Hydrogeological History Research Articles

Sustainability Indicators of Groundwater Withdrawal in a Heavily Stressed System: The Case of the Acque Albule Basin (Rome, Italy)

Groundwater sustainable yield is a concept widely treated theoretically in the literature. Moving from theoretical concepts to the definition of practical measures for groundwater management is not easy due to site-specific characteristics of the system. This study is aimed at identifying which factors influence the sustainable yield of the plain of Tivoli (Central Italy), where thermal springs with considerable flow (over 2 m3/s) emerge (or rather emerged) and supply a thermal plant. In the same plain, another profitable economic activity concerns the extraction of travertine; it caused a progressive decline in groundwater levels and in the discharge of the thermal springs. The hydrogeological history of the site and the data available in the literature and in new focused surveys are encapsulated in a simple flow model addressed to compare the pre- with the under-development conditions. The withdrawal of groundwater from the quarry area determined a significant impact on the water balance of the system. An increase in inflow from surrounding aquifers and a decrease in storage and in natural discharge of the travertine aquifer result in under-development conditions. Residual discharges towards the springs and river are very sensitive to the pumping flow rate of quarries, according to an inverse linear relationship; this hydrogeological feature may be adopted as an indicator of the sustainability of groundwater withdrawals from the plain. The residual discharge is most affected by the position of the pumping center in the groundwater flow net and its distance from boundaries to be captured, as well as on the depth and extent of the quarries. This lays the basis for developing sustainable management models of groundwater considering the economic and environmental aspects of the issue.

Complete mitochondrial genomes and updated divergence time of the two freshwater clupeids endemic to Lake Tanganyika (Africa) suggest intralacustrine speciation

BackgroundThe hydrogeological history of Lake Tanganyika paints a complex image of several colonization and adaptive radiation events. The initial basin was formed around 9–12 million years ago (MYA) from the predecessor of the Malagarasi–Congo River and only 5–6 MYA, its sub-basins fused to produce the clear, deep waters of today. Next to the well-known radiations of cichlid fishes, the lake also harbours a modest clade of only two clupeid species, Stolothrissatanganicae and Limnothrissamiodon. They are members of Pellonulini, a tribe of clupeid fishes that mostly occur in freshwater and that colonized West and Central-Africa during a period of high sea levels during the Cenozoic. There is no consensus on the phylogenetic relationships between members of Pellonulini and the timing of the colonization of Lake Tanganyika by clupeids.ResultsWe use short-read next generation sequencing of 10X Chromium libraries to sequence and assemble the full mitochondrial genomes of S.tanganicae and L.miodon. We then use Maximum likelihood and Bayesian inference to place them into the phylogeny of Pellonulini and other clupeiforms, taking advantage of all available full mitochondrial clupeiform genomes. We identify Potamothrissaobtusirostris as the closest living relative of the Tanganyika sardines and confirm paraphyly for Microthrissa. We estimate the divergence of the Tanganyika sardines around 3.64 MYA [95% CI: 0.99, 6.29], and from P.obtusirostris around 10.92 MYA [95% CI: 6.37–15.48].ConclusionsThese estimates imply that the ancestor of the Tanganyika sardines diverged from a riverine ancestor and entered the proto-lake Tanganyika around the time of its formation from the Malagarasi–Congo River, and diverged into the two extant species at the onset of deep clearwater conditions. Our results prompt a more thorough examination of the relationships within Pellonulini, and the new mitochondrial genomes provide an important resource for the future study of this tribe, e.g. as a reference for species identification, genetic diversity, and macroevolutionary studies.

Paleohydrogeology of the Karstic System of Fuentetoba Spring (Soria, Spain): An Interdisciplinary Approach

As a preliminary phase in the conservation and sustainable management of a karst system in Fuentetoba, Soria, Spain, an interdisciplinary study was carried out to determine its hydrogeological evolution. The hydrogeological history of this aquifer system began during the late Miocene, where discharges were driven by paleo-emergences in the moor, and associated conduits were developed under phreatic (or vadose) conditions—for example, the upper syngenetic galleries in the main known karst cave (Majada del Cura cave). Later on, the nearby karstic massifs, a general flattening of the relief, occurred during the Quaternary Period, during which the karstic base level had been in decline. The aquifer flow was then derived and modified towards the Fuentetoba spring from the earliest stages through the galleries of the aforementioned cave. The observations made in this cave indicate the existence of a unique type of hydrogeological organization. The hypogean network is the result of the excavation of the same water flow that has been entrenching and abandoning the vadose regimen toward the free regimen. The dating of the tuffaceous buildings, associated with the emergences, indicates that since almost the Middle Pleistocene, flow lines have converged in the Fuentetoba spring, inducing a high grade of karstification in the saturated zone of the syncline basin. Moreover, a major drainage conduit was developed by dissolution. During the late Upper Pleistocene, an essential component of the groundwater flow had been derived towards the source of the Mazos River spring. Tufa and paleogour datings in caves indicate that the aquifer has undergone different climatic stages during the latest Quaternary and, therefore, different feeding and recharge processes. These tufas and paleogours are interrelated as well, as they are associated with the warm stages during the most recent Quaternary, according to the regional context, when there was less natural recharge. The simulation of the springs’ flow enabled an approximate quantification of the variation in the aquifer’s hydraulic balance during the different climatic stages. For example, during the last glaciation, the natural recharge was impacted by snowmelt and increased by 160%.

Chemolithotrophy on the Noachian Martian breccia NWA 7034 via experimental microbial biotransformation

Multiple lines of evidence indicate an active hydrogeological history of Mars and chemolithoautotrophy-suited environments within its Noachian terrains. As a result, one of the primary aims of upcoming missions to Mars is to search for signs of ancient life. Here we report on laboratory-scaled microbially assisted chemolithoautotrophic biotransformation of the Noachian Martian breccia Northwest Africa (NWA) 7034 composed of ancient (~4.5 Gyr old) crustal materials from Mars. Nanoanalytical hyperspectral analysis provides clues for the trafficking and distribution of meteorite inorganic constituents in the microbial cell. We decipher biomineralization patterns associated with the biotransformation and reveal microbial nanometer-sized lithologies located inside the cell and on its outer surface layer. These investigations provide an opportunity to trace the putative bioalteration processes of the Martian crust and to assess the potential biogenicity of Martian materials.

Shared response to changes in drainage basin: Phylogeography of the Yunnan small narrow-mouthed frog, Glyphoglossus yunnanensis (Anura: Microhylidae).

AimWith the late Cenozoic uplift of the Qinghai–Tibetan Plateau (QTP), drainage of the southeastern edge of the QTP changed significantly. However, the impact of this dramatic change on the geographical distribution and genetic diversity of endemic organisms is still poorly understood. Here, we examined the geographical patterns of genetic variation in the Yunnan small narrow‐mouthed frog, Glyphoglossus yunnanensis (Microhylidae), and two alternative hypotheses were tested: That is, the geographical distribution of genetic variation was determined by either the contemporary drainage basin or historical drainage basins.LocationThe Mountains of southwest China.Materials and methodsAnalyses were based on 417 specimens collected from across the distribution of the species. We reconstructed the genealogy (Bayesian and maximum parsimony methods) and assessed demographic history based on DNA sequencing data from mitochondrial and nuclear markers. We also mapped the genetic diversity and estimated the divergence times by a relaxed clock model.ResultsThe species has maintained a relatively stable population size without recent population expansion. Four major maternal lineages were identified with good support, one representing a possible cryptic species and the other three showing further subdivision. The distribution of these deeply differentiated lineages/sublineages corresponded well to geographical regions. The secondary contact zones and phylogeographic breaks in distinct lineages of G. yunnanensis were almost concordant with those of Nanorana yunnanensis.Main conclusionsLineage division conformed to the hypothesis of drainage system evolution, that is, the phylogeographic pattern of G. yunnanensis was shaped by historical drainage patterns. Concordance in phylogeographic patterns may suggest a shared response to common hydrogeological history and also might indicate that there was more contribution of the drainage history than ecological or life‐history traits in structuring genetic variation between these two disparate codistributed taxa G. yunnanensis and N. yunnanensis.

ЭВОЛЮЦИЯ ГИДРОГЕОХИМИЧЕСКОГО ПОЛЯ СЕВЕРНЫХ И АРКТИЧЕСКИХ РАЙОНОВ ЗАПАДНО-СИБИРСКОГО ОСАДОЧНОГО БАССЕЙНА В МЕЗОЗОЕ

Актуальность исследования состоит в выявлении фундаментальной роли палеогидрогеологических факторов в эволюции гидрогеохимического поля северных и арктических районов Западно-Сибирского осадочного бассейна в мезозойскую эру. Впервые предложен механизм, объясняющий их вклад в формирование гидрогеохимических аномалий в оксфордском резервуаре (верхнеюрском водоносном комплексе) изучаемого региона, где широко развита гидрогеохимическая инверсия. Цель: выявить особенности состава сингенетичных вод, захораниваемых одновременно с осадком на элизионных и инфильтрационных этапах развития осадочного бассейна на основе установленной цикличности гидрогеологической истории северных и арктических районов Западно-Сибирского осадочного бассейна; выполнить сравнительных анализ состава современных и сингенетичных вод и установить природу гидрогеохимических аномалий. Методы. Использованы методические приемы А.А. Карцева, С.Б. Вагина, Е.А. Баскова и других исследователей по палеогидрогеологическим реконструкциям осадочных бассейнов, выполнена периодизация гидрогеологической истории с выделением основных гидрогеологических циклов и инфильтрационных и элизионных этапов. На основе методики восстановления солевого состава вод древних морских и озерно-аллювиальных бассейнов, палеогеографических карт на юрский и меловой периоды, составленных сотрудниками ИНГГ СО РАН, информационного банка данных лаборатории гидрогеологии осадочных бассейнов Сибири ИНГГ СО РАН по арктическим районам Западно-Сибирского осадочного бассейна проведены палеогидрогеохимические реконструкции юрско-мелового разреза. Результаты. Приводятся результаты палеогидрогеологических реконструкций северных и арктических районов Западно-Сибирского осадочного бассейна. Установлено, что в гидрогеологическом разрезе исследуемого региона доминируют седиментогенные воды, в некоторых случаях разбавленные инфильтрогенными, проникшими при регрессии морского бассейна. Сравнительный анализ захороненных сингенетичных вод оксфордского бассейна и данных по современной гидрогеохимии подземных вод выявил ряд отрицательных и положительных аномалий. Отрицательные аномалии закономерно трассируют границу глинизации оксфордского регионального резервуара и связаны с развитием процессов элизионного водообмена. Геостатическая (литостатическая) водонапорная система на глубинах 2‒2,5 км переходит в термодегидратационную, что сопровождается аномально высокими пластовыми давлениями и появлением в водонапорной системе пресных химически-связанных вод. Большинство положительных аномалий приурочены к структурам Южно-Надымской и Предъенисейской мегамоноклиз, где широко проявлены процессы вертикальной разгрузки подземных вод нижне-среднеюрского и палеозойского водоносных комплексов в зонах тектонических нарушений. Системе «вода–порода–газ–органическое вещество» принадлежит ключевая роль в процессах формирования химического состава подземных вод нефтегазоносных отложений.

НЕФТЕГАЗОВАЯ ГИДРОГЕОХИМИЯ ДОЮРСКИХ КОМПЛЕКСОВ ЮЖНЫХ РАЙОНОВ ОБЬ-ИРТЫШСКОГО МЕЖДУРЕЧЬЯ

Актуальность исследования состоит в решении фундаментальных и прикладных вопросов гидрогеологии и гидрогеохимии доюрского основания Западно-Сибирского артезианского бассейна и имеет большое значение для изучения земной коры платформ и складчатых поясов в целом. Уникальность и сложность объекта заключается в том, что Западно-Сибирский бассейн – самый крупный участок молодой платформы, под чехлом которого сочленяются разновозрастные, геодинамически и гидрогеологически разнообразные комплексы. Научных обобщений имеющегося фактического материала не проводилось более 30 лет! Кроме того, актуальность исследований заключается в практической плоскости – оценке современного состояния водонапорных систем доюрских комплексов, разработке гидрогеологических критериев их нефтегазоносности и уточнении направления поисков и разведки углеводородов в доюрском основании Западной Сибири. Цель работы: выявить особенности химического и газового состава подземных вод и рассолов доюрских комплексов, установить возможные генетические типы подземных вод и рассолов и их пространственное распространение; оценить степень метаморфизации рассолов в сравнении с рядом гидрогеохимических эталонов Сибири. Методы: основываясь на методических приемах В.А. Сулина, А.А. Карцева, С.Л. Шварцева, Н.М. Кругликова, В.В. Нелюбина, О.Н. Яковлева, В.М. Матусевича и других исследователей выявить особенности геохимии подземных вод и рассолов, установить генетический облик подземных вод и рассолов, используя «генетические» коэффициенты, отражающие отношения различных макро- и микрокомпонентов в их составе: rNa/rCl, Сl/Br, Ca/Cl, r(HCO3+CO3)/r(Ca+Mg), B/Br, Br/Cl∙10–3, Sr/Cl∙10–3 и другие. Применяя интегрированный показатель метаморфизации рассолов (S) по С.Л. Шварцеву и отношения Ca/Cl, Br/Cl∙10–3, Sr/Cl∙10–3, оценить степень метаморфизации рассолов. Результаты. Приводятся результаты исследования геохимии подземных вод и рассолов доюрских отложений южных районов Обь-Иртышского междуречья. Установлено, что в исследуемом регионе развиты подземные воды и рассолы с величиной общей минерализации от 4 до 100 г/дм3 Cl-Na, Cl-Na-Ca и Cl-HCO3-Na состава при доминировании первых. Проведя ретроспективу гидрогеологической истории и детальный анализ гидрогеохимических данных, можно предположить доминирование в разрезе седиментогенных рассолов и наличие литогенных (термодегидратационных), древних инфильтрогенных и конденсатогенных вод. Совместное рассмотрение rNa/rCl, Ca/Cl, Br/Cl∙10–3, Sr/Cl∙10–3 отношений с интегрированным показателем метаморфизации рассолов S подтверждает, что в изучаемом районе рассолы находятся на начальной стадии метаморфизации химического состава.

PALEOHYDROGEOLOGY OF THE ANABAR-KHATANGA BASIN

The hydrogeological history of the Anabar-Khatanga basin covers the period from the Archaean to the Quaternary and includes 12 hydrogeological cycles. The Jurassic-Eopleistocene cycle is the longest during which there were continental conditions of sedimentation with the longest infiltration stage (from the Lower Cretaceous to the Neo-Pleistocene). The salts of the Devonian salt basin play a key role in the formation of the groundwater and brines composition within the following structures: Nordvik, Southern Tigyan, Ilya Kozhevnikova, Ledovka and Belaya.

A new species of freshwater flatworm (Platyhelminthes, Tricladida, Dendrocoelidae) inhabiting a chemoautotrophic groundwater ecosystem in Romania

We report the description of a new species of freshwater flatworm of the genus Dendrocoelum inhabiting the chemoautotrophic ecosystem of Movile Cave as well as several sulfidic wells in the nearby town of Mangalia, thus representing the first planarian species fully described from this extreme biotope. The species was also found in non-sulfidic wells localized in villages in the vicinity of the cave with a total of nine examined populations. Dendrocoelum obstinatum Stocchino & Sluys, sp. nov. represents the first triclad being able to live in both sulfidic and non-sulfidic waters. Among the fauna of the Mangalia sulfidic ecosystem it is the only species found also outside of the current boundaries of the sulfidic aquifer. One possible explanation of this peculiar distribution is that the new species is limited to the old boundaries of the sulfidic aquifer. The latter became much smaller during the hydrogeological history of the region, so that D. obstinatum may be considered to be an indicator of the extension of the sulfidic aquifer in the past of the Mangalia region. In the context of a biogeographic discussion on the distribution of the genus Dendrocoelum we provide an annotated checklist of species reported from Romania.

A Geochemical and Isotopic Study of Crystalline Rock at Chalk River, Ontario, Canada

Crystalline rock is one of several proposed long term storage sites for accumulated nuclear waste. The primary concern during long residence times (>100 Ka) is the transportation of hazardous materials by groundwater migration. The main pathways for fluid flow and material transport in crystalline rock tend to be porosity due to fractures caused by the tectonic stresses after initial deposition. Investigation and understanding of existing fractures and the precipitated minerals within them offer powerful tools to understand and predict the future stability of a site. Several methods were utilized to assist in investigating the hydrogeological history of the crystalline bedrock below the Chalk River site. These were chiefly focused on the fracture mineral, chemistry, and isotopes and their relationship to associated groundwaters. Multiple generations were identified within the fracture filling minerals themselves consisting primarily of calcite precipitated from several fluids under variable hydraulic conditions. The overall objective of this investigation was to identify if evidence exists for recent low temperature mineral formation, none of which were found despite a varied depositional history.

Genetic and morphological variation in an ecosystem engineer, Lithophyllum byssoides (Corallinales, Rhodophyta).

Lithophyllum byssoides is a common coralline alga in the intertidal zone of Mediterranean coasts, where it produces biogenic concretions housing a high algal and invertebrate biodiversity. This species is an ecosystem engineer and is considered a target for conservation efforts, but designing effective conservation strategies currently is impossible due to lack of information about its population structure. The morphological and molecular variation of L.byssoides was investigated using morphoanatomy and DNA sequences (psbA and cox2,3) obtained from populations at 15 localities on the Italian and Croatian coasts. Lithophyllumbyssoides exhibited a high number of haplotypes (31 psbA haplotypes and 24 cox2,3 haplotypes) in the central Mediterranean. The psbA and cox2,3 phylogenies were congruent and showed seven lineages. For most of these clades, the distribution was limited to one or a few localities, but one of them (clade 7) was widespread across the central Mediterranean, spanning the main biogeographic boundaries recognized in this area. The central Mediterranean populations formed a lineage separate from Atlantic samples; psbA pair-wise divergences suggested that recognition of Atlantic and Mediterranean L.byssoides as different species may be appropriate. The central Mediterranean haplotype patterns of L.byssoides were interpreted as resulting from past climatic events in the hydrogeological history of the Mediterranean Sea. The high haplotype diversity and the restricted spatial distribution of the seven lineages suggest that individual populations should be managed as independent units.

Ancient river systems and phylogeographical structure in the spring salamander, Gyrinophilus porphyriticus

AbstractAimThe river drainages of the Appalachian Mountains have experienced a dynamic history as glacial cycles, stream capture and other geological processes have led to the fragmentation and fusion of formerly isolated palaeodrainages. Some ancient rivers have gone extinct, including portions of the great Teays River. Here we investigate the contribution of contemporary and historical drainages to patterns of phylogeographical structure in the spring salamander complex, Gyrinophilus porphyriticus.LocationEastern North America, USA.MethodsSampling spanned the range of the G. porphyriticus complex, and included representative samples of the cave species of Gyrinophilus as well. Molecular sequence data included the mitochondrial DNA locus cytochrome b and the nuclear locus recombination‐activating gene 1 (RAG‐1). Time‐calibrated phylogenies were inferred, and Bayes‐LAGRANGE was used to reconstruct ancestral distributions. Contemporary and historical river influences on patterns of genetic diversity were tested using distance‐based redundancy analysis (db‐RDA).ResultsThe G. porphyriticus complex originated prior to the Pleistocene glacial cycles, and historical river systems explained more genetic variation than did contemporary drainages or geographical distance. Patterns of genetic variation suggest that extinct or remodelled palaeodrainages, including the Teays River, played an important role in structuring contemporary patterns of genetic variation.Main conclusionsThe hydrogeological history of eastern North American drainage basins has been instrumental in structuring patterns of regional biodiversity in freshwater species. Here we show that hydrological remodelling has also left its genetic signature in the semi‐aquatic spring salamander complex, G. porphyriticus. Historical drainages accounted for the largest fraction of phylogeographical structure, more so than did contemporary drainages or geographical distance, with spatial and temporal patterns of variation associated with the extinct Teays River.

How can we be sure fracking will not pollute aquifers? Lessons from a major longwall coal mining analogue (Selby, Yorkshire, UK)

ABSTRACTDevelopment of shale gas by hydraulic fracturing (‘fracking’) is opposed by campaigners who propose (inter alia) that freshwater aquifers could be polluted by upward migration of fractures and any fluids they contain. Prima facie hydrogeological analysis of this proposition has been undertaken. For it to occur, two conditions must be satisfied: (i)sufficient hydraulic interconnection (i.e., a continuous permeable pathway); and(ii)a sustained driving head, oriented upwards.With regard to (i), shale gas developers have a major vested interest in avoiding creating such hydraulic connection, as it would result in uneconomically excessive amounts of water needing to be pumped from their wells to achieve gas production. In relation to (ii), nominal upward hydraulic gradients will typically only be developed during fracking for periods of a few hours, which is far too brief to achieve solute transport over vertical intervals of one or more kilometres; thereafter, depressurisation of wells to allow gas to flow will result in downward hydraulic gradients being maintained for many years. The proposition is therefore found to be unsupportable. Albeit for contrasting motivations, developers and environmental guardians turn out to have a strong common interest in avoiding inter-connection to aquifers.A powerful illustration of the potential long-term effects of fracking is provided by the hydrogeological history of underground coal mining in the UK. Where large-scale mining proceeded from the surface downwards, major hydraulic inter-connection of shallow and deep zones resulted in widespread water pollution. However, where new mines were developed at depth without connections to shallow old workings (as in the Selby Coalfield, Yorkshire), complete hydraulic isolation from the near-surface hydrogeological environment was successfully maintained. This was despite far greater stratal disruption and induced seismicity than shale gas fracking could ever produce. The lesson is clear: without hydrogeological connectivity to shallow aquifers, shale gas fracking per se cannot contaminate shallow ground water.

Phylogenetic relationships and biogeographical patterns in Circum-Mediterranean subfamily Leuciscinae (Teleostei, Cyprinidae) inferred from both mitochondrial and nuclear data

BackgroundLeuciscinae is a subfamily belonging to the Cyprinidae fish family that is widely distributed in Circum-Mediterranean region. Many efforts have been carried out to deciphering the evolutionary history of this group. Thus, different biogeographical scenarios have tried to explain the colonization of Europe and Mediterranean area by cyprinids, such as the "north dispersal" or the "Lago Mare dispersal" models. Most recently, Pleistocene glaciations influenced the distribution of leuciscins, especially in North and Central Europe. Weighing up these biogeographical scenarios, this paper constitutes not only the first attempt at deciphering the mitochondrial and nuclear relationships of Mediterranean leuciscins but also a test of biogeographical hypotheses that could have determined the current distribution of Circum-Mediterranean leuciscins.ResultsA total of 4439 characters (mitochondrial + nuclear) from 321 individuals of 176 leuciscine species rendered a well-supported phylogeny, showing fourteen main lineages. Analyses of independent mitochondrial and nuclear markers supported the same main lineages, but basal relationships were not concordant. Moreover, some incongruence was found among independent mitochondrial and nuclear phylogenies. The monophyly of some poorly known genera such as Pseudophoxinus and Petroleuciscus was rejected. Representatives of both genera belong to different evolutionary lineages. Timing of cladogenetic events among the main leuciscine lineages was gained using mitochondrial and all genes data set.ConclusionsAdaptations to a predatory lifestyle or miniaturization have superimposed the morphology of some species. These species have been separated into different genera, which are not supported by a phylogenetic framework. Such is the case of the genera Pseudophoxinus and Petroleuciscus, which real taxonomy is not well known. The diversification of leuciscine lineages has been determined by intense vicariant events following the paleoclimatological and hydrogeological history of Mediterranean region. We propose different colonization models of Mediterranean region during the early Oligocene. Later vicariance events promoted Leuciscinae diversification during Oligocene and Miocene periods. Our data corroborate the presence of leuciscins in North Africa before the Messinian salinity crisis. Indeed, Messinian period appears as a stage of gradually Leuciscinae diversification. The rise of humidity at the beginning of the Pliocene promoted the colonization and posterior isolation of newly established freshwater populations. Finally, Pleistocene glaciations determined the current European distribution of some leuciscine species.

Transfers through argillaceous rocks over large space and time scales: Insights given by water stable isotopes

In order to characterize the large-scale transport properties of the Toarcian/Domerian formation in the Tournemire Underground Research Laboratory, the isotopic composition ( δ 18O and δ 2H) of pore water was determined on samples from a 250 m borehole drilled from the tunnel ground down to the lower aquifer. The isotope data were obtained from core samples by diffusive vapour exchange. The comparison with previous profiles obtained from vacuum distillation shows a clear discrepancy for all the stratigraphic levels. This demonstrates that artefacts, induced by distillation and already highlighted on only one stratigraphic level, occurred all over the shale sequence. Moreover, diffusion parameters were derived from both radial diffusion experiments and petrophysical determinations. To evaluate the large-scale transport properties of the formation, we performed a series of diffusive model calculations and compared them to experimental data. In agreement with the hydrogeological history, the best simulations considered an activation of the embedding aquifers 11–13 Ma ago, corresponding to the beginning of the diffusive process through the argillaceous formations.

ＣＯ２地中貯留のナチュラルアナログ―松代での地化学調査―

Environmental assessments and safety control during and after CO2 injection are essential for CO2 geological storage, and we are required to evaluate long-term environmental changes and safety. However, long-term changes are difficult to detect directly because the leakage of CO2 is expected to be small and the evaluation is, sometimes, requested to cover more than 1,000 years. To solve this problem, a natural-analogue study, which inquires into environmental changes at present through a comparison with past geological phenomena, is one possible approach. When the Matsushiro earthquake swarm began in 1965, a large volume of subsurface water accompanied by CO2 gas was discharged along fracture zones. A natural-analogue study on the CO2 discharge during the earthquake swarm should be helpful to create a scenario of leakage and a guideline for the safety of CO2 geological storage. Surveys of the CO2 content in soil gas and CO2 flux emissions from the surface were carried out with carbon isotope ratio measurements to understand the current state at Matsushiro, and to make a conceptual model for environmental assessments and safety control. From geological and geophysical points of view, it is said that deep water gushing out from the surface caused the swarm of earthquakes. As this deep water is still gushing out, we planned to measure CO2 concentrations in soil gas and CO2 flux to examine present CO2 activities at Matsushiro. Because CO2 in the soil is also produced by activities of microbes, however, we decided to measure the isotope ratio of the carbon to distinguish CO2 in deep groundwater origin from that produced by microbes. We selected five survey lines and three survey areas based on previous geochemical measurements and fissure distribution during the earthquake swarm, and measured CO2 concentration in soil, CO2 flux, and isotope ratio. Although there were survey points on the thick fan deposit where CO2 concentration in the soil and CO2 flux were high, the isotope ratio indicated that the carbon is produced by the activity of microbes. On the other hand, the isotope ratio of the samples collected from the thin fan deposit area shows deep subsurface water as the origin. An investigation well was drilled into the basement. Subsurface water samples were collected near the bottom of the well in the igneous rock formation. Geochemical analyses and carbon isotope ratio measurements show higher concentrations of chloride and abiogenic CO2, indicating that groundwater of a deep origin with CO2 is still rising. We are now making a conceptual model of hydrogeological history at the next step. This natural analogue study of CO2 seepage could indicate the importance of understanding shallow hydrogeological characteristics in a CO2 storage field.

Stable water isotopes in pore water of Jurassic argillaceous rocks as tracers for solute transport over large spatial and temporal scales

In order to characterize the large‐scale transport properties of the Opalinus Clay formation, the pore water isotope composition (δ18O and δ2H) was determined on samples from the deep borehole Benken (northeastern Switzerland) across Jurassic argillaceous rocks. The sequence of claystones and marls, delimited by two aquifers, is located at depth from about 400 to 700 m and exhibits very low hydraulic conductivities (below 10−13 m s−1). The isotope data of the pore water were obtained from core samples by diffusive vapor equilibration, vacuum distillation, and squeezing. Compared with the other methods, vacuum distillation led to too low values. To evaluate the large‐scale transport properties of the formation, we performed a series of advective‐dispersive model calculations and compared them with the experimental data. In accordance with the hydrogeological history, we varied initial and boundary conditions as well as model parameters. The main results can be summarized as follows: (1) Molecular diffusion to the underlying aquifer can explain the general features of the isotope profiles, (2) no signatures of advective flow could be detected, (3) the evolution time is of the order of 0.5–1 Ma (relying on laboratory diffusion coefficients) with a possible range of about 0.2–2 Ma, which is geologically plausible, and (4) parameters measured on small scales (centimeters or meters and months) are also plausible at the formation scale (tens of meters and millions of years) for the sediments investigated.

Gene lineages and eastern North American palaeodrainage basins: phylogeography and speciation in salamanders of the Eurycea bislineata species complex

Contemporary North American drainage basins are composites of formerly isolated drainages, suggesting that fragmentation and fusion of palaeodrainage systems may have been an important factor generating current patterns of genetic and species diversity in stream-associated organisms. Here, we combine traditional molecular-phylogenetic, multiple-regression, nested clade, and molecular-demographic analyses to investigate the relationship between phylogeographic variation and the hydrogeological history of eastern North American drainage basins in semiaquatic plethodontid salamanders of the Eurycea bislineata species complex. Four hundred forty-two sequences representing 1108 aligned bases from the mitochondrial genome are reported for the five formally recognized species of the E. bislineata complex and three outgroup taxa. Within the in-group, 270 haplotypes are recovered from 144 sampling locations. Geographic patterns of mtDNA-haplotype coalescence identify 13 putatively independent population-level lineages, suggesting that the current taxonomy of the group underestimates species-level diversity. Spatial and temporal patterns of phylogeographic divergence are strongly associated with historical rather than modern drainage connections, indicating that shifts in major drainage patterns played a pivotal role in the allopatric fragmentation of populations and build-up of lineage diversity in these stream-associated salamanders. More generally, our molecular genetic results corroborate geological and faunistic evidence suggesting that palaeodrainage connections altered by glacial advances and headwater erosion occurring between the mid-Miocene and Pleistocene epochs explain regional patterns of biodiversity in eastern North American streams.

Prime candidate sites for astrobiological exploration through the hydrogeological history of Mars

The hydrogeological evolution of Mars has been proposed to be dominated by the development of the Tharsis Magmatic Complex through superplume activity, with related magmatic-pulse-driven flood inundations that directly influence the shaping of the northern plains, the evolution of the atmosphere and climate, and subsurface and surface water processes. On the other hand, several possible biological models and terrestrial analogues have been suggested for Mars during the last decade, including the description of putative microfossils and the proposal of sedimentary units. Here we revisit these scenarios and present a possible bridge that integrates the geological, paleohydrological, and the putative biological histories of the planet. We primarily focus on the Noachian, a time period that arguably has recorded an inner dynamo, plate tectonics, and an ocean that may have covered one-third of the total surface area of Mars, due to its implications on the possible origin and early evolution of life. This stage is followed by a long-lived cold and dry phase, briefly punctuated by transient magmatic-driven hydrological cycles, dominated by a stagnant-lid/superplume regime, which directly influences the processes of natural selection on the putative early biosphere. Based on this hypothesized evolution of the planet, we suggest three martian locations as prime candidate sites for astrobiological exploration, each one corresponding to an inundation period: Meridiani Planum (Noachian/Early Hesperian), Mangala Valles (Late Hesperian/Early Amazonian), and Orcus Patera (Amazonian).

Characterization and modeling of diffusion process for mass transport through the Tournemire argillites (Aveyron, France)

Argillites are one of the geological formations studied by IRSN for their confining properties for isolation of radioactive wastes. One of the main objectives is the study of water transport through rocks with very low water content and very low hydraulic conductivity by modeling of natural tracer profiles. This paper presents the protocol developed for and applied to the acquisition of data for chloride content in interstitial water of the Toarcian argillites at the Tournemire site (Southern France). This protocol is based on laboratory diffusion experiments and on modeling. Experimental data obtained during the transient and steady-state parts of diffusion experiments enable, respectively, the assessment of the diffusion coefficient and the determination of Cl concentration in pore water. Using this protocol, profiles with depth for both of these data sets have been acquired along the geological sequence. Taking into account the present knowledge of the geological and hydrogeological history of the Tournemire massif, a conceptual model granting the main role for mass transport to diffusion has been proposed. According to this conceptual model, a one-dimensional numerical model was built for simulating the mass transport of chloride through the sedimentary column, over 53 Ma. The good agreement between experimental data and calculated values for both diffusion coefficients and concentrations of chloride confirms that diffusion is likely the main process for mass transport in the massif. This model was also tested with the deuterium content of interstitial water, applying variable concentrations at the aquifer system boundaries for reflecting the thermal dependency of isotopic composition in precipitation. These simulations also reveal the likely important role of heterogeneities, such as fractures, in the variability of tracer concentrations with regards to a simple diffusion profile.