Geochemical Balance Research Articles

ОЦЕНКА УСТОЙЧИВОСТИ ПОЧВЕННОГО ПОКРОВА К ЗАГРЯЗНЕНИЮ УГЛЕВОДОРОДАМИ НА ТЕРРИТОРИИ НАЗЕМНОГО КОМПЛЕКСА МЕСТОРОЖДЕНИЯ КАШАГАН

The development and operation of the Kashagan offshore hydrocarbon deposit is accompanied by man-made impacts not only in the Caspian Sea, but also on the coast, which is associated with the creation of an onshore infrastructure for the delivery of hydrocarbons to the consumer. Man-made impacts are complex and lead to mechanical and chemical disruption of natural landscapes. The water-air regime is deteriorating, the migration ability of elements and the geochemical balance are changing. There is also a deterioration in the growth and development of vegetation, the death of soil biota. The conducted research made it possible to determine the degree of mechanical disturbance and chemical contamination of the soil cover and to assess the soil resistance of the territory of the location of the Kashagan field's surface facilities in the area of the SPZ IOaGTP Bolashak to chemical contamination. The soil cover on the territory of IOaGTP is characterized by complexity and is represented by 12 types of soils with signs of salinity and salinity. Soils are characterized by low availability of nutrients and have low agricultural production potential or are completely unsuitable for farming. The soil cover of the territory is characterized by a high degree of self-purification from hydrocarbons.

Geochemical balance of the mineral fraction and statistical analyzes of the Ebolowa municipal lake’s sediments (central Africa): Implication for early diagenesis process

The Ebolowa Municipal Lake (EML) (South Cameroon) in order to identify the early diagenesis processes taking place in the lake and the factors influencing them. To this end, 21 samples were collected. In situ, hydrogen potential, redox potential, conductivity, dissolved oxygen content, and turbidity were measured. In the laboratory, the samples were subjected to mineralogical analysis by X-ray diffraction, geochemical analysis by X-ray fluorescence and ICP-MS, and statistical analysis. The coefficient of variation (Qi) was calculated from the geochemical data. In the water column, OD > 2 mg/L, pH > 7 and Eh < 0 mV. In sediments: pH < 7, Eh values are lower. The contents of 2.08 ≤ TOC ≤ 12.65%. The mineralogical procession consists of quartz, kaolinite, gibbsite, goethite, and siderite. The latter is only present in the EML. The sediments are dominated by SiO2 (60.44–89.47%), Al2O3 (6.55–18.17%), and Fe2O3 (1.15–6.21%). The Qi values range from 0.73 to 2.31. The Mn/Fe ratio values are below 0.40. Qi > 1 for Al, Fe, Mn, Mg, K, Na, P, Ni, Co, Zn, Pb, Cd, Cu, Ba, and V, and Qi < 1 for Si; Qi = 1 for Ca. The hierarchical cluster analysis shows two groups: the first one includes the samples from the central and western parts, while the second one includes those from the eastern and southern parts of the lake. The water column is subject to oxic conditions, while the sediments are anoxic. The rapid consumption of oxygen is due to organic mineralization, which is the main diagenesis observed in the lake. This phenomenon is more accentuated in the western part of the lake.

Weathering of soils originated from diabase in the Paraná Basin, São Paulo State, Brazil

ABSTRACT Weathering of the parent material is the initial process that plays an essential role in soil fertility. The study of this process has become crucial to better understand soil dynamics. Most studies on weathering are based on indexes that calculate the feldspar dissolution rate (for example, CIA, CIW, and PIA) which not always reflect the complexity in the soil profile. Other methodologies have been designed to improve these approaches, such as geochemical balance, difference of elemental contents (DE), and the W index. This work aim to assess the efficiency of these methods to identify variations in recent soil profiles developed from diabase as compared to the CIA, CIW, and PIA indexes. Data on the main oxides were used to calculate the geochemical balance, DE, CIA, CIW, PIA, and W indexes to analyze weathering intensity in two profiles originated from diabase in the Sao Paulo State, Brazil. The Ki and Kr indexes and Feo /Fed ratio were also factored and we analyzed the mineralogy of soil horizons and the source rock. The W index and DE presented greater weathering variation than the CIA, CIW, and PIA in both profiles. The geochemical balance, mineralogy, and the Ki, Kr and Feo /Fed ratios explained the variations between the horizons. The DE and geochemical balance together generated new information for the analysis of the weathering process than the isolated indexes.

Geochemical evolution of soils developed from pyroclastic rocks of Trindade Island, South Atlantic

The geochemical behavior of the major, minor, trace and rare earths elements (REEs) in soil profiles from ultramafic volcanoclastic rocks of the Vulcão do Paredão and Morro Vermelho Formation from Trindade Island (TI) was analyzed in this study. Losses and gains of chemical elements were calculated through the mass balance for two profiles along the slope: one located at higher altitude (460 m) and the other at lower altitude (258 m). In all profiles, Al, Fe and Ti accumulate due to their low mobility, whereas Ca, Na, K and Mg are the most intensely leached. Soils located at lower altitude show higher K and Mg values in the surface due to the contribution of saline sprays. Leaching of the REEs from higher to the lower slope led to the enrichment of these elements, especially the light REEs, in the soil at the lowest altitude (258 m). The high altitude profile showed Ce positive anomaly due to longer exposure to weathering. The geochemical balance shows a relative enrichment of Ti, Mn, Fe, Co, Cr, Ni, V, Zr, S related to the loss of mobile elements during the soil formation process, despite the youthful nature of these volcanic rocks.

МЕТОДОЛОГИЯ УПРАВЛЕНИЯ ГЕОХИМИЧЕСКИМ БАЛАНСОМ ВОДОСБОРОВ НА ТЕРРИТОРИИ ЗАПАДНОЙ СИБИРИ

Актуальность определяется наличием нерешенных вопросов оценки состояния водных объектов, их долгосрочного прогноза, нормирования антропогенных воздействий, очистки сточных вод и рекультивации водных объектов в Западной Сибири. Цель: разработка методологии управления геохимическим балансом водных экосистем Западной Сибири в различных природных и антропогенных условиях. Методы: ландшафтно-геохимический, географо-гидрологический, статистические методы, методы математического моделирования водного стока и химического состава вод. Результаты и выводы. Предложена методология управления геохимическим балансом водосборной территории, заключающаяся в: 1) оценке состояния водных объектов, тенденций его изменения и антропогенного влияния; 2) построении комплекса математических моделей, описывающих формирование водного стока и химического состава вод; 3) разработке мероприятий, позволяющих минимизировать антропогенное влияние на водные объекты; 4) оценке эффективности водоохранных мероприятий путем сравнения результатов наблюдений и моделирования. Разработан алгоритм определения элементов геохимического баланса водосборов. Охарактеризована направленность геохимических процессов в водных объектах Западной Сибири. Сформулированы ключевые аспекты выбора методов очистки сточных вод и рекультивации нарушенных земель. Показано, что строительство очистных сооружений целесообразно, если сброс неочищенных сточных вод составляет более 5% от стока в замыкающем створе. Оптимальная структура очистки сточных вод предполагает широкое использование отстойников и сооружений биологической очистки с естественной аэрацией, которые рекомендуется совместить с естественными понижениями рельефа в долинах рек или внутри болот при условии инженерной защиты территории. Рекультивация может считаться эффективной, если разница между значениями элементов баланса до нарушения и после рекультивации не превышает 20 %.

Modeling and prediction of sulfuric acid digestion analyses data from PXRF spectrometry in tropical soils

ABSTRACT Sulfuric acid digestion analyses (SAD) provide useful information to environmental studies, in terms of the geochemical balance of nutrients, parent material uniformity, nutrient reserves for perennial crops, and mineralogical composition of the soil clay fraction. Yet, these analyses are costly, time consuming, and generate chemical waste. This work aimed at predicting SAD results from portable X-ray fluorescence (pXRF) spectrometry, which is proposed as a “green chemistry” alternative to the current SAD method. Soil samples developed from different parent materials were analyzed for soil texture and SAD, and scanned with pXRF. The SAD results were predicted from pXRF elemental analyses through simple linear regressions, stepwise multiple linear regressions, and random forest algorithm, with and without incorporation of soil texture data. The modeling was developed with 70 % of the data, while the remaining 30 % was used for validation through calculation of R2, adjusted R2, root mean square error, and mean error. Simple linear regression can accurately predict SAD results of Fe2O3 (R2 0.89), TiO2 (R2 0.96), and P2O5 (R2 0.89). Stepwise regressions provided accurate predictions for Al2O3 (R2 0.87) and Ki - molar weathering index (SiO2/Al2O3) (R2 0.74) by incorporating soil texture data, as well as for SiO2 (R2 0.61). Random forest also provided adequate predictions, especially for Fe2O3 (R2 0.95), and improved results of Kr - molar weathering index (SiO2/(Al2O3 + Fe2O3)) (R2 0.66), by incorporation of soil texture data. Our findings showed that the SAD results could be accurately predicted from pXRF data, decreasing costs, time and the production of laboratory waste.

Capillarity-driven supersolubility in dual-porosity systems

Capillary phenomena are widespread in unsaturated media such as soils, building stone, deep depleted aquifers and still gas storage/sequestration reservoirs. Processes linked to capillarity depend on pore size and environmental conditions such as relative humidity. When capillary forces are high, water’s internal pressure can reach negative values representative of a tensile state. In those conditions, the capillary tensile water provokes compaction in moist granular materials. In geochemical terms, thermodynamics predict a significant effect on the solvent properties of tensile water. However, very little experimental work has validated thermodynamics models or shown the porosity arrangements that make capillarity a significant player to control the geochemical balance and poromechanics of porous media. In this study, we designed an experimental setup in glass microtubes (o 200 µm) conducive to capillary tension. In the tubes, salts (halite and sodium sulfate) precipitated from an evaporating solution to build a strongly contrasted dual-porosity system. Large pore bodies (o 200 µm) coexisted with nanometric pores that induced capillary tension in the whole volume. We observed mineral–liquid interactions (mass gain/loss, crystal shaping), especially how salt solubility changed as a function of capillary conditions. The water’s tensile state increased salt solubility, changing the reactions’ equilibrium constants at constant composition as predicted by thermodynamics. In addition, mineral grains showed clear evidence of poromechanical tensile stress, driving salts to move towards the interior of the tube or to crack. The results showed the potential significance of capillarity in heterogeneous porous media including nanopores. They should be considered in relation to how porous structures change, in the contexts of increasing droughts due to climate changes and increasing excavation work in deep sedimentary basins.

Indicators of metal pollution in prospective mining regions: a case study from Philippines.

Understanding the baseline geochemistry of stream waters in a prospective mining area is the key to responsible life-of-mine planning and the protection of local rivers. This can be sometimes challenging due to the presence of abandoned mines, small scale mining, and geogenic sources of metals in the same area, particularly under a tropical humid climates with rivers carrying intermittently high solid loads. This study is focused on the Pula Bato, Danlag, Altayan, and Taplan Rivers in such a climatic setting in Philippines. The rivers are located in the vicinity of the Tampakan ore deposit. It was observed that elemental concentrations in water samples from Pula Bato were generally higher when compared to concentrations from Danlag, Taplan, and Altayan samples. In particular, SO42-, TDS, Al, Cu, Fe, Mn, Ni, and Zn present considerably higher concentrations in the water samples from Pula Bato. It was shown that water quality of Pula Bato is influenced by the natural weathering of sulphide minerals which is further enhanced by the small scale mining activities and old underground workings. The mining effects on the water of Pula Bato River were not apparent in the water of the Altayan due to the possible dilution of the uncontaminated water from Danlag River and sorption processes occurring during the course of contaminants transport. The geochemical indicators and water distinctions can be used in future for catchment-scale geochemical balance modelling.

Distribution and Identification of Sources of Heavy Metals in the Voghji River Basin Impacted by Mining Activities (Armenia)

The objective of this research is to assess the distribution of heavy metals in the waters and sediments of the Voghji River and its tributaries impacted by mining activity and to reveal the real source of each of the heavy metals in the environment for assessing the pollution level of heavy metals. Voghji River with two main tributaries (Geghi and Norashenik) drain two mining regions. To identify distribution and pollution sources of heavy metals, the water and sediment samples were collected from eight sampling sites. The results of statistical analysis based on data sets of the period 2014–2016 showed that, after the influence of drainage water and wastewater of mining regions, heavy metal contents in the Voghji River basin dramatically increased. The waters of the Voghji River were highly polluted by Mn, Co, Cu, Zn, Mo, Cd, and Pb. The relation of metals content was highly changed due to anthropogenic impact disturbing the geochemical balance of the Voghji River. The water quality based on only heavy metal contents in the source of the Voghji River belongs to “good” chemical status, and in the sources of Geghi and Norashenik Rivers it is “moderate.” The water quality of Voghji and Norashenik Rivers is sharply worsening after the influence of mining activity, becoming “bad” chemical status. The research revealed the pollution sources of each metal.

SNO KARST: A French Network of Observatories for the Multidisciplinary Study of Critical Zone Processes in Karst Watersheds and Aquifers

Core Ideas SNO KARST is dedicated to the study of karst functioning. Hydrodynamics and geochemistry are measured at springs and in karst compartments. Process sampling was set up at nine sites in various climatic contexts. Continuous monitoring concerns timescales from 10 to &gt;50 yr. New tools and findings are due to the complementarity of gathered data. Karst aquifers and watersheds represent a major source of drinking water around the world. They are also known as complex and often highly vulnerable hydrosystems due to strong surface–groundwater interactions. Improving the understanding of karst functioning is thus a major issue for the efficient management of karst groundwater resources. A comprehensive understanding of the various processes can be achieved only by studying karst systems across a wide range of spatiotemporal scales under different geological, geomorphological, climatic, and soil cover settings. The objective of the French Karst National Observatory Service (SNO KARST) is to supply the international scientific community with appropriate data and tools, with the ambition of (i) facilitating the collection of long‐term observations of hydrogeochemical variables in karst, and (ii) promoting knowledge sharing and developing cross‐disciplinary research on karst. This paper provides an overview of the monitoring sites and collective achievements, such as the KarstMod modular modeling platform and the PaPRIKa toolbox, of SNO KARST. It also presents the research questions addressed within the framework of this network, along with major research results regarding (i) the hydrological response of karst to climate and anthropogenic changes, (ii) the influence of karst on geochemical balance of watersheds in the critical zone, and (iii) the relationships between the structure and hydrological functioning of karst aquifers and watersheds.

Microstructural Control on Perlite Expansibility and Geochemical Balance with a Novel Application of Isocon Analysis: An Example from Milos Island Perlite (Greece)

Representative perlite bulk rock samples from two areas of Milos Island, Greece were collected and the expansion properties of their industrial product were investigated. Coarse crude perlite from Tsigrado exhibits better expansibility, which is assigned to the presence of coarser crystallites in its bulk parent rock. During thermal treatment, the finer crystallites of the coarse crude perlite from Trachilas are entrapped in the groundmass and lead to overheating, which inhibits expansion and eventually results in shrinkage. Geochemical modification of the expanded perlites relative to their crude precursors were investigated, using the isocon method. Volatilisation of crystalline water is the main factor controlling mass reduction of the expanded perlites. Other elements, during the adequate expansion of the Tsigrado perlite, can be classified into three categories. The elements that participate preferentially in crystals decrease in the expanded material at amounts higher than the total mass loss of the rock, due to their escape controlled mainly by the removal of the crystalline phases. The elements equally participating in crystals and the groundmass show losses equivalent to the total mass loss of the rocks, as they escaped in the crystalline phases and airborne particles from the groundmass during thermal treatment. Decrease of highly incompatible elements, which mostly participate in the groundmass, in the expanded products is less than the total mass loss, as they escaped mainly in the airborne particles. The inadequate expansion and burst of the Trachilas perlite did not allow for a similar categorisation, due to random and unpredictable escape of the elements. We propose the application of this method to an artificial system to predict unexpandable mineral phases in bulk perlite, as well as elements that are most likely to participate in the amorphous perlite phase, which cannot be determined from a regular industrial production line. This graphical method may also predict environmental pollution of the atmosphere from the release of volatile compounds and airborne particles during thermal treatment of perlite or other processes of mineral treatment.

Microwave assisted digestion followed by ICP-MS for determination of trace metals in atmospheric and lake ecosystem

The study of trace metals in the atmosphere and lake water is important due to their critical effects on humans, aquatic animals and the geochemical balance of ecosystems. The objective of this study was to investigate the concentration of trace metals in atmospheric and lake water samples during the rainy season (before and after precipitation) between November and December 2015. Typical methods of sample preparation for trace metal determination such as cloud point extraction, solid phase extraction and dispersive liquid–liquid micro-extraction are time-consuming and difficult to perform; therefore, there is a crucial need for development of more effective sample preparation procedure. A convection microwave assisted digestion procedure for extraction of trace metals was developed for use prior to inductively couple plasma-mass spectrometric determination. The result showed that metals like zinc (133.50–419.30μg/m3) and aluminum (53.58–378.93μg/m3) had higher concentrations in atmospheric samples as compared to lake samples before precipitation. On the other hand, the concentrations of zinc, aluminum, chromium and arsenic were significantly higher in lake samples after precipitation and lower in atmospheric samples. The relationship between physicochemical parameters (pH and turbidity) and heavy metal concentrations was investigated as well. Furthermore, enrichment factor analysis indicated that anthropogenic sources such as soil dust, biomass burning and fuel combustion influenced the metal concentrations in the atmosphere.

Absorbed complex of riverine solid substances and its role in geochemical balance of the ocean

Data on the composition of the absorbed complex of riverine solid substances and its transformation in marine environments obtained from field observations and experimental investigations are systematized and generalized. Average values of the specific surface of the riverine suspended particulates (~20 m2/g) and the total exchange capacity of solid substances of the continental runoff (~28 mg-equiv/100 g or 280 g-equiv/t of the transported terrigenous material) are determined. It is shown that the composition of the absorbed complex in the riverine suspended particulates, as well as bottom sediments of rivers and inland water bodies differs principally from that of bottom sediments in oceans and seas: Ca dominates in the first case; Na, in the second case. When the riverine terrigenous material enters oceans and seas, the composition of the absorbed complex is subjected to the ion-exchange transformation reflected in the replacement of exchange Ca (~80%) mainly by Na and also by K and Mg of seawater. This process is responsible for the influx of 45.5 Mt/yr of dissolved Ca to ocean and the removal of 37.3, 12.8, and 3.9 Mt/yr of Na, K, and Mg, respectively. The relative transport of Ca, Na, K, and Mg to ocean with the river runoff is +7.5,–12.3,–22.4, and–2.6%, respectively.

Climatic Consequences of Long-term Global Salination of Ocean

The long-term salination of two major osmolyte systems, the ocean and the inner environment of vertebrates has been compared. The average osmolality of today’s sea (1.09 Osm) is more than three times higher than that of the blood of land vertebrates (~0.3 Osm). Of the two major strategies for ionic adaptation, in the first pattern the osmolarity of organisms (unicells, invertebrates, primitive vertebrates) equals that of the surrounding water, but the qualitative composition of body or cells fluid differ from those of the environment. In the second pattern of ionic adaptation advanced invertebrates and vertebrates maintain their energy consuming osmotic content and ionic composition of their extracellular environment. In spite of geological changes, terrestrial vertebrates maintained their physiological ionic concentration that corresponded to the sea at the time of their emergence in the Devonian era, rather than the osmolality of the ocean maintained its constancy. Paradoxically, the recent global melting of ice and snow with its temporary dilution effect is opposed by the long-term salination of the ocean. To resolve the contradiction between the salination process and its short term oscillations supported by Raoult’s law of dilute solutions, glacial periods favoring salination and interglacial periods of dilutions are: a) characterized as salinity fluctuations over geological ages, b) representing a dynamic osmolyte system against a general geochemical balance, c) directed towards a general salination process of oceans interrupted by glacial and interglacial oscillations. The gradually increasing salinity of ocean poses a long-term threat to the biodiversity and global life. It is assumed that unless mitigative measures of global proportion will be implemented, biodiversity of life on Earth will be endangered by the salinity of oceans and the shrinkage of the fresh water resources.

The distribution and geochemical assessment of trace elements from the semi-arid to sub-humid savanna of Nigeria

The results of a study of the distribution and origin of trace elements in the surface soils of the Nigerian savanna are reported. Composite surface soil samples representing the four savanna zones: Southern Guinea, Northern Guinea, Sudan and Sahel and the major soil parent materials: aeolian deposit, Basement complex, sedimentary, basaltic rocks were examined. Instrumental Neutron Activation Analysis was used to determine four trace elements, aluminum (Al), titanium (Ti), vanadium (V), dysprosium (Dy) commonly found in plant and animal tissues. The values obtained for all the samples were comparable to the range of values reported by FOREGS for topsoils worldwide. On the average, the Nigerian savanna soils contained about 4.6 % Al, 0.5 % Ti; 67 mg V kg−1 and 4.5 mg Dy kg−1. Except for soils of the semi-arid Sahel region, with very low values, elemental values reported in this study are within the tolerable range in soils, indicating the unlikelihood of problems associated with either deficiency or toxicity of these trace elements. Clay, organic carbon and free iron oxides which are the principal constituents of the soil colloid correlated positively and significantly with all the elements. Soil contamination assessment using contamination factor (cf) and geoaccumulation index (Igeo) revealed no contamination by the elements studied and are likely to have originated from the soil parent materials. Igeo values were 0.01 for V and 0.23 for Dy for all the locations indicative of near similar levels of pollution within the Nigerian savanna. Geochemical balance evaluation indicates a depletion of V with reference to levels in the earth crust while Dy enrichment in a few locations like Kanji could be ascribed to likely higher values in soil parent materials from such locations. All the elements were significantly influenced by the soil parent materials while only V and Dy were influenced by ecological zones. In the management of these elements in the Nigerian savanna, manipulation of these three soil properties holds the key to the successful and sustainable management of these elements in the soils.

A possible geochemical mechanism of the conjugation of the carbon and calcium cycles in the ocean

The geochemical balance of carbon in the ocean is considered for the conditions of constant carbonate alkalinity. It is shown that the intrabasin processes result in the annual transformation of 487 million t of organic carbon into calcium-magnesium carbonates, which is accompanied by the extraction of 1628 million t of calcium from silicates. It is concluded that the hypothesis of the reverse weathering based upon the notion of the inversion of the mineral formation processes in the ocean against the overland weathering processes requires a substantial correction.

Contribution of volcanic ashes to the regional geochemical balance: The 2008 eruption of Chaitén volcano, Southern Chile

The environmental geochemical behaviour of the rhyolitic ashes from the 2008 eruption of Chaitén volcano, Southern Chile, has been studied. After the bulk characterisation, the potential contribution to the regional geochemical fluxes was examined using: i) single batch leaching tests to provide a rapid screening of the implied major and trace elements; and ii) column experiments to evaluate the temporal mobility of leached elements. The environmental concerns of these ashes are related to the fine grained component present in each sample (independent of distance from the source), in particular the presence of cristobalite, and the geochemical hazards posed by ash–water interaction. Leaching experiments show the fast dissolution of surface salts and aerosols, which dominate over glass dissolution during the first steps of the ash–water interaction. Chaitén ashes could transfer to the environment more than 1×1010g or 10,000metric tonnes (mt) of Cl, S, Ca, Na, Si, and K; between 1000 and 10,000mt of F, Mg, and Al; between 100 and 1000mt of As, Pb, P, Fe, Sr, Zn, Mn, and Br; between 10 and 100mt of Ba, Li, Ti, Ni, Nb, Cu, Rb, Zr, V, Mo, Co, and Sc; and less than 10mt of Cr, Sb, Ce, Ga, Cs, and Y. These results show the fertilising potential of the ashes (e.g., providing Ca and Fe) but also the input of potentially toxic trace elements (e.g., F and As) in the regional geochemical mass balance. The Chaitén results evidence lower potentials for poisoning and fertilising than low silica ashes due to the lower contents released of practically all elements.

Indirect uptake of atmospheric CO2 by the ocean

During the last ten years, the reasons for modern global climate warming have been actively discussed. Many scientists consider the strengthening of the greenhouse effect to be the result of СО 2 introduction into the atmosphere, which is formed by burning of fuel mineral. At the end of the twentieth century and beginning of the twentyfirst century, the volume of anthropogenic СО2 outburst reached 7 billion tons C per year, which corresponds to 1% of the total СО 2 in the Earth's atmosphere. Observations demonstrate a lower rate of СО2 concentration increase in the atmo� sphere, and it is considered that the ocean absorbs 30- 50% of the anthropogenic outbursts of carbon dioxide (8, 9). In addition, there are arguments supporting the opposite point of view, according to which the ocean does not absorb, but, on the contrary, releases СО2 into the atmosphere (2, 7). The solution of this contra� diction should determine the direction and intensity of СО 2 exchange between the atmosphere and the ocean, which also may be directly applied to one of the funda� mental problems of geochemistry related to the study of the geochemical cycle of carbon in the biosphere. As a rule, СО2 exchange between the ocean and the atmosphere is studied on the basis of measurements and calculations of flows at the water-air boundary, without account for one more onesided relationship, including the transport of atmospheric СО2 to the ocean through a number of processes occurring on land and in totality called land runoff in the broad sense of this term. In this study we make an attempt to consider the geochemical mechanism of this process and its quantitative characteristics. The estimations given below are based on calcula� tions of the geochemical carbon balance in the ocean (2) confirmed indirectly in (3). Although the character of geochemical information available does not allow us to apply the methods of mathematical statistics to determine the accuracy of estimations of carbon flows, their accuracy may be judged from comparison of the results of different works. Calculations of carbon flows (2) providing the most complete account of the terrig� enous carbon runoff are usually consistent with esti� mations of flow values obtained by other authors (10) within 30-50%, which may most likely be considered as their accuracy. The land runoff of dissolved and solid compounds is one of the main incoming positions of the carbon geochemical balance in the ocean, and various carbon forms have different geneses. Dissolved organic carbon and most of the sus� pended organic carbon are the products of photosyn� thesis of land plants using atmospheric СО2 trans� formed to one degree or another:

Environmental geochemistry of recent volcanic ashes from the Southern Andes

Environmental contextExplosive volcanic eruptions may have significant environmental repercussions for many Earth system cycles, particularly the water cycle. We investigate the potential contribution to local geochemical fluxes through water of five historical eruptions that occurred over a 20-year period in the Southern Andes. In all five cases, the major potentially toxic trace elements were arsenic, copper, fluoride, molybdenum, nickel, lead and zinc. AbstractThe potential contribution to the local geochemical balance of five historical eruptions that occurred during the 20th Century has been investigated in the Southern Volcanic Zone (SVZ) of the Andean volcanic arc of South America (Lonquimay 1988, Hudson 1991, Copahue 2000, Llaima 2008, Chaitén 2008). These ashes were characterised by SEMEDX and XRD, and their potential released geochemical fluxes were examined using water and nitric acid batch leaching tests. Leachates were analysed by ICP-OES, ICP-MS and ISE. The major contents removed correspond to SO42– and Cl–. The potential toxic trace element (PTTE) content was highly variable among the ash samples following this order: Chaitén &gt; Copahue &gt; Hudson &gt; Llaima &gt; Lonquimay. The trace elements with significant load in water batch leaching tests include Fe &gt; F &gt; B &gt; P &gt; Zn &gt; As &gt; Mn &gt; Sr &gt; Ba &gt; Ti &gt; Cu &gt; Ni &gt; Li &gt; Rb &gt; Co &gt; Cr &gt; Cd &gt; Sb. Some of these elements (As, Cu, F, Mo, Ni, Pb and Zn) are included in the drinking water guidelines due to their potential toxicity and must be especially monitored in the environmental assessment of these ashfall deposits.

Weathering rates at Alto Sorocaba basin, Brazil, using U-isotopes and major cations

The aim of this paper was to evaluate the chemical weathering rate at Alto Sorocaba basin, Sao Paulo State, Brazil, as it is an important parameter on geomorphological characterization of continents. Several tools may be used for such evaluation, and this work compares the results obtained from analytical data involving the uranium concentration, the 234U/238U activity ratio and the major cation concentration for samples of waters, soils, and rocks from that basin. The use of the natural uranium as a tracer in weathering rate rocks studies is advantageous since this element is virtually absent in rainwater and also allows obtaining the dissolution rocks coefficient by the 234U/238U activity ratio. The Alto Sorocaba basin has serious environmental problems in terms of the quality of the rainwater and river waters, and, consequently, the geochemical balance using the main cations presented some difficulties. However, measuring of the weathering rate utilizing the U-isotopes method corresponded to 14 μm/year that allows estimating a time of 72,000 years to weather 1 m of rock at Sorocaba River upstream from Itupararanga Reservoir, under the present climatic conditions.