OF PIPEFLOW AT PLYNLIMON,WALES, UK

Residence times and flow paths of pipe and stream flow were studied during low flow in the Nant Gerig and Gwy experimental catchments at Plynlimon in mid-Wales, UK, using a two-month time series of natural deuterium and electrical conductivity data from perennial and ephemeral pipe flow, stream flow, groundwater and rainfall. Low flow in both the perennial pipe and the stream was maintained by ‘old’ groundwater discharge. This groundwater was at least 40 days old. Flow in the ephemeral pipe was dominated by old groundwater and was only slightly affected by direct inputs of new water. Although direct rainfall inputs contributed minimally to runoff in the perennial pipe and the stream, rainfall influenced the isotopic and chemical character of the groundwater. Rainfall also affected the water-table elevation, which determined the flashiness of the perennial pipe flow and whether the ephemeral pipe flowed. The isotope and electrical conductivity data suggest that storm runoff in both the main pipe and the stream is overwhelmingly old water. A sensitivity analysis suggests that the old water is supplied both from near-stream groundwater and upslope groundwater delivered by the ephemeral pipes.     

水体同位素组成及氘过量参数在地热勘探中的示踪作用--以四川绵竹三箭水温泉开发为例

本文研究了四川绵竹三箭水及其邻区水体的同位素组成特征,以氚过量参数(d=δD-8δ^18O)在地热勘探中的示踪作用，再通过对研究区地下水氚过量参数和水笨氰含量(T)的相关性分析，综合运用于查明区内温泉地下水的成因，包括地下热储层内地下水的来源、补给源区、运移途径等等；确定水体均来源于大气降水，山前盆地深部地下水的补给源区在西、西北部高山区,径流方向由西北向东南，径流途径和在地下滞留时间都很长，并由此圈定了几个地热勘查的重点靶区。     

The Hydrogen Kinetic Isotope Effects of the Reactions of <Emphasis Type="Italic">n</Emphasis>-Alkanes with Chlorine Atoms in the Gas Phase

The stable-hydrogen kinetic isotope effects (KIEs) for a series of n-alkanes in reaction with chlorine atoms in the gas phase were studied in a 25-L PTFE reaction chamber at 298 K. The time dependence of both the stable hydrogen isotope ratios and the concentrations was determined using a gas chromatography pyrolysis isotope ratio mass spectrometry (GC-P-IRMS) system. The following KIE values, in per mil (‰), were obtained: 39.6 ± 2.7 (n-butane), 28.2 ± 0.9 (n-pentane), 24.6 ± 1.0 (n-hexane), 24.0 ± 1.2 (n-heptane), 17.9 ± 3.3 (n-octane), 15.1 ± 0.7 (n-nonane), and 14.9 ± 1.8 (n-decane). The errors given are the ±1σ standard errors. These measured values were used to derive structure–reactivity relationship (SRRs), which allow for the calculation of the KIEs for the reaction of n-alkanes with Cl atoms. The results of the calculations agree with the measurements within few per mil or better. The site specific stable hydrogen isotope fractionation effects for methyl groups are approximately a factor of 3 larger than those for methylene group, a finding which is qualitatively similar to site-specific stable hydrogen isotope effects reported in literature for reactions of alkanes with the OH radical. Because n-alkanes with close to natural isotope ratios (i.e. neither artificially labeled, nor enriched or depleted) were used, the KIE data are directly applicable to atmospheric studies. Based on these KIE values, the impact of Cl-atom reactions of the stable hydrogen isotope ratio on alkanes are estimated for different levels of Cl-atom concentrations. On average in the troposphere, the impact of Cl-atom reactions of the stable hydrogen isotope ratio of n-alkanes will be small. However, in regions of the troposphere with high concentrations of Cl atoms, such as the tropospheric ozone depletion episodes during polar sunrise, the impact of Cl-atom reactions is substantial. An erratum to this article is available at .     

淮河下游地区地表水与地下水同位素特征分析

为探明淮河下游地区地表水与地下水稳定同位素的组成特征,于2020年11月对该区域进行代表性采样,共采集地表水样13个,地下水样82个.结合全球大气降水同位素监测网(GNIP)公布的南京降水同位素数据,根据最小二乘法得出当地大气降水线(LMWL)方程为:δD=8.49δ18O+17.71,其斜率和截距高于全球大气降水线(...