<Superscript>226</Superscript>Ra, <Superscript>232</Superscript>Th and <Superscript>40</Superscript>K activities in soils of Cuihua Mountain National Geological Park,China

Gamma activity from the naturally occurring radionuclides namely, ²²⁶Ra, ²³²Th, the primordial radionuclide ⁴⁰K was measured in the soil of Cuihua Mountain National Geological Park, China using γ-ray spectrometry technique. The mean activity of ²²⁶Ra, ²³²Th and ⁴⁰K were found to be 27.2 ± 6.5, 43.9 ± 6.2 and 653.1 ± 127.6 Bq kg⁻¹, respectively. The concentrations of these radionuclides were compared with the typical world values and the average activities of Chinese soil. The radium equivalent activity, the air absorbed dose rate, the annual effective dose rate, and the external hazard index were evaluated and compared with the internationally approved values. All the soil samples have Ra_eq lower than the limit of 370 Bq kg⁻¹ and H _ex less than unity. The overall mean outdoor terrestrial gamma dose rate is 66.3 nGy h⁻¹ and the corresponding outdoor annual effective dose is 0.081 mSv.     

Environmental risk evaluation of the use of mine spoils and treated sewage sludge in the ecological restoration of limestone quarries

The ecologic restoration criteria in areas degraded from extraction activities require making use of their mine spoils. These materials do not meet fertility conditions to guarantee restoration success and therefore, need the incorporation of organic amendments to obtain efficient substratum. Reducing the deficiencies in the organic material and restoration material nutrients with the contribution of treated sewage sludge is proposed in this work. This experiment was based on a controlled study using columns. The work was conducted with two mine spoils, both very rich in calcium carbonate. The first mineral, of poor quality, came from the formation of aggregates of crushed limestone (Z). The other residual material examined originated in limestone extraction, formed by the levels of interspersed non-limestone materials and the remains of stripped soils (D). Two treatments were undertaken (30,000 and 90,000 kg/ha of sewage sludge), in addition to a control treatment. The water contribution was carried out with a device that simulated either short-duration rain or a flooding irrigation system in order to cover the surface and then percolate through the soil. The collection of leached water took place 24 h after the applications. Different parameters of the leached water were determined, including pH, electrical conductivity, nitrate anions, ammonium, phosphates, sulphates and chlorides. The values obtained for each irrigation application are discussed, and the nitrate values obtained were very elevated.     

Magnesium isotope systematics of the lithologically varied Moselle river basin, France

Magnesium and strontium isotope signatures were determined during different seasons for the main rivers of the Moselle basin, northeastern France. This small basin is remarkable for its well-constrained and varied lithology on a small distance scale, and this is reflected in river water Sr isotope compositions. Upstream, where the Moselle River drains silicate rocks of the Vosges mountains, waters are characterized by relatively high ⁸⁷Sr/⁸⁶Sr ratios (0.7128-0.7174). In contrast, downstream of the city of Epinal where the Moselle River flows through carbonates and evaporites of the Lorraine plateau, ⁸⁷Sr/⁸⁶Sr ratios are lower, down to 0.70824.Magnesium in river waters draining silicates is systematically depleted in heavy isotopes (δ²⁶Mg values range from −1.2 to −0.7‰) relative to the value presently estimated for the continental crust and a local diorite (−0.5‰). In comparison, δ²⁶Mg values measured in soil samples are higher (∼0.0‰). This suggests that Mg isotope fractionation occurs during mineral leaching and/or formation of secondary clay minerals. On the Lorraine plateau, tributaries draining marls, carbonates and evaporites are characterized by low Ca/Mg (1.5-3.2) and low Ca/Sr (80-400) when compared to local carbonate rocks (Ca/Mg = 29-59; Ca/Sr = 370-2200), similar to other rivers draining carbonates. The most likely cause of the Mg and Sr excesses in these rivers is early thermodynamic saturation of groundwater with calcite relative to magnesite and strontianite as groundwater chemistry progressively evolves in the aquifer. δ²⁶Mg of the dissolved phases of tributaries draining mainly carbonates and evaporites are relatively low and constant throughout the year (from −1.4‰ to −1.6‰ and from −1.2‰ to −1.4‰, respectively), within the range defined for the underlying rocks. Downstream of Epinal, the compositions of the Moselle River samples in a δ²⁶Mg vs. ⁸⁷Sr/⁸⁶Sr diagram can be explained by mixing curves between silicate, carbonate and evaporite waters, with a significant contribution from the Vosgian silicate lithologies (>70%). Temporal co-variation between δ²⁶Mg and ⁸⁷Sr/⁸⁶Sr for the Moselle River throughout year is also observed, and is consistent with a higher contribution from the Vosges mountains in winter, in terms of runoff and dissolved element flux. Overall, this study shows that Mg isotopes measured in waters, rocks and soils, coupled with other tracers such as Sr isotopes, could be used to better constrain riverine Mg sources, particularly if analytical uncertainties in Mg isotope measurements can be improved in order to perform more precise quantifications.     

Origins of high pH mineral waters from ultramafic rocks, Central Portugal

This paper reviews the geochemical, isotopic (²H, ¹⁸O, ¹³C, ³H and ¹⁴C) and numerical modelling approaches to evaluate possible geological sources of the high pH (11.5)/Na–Cl/Ca–OH mineral waters from the Cabeço de Vide region (Central-Portugal). Water–rock interaction studies have greatly contributed to a conceptual hydrogeological circulation model of the Cabeço de Vide mineral waters, which was corroborated by numerical modelling approaches. The local shallow groundwaters belong to the Mg–HCO₃ type, and are derived by interaction with the local serpentinized rocks. At depth, these type waters evolve into the high pH/Na–Cl/Ca–OH mineral waters of Cabeço de Vide spas, issuing from the intrusive contact between mafic/ultramafic rocks and an older carbonate sequence. The Cabeço de Vide mineral waters are supersaturated with respect to serpentine indicating that they may cause serpentinization. Magnesium silicate phases (brucite and serpentine) seem to control Mg concentrations in Cabeço de Vide mineral waters. Similar δ²H and δ¹⁸O suggest a common meteoric origin and that the Mg–HCO₃ type waters have evolved towards Cabeço de Vide mineral waters. The reaction path simulations show that the progressive evolution of the Ca–HCO₃ to Mg–HCO₃ waters can be attributed to the interaction of meteoric waters with serpentinites. The sequential dissolution at CO₂ (g) closed system conditions leads to the precipitation of calcite, magnesite, amorphous silica, chrysotile and brucite, indicating that the waters would be responsible for the serpentinization of fresh ultramafic rocks (dunites) present at depth. The apparent age of Cabeço de Vide mineral waters was determined as 2790 ± 40 a BP, on the basis of ¹⁴C and ¹³C values, which is in agreement with the ³H concentrations being below the detection limit.     

Quantitative sinkhole hazard assessment. A case study from the Ebro Valley evaporite alluvial karst (NE Spain)

Quantitative sinkhole hazard assessments in karst areas allow calculation of the potential sinkhole risk and the performance of cost-benefit analyses. These estimations are of practical interest for planning, engineering, and insurance purposes. The sinkhole hazard assessments should include two components: the probability of occurrence of sinkholes (sinkholes/km² year) and the severity of the sinkholes, which mainly refers to the subsidence mechanisms (progressive passive bending or catastrophic collapse) and the size of the sinkholes at the time of formation; a critical engineering design parameter. This requires the compilation of an exhaustive database on recent sinkholes, including information on the: (1) location, (2) chronology (precise date or age range), (3) size, and (4) subsidence mechanisms and rate. This work presents a hazard assessment from an alluvial evaporite karst area (0.81 km²) located in the periphery of the city of Zaragoza (Ebro River valley, NE Spain). Five sinkholes and four locations with features attributable to karstic subsidence where identified in an initial investigation phase providing a preliminary probability of occurrence of 0.14 sinkholes/km² year (11.34% in annual probability). A trenching program conducted in a subsequent investigation phase allowed us to rule out the four probable sinkholes, reducing the probability of occurrence to 0.079 sinkholes/km² year (6.4% in annual probability). The information on the severity indicates that collapse sinkholes 10–15 m in diameter may occur in the area. A detailed study of the deposits and deformational structures exposed by trenching in one of the sinkholes allowed us to infer a modern collapse sinkhole approximately 12 m in diameter and with a vertical throw of 8 m. This collapse structure is superimposed on a subsidence sinkhole around 80 m across that records at least 1.7 m of synsedimentary subsidence. Trenching, in combination with dating techniques, is proposed as a useful methodology to elucidate the origin of depressions with uncertain diagnosis and to gather practical information with predictive utility about particular sinkholes in alluvial karst settings: precise location, subsidence mechanisms and magnitude, and timing and rate of the subsidence episodes.     

Flood hazard delineation combining geomorphological and hydrological methods: an example in the Northern Iberian Peninsula

Flood mapping requires the combination and integration of geomorphological and hydrological-hydraulic methods; however, despite this, there is very little scientific literature that compares and validates both methods. Two types of analysis are addressed in the present article. On the one hand, maps of flood plains have been elaborated using geomorphological evidence and historical flood data in the mountainous area of northwestern Spain, covering an area of more then 232 km² of floodplains. On the other hand, a hydrometeorological model has been developed (Clark semidistributed unit hydrograph) in the Sarria River basin (155 km², NW Spain). This basin is not gauged, hence the model was subjected to a goodness-of-fit test of its parameter (curve number) by means of Monte Carlo simulation. The peak flows obtained by means of the hydrological model were used for hydraulic modeling (one-phase, one-dimensional and steady flow) in a 4 km² urban stretch of the river bed. The delineation of surface areas affected by floods since 1918, as well as those analyzed subsequent to the geomorphological study, reveals a high degree of reliability in the delineation of the flooded areas with frequent recurrence intervals (<50 years). If we compare these flooded surface areas with the estimate obtained by the hydrological-hydraulic method we can see that the latter method overestimates the extent of the surface water by 144% for very frequent recurrence intervals (>10 years) and underestimates it as the recurrence interval increases, by up to 80% less floodplain for exceptional events (>500 years). Finally, a management map is put forth combining the most reliable results available by integrating both methods. Originally presented at the Sixth International Conference on Geomorphology.     

针式微萃取结合GC-IRMS测定水溶液中甲酸、乙酸的稳定碳同位素组成

甲酸和乙酸稳定碳同位素组成（δ^13C）的分析对环境、食品、制药和自然产品等的研究具有重要的应用价值。但目前尚缺乏有效的测定方法。本研究利用最近出现的针式固相微萃取技术（NeedlEX）,以吹扫．捕集方式对水溶液中的有机酸进行了萃取,然后利用气相色谱．同位素比值质谱联用仪（GC—IRMS）对所萃取的有机酸分子进行了占δ^13C的测定。结果显示,质谱计的信号强度与水溶液中有机酸的浓度存在显著的线性相关关系（R^2〉0．99,P〈0．05）,表明Needl EX对水溶液中有机酸具有稳定的萃取能力。在甲酸与乙酸含量分别不低于300μg／mL与200μg／mL的水溶液中,1000mL的吹扫体积可以使两者δ^13C多次分析结果的相对误差分别保持在3％和1％左右,且整个实验流程没有造成可检测的碳同位素分馏作用。低于这两个浓度界线,则分析误差随浓度的降低迅速增加。本研究虽然是针对水溶液中有机酸δ^13C的测定,其萃取方法对其他水溶性挥发和半挥发有机物δ^13C的分析也同样具有应用价值。     

华南前寒武系基底变质杂岩和中-新生代地幔岩的稀有气体同位素组成及其大地构造意义

对华南前寒武系变质岩浆杂岩稀有气体He、Ne、Ar和Xe的系统研究表明:扬子克拉通基底为含高³He的下地壳"原始岩石层",(³He/⁴He)×10^-6比值为2.8～4.6;而华夏板块基底变质岩浆杂岩则是在缺乏³He、低(³He/⁴He)×10^-8比值(3.15～17.7)的构造环境下形成的大陆中-上地壳变质岩浆杂岩层,反映出两者基底性质迥然不同。华南中-新生代爆破岩筒He同位素组成相反,相对稳定的扬子克拉通(³He/⁴He)×10^-8比值仅0.18～4.22,而郯庐-四会-吴川断裂以东,中-新生代活动地块(太平洋构造域)(³He/⁴He)×10^-8比值高达3.7～20.5。He同位素表明郯庐-四会-吴川断裂带为切割深至地幔的边界深大断裂,是扬子克拉通与华夏板块间的边界且控制了燕山期火山-侵入岩浆向西扩展。Ar同位素组成表明华南大陆中-新生代地幔形成接近"均一"的地幔组份。¹³⁶Xe/¹³⁰Xe-¹²⁹Xe/¹³⁰Xe相关组份表明它们具有地幔柱岩石同位素组成特征。