Chemical weathering and CO2 consumption rate in a multilayered‐aquifer dominated watershed under intensive farming: The Orgeval Critical Zone Observatory,France

The impact of intensive farming on chemical weathering in the Critical Zone is still an open question. Extensively instrumented and monitored over the last 50 years, the Orgeval Critical Zone Observatory (CZO) in France is an observation site impacted by intensive farming since the 1960s. The Orgeval observatory represents an ideal place to study the response and resilience capability of the Critical Zone under agricultural stress. This paper investigates the chemical composition of different water bodies in two nested catchments of the Orgeval CZO, including rainfall, springs, rivers, and rocks, over one and half hydrological year. We show that elemental and strontium isotopic ratios are powerful to constrain the origin of the elements. The results show that the river chemistry at the outlet of the two nested catchments is dominated by rain inputs (particularly atmospheric dust dissolution) and the chemical weathering of limestone and gypsum. Fertilizer input is clearly visible, although the distinction between gypsum dissolution and fertilizer inputs needs more investigation. The mixtures of water masses inferred from our data are in good agreement with the hydrological context of the watershed, that is, a multilayered aquifer structure. At the main outlet of the CZO, we estimate that the input of ocean‐derived solutes through rainfall represents 7 t km^?2 year^?1, on the same order of magnitude as the net fertilizer input (10 t km^?2 year^?1), and that rock weathering releases 50 t km^?2 year^?1. Including previously published physical erosion rates, we estimate that the total denudation rate (physical and chemical) of the Orgeval CZO is 20 mm (1,000 year)^?1, which, along with the entire Seine watershed, is among the lowest chemical denudation rates for carbonate terrains under temperate climate. Chemical denudation is about 10 times higher than physical erosion in the Orgeval CZO. The consumption of CO₂ by rock weathering is estimated to be between 265.10³ and 360.10³ molC km² year^?1, similar for the two nested catchments. Compared with the rivers, the springs show a higher CO₂ consumption rate that suggests, as pointed out earlier, a enhancement of carbonate dissolution linked to nitrification and thus fertilizer application. The hyporheic zone appears to be a hot spot in the carbon cycle at the Orgeval CZO. This study sheds light on the complex, anthropocenic, interplay between geology, climate, and human activities that characterize and that take place in intensive agriculture regions.     

Chemical characteristics of rainwater in karst rural areas,Guizhou Province,Southwest China

The chemical composition of rainwater has been studied in a karst rural area from September 2012 to August 2013 in Guizhou Province,Southwest China.The results indicated that the VWM value of p H was 5.4,varied from 4.6 to 6.9.Ca~(2+)and NH_4~+were the major cations,and SO_4~(2-)was the dominant anion.Neutralization factors show that the acid was mainly neutralized by Ca~(2+),NH_4~+and Mg~(2+).Investigations of correlation coefficients and enrichment factors revealed that Ca~(2+)and Mg~(2+)were mainly crust origins,and NH_4~+was from agriculture and livestock manure.SO_4~(2-)and NO_3~-were mainly from anthropogenic sources.     

Carbon stable isotopic composition of karst soil CO2 in central Guizhou, China

The δ¹³c values of soil CO₂ are less than that of atmosphere CO₂ in the karst area. On the soil-air interface, the δ¹³c vlaues of soil CO₂ decrease with the increase in soil depth; below the soil-air interface, the δ¹³c values of soil CO₂ are invariable. The type of vegetation on the land surface has an influence on the δ¹³C values of soil CO₂. Due to the activity of soil microbes, the δ¹³C values of soil CO₂ are variable with seasonal change in ps. Isotopic tracer indicates that atmosphere CO₂ has a great deal of contribution to soil CO₂ at the lower parts of soil proflie. Project supported by the National Natural Science Foundation of China (Grant Nos. 49703048 and 49833002)     

Probing deep weathering in the Shale Hills Critical Zone Observatory,Pennsylvania (USA): the hypothesis of nested chemical reaction fronts in the subsurface

Weathering is both an acid‐base and a redox reaction in which rocks are titrated by meteoric carbon dioxide (CO₂) and oxygen (O₂). In general, the depths of these weathering reactions are unknown. To determine such depths, cuttings of Rose Hill shale were investigated from one borehole from the ridge and four boreholes from the valley at the Susquehanna Shale Hills Observatory (SSHO). Pyrite concentrations are insignificant to depths of 23 m under the ridge and 8–9 m under the valley. Likewise, carbonate concentrations are insignificant to 22 and 2 m, respectively. In addition, a 5–6 m‐thick fractured layer directly beneath the land surface shows evidence for loss of illite, chlorite, and feldspar. Under the valley, secondary carbonates may have precipited. The limited number of boreholes and the tight folding make it impossible to prove that depth variations result from weathering instead of chemical heterogeneity within the parent shale. However, carbonate depletion coincides with the winter water table observed at ~20 m (ridge) and ~2 m depth (valley). It would be fortuitous if carbonate‐containing strata are found under ridge and valley only beneath the water table. Furthermore, pyrite and carbonate react quickly and many deep reaction fronts for these minerals are described in the literature. We propose that deep transport of O₂ initiates weathering at SSHO and many other localities because pyrite commonly oxidizes autocatalytically to acidify porewaters and open porosity. According to this hypothesis, the mineral distributions at SSHO are nested reaction fronts that overprint protolith stratigraphy. The fronts are hypothesized to lie subparallel to the land surface because O₂ diffuses to the water table and causes oxidative dissolution of pyrite. Pyrite‐derived sulfuric acid (H₂SO₄) plus CO₂ also dissolve carbonates above the water table. To understand how reaction fronts record long‐term coupling between erosion and weathering will require intensive mapping of the subsurface. Copyright © 2013 John Wiley & Sons, Ltd.     

Element geochemistry of weathering profile of dolomitite and its implications for the average chemical composition of the upper-continental crust--Case studies from the Xinpu profile,northern Guizhou Province,China

Geochemical behavior of chemical elements is studied in a dolomitite weathering profile in upland of karst terrain in northern Guizhou.Two stages can be recognized during the process of in situ weathering of dolomitite:the stage of sedentary accumulation of leaching residue of dolomitite and the stage of chemical weathering evolution of sedentary soil.Ni,Cr,Mo,W and Ti are the least mobile elements with reference to Al.The geochemical behavior of REE is similar to that observed in weathering of other types of rocks.Fractionation of REE is noticed during weathering,and the two layers of REE enrichments are thought to result from downward movement of the weathering front in response to changes in the environment.It is considered that the chemistry of the upper part of the profile,which was more intensively weathered,is representative of the mobile components of the upper curst at the time the dolomitite was formed,while the less weathered lower profile is chemically representative of the immobile constitution.Like glacial till and loess,the "insoluble" materials in carbonate rocks originating from chemical sedimentation may also provide valuable information about the average chemical composition of the upper continental crust.     

A preliminary study on ore-forming environments of Xianglushan-type iron deposit and the weathering mineralization of Emeishan basalt in Guizhou Province,China

Xianglushan-type iron deposits are one of the new types of iron deposits found in the Weining Area of Western Guizhou. The iron-bearing rock system is a paleo-weathered crustal sedimentary(or accumulating) stratum between the top of the Middle-Late Permian Emeishan basalt formation and the Late Permian Xuanwei formation. Iron ore is hosted in the Lower-Middle part of the rock system. In terms of the genesis of mineral deposit, this type of deposit should be a basalt paleo-weathering crustal redeposit type, very different from marine sedimentary iron deposits or continental weathering crust iron deposits. Based on field work and the analytical results of XRD Powder Diffraction, Electron Probe, Scanner Electron Microscope, etc., the geological setting of the ore-forming processes and the deposit features are illustrated in this paper. The ore-forming environment of the deposit and the Emeishan basalt weathering mineralization are also discussed in order to enhance the knowledge of the universality and diversity of mineralization of the Emeishan Large Igneous Province(ELIP), which may be a considerable reference to further research for ELIP metallogenic theories, and geological research for iron deposits in the paleo-weathering crust areas of the Emeishan basalt,Southwestern, China.     

Element geochemical characteristics of a soil profile developed on dolostone in central Guizhou,southern China: implications for parent materials

This study presents bulk chemical compositions of the Tongmuling soil profile, which developed on dolostone, and the overlying strata covering the bedrock in the central Guizhou province(southern China). The chemical weathering characteristics of the studied profile were investigated and the inheritance relationships between the terra rossa and overlying strata were discussed. The results show that there is no remarkable variation in the major elements and weathering indices from the rock–soil interface to the topsoil, indicating that the studied profile was not typical for in situ crustal chemical weathering. The terra rossa were mainly composed of Si O_2, Al_2O_3 and Fe_2O_3. Compared with the insoluble residues and overlying strata, the terra rossa are characterized by an enrichment of Y and Cs and depletion of Ba and Sr. The subsoil shows a notable Ce negative anomaly, characterized by heavy rare earth element enrichment(L/H = 1.55–3.74), whereas the topsoil shows a positive Ce anomaly with light rare earth element enrichment(L/H = 5.93–9.14). According to Laterite-forming capacity estimates, the terra rossa could not have only been formed from acid-insoluble residues from the bedrock; Al_2O_3 versus Fe_2O_3and Nb plotted against Ta show significant positive correlations between the terra rossa and overlying strata. The Eu/Eu* versusGd_N/Yb_Nand ternary diagrams for Sc, Th, Zr, and Ta suggest that the overlying strata could also provide parent materials for the genesis of terra rossa.     

Characteristics and planation surface formation environment of the red weathering crust in Hunan,Guangxi, Yunnan,Guizhou and Tibet

The characteristics of red karst weathering crust in the research region can be divided into three subtypes. The first one includes the silicon to aluminum ratio, the composition of the clay minerals, etc., and reflects the weak action of de-silicon and aluminum enrichment. The second one, for example the granularity, shows that the viscous action is strong. The third one, such as the CaCO₃ content and pH value, has regional difference in a large scale, which is consistent with the condition of modern scenery, so it is not important as for the ancient environment.

     

Modeling soil erosion using a spatially distributed model in a karst catchment of northwest Guangxi,China

Reliable assessment of the spatial distribution of soil erosion is important for making land management decisions, but it has not been thoroughly evaluated in karst geo‐environments. The objective of this study was to modify a physically based, spatially distributed erosion model, the revised Morgan, Morgan and Finney (RMMF) model, to estimate the superficial (as opposed to subsurface creep) soil erosion rates and their spatial patterns in a 1022 ha karst catchment in northwest Guangxi, China. Model parameters were calculated using local data in a raster geographic information system (GIS) framework. The cumulative runoff on each grid cell, as an input to the RMMF model for erosion computations, was computed using a combined flow algorithm that allowed for flow into multiple cells with a transfer grid considering infiltration and runoff seepage to the subsurface. The predicted spatial distributions of soil erosion rates were analyzed relative to land uses and slope zones. Results showed that the simulated effective runoff and annual soil erosion rates of hillslopes agreed well with the field observations and previous quantified redistribution rates with caesium‐137 (¹³⁷Cs). The estimated average effective runoff and annual erosion rate on hillslopes of the study catchment were 18 mm and 0.27 Mg ha^?1 yr^?1 during 2006–2007. Human disturbances played an important role in accelerating soil erosion rates with the average values ranged from 0.1 to 3.02 Mg ha^?1 yr^?1 for different land uses. The study indicated that the modified model was effective to predict superficial soil erosion rates in karst regions and the spatial distribution results could provide useful information for developing local soil and water conservation plans. Copyright © 2014 John Wiley & Sons, Ltd.     

Characteristics of soil water movement in a grass slope in a karst peak‐cluster region,China

Soil water is very important in hilly areas with thin soil layers and deep groundwater tables, such as the karst peak‐cluster region of Southwest China. An investigation into soil water movement can provide insights into management of shallow water resources and soil nutrients, as well as prevention of groundwater pollution. In this study, ¹⁸O and ²H tracers were used to trace soil water movement in planar soil mass type microhabitats in the middle part of a steep hillslope covered by grasses in a karst peak‐cluster region of China. From May 2008 to July 2009, samples of precipitation and two types of soil water, which had different integrated degrees of mobility and were of different depth intervals or depths, were collected. The hydrogeochemical characteristics were compared between precipitation and soil water, and these data were applied in convolution‐based lumped parameter models. Our results indicated that vertical piston flow, rather than lateral flow along the soil–bedrock interface, played an important role in soil water percolation at least in the upper soil layer approximately 7 cm over the permeable bedrock. The mixing effect and preferential flow might also play a role in soil water percolation. In general, the evaporation effect on soil water was weak except for the uppermost 10 cm soil matrix water during winter. The lower limits of mean transit time of soil matrix flow passing through 5, 15, 25, 35, and 41.5 cm depths were 4.81, 7.70, 16.19, 21.85, and 27.44 days, respectively. Our study demonstrated the crucial functions of the soil reservoir in regulating the water cycle and could provide guidance on conservation of soil water and hydrological studies. The applied method was proved to be a suitable approach for investigating soil water movement on a monthly scale.     

Modelling hydrological processes influenced by soil,rock and vegetation in a small karst basin of southwest China

Hydrological processes in karst basins are controlled by permeable multimedia, consisting of soil pores, epikarst fractures, and underground conduits. Distributed modelling of hydrological dynamics in such heterogeneous hydrogeological conditions is a challenging task. Basing on the multilayer structure of the distributed hydrology‐soil‐vegetation model (DHSVM), a distributed hydrological model for a karst basin was developed by integrating mathematical routings of porous Darcy flow, fissure flow and underground channel flow. Specifically, infiltration and saturated flow movement within epikarst fractures are expressed by the ‘cubic law’ equation which is associated with fractural width, direction, and spacing. A small karst basin located in Guizhou province of southwest China was selected for this hydrological simulation. The model parameters were determined on the basis of field measurement and calibrated against the observed soil moisture contents, vegetation interception, surface runoff, and underground flow discharges from the basin outlet. The results show that due to high permeability of the epikarst zone, a significant amount of surface runoff is only generated after heavy rainfall events during the wet season. Rock exposure and the epikarst zone significantly increase flood discharge and decrease evapotranspiration (ET) loss; the peak flood discharge is directly proportional to the size of the aperture. Distribution of soil moisture content (SMC) primarily depends on topographic variations just after a heavy rainfall, while SMC and actual ET are dominated by land cover after a period of consecutive non‐rainfall days. The new model was able to capture the sharp increase and decrease of the underground streamflow hydrograph, and as such can be used to investigate hydrological effects in such rock features and land covers. Copyright © 2011 John Wiley & Sons, Ltd.     

北京石景山工业区附近一个污染土壤剖面的磁学研究

对北京西郊石景山工业区附近的土壤剖面进行环境磁学研究,结合粒度、金属元素分析、磁学指标测试和多元统计分析,发现磁参数(χ,ARM,SIRM)与重金属元素(Mn,Cu,Fe,Pb,Zn,Al,Sr)含量呈同步垂向变化趋势.来源于工业区附近工业生产排放(钢铁厂、发电厂、水泥厂)的污染物是土壤剖面上部(0～3 cm)磁性和金属含量增强的主要原因,由富集在细粉砂和中粉砂的多畴磁铁矿主导了样品的磁性特征.3～10 cm重金属含量逐渐下降,土壤的磁性特征与上层相似,但磁性矿物含量降低,属于剖面中的迁移过渡阶段.10 cm以下,土壤基本未受到污染,磁性矿物和重金属含量都低,磁性颗粒大小变化稳定,基本代表了该地区土壤的自然背景.指标聚类和相关分析表明,土壤磁参数与重金属元素含量显著相关.结合模糊聚类分析,磁参数可用于追踪、识别工业污染物质在土壤剖面中的富集、迁移状态,揭示不同深度土壤的污染程度.     

The formation mechanism of accretionary wedge at Karamay in West Junggar,NW China

Accretionary wedge is the typical product of subduction-zone processes at shallow depths.Determining the location,composition and mechanism of accretionary wedge has important implications for understanding the tectonism of plate subduction.The Central Asian Orogenic Belt(CAOB) is one of the world's largest accretionary orogenic belts,and records the bulk evolution of Paleo-Asian Ocean from opening to closure,with multi-stages and multi-types of crust-mantle interaction in the Paleozoic.West Junggar(western part of Junggar Basin),located in the core area of CAOB,is characterized by a multiple intra-oceanic subduction system during the Paleozoic.In its eastern part crop out Devonian-Carboniferous marine sedimentary rocks,Darbut and Karamay ophiolitic melanges,alkali oceanic island basalts,island arc volcanic rocks and thrusted nappe structure.Such lithotectonic associations indicate the occurrence of accretionary wedge at Karamay.In order to decipher its formation mechanism,this paper presents a synthesis of petrography,structural geology and geochemistry of volcanic rocks.In combination with oceanic subduction channel processes,itis suggested that the accretionary wedge is acomposite melange with multiple stages of formation.The application of oceanic subduction channel model to the Karamay accretionary wedge provides new insights into the accretion and orogenesis of CAOB.     

The deposition of stony colluvium on clay soil as a cause of gully formation in the Rif Mountains,Morocco

V-shaped gullies are formed on slopes in the Rif Mountains where stony colluvium covers a truncated Luvisol in finegrained, early pleistocene slope deposits. The colluvium resulted from large-scale deforestation of summit areas in recent times. A number of properties related to the response of soil material to rainfall were investigated. Colluvium has a high infiltration capacity compared to the Luvisol. Consequently, the deposition of colluvium reduced overland flow and erosion by surface wash. Gully-forming processes on the other hand were activated by the superposition of permeable over impermeable material.     

The record of paleoclimatic change from stalagmites and the determination of termination II in the south of Guizhou Province,China

A high-resolution climate record from 163.00 kaBP to 113.80 kaBP has been obtained through TIMS-U series dating and carbon and oxygen isotope analysis of the three large stalagmites from two caves in the south of Guizhou Province, China. The record of the oxygen isotopes from the stalagmites reveals that the undulation characteristics between the cooling event of the glacial period and the warming event of the interglacial period in the research area can compare well to those of ice cores, lake sediments, loess and deep sea sediments on the scale of ten-thousand years or millennium time scale. The climate undulation provided by the record of the stalagmites has a coherence with the global changes and a tele-connection to the paleoclimate changes in the north polar region. Our results suggest that the direct dynamics of paleo-monsoon circulation changes reflected in the record of the stalagmites might be caused by changes of the global ice volume, and in turn related to various factors, including the solar radiation strength at the mid-latitudes in the Northern Hemisphere, the southern extension of the ice-rafted event in the North Atlantic, and changes of the equatorial Pacific sea surface temperature at the low-latitudes. Using °¹⁸O values, we have calculated the temperatures and the results show that the temperature difference between the penultimate glacial period (with an average temperature of 8.1°C, and a minimum temperature range from 0.65°C to-1.43°C at stage 6) and the last interglacial period (with an average temperature of 18.24°C at sub-stage 5e) was about 10°C. This temperature difference from the record of the stalagmites corresponds in general to the record temperature variation (about 10°C) of measured ice cores. The climate records from the three stalagmites in the two caves have shown that the circulation strength of the Asian summer monsoon and the winter monsoon in the penultimate glacial period and the last inter-glacial period had a clear change. With the TIMS-U series method, termination II of the penultimate glacial period has been precisely dated at an age of (129.28± 1.10) kaBP for the three stalagmites in the south of Guizhou Province, China. This borderline age represents the beginning of the last interglacial period or the boundary between the Middle Pleistocene and the Late Pleistocene, and corresponds to the beginning age of the last interglacial period shown by the ice cores and in the SPECMAP curve of the marine oxygen isotopes. The chronology determination of termination II is not only of stratigraphic and chronological significance, but also lays an important foundation for discussing the short time scales of climate oscillation and rapidly changing events of paleoclimate in the circulation region of the East Asian monsoon.     

The role of aerial algae in the formation of the landscape of the Yunnan Stone Forest,Yunnan Province, China

~~The role of aerial algae in the formation of the landscape of the Yunnan Stone Forest,Yunnan Province, China~~     

Enrichment characteristics and sources of the critical metal yttrium in Zhijin rare earth-containing phosphorites,Guizhou Province,China

Yttrium(Y) is a critical metallic element that is used widely in modern scientific,technological,and industrial applications.Phosphorites in the Zhijin area of Guizhou Province,China,are famous for Y enrichment,but the enrichment characteristics and sources remain unclear.Previous studies suggested that the sources of rare earth elements(REEs,La-Lu) and Y(REYs,La-Lu+Y)were related to hydrothermal deposition.However,this study presents evidence refuting that hypothesis,with major and trace elemental data collected with quadrupoleinductively coupled plasma-mass spectrometry(Q-ICPMS) analysis.These data show that Y in Zhijin REYscontaining phosphorites has a normal distribution and is particularly enriched relative to other REYs.The Y enrichment degree is different at different ∑REY intervals.Specifically,the Y enrichment degree is higher at lower ∑REY values and lower at higher ∑REY values.The REYs-containing phosphorites show features of primary phosphorites.Both REEs and Y have good correlations with P_2 O_5 in the phosphorites with low REYs contents(total REYs 535 ppm),whereas at high REYs contents(total REYs 535 ppm),REEs have a good correlation with P_2 O_5 but Y does not.Inconsistent enrichment processes of REYs are suggestive of complex sources of Y.Thus,seafloor hydrothermal fluids were not the direct source of Y.Normal seawater mixed with terrestrial sources might have contributed to the origin of Y here.This study could lead to improvements in Y mineral resource explorations and the situation involving the global REYs supply crisis.     

Application of data assimilation with the Root Zone Water Quality Model for soil moisture profile estimation in the upper Cedar Creek,Indiana

Data assimilation techniques have been proven as an effective tool to improve model forecasts by combining information about observed variables in many areas. This article examines the potential of assimilating surface soil moisture observations into a field‐scale hydrological model, the Root Zone Water Quality Model, to improve soil moisture estimation. The Ensemble Kalman Filter (EnKF), a popular data assimilation technique for nonlinear systems, was applied and compared with a simple direct insertion method. In situ soil moisture data at four different depths (5, 20, 40, and 60 cm) from two agricultural fields (AS1 and AS2) in northeastern Indiana were used for assimilation and validation purposes. Through daily update, the EnKF improved soil moisture estimation compared with the direct insertion method and model results without assimilation, having more distinct improvement at the 5 and 20 cm depths than for deeper layers (40 and 60 cm). Local vertical soil property heterogeneity in AS1 deteriorated soil moisture estimates with the EnKF. Removal of systematic bias in the forecast model was found to be critical for more successful soil moisture data assimilation studies. This study also demonstrates that a more frequent update generally contributes in enhancing the open loop simulation; however, large forecasting error can prevent more frequent update from providing better results. In addition, results indicate that various ensemble sizes make little difference in the assimilation results. An ensemble of 100 members produced results that were comparable with results obtained from larger ensembles. Copyright © 2011 John Wiley & Sons, Ltd.     

南北地震带等地区强地震在华北中南部的“响应地震”研究

2008年5月12日T14:28汶川发生8.0级大地震,2008年5月13日T5:00江苏省发生滨海ML3.8地震。滨海地震是否是由汶川地震触发的、可指示滨海附近中短期内将发生中强地震的"诱发前震"?基于此,本文进行了如下研究:①统计南北地震带及中国台湾7.3级以上、日本7.5级以上大地震;②统计①中大震发生后3天时间(72 h)内,华北中南部地区发生的M_L 3以上地震;③统计大震发生后1年内在M_L 3地震附近地区(距震中350 km以内)发生的5级以上地震;④对上述3组地震是否存在链式关系进行统计研究,即研究特定条件下的A—F—B链式地震现象在华北中南部的预报效果。研究结果表明:根据目前所拥有的统计资料,无法确定2008年5月13日滨海M_L 3.8地震是由汶川8级地震诱发的"前兆地震"。