Calcium Carbonate Accumulation Research Articles

Features of selected benchmark soils along an elevational transect of the northeastern part of the Moldavian Plateau (Romania)

Soil morphological, physical and chemical properties are described at four locations along an elevational transect in the northeastern part of the Moldavian Plateau (Romania). These data contribute to the knowledge of the soils of this area and to their classification according to the USDA-Soil Taxonomy, FAO-WRB and the SRTS-Romanian System. The soils were classified as Inceptisols, Alfisols and Mollisols, according to the USDA-Soil Taxonomy; Gleysol, Chernozem and Luvisol, according to the FAO-WRB and Gleiosol, Cernoziom, Preluvosol, Luvosol, according to the SRTS-Romanian System. The selected soils have a range of properties that represent the soilscape of the Moldavian subcarpathian plateau, characterised by a natural forest with oak as the dominant species. The selected soil parameters decreased with increasing elevation; calcium carbonate and clay leaching and accumulation are the main soil formation processes.

Radiocarbon dating reveals the timing of formation and development of pedogenic calcium carbonate concretions in Central Sudan during the Holocene

Calcic soil horizons are common in arid and semi-arid lands and represent the result of the progressive accumulation of calcium carbonate in the soil profile over time. This process leads to the occurrence of several pedogenic phases of calcium carbonate dissolution/precipitation. For this reason, timing the formation and development of calcic horizons through radiometric dating is not straightforward as time-averaging effects, due to the superimposition of the same process over time, occur. On this basis, this study aims to define the timing and dynamics of formation and development of pedogenic calcium carbonate concretions from semi-arid Central Sudan, highlighting the relevance of a multi-disciplinary approach and the effectiveness of radiocarbon dating (coupled to an accurate sampling strategy) applied to pedogenic carbonates. Calcic soil horizons (Bk) were sampled during the archaeological excavation of site 16-D-4 at Al Khiday (Central Sudan) and studied by optical, cathodoluminescence and scanning electron microscopy, as well as by chemical-physical and stable isotopes (C and O) analyses. Micromorphological analyses reveal the occurrence of distinctive calcitic pedofeatures, here described as calcitic-cemented nodules and calcitic-rich matrix. Radiocarbon ages obtained for these pedofeatures mostly refer to the Early Holocene for calcitic-cemented nodules (11.5, 9.9 and 9.6 cal. ka) and to the Middle Holocene for powdery calcitic-rich matrix (7.9, 7.7, 6.3 and 6.1 cal. ka) samples. Additionally, δ13C and δ18O values indicate major shifts of environmental conditions from the Early to the Middle Holocene, in agreement with the available information from detailed palaeoenvironmental studies carried out in the region. In particular, Early Holocene pedogenic calcitic features can be related to short arid phases during general wetter climate conditions, whereas those formed in the Middle Holocene can be related to short humid phases. Results show that Bk horizons were characterized by alternate periods of calcite accumulation (precipitation) and dissolution, and periods of quiescence or extremely slow growth rates. Thus, the formation and development of Bk horizons have been a long-lasting process significantly influenced by climatic fluctuations. This study represents a further step in the comprehension of the development of calcium carbonate concretions and (at a wider perspective) calcrete; the paper also contributes to the definition of a reliable method to radiometrically date the formation of calcic pedofeatures. On a broader perspective, this work may offer a significant tool for archaeometric studies, where the interaction between secondary calcite and archaeological material is significant (e.g., radiocarbon dating of bioapatite in bones), and palaeoenvironmental studies in arid lands, where Bk horizon development is a function of past rainfall.

TAPHONOMY, GEOLOGICAL AGE, AND PALEOBIOGEOGRAPHY OF LOTOSAURUS ADENTUS (ARCHOSAURIA: POPOSAUROIDEA) FROM THE MIDDLE-UPPER TRIASSIC BADONG FORMATION, HUNAN, CHINA

Lotosaurus adentus is an unusual sail-backed, edentulous poposauroid pseudosuchian primarily known from a single, nearly monospecific bonebed discovered and excavated in the 1970s in the Middle-Upper Triassic Badong Formation of Sangzhi County, Hunan Province, South China. Renewed interest in this unique taxon prompted exposure of an additional 90 m2 of the bonebed. Almost 1000 new L. adentus bones, 28% of which were articulated, were discovered during this excavation. The bones lack evidence of tooth marks, trample marks, or insect modification, and display minimal weathering. The site is reinterpreted as a pedogenically modified floodplain pond (and overlying fluvial channel) within a warm, semi-arid sub-tropical region (paleolatitude ∼ 34°N), contrasting with previous interpretations of the locality as a tidal flat deposit. The occurrence of mudcracks, conchostrachan fossils, and vertic paleosol development with calcium carbonate accumulations in both overlying and underlying facies indicates periodic aridity and ephemeral conditions. The bonebed is characterized by partial disarticulation and minor transport, and is confined to a thin, < 30 cm-thick interval. Considered together, these features are most consistent with a mass mortality event, possibly drought related considering the sedimentological context, followed by minor transport during a rapid burial event. U-Pb detrital zircon geochronology and Lu-Hf isotope analysis were utilized to reassess the provenance and age of the deposit, and suggest that L. adentus was likely Ladinian or possibly even Carnian in age, rather than Anisian as previously reported. Paleocurrent data, detrital zircon age spectra, and Lu-Hf isotopes indicate that fluvial sediments were partially derived from sources in the North China craton and Qinling-Dabieshan tectonic belt, implying that faunal interchange between the North and South China blocks was possible by this time.

Carbonate Accumulation in the Bark of Terminalia bellirica: A New Habitat for the Oxalate-Carbonate Pathway

ABSTRACTOxalate oxidation and carbonate precipitation associated with the oxalogenic tree Terminalia bellirica were investigated. Calcium oxalate crystals, oxalotrophic bacteria (dominated by genera Methylobacterium and Burkholderia), and carbonate accumulation (82% dry weight), were detected in the bark. In contrast, only a slight accumulation of carbonate was observed in soil (1.5%). The combined geochemical and microbiological analyses suggest that bark of an Indian living tree represents a novel habitat for the accumulation of carbonate associated with bacterial oxalate oxidation. The importance of these types of habitats needs to be quantified when considering the biogeochemical cycling of carbon and calcium in tropical ecosystems.

Soils in the karst landscape of Bodoquena plateau in cerrado region of Brazil

The aim of this study was to evaluate chemical, physical, mineralogical, and micromorphological characteristics of soils in a toposequence formed from carbonate rich material in the karst landscape of Bodoquena plateau in Brazilian cerrado region, in the State of Mato Grosso do Sul, as a support for soil classification and pedogenesis. The hypothesis was that the limestone and slope shape and position influenced the soil attributes and the genesis. Also, that the parent material and weather conditions of the region could result in an excess accumulation of calcium carbonate in the soils, with consequent formation of calcic horizons. Soil profiles were sampled along a toposequence, at the river terrace (P1), plain (P2), footslope (P3), lower backslope (P4), middle backslope (P5), and shoulder (P6) positions. The profiles showed a large variation of attributes, accordingly to the parent material and landscape position that influenced the degree of weathering and pedogenesis intensity. Noticeably the sum of bases and cation exchange capacity, with maximum values of 30.9cmolckg−1 and 32.5cmolckg−1, respectively; pH in water varying between 6.6 and 9.1; and dominance of quartz in the sand mineralogy, with calcite and illite in the clay fraction, followed by kaolinite. Also, soils showed a high content of CaCO3 and micromorphology features such as coatings of pores by acicular calcite. The soil classification corroborates the lesser development of the profiles, where P1, P4 and P6 were classified as Entisols; P2 and P3 as Alfisols; and P5 as Molisols.

Soils and climate of Cul de Sac Valley, Haiti: A soil water and geomorphology perspective

Soil is an important natural resource, yet for many countries, including Haiti, the only soil inventory is a general soil map at 1:250,000 scale, which is not suitable for management planning at the farm level. A soil survey for a 3,000 ha (7,400 ac) segment of Cul de Sac Valley was conducted at 1:24,000 scale. Eleven soil types and soil map units were identified. Approximately 60% of the study area consisted of soils on Floodplains, while 40% were soils on Foothills, Hills, and Dissected Alluvial Fans. The combination of the parent material, predominantly marine sediment and limestone bedrock, and spatial-temporal precipitation patterns resulted in soils dominated by calcium carbonate (CaCO3) and sodium (Na) accumulations throughout their profile. The new soil geomorphology map derived from the detailed soil map was similar to the existing general soil map and geomorphology map. It was spatially more accurate and provided better understanding of soil and climate influence on soil water movement. Cul de Sac Valley resulted from uplifting and erosion and deposition processes. This, combined with aridic to semiaridic climate conditions, resulted in cemented CaCO3 accumulation and Na rich soils. The water management for irrigation was limited by a combination of soil properties such as high gravel and steep slopes for Dissected Alluvial Fans and Hills soil geomorphic units, presence of cemented CaCO3 for Foothills, and high Na content for Lower Flat Plains. Further studies are needed for a complete and comprehensive understanding of the soil geomorphology processes and climate interactions of this complex system.

Szekunder karbonátok mennyisége és vertikális eloszlása tokaji talajszelvényekben

The forms and stocks of secondary carbonate accumulations and the distribution of secondary carbonate content were investigated in 20 soil profiles from Nagy-hegy, Tokaj. The secondary carbonate content varied to a great extent under different lithological conditions. The frequency of carbonate crusts coating the coarse fragments to a thickness of 1–7 mm was especially conspicuous. In selected profiles the amount of secondary carbonates was analysed separately for three carbonate pools: in the fine earth (&lt;2 mm), in carbonate crusts and other concentrations, and in the skeletal part of the soils (dominantly dacite blocks and boulders). In one profile a calculation was made of the calcium carbonate stocks (in kg m−2) in the separate fractions of the fine earth, the skeletal fraction and the carbonate crusts and concentrations. The values obtained for the distinct soil horizons were then summed for the whole profile above the continuous hard rock. The loess deposits can be regarded as the primary source of calcium carbonate, but many types of secondary carbonate accumulations occurred in places where the loess deposits were completely eroded or the original surface of the soil was only preserved on terraces with retaining walls. The results suggest that the highest accumulation of calcium carbonate occurs in profiles where loess, redeposited loess or colluvial deposit covers weathered volcanic rocks (pyroxene dacite), resulting in lithological discontinuity. The carbonate crusts consisted of 55–96 % (m/m) CaCO3, and the coarse fraction (dacite boulders and blocks) also had a higher calcium carbonate content (5–10 % m/m) than the non-weathered pyroxene dacite. The calcium carbonate stocks in Calcic accumulation horizons proved to be 2.5 times higher than in the overlying soil horizons. The accumulation forms of carbonates in the soil profiles and the lack of loess deposits on the top of the soil profiles suggest that the calcium carbonate was accumulated in the transitional zone between the loess and the weathered volcanic rocks. This appears to have taken place under humid climatic conditions, unlike the recent climate, and can thus be regarded at least partially as the result of paleoecological processes.

Distribution of calcium carbonate in the process of concrete self-healing

The complete deposition distribution process of calcium carbonate is summarized in three directions of cracks. Distribution of calcium carbonate in the self-healing process of microbial concrete is studied in detail, with the help of a variety of analytical techniques. The results show that carbonate deposits along the x-axis direction of the cracks. The farther from the crack surfaces of concrete matrix in x-axis direction, the more the content of the substrate, the less content of calcium carbonate. Gradual accumulation of calcium carbonate along the y-axis direction is like building a house with bricks. Different repair points are gradually connected, and ultimately the whole of cracks are completely filled. In the z-axis direction, calcium deposits on the surface of fracture direction, when the crack is filled on the surface, because the internal crack hypoxia in the depths of cracks hardly produces calcium carbonate.

REAL KARST COMPONENT OF THE LANDSCAPE DEVELOPMENT IN THE SMOLENSK LAKE COUNTRY

The karst processes took part in the formation of the natural complexes in the Belorussian-Baltic region of the East-European Plain since the Devon. Role of the karst is not confined to areas of exposed forms of karst denudation and sporadic accumulation of derivative calcium carbonate. Under the quaternary cover of glacial and fl uvio-glacial deposits there are large buried karst complexes developed under the conditions similar to recent landscapes of the low latitudes. Relic karst forms, including the buried ones, look more prominent than exposed ones and have wider expansion.

Influence of asphalt pavement construction processes on urban soil formation in Tokyo

Urban soils have been drastically disturbed and modified by human activities. Soil sealing, necessary for transportation and infrastructure development, is one such process, which often results in negative effects on the soil ecosystem functions. However, sealed soils can play a critical role in material cycling through ground surfaces in urban ecosystems. This study investigated the effects of asphalt sealing on the mineral soils beneath the roads in Tokyo. The results confirmed that mineral soils beneath asphalt pavements were characterized by high pH levels, CaO content, inorganic carbon (IC), and electric conductivity (EC) due to liming for road material fixation at the subbase layers. An analysis of the concentrations of IC and Ca, or pH value suggested existence of calcium carbonate (CaCO3) mainly due to liming and absorption of atmospheric CO2 at subbase layers. Relatively high content of sulfur in the subbase layers is likely attributed to asphalt contaminants originating from petroleum. Removal of the original surface soils, for new road development, decreased oxides and organic matter content. Contents of oxides in top mineral soils were low as compared to those of natural Andosols by mixing of subbase materials. This study suggested that construction of asphalt pavement induced specific soil genesis beneath asphalt pavement such as soil alkalinization, calcium carbonate accumulation, and technogenic material mixing. First, surface soil removal for the construction of asphalt pavement decreases organic matter content in mineral soils. Concurrently technogenic materials mix with top mineral soils. Second, Ca dissolved into water from the subbase layer can react with dissolved inorganic carbon followed by calcium carbonate formation and Ca cation migration into the deeper horizon. As asphalt pavement intercepts litter supply, organic matter accumulation was prevented in mineral soils beneath the asphalt pavement. Our study confirmed that owing to the water infiltration, through pervious asphalt and the cracks developed on the asphalt surface by heavy traffic, material cycling exists even in mineral soils beneath the asphalt pavements.

Amorphous calcium carbonate controls avian eggshell mineralization: A new paradigm for understanding rapid eggshell calcification.

Avian eggshell mineralization is the fastest biogenic calcification process known in nature. How this is achieved while producing a highly crystalline material composed of large calcite columnar single crystals remains largely unknown. Here we report that eggshell mineral originates from the accumulation of flat disk-shaped amorphous calcium carbonate (ACC) particles on specific organic sites on the eggshell membrane, which are rich in proteins and sulfated proteoglycans. These structures known as mammillary cores promote the nucleation and stabilization of a amorphous calcium carbonate with calcitic short range order which predetermine the calcite composition of the mature eggshell. The amorphous nature of the precursor phase was confirmed by the diffuse scattering of X-rays and electrons. The nascent calcitic short-range order of this transient mineral phase was revealed by infrared spectroscopy and HRTEM. The ACC mineral deposited around the mammillary core sites progressively transforms directly into calcite crystals without the occurrence of any intermediate phase. Ionic speciation data suggest that the uterine fluid is equilibrated with amorphous calcium carbonate, throughout the duration of eggshell mineralization process, supporting that this mineral phase is constantly forming at the shell mineralization front. On the other hand, the transient amorphous calcium carbonate mineral deposits, as well as the calcite crystals into which they are converted, form by the ordered aggregation of nanoparticles that support the rapid mineralization of the eggshell. The results of this study alter our current understanding of avian eggshell calcification and provide new insights into the genesis and formation of calcium carbonate biominerals in vertebrates.

Quaternary subsurface paleosols in Haifa Bay, Israel: A new perspective on stratigraphic correlations in coastal settings

Abstract This study presents the first in-depth analysis of properties, micromorphology, clay mineralogy, magnetic susceptibility, and general properties of Quaternary paleosols from two boreholes in Haifa Bay subsurface, whose chronostratigraphic position was determined previously. The current analytical results allowed us to identify the type, hydrologic regime, polygenesis, mode of pedosedimentary evolution, and some subsequent alterations of paleosols. The analogs of polygenic Haplo- and Rhodo-xeralf soils (Brown, Mollic, and Ortho-Hamra) are associated with marine isotope stages (MIS) 3.1, 5.4, 6 and 8.0 (or 7.4) and likely developed in response to a changing climate. Paleosols prior to MIS 12, yet difficult to attribute to specific MIS, are distinct from Hamra soils by striking mottling, poor preservation of argillic horizons, abundant deformations in microfabric, and overprinting processes of gley and calcium carbonate accumulation. It is assumed that calcification may have affected the earlier formed clay illuviation and amorphous features, and was related with marine/coastal groundwater interface. The older calcic gleyed paleosols of earlier Middle Pleistocene likely indicate that coastal paleogeography was characterized by both high discharge of the ancient Qishon River and a high water table. The thin section micromorphology is particularly valuable for refined paleopedological taxonomy. Identified Pleistocene paleosols including their type, hydrology and mode of evolution, are proposed to serve additional stratigraphic markers in coastal settings.

Benchmark soils on alluvial, fluvial and fluvio-glacial formations of the upper-Segre valley .

The upper reaches of the Segre river, flowing through the Pyrenees, offers a variety of geomorphic surfaces that allow us to study soil chronosequences. The objective of this work is to widen the knowledge about the main characteristics and formation processes of some benchmark soils developed on fluvio-glacial, alluvial-fan and terrace materials of Pleistocene and Holocene age related to the Segre river, either siliceous or carbonatic. This knowledge will allow us to identify soil forming processes, commonly found in Mediterranean environments such as carbonate redistribution, clay formation and mobilization and rubefaction, all as functions of parent material and age. Five profiles, ranging from the Lower Pleistocene to the Holocene were classified according to Soil Taxonomy/WRB. The Montferrer profile (Calcic Palexeralf /Calcic Cutanic Luvisol (Chromic) is a deep, partly decarbonated soil, with calcium carbonate accumulation in depth covering glacial features. The Torre del Remei profile (Typic Paleustalf /Cutanic Luvisol) developed on silicic moraines and shows an extreme clay formation and illuviation. The Alp (Typic Haplustalf /Cutanic Luvisol) and Tartera (Petric Calciustept /Petric Calcisol) soils are developed on alluvial fans with calcium carbonate sources. The former is partly decarbonated, whilst the latter is rubefacted on top and shows speleothem-like carbonate pendants with superposition of clay illuviation. The youngest profile, Abellerols, (Typic Calciustept /Typic Calcisol) shows only a partial decarbonation and calcite accumulation at depth. The results show that soil development is determined by the age of the surface and the source of calcite, either in the parent rock or brought by subsurface flow: clay illuviation is extreme in absence of it. Special morphologies of carbonate pendants are indicators of environmental conditions. The coexistence of clay coatings and secondary calcite can be explained by recarbonatation or by spatial differentiation of soil environments in the profile. One of the implications of this research is the inconsistence of using soil development indices based on morphological indicators when soils are formed on different parent materials and are subjected to different geomorphic dynamics.

Unravelling the enigmatic origin of calcitic nanofibres in soils and caves: purely physicochemical or biogenic processes?

Abstract. Calcitic nanofibres are ubiquitous habits of secondary calcium carbonate (CaCO3) accumulations observed in calcareous vadose environments. Despite their widespread occurrence, the origin of these nanofeatures remains enigmatic. Three possible mechanisms fuel the debate: (i) purely physicochemical processes, (ii) mineralization of rod-shaped bacteria, and (iii) crystal precipitation on organic templates. Nanofibres can be either mineral (calcitic) or organic in nature. They are very often observed in association with needle fibre calcite (NFC), another typical secondary CaCO3 habit in terrestrial environments. This association has contributed to some confusion between both habits, however they are truly two distinct calcitic features and their recurrent association is likely to be an important fact to help understanding the origin of nanofibres. In this paper the different hypotheses that currently exist to explain the origin of calcitic nanofibres are critically reviewed. In addition to this, a new hypothesis for the origin of nanofibres is proposed based on the fact that current knowledge attributes a fungal origin to NFC. As this feature and nanofibres are recurrently observed together, a possible fungal origin for nanofibres which are associated with NFC is investigated. Sequential enzymatic digestion of the fungal cell wall of selected fungal species demonstrates that the fungal cell wall can be a source of organic nanofibres. The obtained organic nanofibres show a striking morphological resemblance when compared to their natural counterparts, emphasizing a fungal origin for part of the organic nanofibres observed in association with NFC. It is further hypothesized that these organic nanofibres may act as templates for calcite nucleation in a biologically influenced mineralization process, generating calcitic nanofibres. This highlights the possible involvement of fungi in CaCO3 biomineralization processes, a role still poorly documented. Moreover, on a global scale, the organomineralization of organic nanofibres into calcitic nanofibres might be an overlooked process deserving more attention to specify its impact on the biogeochemical cycles of both Ca and C.

涠洲岛滨珊瑚中的生物侵蚀及其环境指示意义

The negative impacts of water pollution and eutrophication on coral reefs at Weizhou Island in the northern South China Sea have been preliminarily affirmed, but quantitative research examples supporting these effects are still lacking. Here, we analyzed the species and bioerosion intensity of boring organisms in samples of <italic>Porites </italic>corals collected at Weizhou Island as well as the relationship between eutrophication and bioerosion to assess the impacts of local pollution on corals and coral reefs. The observed bioeroders included bivalves (<italic>Lithophaga</italic> spp.), sponges (<italic>Cliothosa</italic> spp. and <italic>Cliona</italic> spp.), barnacles, and sipunculid and polychaete worms. Additionally, traces of micro-bioerosion were observed. The most important borers were filter-feeding bivalves (<italic>Lithophaga</italic> spp.), especially south of the island, where the environment has been heavily impacted by intensive human activities and eutrophication. Bioerosion intensity in corals collected from the south was significantly higher than that in corals collected from the north. Eutrophication stimulated boring organisms and subsequently caused the bioerosion intensity to increase significantly, which subsequently threatened local coral survival, calcium carbonate accumulation, and reef framework development. The results of this study also suggested that the bioerosion intensity of macrobioeroders, especially boring bivalves and sponges, can be interpreted as an indicator of chronic exposure to decreased water quality in coastal coral areas, especially those lacking water quality monitoring activities.

Using elemental profiles in the sediment of a lake used to supply drinking water to understand the impacts of urban stormwater recharge

The regional city of Mount Gambier, South Australia, recharges stormwater directly into the underlying unconfined, karstic Gambier Limestone aquifer. This aquifer provides the majority of recharge to Blue Lake, a groundwater-fed volcanic crater lake, used for Mount Gambier’s drinking water supply. However, concern remains regarding the risk posed by contaminants within stormwater, in particular when stormwater recharge may ultimately contribute to a source of drinking-water supply. The present research examined the role of the annual calcite precipitation in the lake, in protecting the quality of its water supply, by examining the composition of particulate matter in the lake and on the lake bottom. The sediment did not reveal negative impacts of stormwater recharge, but did highlight the increase in erosion as a result of settlement and extensive land clearing for agriculture at the time of settlement. Analysis of lake-floor sediment revealed increased accumulation of the lithogenic elements within the lake-floor sediment during this interval, owing to the cleansing capacity of the calcite precipitation cycle. Extraction of water from Blue Lake for water supply has resulted in a reduced water residence time in the lake and a three-fold increase in the accumulation of calcium carbonate on the lake floor.

The influence of flood duration on the surface soil properties and grazing management of karst wetlands (turloughs) in Ireland

Irish turloughs are hydrologically dynamic karst wetlands that are frequently used as marginal grazing land. We hypothesised that flood duration (FD) is a key driver of the spatial distribution of selected soil properties, and consequently turlough grazing practices. Six soil samples were collected during dry periods from eighteen turloughs between 2006 and 2008. Samples (n = 104) were analysed for pH, organic matter (OM) content, calcium carbonate content (CaCO3), sand/silt/clay content (INORG), total nitrogen (TN) and total phosphorus (TP). Data on flooding duration, flood frequency, grazing regime and vegetation type were collated for each soil sampling point. Multivariate and univariate statistical analyses were used to examine the relationships between soil properties, grazing regime and flooding variables. There was a positive association between CaCO3, FD and sedge-dominated communities, whereas INORG had a positive association with grazing and grassland. There was a strong positive association between TN, TP, OM and soil depth rather than FD, and OM was found to be an efficient predictor of TN. Extended FDs in ephemeral karst wetlands are likely to increase the extent and degree of calcium carbonate accumulation in soils, thus, reducing the grazing potential of land.

Pore Pressures in Concrete Dams

Assuming that concrete is a homogeneous porous material in gravity dams, pore pressure intensities at drain wells near the upstream face of dams were studied. In general, the piezometric head of the seepage flow through a gravity dam may be mathematically represented by the well-known Laplace equation. This equation can be solved numerically by the finite-difference equation developed from a block-centered formulation. By using the boundary conditions of the height of the seepage face in drain wells from the concept in hydraulics of wells and the seepage face along the downstream face of dams, piezometric heads, and in turn, pore pressures in the dam body were obtained. This approach of predicting pore pressures has been verified by 40 years of data from the Tennessee Valley Authority’s (TVA’s) Fontana Dam. The pore pressure intensities in dam bodies and at the drain wells are presented. They are expressed in dam heights, size of drains, and locations of drains from the face of the dams for inspection galleries located at the dam base. The results obtained show the location of the inspection galleries for the lowest pore pressures. The inspection galleries are usually used to intercept seeping water from the drain wells in the dam foundation and dam body. The seeping water intercepted by the dam body can be estimated when the values of hydraulic conductivity of concrete are known. The accumulation of calcium carbonate deposited in the drains can then be studied on the basis of the known values of the calcium carbonate concentration of the seeping water. The data presented may be useful for design engineers in the stability and stress analyses of concrete gravity dams. In addition, the effects of the location (i.e., elevation) of the inspection gallery and the tailwater pressures on pore pressures were studied by using the Fontana Dam as a case study.

“Coral Dominance”: A Dangerous Ecosystem Misnomer?

Over 100 years ago, before threats such as global climate change and ocean acidification were issues engrossing marine scientists, numerous tropical reef biologists began expressing concern that too much emphasis was being placed on coral dominance in reef systems. These researchers believed that the scientific community was beginning to lose sight of the overall mix of calcifying organisms necessary for the healthy function of reef ecosystems and demonstrated that some reefs were naturally coral dominated with corals being the main organisms responsible for reef accretion, yet other healthy reef ecosystems were found to rely almost entirely on calcified algae and foraminifera for calcium carbonate accumulation. Despite these historical cautionary messages, many agencies today have inherited a coral-centric approach to reef management, likely to the detriment of reef ecosystems worldwide. For example, recent research has shown that crustose coralline algae, a group of plants essential for building and cementing reef systems, are in greater danger of exhibiting decreased calcification rates and increased solubility than corals in warmer and more acidic ocean environments. A shift from coral-centric views to broader ecosystem views is imperative in order to protect endangered reef systems worldwide.

The pedo-geochemistry of Vertisols under tropical savanna climate

Fourteen representative Thai Vertisols on lowland and upland areas under a tropical savanna climate were investigated to ascertain parent material and pedogenic influences on their geochemistry. Physico-chemical, mineralogical and geochemical properties were determined for 98 soil samples. Multivariate analysis was used to interpret the dataset and identify affinity groups of samples and properties. Silicon, Al, Fe and Ca are the major constituents of the soils. Mean concentrations of elements are mostly within the range for worldwide normal soils. The variations in concentration of elements between soils reflect differences in the abundance of the major mineral constituents: beidellite, calcite, iron oxides and quartz. Factor analysis of geochemical data showed that most elements do not cluster into discrete affinity groups. The composition of soils is mostly quite uniform throughout the profiles with no evidence for depositional layers. Beidellite is the dominant clay mineral and acts as a reservoir of many major and trace elements in these soils. The accumulation of pedogenic calcium carbonate and Fe–Mn nodules in distinct horizons has resulted in systematic variations in composition within and between soil profiles for those elements that are associated with these neoformed materials (e.g. Fe, Mn, Co, V, Th, Ba and Ge).