Calcareous Surface Research Articles

Elemental ratios as tracers of the sources of mineral dust in north-eastern Sahara

The objective of this study is to confirm the possibility of tracing sources of airborne mineral dust using elemental ratios. The region of study is the north-eastern part of the Sahara where dust compositional data were lacking; 272 mineral dust samples collected at 3 experimental stations of Egypt were analyzed by X-ray fluorescence. Based on the mineral dust concentration, 65% of the samples correspond to moderate (3–10 μg m−3), 22% to medium (10–25 μg m−3), and 13% to intense (> 25 μg m−3) dust events. The Ca/Al and (Mg + Ca)/Fe ratios were found to be strongly correlated and their ranges of variation to cover are more than one order of magnitude, which confirms their interest for the tracing of the dust sources. Using a combination of MODIS satellite observations, HYSPLIT back-trajectory analysis, and simulations with dust emission models, the large (> 6) and intermediate (2–6) Ca/Al ratios were shown to correspond to dust originating from saline playas (chotts) and calcareous surfaces, respectively. Conversely, the lowest (< 2) ratios correspond to dust emitted by siliceous sand seas (ergs). Therefore, a classification of the dust in 3 categories (erg-like, calcareous, and chott-like) based on Ca/Al is proposed. The events of moderate to medium intensity are dominated by chott-like and calcareous dust, which suggests that these sources are activated during erosion events of limited (local) extension. Conversely, the fact that the dust composition is more likely to be of the erg-like type during intense events underlines the dominant role played by sand dune fields during major erosion events.

СРЕДНЕ-ВЕРХНЕЧЕТВЕРТИЧНЫЕ ОТЛОЖЕНИЯ СЕВЕРНОГО СЕКТОРА КОНТУРИТОВОЙ СИСТЕМЫ КОНТИНЕНТАЛЬНОГО СКЛОНА ПАТАГОНИИ (ЮГО-ЗАПАДНАЯ АТЛАНТИКА)

Lithological and micropaleontological (planktonic and benthic foraminifers, diatoms) studies in four sediment cores revealed major patterns of lithostratigraphy and biostratigraphy of contourites and gravitites in the uppermost sediment layer within the depth range 3500–4300 m of the northern sector of the Patagonian continental slope contourite system. It is ascertained that in conditions of low terrigenous material supply from the land and high, although variable bottom contour current velocities of waters of Antarctic origin, hemipelagic calcareous nanno-foraminiferal ooze deposited in the Holocene over middleupper Pleistocene contourites in the southern part of the study area (cores AI–2609, AI–2610). The Holocene calcareous surface layer is absent in the northern part of the study area (cores AI–2611, AI–2612). Middle-Upper contourites and gravitites are unevenly enriched in diatoms and radiolarians here, up to formation of slightly siliceous-terrigenous diatomaceous mud. Reworked Neogene foraminifers and diatoms evidence for erosion of Neogene deposits bottom currents and gravity flows.

Photoacoustic monitoring of water transport process in calcareous stone coated with biopolymers

Moisture is a critical control of chemical and physical processes leading to stone deterioration. These processes can be enhanced by microbial biofilms and associated exopolymers (EPS). There is limited current understanding of the water transport process across rocks covered by EPS. In the present work, we employed the photoacoustic technique to study the influence of three biopolymers (xanthan, microbactan and arabic gum) in the water transport process of two types of limestone rock of similar mineralogy but contrasting porosity. Both controls of RL (low porosity) and RP (high porosity) presented the higher values of water diffusion coefficient (D) than biopolymer-coated samples, indicating that biopolymer layers slowed down the transport of water. This trend was steeper for RP samples as water was transported seven times faster than in the more porous rock. Important differences of D values were observed among samples coated by different biopolymers. Scanning electron microscopy and optical microscopy showed that surface topography was different between both types of rocks; adherence of coatings was seen predominantly in the less porous rocks samples. FTIR and NMR analysis showed the presence of pyruvate and acetate in microbactan and xanthan gum, suggesting their participation on adherence to the calcareous surfaces, sealing surface pores. These results indicate that water transport at rock interfaces is dependent on the chemistry of biopolymer and surface porosity. The implications for reduced water transport in stone conservation under the influence of biopolymers include both enhanced and lower deterioration rates along with altered efficiency of biocide treatment of epilithic biofilms.

Phosphorus Release to Floodwater from Calcareous Surface Soils and Their Corresponding Subsurface Soils under Anaerobic Conditions.

Enhanced phosphorus (P) release from soils to overlying water under flooded, anaerobic conditions has been well documented for noncalcareous and surface soils, but little information is available for calcareous and subsurface soils. We compared the magnitude of P released from 12 calcareous surface soils and corresponding subsurface soils to overlying water under flooded, anaerobic conditions and examined the reasons for the differences. Surface (0-15 cm) and subsurface (15-30 cm) soils were packed into vessels and flooded for 8 wk. Soil redox potential and concentrations of dissolved reactive phosphorus (DRP) and total dissolved Ca, Mg, Fe, and Mn in floodwater and pore water were measured weekly. Soil test P was significantly smaller in subsurface soils than in corresponding surface soils; thus, the P release to floodwater from subsurface soils was significantly less than from corresponding surface soils. Under anaerobic conditions, floodwater DRP concentration significantly increased in >80% of calcareous surface soils and in about 40% of subsurface soils. The increase in floodwater DRP concentration was 2- to 17-fold in surface soils but only 4- to 7-fold in subsurface soils. With time of flooding, molar ratios of Ca/P and Mg/P in floodwater increased, whereas Fe/P and Mn/P decreased, suggesting that resorption and/or reprecipitation of P took place involving Fe and Mn. Results indicate that P release to floodwater under anaerobic conditions was enhanced in most calcareous soils. Surface and subsurface calcareous soils in general behaved similarly in releasing P under flooded, anaerobic conditions, with concentrations released mainly governed by initial soil P concentrations.

ACTIVIDAD ANTAGÓNICA ENTRE BACTERIAS EPIBIÓTICAS AISLADAS DE ESPONJAS MARINAS DEL CARIBE COLOMBIANO Y SU RELACIÓN CON LA MACROEPIBIOSIS

Surfaces submerged in the sea are densely colonized by bacteria, and inter-specic interactions such as growth inhibition are important determinants of the development of bacterial communities, as well as of later phases of macrofouling. To determine the potential interactions among biolm bacteria from sponges we carried out in vitro growth inhibition tests between bacterial strains isolated from surfaces with various degrees of macrofouling, from the sponges Aplysina insularis (clean), Aplysina lacunosa (fouled), and from the calcareous surface of the bivalve mollusk Donax sp. The total percentage of antagonistic interactions among these strains was 64 %; strains isolated from clean surfaces inhibited the growth of strains from well-colonized surfaces in a 1:1 ratio. Strains from clean surfaces had a higher frequency of antagonistic interactions. We propose bacterial antagonistic interaction as a possible mechanism of population growth regulation and, consequently, of the development of subsequent phases of macrofouling.

A Comparative Study of Element Cycling in the Soil-Plant System: A Case Study of Shaly and Calcareous Soils, Southern Benue Trough, Nigeria

This study focused on the cycling of major and trace elements in the soil-plant system in parts of Southern Benue Trough, Nigeria. Surface soil samples and cassava crop samples were collected from cultivated farmlands underlined by shaly and calcareous soils and were analysed using standard techniques. The results show that shaly soils are relatively acidic (pH, 4.8 - 6.6) with high level of organic matter content (OM, 3.2% - 8.7%) compared to calcareous soils (pH, 5.6 - 7.2; OM 1.6% - 7.0%). The soils are enriched in elemental composition relative to the world average abundances in soil. The maximum levels of K, Al, and Zn were obtained from shaly soils. The computed accumulation factors are generally leaf > stem. Significant correlation was obtained between elemental associations of calcareous surface soils compared to that of shaly soils. R-mode factor analysis revealed the controls of soil geochemistry to include lithology, anthropogenic and environmental factors. A stepwise linear regression analysis identified soil elemental component, pH and organic matter as some of the factors influencing soil-plant metal uptake.

Lichen-induced biomodification of calcareous surfaces: Bioprotection versus biodeterioration

Studies demonstrate the active and passive capability of lichens to inhibit or retard the weathering of calcareous surfaces. Lichen coverage may actively protect a surface through shielding by the thallus and the binding and waterproofing of the rock surface and subsurface by fungal hyphae. Passive protection of rock surfaces may be induced by the formation of an insoluble encrustation, such as calcium oxalate, at the lichen-rock interface. Recent research suggests that the decay of hyphae, induced by changes in microenvironmental conditions, necrosis, parasitism or the natural physiological traits of particular lichen species, may expose a chemically and physically weakened substrate to dissolution, triggering relatively rapid weathering-related surface lowering. Consequently, certain epilithic crustose and endolithic lichens may induce a period of surface stability throughout the course of their lifespan, followed by a phase of instability and rapid episodic microtopographical evolution after death and decay. A series of conceptual models is proposed to illustrate this idea over short (single lichen lifespan) and long (multiple lichen lifespans) timescales. The models suggest that the microscale biogeomorphological system of lichen-rock interaction is underpinned by non-linear dynamical system theory as it exhibits dynamical instability and is consequently difficult to predict over a long timescale. Dominance by biodeterioration or bioprotection may be altered by changes in lichen species or in environmental conditions over time.

Origin, palaeoecology and stratigraphic significance of bored and encrusted concretions from the Upper Cretaceous (Santonian) of southern Israel

Reworked concretions have been significant substrates for boring and encrusting organisms through the Phanerozoic. They provide large, relatively stable calcareous surfaces in systems where sedimentation is minimal. Diverse sclerobiont communities have inhabited reworked concretions since the Ordovician, so they have been important contributors to our understanding of the evolution of these ecological systems. Here, we describe reworked concretions from southern Israel where they are critical for interpreting the stratigraphy and paleoenvironment of an Upper Cretaceous sedimentary sequence. These cobble-sized concretions (averaging roughly 1,000 cm3) are found at the base of the Menuha Formation (Santonian to lower Campanian, Mount Scopus Group) unconformably above the top of the Zihor Formation (Turonian-Coniacian, Judea Group) exposed in the Ramon region of the Negev Highlands. The concretions are almost entirely composed of micritic limestone, and many are exhumed, cemented burrow-fills apparently from 10–20 m of upper Zihor Formation strata removed by erosion. There are also a few cobbles of dolomitic limestone and rare vertebrate bone. The cobbles are moderately to heavily bored by bivalves (producing Gastrochaenolites) and worms (forming Trypanites), and a few have cemented oysters. They are densely arrayed in a single layer, often touching each other or only a few centimeters apart. The sclerobionts associated with the cobbles, along with their hydrodynamic arrangement, strongly suggest that these cobbles accumulated in very shallow water above normal wave base. Most of them (77%) are encrusted on their top surfaces only, indicating that they were bored in place and not later delivered to a deeper environment by submarine currents. The rest of the Menuha Formation above is a chalk with relatively few macrofossils (primarily shark teeth and oysters) and a few trace fossils (Planolites and Thalassinoides are the most common). These reworked cobbles show that the initial deposits of the Menuha Formation accumulated in very shallow water. This has important implications for the development of the Syrian Arc structures in this region, especially the Ramon Monocline.

Effects of low-molecular-weight organic acids on phosphorus sorption characteristics in some calcareous soils

Understanding the role of organic acids in phosphorus sorption in soils is very important for economic and environmentally friendly management of soil P. Thus, calcareous surface soils (0-30 cm) from West Azerbaijan Province, Iran, were sampled to study the effect of different organic acids on P sorption. Soil samples (2.5 g) were equilibrated with 25 mL of 0.01 M CaCl_2 solution containing 0-20 mg P L^{-1} and 5 mmol L^{-1} of different organic acids (citric, oxalic, and malic acid). The sorption data were well fitted to Freundlich and linear equations but not to the Langmuir equation. The standard P requirements (SPRs) were lower in soils treated with organic acids than in untreated soils. The minimum and maximum values of calculated parameters (extent of sorption, energy of sorption, equilibrium buffering capacity, equilibrium P concentration, and SPR) by Freundlich and linear sorption isotherms were observed in soil 5 (sandy) and soil 4 (clayey-calcareous), respectively. Generally, organic acids decreased the amount of sorbed P and other sorption parameters in the studied soils. Oxalic acid was the most effective reagent for reducing the P sorption.

Biosorption of thorium on the external shell surface of bivalve mollusks: The role of shell surface microtopography

External shell surface (ESS) of bivalve mollusks is known to adsorb various metals dissolved in ambient water in high concentration. It is hypothesized here that the surface microtopography of the thin organic coating layer, periostracum, or calcareous shell (if periostracum was destroyed) plays a major role in the adsorption of actinides on ESS. Thorium (natural alpha-emitter) was used in short-term biosorption experiment with shell fragments of five bivalve mollusks. After a 72 h exposure to Th (∼6 kBq L −1), thorium concentration was measured on ESS using laser ablation inductively coupled plasma mass spectrometry; the distribution and density of alpha tracks were subsequently visualized by α-track autoradiography. A trend in reduced Th concentrations on the ESS was observed depending upon the species tested: (group 1 ∼4000 μg g −1) Chlamys islandica (M.), Mercenaria mercenaria (L.), Dreissena polymorpha (P.) > (group 2 ∼1200 μg g −1) Crassostrea virginica (G.) ≫ (group 3 ∼150 μg g −1) Mytilus edulis L. The microtopography of ESS was characterized by scanning electron microscopy revealing the high porosity of the calcareous surface of C. islandica and M. mercenaria, lamellate surface of periostracum in D. polymorpha, uneven but a weakly porous surface of periostracum of C. virginica, and a nearly smooth surface of the periostracum of M. edulis. This work has demonstrated, for the first time, the presence of a strong correlation between concentration of adsorbed Th and ESS microtopography, and the role of the periostracum in this process is discussed.

Lecanora antiqua, a new saxicolous species from Great Britain, and the nomenclature and authorship of L. albescens, L. conferta and L. muralis

AbstractLecanora albescens (Hoffm.) Branth &amp; Rostr. is the correct authorship of this species, and the combination cannot be attributed to Flörke. Lecanora antiqua J. R. Laundon is described for the lichen previously, but wrongly, known in Britain as L. conferta; it is remarkable in occupying the interface between acid and calcareous surfaces on the vertical walls of medieval churches. The nomenclature of the lobed Lecanora, which has had two alternative Latin names since the early 19th century, namely L. muralis Rabenh. and L. saxicola (Pollich) Ach., has been studied and the latter was found to be correct.

A non-linear model of sulphation of porous stones: Numerical simulations and preliminary laboratory assessments

Abstract Sandstones, limestones, and marble stones with different porosity were used as building materials for thousands of years. In the last century these materials have become vulnerable to atmospheric pollutants; the reaction of sulphur dioxide with calcareous (and decorated) surfaces is well known to form gypsum and black crusts. More recently, some mathematical models used for civil works have been applied to study the evolution of degradation phenomena; however, they did not fit sufficiently for artistic and historical hand-works, since they only give an averaged description of the damage. Between these mathematical models the Lipfert formula is the more diffuse, based on statistical models of atmospheric corrosion. In this paper a differential model was approached, which gives a quantitative description of the diffusion and the chemical action of sulphur dioxide on the porosity of calcium carbonate stones starting from the hypothesis that the interaction between stone surface and polluted air is due to its diffusion in the porosity of the material. The model has been validated by numerical simulations and a number of experimental tests in the laboratory. This approach gives a quantitative law for the penetration of the sulphation front inside of the stone, in accordance with the experimental data. Moreover, it is important to assess and prevent damage on the surfaces of historical monuments, considering also the local geometry, the nature of the polluted air, and the type of exposures.

Estimation of the Biological Methods of Assessing Soil N-Supplying Capacity in Calcareous Soil

Although many biological methods are used to determine soil nitrogen supplying capacity, there are certain differences in the results for different types of soils and various ways of measurement due to the complexity of soil N conformation, the high variance of soil and microorganism, and the difference of environment. Therefore, it is not clear about which biologic incubation method is better for calcareous soil. In this study, pot experiments were performed by using 25 different calcareous surface soil samples on the Loess Plateau and taking the N uptake of wheat and corn with leaching soil initial nitrate and without leaching in pot experiments as the control to investigate the difference of eight biological incubation methods for reflecting soil nitrogen supply capacity. The eight biological methods are waterlogged incubation, aerobic incubation for 2 weeks and for 4 weeks, dry-wet alternation aerobic incubation for 2 weeks, long-term alternate leaching aerobic incubation (and N mineralization potential, N o), short-term leaching aerobic incubation, microbial biomass carbon (B c), and microbial biomass nitrogen (B N) method, respectively. Among these methods, the dry-wet alternation aerobic incubation and aerobic incubation for 4 weeks were the modification of the method of aerobic incubation for 2 weeks according to the actual farmland moisture. The results showed that the correlation coefficients between these methods and crop uptake N w with leaching soil initial nitrate were 0.530, 0.700, 0.777, 0.768, 0.764 (and 0.790, N 0), 0.650, 0.555, and 0.465, respectively ( r 0.05 = 0.369, r 0.01 = 0.505). While without leaching soil initial nitrate, their coefficients were 0.351, 0.963, 0.962, 0.959, 0.825 (and 0.812, N 0), 0.963, 0.289, and 0.095, respectively ( r 0.05 = 0.369, r 0.01=0.505). In conclusion, excluding the soil initial nitrate, the correlation coefficients between the eight methods and crop uptake N were, from high to low, N 0, aerobic incubation for 4 weeks, dry-wet alternation aerobic incubation for 2 weeks, and long-term alternate leaching aerobic incubation, while including the soil initial nitrate the correlation coefficients between them increased significantly and the values were all beyond 0.950 for these four methods, including aerobic incubation for 2 weeks and for 4 weeks, dry-wet alternation aerobic incubation for 2 weeks and short-term leaching aerobic incubation. The waterlogged incubation method, B C and B N in the calcareous soil, had lower correlation coefficient with crop uptake nitrogen compared with other methods. Thus, dry-wet alternation aerobic incubation for 2 weeks was a better index for evaluating calcareous soil N supply capacity due to some other methods having disadvantages and not suitable for the actual farmland characteristics.

The nature of calcareous deposits along pan margins in eastern central Namibia

AbstractIn a region along the western margin of the Kalahari in eastern Namibia and western Botswana, many pan basins have mainly calcareous deposits along part of their margins. These are typically lined by low vertical scarps. In Namibia, these pans are mainly located in dry river beds. The petrographical study of these deposits demonstrates that they consist of lacustrine sediments that have to a varying extent been affected by early‐diagenetic processes and by the formation of late‐diagenetic features.The original composition of the deposits ranges from highly calcareous sediments, typically with ostracod, diatom and charophyte remains, to entirely non‐calcareous diatomites. The deposits generally show an upward increase in total carbonate content, which is mainly a synsedimentary feature. The early‐diagenetic processes that affected the deposits include the formation of orthic siliceous nodules. At a later stage, secondary calcite enrichment occurred, leaving only the silica‐impregnated sections unaffected. This enrichment partly accounts for the upward increase in total carbonate content in some profiles and often resulted in the development of a highly calcareous surface horizon. Sepiolite and amorphous silica that are part of the groundmass of the deposits may also partly have formed at this stage. Late‐diagenetic features include various forms of secondary calcite and silica.This study of pan basins in eastern central Namibia indicates that a lacustrine rather than purely pedogenic origin should also be considered for calcareous deposits that commonly occur along pan margins in other parts of southern Africa. Copyright © 2002 John Wiley &amp; Sons, Ltd.

Characteristics of Seafloor Morphology and Ferromanganese Nodule Occurrence in the Korea Deep-sea Environmental Study (KODES) Area, NE Equatorial Pacific

Seafloor morphology and ferromanganese nodule occurrence were studied using a multibeam side scan sonar (SeaBeam, 2000) and a deep-sea camera system in the Korea Deep-sea Environmental Study (KODES) area, northeast equatorial Pacific. Seafloor morphology and nodule abundance are highly variable even in this small study area. The NNE-SSW oriented hills are parallel and about 100–200 m high. Valleys are very flat-floored, while hilltops are rugged with depressions of tens of meters. Cliffs to about 100 m bound the valleys and the hills. The study area can be classified into three types based both on nodule occurrence and seafloor morphology, mostly G- and B-types and some M-type. G-type is characterized by high nodule abundance, ubiquitous bioturbation, and flat seafloor morphology, while B-type is characterized by irregular-shaped nodules, variable nodule abundance, occurrence of giant nodules and sediment lumps, rugged bottom morphology with depressions, and white calcareous surface sediments. Medium nodule abundance and a generally flat seafloor characterize M-type. G-type occurs mostly in the valley regions, while B-type is on the hilltop areas. M-type is located between the hilltop and the valley. Tectonic movement of the Pacific plate resulted in the elongated abyssal hills and cliffs. The rugged morphology on hilltops resulted from erosion and redistribution of surface siliceous sediments on hilltops by bottom currents, outcropping of underlying calcareous sediments, and dissolution of the carbonate sediments by corrosive bottom water undersaturated with CaCO3. Sediment eroded from the hills, which is relatively young and organic-rich, is deposited in the valleys, and diagenetic metal supply to manganese nodules in the valley area is more active than on the hills. We suggest that tectonic movement ultimately constrains morphology, surface sediment facies, bottom currents and sediment redistribution, bioturbation, thickness of the sedimentary layer, and other conditions, which are all interrelated and control nodule occurrence. The best potential area for mining in the study area is the G-type valley zones with about 3–4 km width and NNW-SSE orientation.

O Quaternário, a Morfologia Cársica e o Património Ambiental. Exemplos no sector Setentrional do Maciço de Sicó

In the main Portuguese calcareous massifs, the karstic process, which led to the formation of unique landforms and landscapes, nowadays considered of high heritage value, was a long and complex process in which the Quaternary represents only a very small part of the time involved.&#x0D; Considering only the calcareous massifs of the Westem Portuguese Mesocenozoic Border, if we except the calcareous tufas (and especially the largest outcrop, the Tufas of Condeixa) which were formed well into lhe Quaternary, the karstic forms (Karren, dolines, small caves) that developed there therefore being very recent, in the remaining calcareous rocks the karstic process began in the Jurassic period, and was marked by phases of different intensity at the mercy of tectonic changes, and especially of the successive bioclimatic environments registered in the region. 80th in the Calcareous Massif of Extremedura and in the Sicó Massif the Quaternary seems to have been essentially the setting for the exhumation of paleoforms, some pre-cretaceous, others perhaps tertiary, a1 the same time as a karstic retouching of the calcareous surfaces thus uncovered was taking place.&#x0D; In spite of this, the most spectacular Landforms, those which have an incontestable heritage value and often correspond to the best known image or these massifs, have the indelible mark of the fluvio-karstic and karstic processes that developed in the Qunternary.&#x0D; Following the raising of the massifs, and depending on the sandstone coverings progressively mobilized since cretaceous times, which at the beginning of the Quaternary still had, if not a continuous nature, at least larger and thicker extension than the ice remains that can be seen today, conditions were created for the development of the networks of rivers responsible for spectacular canyons, such as, in the case of Sicó, the canyons of Poios, Vale das Buracas and Vale da Grota. Other small canyons, perhaps more worthy of the name, given the almost absolute verticality of their sides, as is the case of the canyon of Rio dos Mouros which was only one of the reasons for the establishment of the Roman city of Conimbriga, despite being perhaps more recent,were born for the same reasons.&#x0D; An important part of the geological interest of these fluvio-karstic canyons arises from the shape of their sides, and especially from the «buracas», shapes of surface karst which seem to be linked to processes of frost shattering and dissolution under the action of cold climates. Short, almost vertical sectors (the «penas»), openings under rock (the «buracas») and debris of various origins are, without a shadow of doubt, quaternary marks on the sides of the fluvio-karstic canyons and other scarped slopes which contribute a great deal to the valorization of the landscape.&#x0D; The same is true of formations of two other types, authentic signatures of karstic shaping: the karren, responsible for the «stony desert»)with which classic karst is identified, and the caves which are valuable in themselves because of the beauty they enclose, the challenges they lay down and also, particularly, because of their importance in the process of water circulation and storage. In this case, it was also in the&#x0D; Quaternary that the responsible processes evolved, for the integral sculpture of many karren formations as for the finishing touches seen in them, this was the time that permitted the final restructuring of the network of galleries wl1ich lay out lhe hydrological functioning of the karst of today.&#x0D; This article discusses the importance of the processes that took place during the Quaternary in the&#x0D; construction of the karstic landscape, with particular influence on the formations which, for their genetic specificity, spectacular nature and singularity represent more in terms of environmental heritage.

Analysis of Load Tests on Piles Driven through Calcareous Desert Sands

The ultimate bearing capacity of short, precast concrete piles driven into calcareous sands was examined by pile-load tests carried out at two sites in Kuwait. The piles had a 0.3 m × 0.3 m square cross section and extended to a maximum depth of 12 m. They were driven through a loose-to-compact calcareous surface sand layer underlain by a competent dense-to-very-dense siliceous cemented sand deposit. The pile tips and part of the pile shafts were embedded in the lower layer. The base resistance and shaft friction were calculated using the Meyerhof method for a layered soil profile. The method employs the standard penetration test N values. The results indicate that a great portion of the pile capacity is due to base resistance. The skin friction mobilized is small and consists of two components corresponding to the two layers penetrated along the pile shafts. The calculated pile capacities were very close to the measured values. The unit skin friction is not constant along the pile shafts.

Principal component analysis of near-infrared spectra of alteration products in calcareous samples: An application to works of art

Works of art made of calcareous stone are usually affected by decay processes when they are exposed to the wet and dry deposition of atmospheric pollutants in urban and industrialized areas. For many years now in our laboratory, we have been developing totally non-destructive and non-invasive spectroscopic techniques in the visible and near-infrared regions. Principal component analysis (PCA) of diffuse reflectance near-infrared (NIR) spectra has been used as a suitable methodology for discriminating areas involved in the degradation process of calcareous stones. NIR spectra of standard mixtures, containing gypsum (CaSO 4. 2H 2O), calcium sulfite hemihydrate (CaSO 3· 1/2H 2O) and calcium carbonate (CaC0 3), and of calcite tablets, differently treated in order to simulate the formation of gypsum and calcium sulfite hemihydrate on real calcareous surface, have been recorded. For all data sets submitted to PCA, a good discrimination between the two reaction products, i.e. calcium sulfite hemihydrate and gypsum, in the alteration process was obtained. In an actual case, we tried to detect and to distinguish the alteration products, such as gypsum and calcium oxalate dihydrate, CaC 2O 4 · 2H 2O (weddellite), in the limestone (calcirudites, packstones and wackestones) which constitutes the coating of the supportive brickwork structure of the Parma Baptistery (Italy). Preliminary results are reported with regard to the application of PCA to all the in situ spectra collected on the calcareous surface of the monument.

Restoration of eutrophied shallow softwater lakes based upon carbon and phosphorus limitation

Plant communities from oligotrophic, poorly buffered waters are seriously threatened by both, acidification and eutrophication/alkalinization. Acidification is mainly caused by atmospheric deposition of acidifying substances while eutrophication is often the result of inlet of nutrient enriched, calcareous brook- or groundwater. The plant production in very soft waters is often limited by low levels of inorganic carbon, nitrogen and/or phosphorus. This paper deals with the possibilities for restoration of formerly oligotrophic but now eutrophied and alkalinized softwater systems. Restoration based upon nitrogen limitation is not likely to be successful as the atmospheric deposition of nitrogen in The Netherlands is very high. Phosphorus limitation can also be a problem. One can stop the input of phosphorus and remove the mud layer, but the problem remains that also the deeper mineral sandy sediments are saturated with phosphate. A possible remedy, however, is a combination of carbon- and phosphorus limitation. Many plants from eutrophic environments never occur in very soft waters, probably as a result of carbon limitation. In addition, mobilisation of phosphate is much lower in waters with very low bicarbonate levels. Restoration of a former oligotrophic softwater lake by reducing the inlet of calcareous surface water, in combination with removal of the organic sediment layer, appeared to be very successful. Many endangered plant species such asIsoetes echinospora, Luronium natans, Deschampsia setacea andEchinodorus repens developed spontaneously from the still viable seedbank.

Model study of the first steps in the deterioration of calcareous stone III. Manganese and iron mediated sulphation of natural stone

Transition-metal-mediated sulphation of calcareous stone is investigated. Mixes of iron and manganese compounds with precipitated or ground calcite are employed to model natural calcareous stones containing these metals in trace concentrations. The products are characterized by Diffuse Reflectance Infrared Fourier Transform spectrometry. Sulphation is shown to depend strongly on the amounts of transition metals in the mixture, and calibration curves are constructed. Sulphate formations at natural calcareous stone surfaces are discussed within the framework of the assumed model.